PHYSICO-CHEMICAL STUDIES

PHYSICO-CHEMICAL STUDIES

OF MIXED LIGAND ZINC (II)

COMPLEXES

By

Dr. Dinesh Vasant Bhagat

M. Phil., Ph.D. University of Mumbai (SET Qualified)

Associate Professor, HOD, Department of Chemistry

K.E.S. Anandibai Pradhan Science College, Nagothane.

[email protected]

2021

Ideal International E – PublicationPvt. Ltd. www.isca.co.in

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E-mail: [email protected], Website:www.isca.co.in

Title: PHYSICO-CHEMICAL STUDIES OF MIXED LIGAND ZINC (II)

COMPLEXES

Author(s): Dr. Dinesh Vasant Bhagat

Edition: First

Volume: I

© Copyright Reserved

2021

All rights reserved. No part of this publication may be reproduced, stored, in a

retrieval system or transmitted, in any form or by any means, electronic,

mechanical, photocopying, reordering or otherwise, without the prior

permission of the publisher.

ISBN: 978-93-89817-48-5

PHYSICO-CHEMICAL STUDIES OF MIXED LIGAND ZINC (II) COMPLEXES 1

Ideal International E- Publication

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This book is dedicated to my Parents and

“All My Respected Teachers”

Who taught me at different level.



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ACKNOWLEDGEMENT

I take this opportunity to express my sincere gratitude to my Guru Dr. Vikas V.

Vaidya, Associate Professor, Department of Chemistry, Dr. Sunil Patil, Director, Department

of Student Development University of Mumbai who always inspired and encouraged me to

write books on my subject of specialisation.

I also extended my sincere thanks to all my teachers who taught me at

different levels and make me able to write my first book on, “Physico-Chemical Studies of

Mixed Ligand Zinc (II) Complexes”. I am very much gratified by my research supervisors

who always encouraged me towards the synthesis element detection, spectral interpretation

and biological study indeed in this book throughout for all the synthesis. I have given some

reactions, preparations in same style and it will be very easily to understand the procedure of

making mixed ligand complexes using primary and secondary ligands.

I express my sincere thanks to the publisher Ideal International e-Publication Pvt..

Ltd. for publishing this book and taking keen interest in it. Finally, I owe a sense of gratitude

to my mother Prema Bhagat, wife Mrs. Vidya Dinesh Bhagat, my son Tanuj and daughter

Prachiti for their pleasant cooperation and moral support during writing this book.

Dr. Dinesh Vasant Bhagat



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Preface

This book entitled, “Physico-Chemical Studies of Mixed Ligand Zinc (II)

Complexes” has been particularly addressed to the graduate and postgraduate students who

have opted for the Inorganic and Analytical Chemistry study course as per the UGC syllabus.

This book is equally useful for those students who are preparing for the NET-JRF-CSIR,

SET, SLET, GATE, NET-ICAR and other competitive examinations like MPSC and UPSC.

This book includes six chapters and covers basic theory of metal complexes, analytical

techniques, spectral analysis, biological studies and structures of metal complexes. Oxidation

is discussed in details with different sets of examples. The number of metal complexes is

studied with their spectra’s and biological activities.

Although almost precautions is taken to make this book error free but few

errors may creep in, for which I apologies in advance. Suggestions are welcome for

improvement of work and publication.

Place: - Nagothane, Dist: - Raigad (M.S.) Dr. Dinesh Vasant Bhagat Date: - 04/04/2021



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INDEX

Chapter Title Page no.

1 Introduction

2 Theoreticals

3 Experimental

4 Results and discussion

5 Biological activity

6 Summary



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Chapter No. 1

Introduction



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INTRODUCTION

The chapter deals with the several aspects that are associated with the formation of

coordinated complexes. The fundamentals that govern the formation of such complexes

continue to grow as new compounds are synthesized and new principles are formulated.

Coordination chemistry is an important branch of science and well known for its association

with the life. The relation between coordination chemistry and life can be illustrated by an

example of vitamin B12 which is one of the naturally occurring coordination compound in

biology. Some other important complexes are chlorophyll, haemoglobin, myoglobin,

cytochrome, etc.

Numbers of attempts have been done on the study of biological importance of

complexes containing more than one ligand. This chapter deals with several facets of

polydentate ligands, factors affecting stability of chelates and mixed ligands and the literature

survey of amino acid and 8-hydroxyquinoline as ligand.

The coordination chemistry has also an industrial application. The complex of

aluminium and titanium is used as a catalyst for low pressure polymerization of ethylene.

Fiber and fiber reinforced plastic materials are made by using coordination compounds of

silica and copper. Coordination chemistry has also left its foot prints in the field of medicine,

analytical chemistry and physics. The coordination chemistry is an amalgamation of organic,

inorganic and biochemistry. It is an interdisciplinary science and extended vastly from

defined to unlimited research field because of its significant industrial application and

relevance with life. The interest in coordination chemistry has undergone rapid development,

which has been reported in a large number of publications, reviews, conferences and

symposia.

Historical Background:-

In 1704, Purssian Blue was discovered by Diesback and this discovery was a key

for the development of coordination compounds. Many compounds were discovered

thereafter and many theories were put forth to explain the electronic structure and chemical

bonding of these compounds. The ‘Werner’s Coordination Theory was then proposed by

Alfred Werner in 1893. Today’s inorganic chemistry research is centred on Werener’s

Coordination Theory.

He introduced the concept of secondary or auxiliary valence and synthesized

many compounds based on the concepts of primary and secondary valencies. By means of the

numbers and properties of the isomers obtained, Werner was able to assign the correct

geometric structures to many coordination compounds long before any direct experimental

method was available for structure determination. He put forth that the factor determining a

structure of a coordination compound was the number of groups or atoms directly attached to

it, i.e. its coordination number. His views on coordination compounds are still the foundation

of this subject and fundamental postulates that he proposed are still found to be valid.

Lewis proposed the ‘Electronic Theory of Valence’by referencing the ideas of

Werner. His theory was extensively applied to coordination compounds by Sidgwick who

made significant contributions to the theory of valency and chemical bonding. Sidgwick

easily incorporated most of the structures given by Werner into electron pair bonds proposed

by Lewis. The concept of coordinated bond was developed by him. He proposes that the



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ligand species share a pair of electrons with the central atom to form bond of the same

general nature which was found in classical covalent compound. The research in coordination

chemistry has progressed leaps and bounds in the last couple of decades.

Metal Chelates And Chelating Agents:-

When a central metal ion (M) unites with a group of neutral molecules or ions, a

coordination compound is formed. The ligand is a neutral molecule or an ion capable of

functioning as the donor partner to the central metal ion. A bond thus formed between metal

and ligand is called metal-ligand (M-L) bond. A chelate or a metal chelate is formed by the

process called chelation, if the coordinating ions or molecules are attached to the central

metal atom in such a way so as to produce a closed ring. The molecule forming chelate with

the ions is called chelating agent. The metal chelate thus formed is studied by considering

central metal atom, chelating molecules or ligands and the nature of bonding between metal

and the ligand.

a) Central Metal Atom:-

Nature, oxidation state and the coordination number of the central metal atom

influence the properties of metal chelate to a considerable extent. This can be studied by

comparing the compounds formed by different metal atoms with a particular chelating agent.

The variation in the structures and properties of complex formed by a metal depends on its

oxidation state and coordination number. The coordination number is a number of donor or

ligand atoms that are directly bound to the central metal atom. The coordination number

varies from metal to metal.

b) Chelating Molecules:-

As discussed above, the chelate molecule forms a closed ring of coordinating

molecules and central atom. These molecules are mostly organic in nature and form covalent,

coordinate or both types of bonds with donor atom. The chelating agent can undergo

chelation only if -

i) It has two appropriate functional groups that can combine with a metal atom by donating a

pair of electrons. Some functional groups are acidic and unite either by replacing hydrogen or

without replacing it. Some acidic groups that unite with metal ions by replacing hydrogen are

–COOH, -OH, -SO3H and =N-OH. The functional groups that form coordination linkage but

do not replace hydrogen donate a pair of electrons. Such type of linkages are seen in most

functional groups such as primary, secondary and tertiary amines,=N-OH (oxime), -OH

(alcoholic hydroxyl), >C=O (carbonyl) and –SCN (thiocyanate), etc.

ii) The molecule has its functional group situated so as to allow the formation of a closed ring

with the metal atom.

Generally, when there are one or more ring structures and there are 5 or 6 atoms in

the ring, the complex so formed is stable as the strain is reduced. The rings get closed by the

formation of covalent linkages or coordinate bonds or by combination of the two. One of the

examples for such chelate compound used for determination of nickel is formed by the

reaction between Ni2+

and dimethylglyoxime.



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The classification of chelate compounds follows the number and the kind of

attachment involved. A polydentate molecule may be attached to the central metal atom

through two kinds of functional groups which may be acidic or coordinating by means of

covalent and coordinate linkages.

According to the classification given by Diehl, the chelate compounds are classified

as follows –

a) Bidentate:- It has two donor groups. Both the groups may be either acidic or coordinating.

Or there may be one acidic and one coordinating group.

b)Tridentate:- It has three donor groups. All the three groups may be either acidic or

coordinating. Or there may be two acidic and one coordinating group or one acidic and two

coordinating groups.

c) And so on, for quadridentate, quindentate, hexadentate and polydentate ligands.

Several organic molecules have six groups (two acidic and four coordinating). They

are capable of attaching themselves in six octahedral positions of the coordination sphere of a

central metal atom One of the examples of such organic molecule is 1,8-bis-

salicylideneamino-3,6-dithiaoctane that reacts with Zn, Ni, Cu or Co to form a chelate

compound.

The maximum coordination position can be attained by a polydentate molecule

which is wrapped itself around the central metal atom. Martell and Calvin have summarized

the chelating agents and their uses.

The stability of chelates is affected by-

a) Size of the chelate ring:-

Chelates having more membered rings including central metal atom are more stable

than those having less membered ring. For example, six membered ring chelates are more

stable than five membered ring chelates, which in turn are still more stable than four

membered ring chelates.

b) Number of chelate rings:-

More the number of the chelate rings, greater is the stability of the chelate.

c) Resonance effect:-

Resonance enhances the stability of chelate.

d) Chelate effect:-

The chelated complexes have more stability than the non-chelated complexes.

e) Steric effect:-

If the bulky group is attached to the donor atom of the ligand or it is present near the

donor atom then the metal ligand bond is weakened resulting in the lowering of the stability

of the complex.



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Classification of Chelating Agents:-

The chelating agents establish linkages with the metal ion by more than two positions

through covalent or coordinate bond. Such chelating agent is referred as bi, tri, quadri, penta,

hexadentate, etc. depending on the number of donor sites two, three, four, five, six, etc.

respectively.

The classification of the chelating agents and their metal complexes is also done on

the basis of donor atoms present in the ligand. There are number of organic and inorganic

ligands containing donor atoms like O, N, halogens, P, As, Sb, S, Se, Te, etc. Some classes of

chelating agents are

a) Metal Chelates of Oxygen Ligands:-

The chelating agents like oxyanions, alkanoates, dicarboxylates, β-diketones, o-

hydroxy carbonyl compounds, etc. coordinate through the oxygen donor atoms. The rare four

membered chelates are observed with the chelating agents containing oxyanions like SO4-2

,

SO3-2

, SeO4-2

, MoO4-2

and PO4-3

. A five membered ring structures is suggested for metal

complexes of dicarboxylic acids by electronic and infrared spectral studies. For higher

homologues of dicarboxylic acids, an eight membered ring structure is also reported. The six

membered ring structure has been reported for the complexes with acetylacetone (β-

diketones).

The same type of ring structure is also observed in uranium complexes of β-diketones

of the type [U(R.CO.CH.CO.R/)4] and [UO2(R.CO.CH.CO.R/)2]which is confirmed by

infrared spectral studies.Vanadyl complexes of some β-diketones have also been studied for

their magnetic spectra and ESR spectra. Stable octahedral complexes are readily formed by

acetyl acetonatesof certain bivalent metals by taking up two extra ligands such as water,

alcohol or ammonia and organic amines. Spectral studies of metal complexes of β-diketones

have been reviewed. The literature shows extensive studies on metal complexes of various

oxygen containing ligands.

b) Metal Chelates of Nitrogen Ligands:-

Alkyl and aryl diamines, substituted 1,10-phenanthroline and 2.2-bipyridyl

derivatives, biguanide, guanylurea and their derivatives are categorized as metal chelates of

nitrogen containing ligands. There are two main groups of complexes of this class viz. alkyl

and aryl amine metal complexes and aromatic heterocyclic base complexes. The extensive

study has been carried out on metal chelates of ethylenediamine and its derivatives. Sahu and

Mohopatra have studied the Mn (II) and Cd(II) complexes of dicyanodiamide. The aromatic

heterocyclic bases such as 1,10-phenanthroline and 2, 2-bipyridyl were first used as

coordinating agentsand Brandt and others have worked on metal chelates of these and related

ligands. Ahuja and Singh synthesized uranyl complexes and their structures8were confirmed

through physical methods. Metal complexes of biguanide, guanylurea and their derivatives

were studied by Ray and they are found to be highly stable. Birdar and Gaudar developed the

synthetic procedure that affords a series of six coordinated Ni(II) complexes distinguished by

a bicyclic ligand frame work which encapsulates the metal ion and imposes a trigonal

prismatic or near trigonal prismatic stereochemistry.



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c) Metal Chelates of Nitrogen and Oxygen Ligands:-

Several polydentate ligands containing nitrogen and oxygen are reportedwhich

functions mainly as bidentate and multidentate chelating agents. The complexes of

polydentate ligands containing nitrogen and oxygen donor atoms are interested because of the

mode of coordination. Following are few of the examples

i) Amino Carboxylic Acids:-

The amino acids like anthranilic acid, glycine and other α and β-amino carboxylate

ions have been used as chelating agents to form complexes with various metal ions.

The complexes of neodymium with glycine have been studied by polarographic

technique. Cu (II) complexes of α and β-amino butyric acids show that the chelating agents

behave as bidentate ligands. Cotton studied the infrared spectra of amino acid complexes.

The formation and stability of mixed ligand complexes of Cu (II) with malonic acid as

primary ligand and some amino acids as secondary ligands have been reported.In most cases,

the amino acids act as bidentate ligands, coordinating through the amino and carboxylate

group resulting into thermodynamically stable five membered rings for the α-amino acids and

six membered ring for the β-amino acids. The amino acid such as methionine may offer

additional coordination site through sulphur atom. The anions of amino acid form stable

complexes with a wide variety of metal ions. Tridentate bonding in solids is seen in aspartic

acid complexes of Co(II), Ni(II), Zn(II) and Cu (II) and is illustrated by X-ray spectral

studies. In contrast, similar studies show that glutamic acid coordinates to one metal ion via –

NH2 and one –COO – while second –COO –binds to a second metal ion.

Binary complexes of amino acids are known from the time of Werner, e.g.

[Pt(glycinato)2]. Some other binary complexes of amino acids known are [Cu(alaninato)2],

[Co(histidinato)2], etc.

The advanced research concentrates on ternary complexes than the binary metal-

amino acid complexes, particularly the complexes of the type (aa)–M–L, Where (aa) is an

amino acid, L is other ligand or may be different amino acid and M is a metal ion, e.g.

Co(asp)(ala) and Co(glu)(ala).

ii) Amino phenols:-

As o-aminophenols have an ability to coordinate with metal ions in body they are

found to be carcinogenic. The metal chelates of o-aminophenols are more stable than those of

diketones and substituted salicylaldehydes. The stability constants of several metal chelates

of o-amino phenols have also been studied.

iii) Nitro and Nitroso Compounds:-

These compounds have weak donor properties. Even though, the basicity of nitroso

group in aromatic compounds can be enhanced by the presence of strong electron donating

group at para position. When p-nitrosoaniline (and its N-methyl and N,N/-dimethyl

derivatives) form complex with Co(II), Cu (II) and Ni(II), there is decrease in N-O stretching

frequency. It indicates that nitroso-oxygen is involved in the coordination. Several transition

metal complexes of simple nitro compounds are known though they are commonly used as

solvents. A compound of Cu(NO3)2.CH3NO2 has nitromethane molecule coordinated by one



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oxygen atom but is bidentate as in TiCl4.CH3NO2. The spectral data revealed the structure of

the complexes of Ln (II), Ce (III), Th (IV) and U (VI) with 7-nitroso-8-hydroxyquinoline-5-

sulphonic acid.

iv) Oximes:-

Oxy-imine is abbreviated as oximes. The structure of oxime is denoted as C=N-

OH. They coordinate with metals to form metal complexes. The nitrogen of oxime has very

strong donor property because of which it can form chelates through oxime nitrogen.

Dimethyl glyoxime is most commonly used oxime in inorganic analysis. Many workers have

reported metal complexes of oximes. The successful work has also been carried on the

structural information of metal complexes of oximes by Chakravorty. Spectral data has

revealed the structural information of complexes of dioxouranium(VI) with aldoximes. The

complexes of U(VI) and Mo(VI) with oximes are studied for their stability constant using

colorimetric techniques.

v) 8-Hydroxyquinoline (Oxine):-

It is N- and O- donor bidentate ligand and also an earliest analytical reagents

used for metal ion estimation. It forms neutral complexes with bivalent, trivalent and

tetravalent metal ions by loss of proton. Philip has studied the coordination chemistry of

oxines. Schulman and Dwyershowed the in vivo use of oxines in microbial system. The

detailed study has been carried out on wide useof oxine and its closely related bidentatesfor

analytical solvent extraction and colorimetric determination. The stability constant and X-ray

diffraction studies of some bivalent metal oxinates have been reported. Spectral properties of

platinum and palladium chelates of 8-quinolinols have been reviewed. The Co(II)bis/-chelate

of 2-methyl-8-hydroxyquinoline has property to catalyze the disproportionation of nitric

oxide. The extensive work has been carriedout by Y. Yamamoto and E. Toyota on the

preparation and properties of some ternary Co (II) complexes of this ligand. Recent work

indicates the antimicrobial studies of some mixed ligand transition metal complexes of 8-

hydroxyquinoline.

Binary Complexes:-

Binary complexes are the one in which metal atom or ion is bound to two or more

ligands of the same type. They are well known since the time of Werner. They are well

studied for their structural and stereo chemical properties.

Stability of Binary Complexes:-

The stability of binary complexes is affected by following factors

a) Nature of the metal ion

For the formation of stable complex a high charge on metal and a small radial

distance are important factors. A hard metal ion (Li+, Na

+, Ca

2+, Co

3+, etc.) would most

strongly bind with the donor atoms (N, O or F) that possess high electronegativity, low

polarisability, small radii and are difficult to oxidize.



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b) Nature of the ligand

The stability of binary complexes depends upon basicity of the ligand. This is due

to the fact that H+

and metal ion both act as Lewis acids towards Lewis base ligands.

c) Chelation

Chelation is also one of the factors that affect stability of complexes. Non-

chelating ligands are less stable than the complexes of chelating ligands. The stability of

chelate complexes decreases as the chelate ring size increases from 5 to 7 where as a chelate

with more chelate rings form even more stable complex.

Mixed Ligand Complexes:-

Mixed ligand complexes are the one in which metal atom or ion is bound to two

or more different ligands. A mixed ligand is known as ternary ligand if a metal is bound to

two different ligands. For example, MAB, where MAB is a complex species and A and B are

two different ligands. This is 1:1:1 ternary complex. Similarly the quaternary complexes have

a metal and three different ligands.

Stability of Ternary Complexes:-

Equilibrium constant is the key factor to study the stability of ternary

complexes. The equilibrium constant for binding a second ligand is usually lower than that

for the first, except in some special cases where K2 is greater than K1 for the same ligand.

When the metal binds to two different ligands A and B, there are many instances of increased

affinity of the metal for ligand B, due to binding of ligand A and vice versa. The complex

formation can be represented as follows,

M + B MB + KMB = [MB]/[M] [B]

MA + B MAB + KMAB = [MAB]/[MA] [B]

For a binary system A = B, the difference in stability, log k, usually varies from -0.5

to -0.8 for the monodentate ligands and from -1 to -2 for bidentate ligands. For the above

equations, it follows that the influence of both ligands in a ternary complex is mutual and of

the same extent both the ligands are either stabilized or destabilized in their coordination to a

particular metal ion. Actually log k corresponds to log Keq for the process,

MA + MB MAB + M Keq = [MAB] [M]/[MA] [MB]

Hence, a positive value for log k would indicate that the equilibrium is in favour of

formation of the ternary complex. It therefore indicates, enhanced binding of B as a result of

the effect of A on the properties of central metal and vice versa.

An examination of the results of the studies leads to several interesting conclusions.

For example, in M-(bipy)-L complex, where L=en, glycine, pyrocatechol, the ligand L

enhances the stability of the complexes of oxyanion ligands such as acetate, oxalate,

phenolate, etc. but reduces the affinity of the metal for amine to amino acid ligands. The very

large difference in K1 and K2 for bipyridyls results from steric interactions of the ligands as

well as from the antagonistic or competitive bonding effects associated with two trans -

acceptor ligands. Exactly opposite trend is observed for Cu2+

-en system, where the strong -



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donor effect of the saturated amine reduces the Lewis acidity of the metal. Amino acid

ligands have similar effect of destabilization of -donor ligands, especially oxyanions and

stabilization of -acceptor ligands.

Applications of Mixed Ligand Complexes:-

Mixed ligand complexes are widely used in industries. On account of their

catalytic property, they are well known as catalyst in the industrial processes such as

hydrogenation, hydroformylation, oxidative hydrolysis of olefins and carboxylation of

methanol. The alkenes are activated through catalytic property of platinum complexes. The

catalytic property of ternary transition metal complexes is useful in various oxidation

reactions of industrial and environmental importance. They are also known for catalysing

decomposition activity of hydrogen peroxide and their participation in biological activity.

The antibacterial and antifungal activity of 8-hydroxyquinoline and some of its complexes

has been reported. Bis-(3,5-diisopropylsalicylato) Copper (II) complex is known for its anti-

convulgant and antitumor activities. The role of ternary complexes in activation of enzymes

and in the storage and transport of active substances is well sighted in literature.

Aim of the Present study:-

The literature survey and a brief account of the former work justify the task

undertaken for the investigation.

Extensive research has been carried out for the study of mixed ligand complexes

and their importance in various biological processes. It has been found that many ternary

complexes of some metals are important for activation of enzymes and they are used for

storage as well as for transport of active materials. The correlation between the stability of the

metal-ligand complexes with their anti-microbial activity has been studied. Antitumor

activity of some mixed ligand complexes also has been reported.

Complexes of many metals with 8-hydroxyquinoline have been studied for their

biological activity. Metabolic enzymatic activities for many metal complexes of amino acids

have been reported. Many researchers have studied characterization, antimicrobial and

toxicological activity of mixed ligand complexes of transition metals and actinide metal ions.

Synthesis and characterization of some transition metal complexes derived from amino acids

have been reported.

It is well known that the copper complexes play important role in various biological

processes. The antibacterial and anti-fungal properties of copper (II) complexes have been

reported. Recently synthesis, structural characterization and antibacterial studies of some

biosensitive mixed ligand copper (II) complexes have been reported. Many complexes of

copper (II) metal ion have been investigated for their chelation and biological properties.

Antioxidative and anti-tumour properties of copper (II) metal complexes have also been

reported. The spectral, magnetic and biological properties of ternary complexes of copper(II)

metal ion with amino acid as secondary ligand have been studied.

The present work was therefore undertaken to study the mixed ligands of copper(II)

a with 8-hydroxyquinoline (HQ) as a primary ligand and different amino acids (HL) such as

L-valine, L-asparagine, L-glutamine, L-arginine and L-methionine as secondary ligand. The

metal complexes have been characterized by elemental analysis and various physico-



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chemical techniques such as molar conductance, room temperature magnetic susceptibility,

electronic spectra, IR spectra, thermal studies and XRD.

Microbial techniques were applied for preliminary screening of antibacterial activities

of these complexes and it is discussed in the Chapter 5 of this book.

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CHAPTER 2

THEORETICALS



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THEORETICALS

Elemental Analysis:-

Elemental analysis is a process where a sample is analysed for its elemental and

sometimes isotopic composition. Elemental analysis can be qualitative and it can be

quantitative.

Methods:-

The most common form of elemental analysis is CHN analysis and is accomplished

by combustion analysis. In this technique, a sample is burned in an excess of oxygen and

various traps collect the combustion products such as carbon dioxide, water and nitric oxide.

The masses of these combustion products can be used to calculate the composition of the

unknown sample. This information is important to determine the structure of an unknown

compound as well as to ascertain the structure and purity of a synthesized compound.

Carbon is converted to carbon dioxide, hydrogen is converted to water, nitrogen is

converted to nitrogen gas / oxides of nitrogen and sulphur is converted to sulphur dioxide

during combustion process. If in the sample other elements such as chlorine are present, they

will also be converted to hydrogen chloride. If determination of additional element is not

required then a variety of absorbents are used to remove these additional combustion

products.

The inert gas such as helium is used to remove the combustion products from

combustion chamber and then combustion products are passed over heated (about 600oC)

high purity copper. This copper is situated at the base of the combustion chamber or in a

separate furnace. The main role of copper is to remove any oxygen not consumed in the

initial combustion and to convert oxides of nitrogen to nitrogen gas.

The combustion products are then passed through the absorbent traps in order to

remove only carbon dioxide, water, nitrogen and sulphur dioxide. The combustion gases can

be detected by (i) GC followed by thermal conductivity (ii) partial separation by GC followed

by thermal conductivity and (iii) infra-red technique and thermal conductivity. Quantification

of the combustion gases requires calibration. The calibration is performed by using high

purity ‘micro-analytical standard’ compounds such as acetanilide and benzoic acid.

Analysis of Results:-

The analysis of results is performed by determining the ratio of elements within the

sample and working out a chemical formula that fits with results. The method for

determination of ratio of elements from the results is shown below

1) Take the percentage of each element found and divide by the elements mass.

Perform the same procedure for all elements.

2) Find the smallest value from step 1 and divide every value obtained in step 1 by

this smallest value.

3) Multiply the results in step 2 by a factor to obtain reasonable values for either

carbon or nitrogen and then compare it with standard.



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Automated tools have been released to simplify this process. Each of the tools is

different in its working.

Conductometry:-

Electrolyte is substance which produces free ions when it is placed into a solvent

such as water. The molecules of electrolyte split up into individual atomic components which

form ions. The process is called as dissociation. Positively charged ions are cations and

negatively charged ions are anions. Due to the presence of free ions, electrolyte solutions

behave as an electrically conductive medium. They represent conductors of kind two, in

which the electric current is conducted by free ions, as oppose to the free electrons in

conductors of kind one (e.g. metals). Common electrolytes consist of salts, acids or bases.

Electric properties of the conductor of kind one are described by Ohm's law

I =U/R

Where, I corresponds to a current, U is a voltage and R describes electric resistance.

This resistance depends on the intrinsic properties of a conductor and its shapeand it

is given as R =ρ .l/s

Where, R is resistance, ρ is specific resistance, is a conductor's length and s is a

cross-sectional area.

Every material is characterized by a specific resistance, ρ , that is given in units ofΩ

.m (Ω is ohm, a unit of electric resistance). Electrical properties can be expressed also

through the quantity, conductance G. It is the inverse of resistance.

G =l/R

Its unit is S (siemens), where, 1S=1/ Ω

A specific conductance k is defined as

G =k//l/s

Similar to the relation between the conductance and resistance, specific conductance

is inversely proportional to the specific resistance. Its unit is Sm-1

.

If the measurement is done at alternating current and voltage then the same

equations as for metallic conductors can be used for electrolyte solutions. Such a

measurement is then done with conduct meter. It consists of a conduct metric container and

platinum electrodes covered with a platinum black; they are formed by the three fillets in the

conductometer. The cross-sectional area‘s corresponds to the surface of electrodes and l is the

distance between them. Ratio l/S is an intrinsic parameter of each conductometric container

and is called resistive capacity of conductometric container C.

C =l/s

The conductance is then calculated from the equationG =k/C



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Where, resistive capacity C is experimentally determined using the solution with

known specific conductance. The KCl solution (concentration c = 0.1 mol.dm-3

) is used for

the same.

Apparatus: -

The conductivity meter is used to measure conductivity of an electrolyte or solution. It

consists of conductivity cell and conductivity meter to measure conductivity.

The conductivity cell consists of two electrodes (platinum plates) firmly held at a

constant distance from each other and are attached by electrical wires to the meter.

The conductivity meter consists of a Wheatstone bridge circuit as shown in the figure

2.1

Figure 2.1 Schematic Diagram of Wheatstone bridge Circuit

The source of electric current in the conductivity meter applies a potential to the

plates and it measures the electrical resistance of the solution. In order to avoid change of

apparent resistance with time due to chemical reactions (polarization effect at the electrodes)

alternating current is used. Some meters read resistance (ohm) while othersread in units of

conductivity (milli-Siemens per meter). Platonized electrodes must be ingood condition

(clean, black-coated) and require replating if readings of the standard solution become

inconsistent. Replanting should be done in the laboratory. The cell should always be kept in

distilled water when not in use, and thoroughly rinsed in distilled water after measurement.

The Cell Constant (Calibration):-

The size, shape, position and condition of the plates in the conductivity cell

determines the conductivity measured and is reflected in the cell constant (Kc), The values

for Kc are 0.1 to 2.0. The cell constant can be determined by using the conductivity meter to

measure the resistance of a standard solution of 0.01 mol.dm-3

KCl. The conductivity of the

solution (1.413 mS.cm-1

at 25ºC) multiplied by the measured resistance gives the value of Kc.

The cell constant is subject to slow changes in time, even under ideal conditions. Thus,

regular determination of the cell constant must be required.



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Temperature Correction

Conductivity of solution changes with the temperature. Conductivity of electrolyte

increases with temperature at a rate of 0.0191 mS/mºC for a standard KCl solution of 0.01

mol.dm-3

. For natural water, this temperature coefficient is approximately the same as that of

the standard KCl solution. Thus, more the sample temperature deviates from 25°C greater the

uncertainty in applying the temperature correction. Thus the temperature of a sample (+

0.1ºC) is recorded and the conductivity is measured at 25ºC (using a temperature coefficient

of 0.0191 mS/mºC). Most of the modern conductivity meters have a facility to calculate the

specific conductivity at 25ºC using a built in temperature compensation from 0 to 60ºC. The

compensation can be manual (measure temperature separately and adjust meter to this) or

automatic (there is a temperature electrode connected to the meter).

Magnetism:-

From the property of attraction in magnetite, the iron ore, the term ‘Magnet’ is

supposed to have been discovered. Earlier it was thought that this property was associated to

the elements of iron group only. But with remarkable discoveries like earth as a magnet, this

belief was slowly given up. Chemists, in recent times have started taking a great deal of

interest in magnetism with a view to study the structures of molecules. Theoretical

standpoint, quantum mechanics and study of physical properties of molecules gave more

significance to this field. The important properties, which ascertain the structure of

molecules, are ultra-violet spectra, infrared spectra, nuclear magnetic resonance spectra,

electron diffraction studies, x-ray diffraction studies, dipole moments, molar refraction, etc.

Measurement of magnetic susceptibility is also a useful tool in the elucidation of structure of

molecules.

Diamagnetism and Paramagnetism:-

Faraday, the founder of magneto chemistry revealed that electric current and

magnetic field exists together. Faraday concluded that all substances whether elements or

compounds possessed magnetic property in varying degrees. During investigation, he found

that some substances when placed in a magnetic field tend to move away from the region of

maximum field intensity (diamagnetic), while others move towards it(paramagnetic).

Diamagnetism is a universal property of matter. It depends upon the structure of the

atom which will be practically unaffected by temperature. The magnetic susceptibility of a

diamagnetic substance is independent of temperature and field strength. Paramagnetism is

observed among the transition group elements and varies inversely as the absolute

temperature. A paramagnetic substance possesses underlying diamagnetism, but generally

paramagnetism is so large that it completely masks diamagnetism. There is also a third type

called ‘ferromagnetism’ which is very rare in nature and occurs among a few metals, alloys

and compounds. It depends on both temperature and field strength.

Magnetism and Electronic Theory:-

Several attempts were made to interpret the magnetic phenomena depending on the

behaviour of the extra nuclear electrons in the atom on the basis of electronic theory. The

revolving electrons acquire two types of angular moments

1) Due to orbital motion in a closed circuit



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2) Due to spin around their own axis

The net result of these two moments gives rise to magnetic moments in an atom

which is multiples of a unit known as ‘Bohr Magneton’.

If the net magnetic moment of an atom is zero the substance is said to be

diamagnetic. However, if the atom has an incomplete shell, then the net of the spin and

orbital moment has a definite value. The substance is then said to be paramagnetic. An atom

will have a permanent magnetic moment if it has an odd number of electrons or if all the

electrons are not paired off.

Ferromagnetism is observed in lattice of magnetic particles with loose inter-atomic

binding and with parallel electron spins.

Diamagnetic susceptibility is the useful aspect for the structural elucidation of

molecular structure of organic substances6for the inorganic compounds. Gray and

Cruickshank suggested that diamagnetic susceptibility could be used with advantage to

explore the structure of those compounds, which cannot be investigated by any other physical

method. This claim has to be validated by a large amount of data on the subject. Magnetic

method has certain unique advantages over other physical methods. For example the

measurement of susceptibilities does not involve a difficult procedure and these

measurements can be made on substances in any physical state. Generally other methods

have certain restrictions.

Langevins Theory of Diamagnetism and Paramagnetism:-

Langevin laid the foundation of the modern electronic theory of magnetism in 1905.

He formulated an exact mathematical expression on the basis of this theory, which

satisfactorily explained diamagnetism and paramagnetism. This treatment covers the

behaviour of many paramagnetics, which do not obey curie law, and correlates many

phenomena of ferromagnetism. Langevin attributed this effect to the electrons revolving in

the closed orbits of the atom producing at distance magnetic effects similar to those arising

from a current circuit. If an external magnetic field is applied, a modification in the orbital

motion will be exhibited and diamagnetic effects are produced. However, diamagnetic effects

will be produced if the molecules behave as permanent magnets owing to their net magnetic

moment. Eventually, paramagnetic effect will be produced as a result of change brought

about by collision in the orientation distribution of molecules, which behave as permanent

magnets.

Magnetic Susceptibility:-

When a substance is placed in a magnetic field, it may or may not become

magnetized. If I is the intensity of magnetization induced and H is strength of magnetic field

inducing in it then the strength of the magnetic field in the material represented by B and

known as the magnetic induction, is given by-

B = H + 4 π I

In the above equation the ratio B/H is called the magnetic permeability, μ of the

material, which can be obtained as,

B = H + 4 π I



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B/H = 1 + 4 π I/H

As, B/H is μ, and I /H = k, hence

μ = 1 + 4 π k

Where, k is the volume magnetic susceptibility of the material.

A more useful quantity than k is the molar magnetic susceptibility, Χm obtained from

the equation,

Χm = k ∙ M/ρ = I M/H ρ

Where, M is molecular weight of the compound and ρ is the density.

Now, the volume I (magnetic moment produced per unit volume of the substance)can

be positive or negative (i.e. strength of the field B, in the material may be greater or smaller

than the applied magnetic field H). If I is negative, then Χm is also negative and the material

is said to be diamagnetic. If I is positive, then Χm is positive and the material is said to be

paramagnetic.

Electrons possess magnetic dipoles because of their spin. When electrons are paired

(i.e. their spins are antiparallel), then the magnetic field is cancelled out. Most organic

compounds are diamagnetic, since their electrons are paired; however, odd electron

molecules are paramagnetic.

In the study of coordination compounds, magnetic susceptibility has been used to

obtain information about the nature of bonds and the configuration of coordination

compounds. Organic compounds, which are paramagnetic, are generally free radicals (odd

electron molecules), and the degree of dissociation of the compounds such as hexaphenyl

ethane into triphenyl methane can be measured by means of magnetic susceptibility. In the

same way an atomic and structural refractions have been determined so that corresponding

diamagnetic susceptibilities can be calculated as the molar magnetic susceptibility, which has

both additive and constructive properties.

Methods for Measurement of Magnetic Susceptibility:-

The methods frequently used for susceptibility measurements depend directly or

indirectly on the measurements of this force exerted upon the specimen when placed in a

magnetic field. The methods are classified into two main groups,

1) Non-uniform field methods

2) Uniform field methods

Non-Uniform Field Methods:-

It is employed by Faraday. According to this method a non-homogeneous field with

an axis of symmetry was produced when the poles of the magnet are inclined towards each

other. If a substance is placed in such a non-uniform field in a region where the strength of

the field changes quickly with displacement along the axis of symmetry, then the substance

will be subjected to a force along the axis, which is given by the expression

fx = m∙X∙H∙ (dH/dx)



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Where, m is mass of the substance, X is susceptibility of the substance, H is field

strength, dH/dx is field gradient along the axis.

This method is quite sensitive but according to Hoare and Brindly, it requires very

precise centering of the specimen, which is very difficult to achieve with certainty. Moreover

the measurement of field gradient is also very difficult. This method was proposed by

Faraday and then it was modified by several other workers such as, Curie-Wilson, Oxley,

Bhatnagar-Mathurand Decker.

Uniform Field Methods:-

The substance will suffer an orienting effect, if it is placed in a uniform magnetic

field, unless the body is magnetically isotropic. The moment acquired by the body will be

proportional to the susceptibility per unit volume times the volume of the body multiplied by

the field. The substance however will not experience any displacement.

The force acting on the body is given by,

f = 1/2 k∙ H2/A

Where, A is cross sectional area of the sample, H is uniform field strength and k is

volume of susceptibility of the substance.

The force acting on the specimen can be measured in absolute units by this method.

Out of the methods employing uniform magnetic field, the most important ones are Guoy’s

method for solids and liquids and Quincke’s method for liquids only.

Guoy’s Method :-

The Gouy’s method is less sensitive than the Faraday’s method. It has following

advantages

1. It is easy to adjust and set the apparatus.

2. There is less chance of damage in transit.

3. Relatively small amount of the sample is required to determine the

measurements of the susceptibility.

4. Precise centering of the tube between the two magnetic poles is not necessary

because the method utilizes uniform magnetic field.

5. The determination of the strength of the magnetic field is generally avoided by

making measurements relative to a substance whose susceptibility is known

with accuracy.

Principle:-

In the Gouy’s method a specimen in the form of a uniform cylinder is suspended in

a uniform magnetic field in such a way that one of the ends is in the region of large field

intensity, while the other is in the region of negligible field strength, it experiences a force

due to this field. As a result of this force the specimen tends to move away from the stronger

part to the weaker part of the field, if it is diamagnetic and vice-versa, if it is paramagnetic.

This force can be determined with the help of a sensitive balance in terms of an apparent

change in the weight of the specimen produced due to the application of the magnetic field.

In order to eliminate the difficulty involved in the accurate measurement of the intensity of



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the impressed magnetic field, a substance whose susceptibility is known with certainty is

used as a standard for comparison. The procedure improves significantly with the accuracy of

the susceptibility values obtained by the Guoy’s method.

The Guoy balance represented in Figure 2.2 consists of two parts,

1) Analytical balance

2) Electromagnet

Figure 2.2 Schematic Diagram of Goy Balance

Analytical Balance:-

A 0.01 mg sensitive, air damped semi-micro ‘Mettler’ single pan balance, is used for

magnetic measurements. In order to minimize effects due to vibrations the balance is

enclosed in a wooden case with glass doors and kept on a marble platform. A phosphor-

bronze rod (R), with a small hook at its lower end is attached to the bottom of the pan (P)

through a U-shaped metal extension. The rod passes below the pan into a wooden case

enclosing the electromagnet. The lower end of the phosphor-bronze rod carries an inverted Y-

shaped stirrup (S). The latter supported the horizontal arms of the glass collar in which the

specimen tube (T) is suspended vertically between the poles of the magnet.

Electromagnet:-

In the Gouy’s method the electromagnet used has poles pieces of truncated conical

shape and nickel-plated. The magnet core is made of soft iron having high permeability and

low hysterics. The coils of the magnet are wound in eight sections placed in series of wooden

formers so that any number of turns can be used as desired. The windings are of gauge d.c.

These sections are made of brass spiders for providing ample ventilation. The current of one

ampere at 460 volts is used. The low current employed is beneficial as it minimizes the

heating of the magnetic coils. An ammeter, which could read up to 0.05 ampere and a

rheostat to adjust the current exactly are placed in series with the magnet.

Specimen Tube:-

The Pyrex glass specimen tube of 10 cm in length and with a uniform diameter of

about 0.5 cm is used in the method. The tube is having a ground glass stopper and a mark was

etched at a height of 7 cm from the base, which indicates a level up to which the substance is

to be filled. The tube is held vertically and centrally between the pole pieces in such a way



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that the flat base is between the pole pieces and the other end is in a region of negligible

magnetic field.

Experimental Determination of Magnetic Susceptibility

In the method the specimen tube was washed with chromic acid first and then

thoroughly with distilled water and finally with pure acetone and dried in an oven.

The dry specimen tube was suspended between the pole pieces for sometime for

temperature equilibrium and weighed in the absence of the magnetic field. The same was

weighed in the presence of a magnetic field when a current of 0.35 ampere was passed

through the magnet. The glass tube being diamagnetic showed reduction in weight. The

difference between these two weights represented the diamagnetic ‘pull’ acting on the

specimen tube. Mean of the three closely agreeing readings was obtained to represent the

pull. When the current passed through the magnet, heating of the coils was negligible because

current was passed for only a fraction of a minute. The tube was then filled with different

standard substances and similar apparent change in weight was determined. Deducting the

‘pull’ due to empty tube alone from the above weight, the magnetic force exerted on the

specimen alone was measured. In case of liquids as specimen, they should be allowed to

stand for some time to make them free from air bubbles. The solids used in 41this study were

carefully dried and finally powdered in non-ferrous agate mortar. Small amount of these

substances were taken at a time in the specimen tube and packed as tightly as possible with

the help of a closed fitting glass rod. The substance was packed up to the etched mark.

Adherences of any particles on the side of the tube were removed by means of filter paper

strip.

Precautions:-

During the magnetic susceptibility measurements, the following precautions were

taken

1. The field strength of the magnet was kept constant by maintaining constant

current.

2. The specimen tube was packed as uniformly and as firmly as possible.

3. The tube was suspended vertically between the poles so that the tube should

not touch them.

4. The equipment was installed in such a way that there was no effect of droughts

and convection currents.

Calculations for Magnetic Susceptibility:-

The magnetic susceptibility is determined from the force exerted on a specimen,when

placed in a magnetic field by the expression,

X =2 ℓ F/ (H12- H2

2) +V KmW /W

where, ℓ is length of the specimen tube, F is magnitude of force on the body, W is

mass of specimen, V is volume of the tube up to the mark, Km is volume susceptibility and

H1 and H2 are limits of applied magnetic field.



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During the measurement of the force, ℓ, V and Km remained constant when the

temperature variation in the pole gap is negligible. The magnitude of the current remains

constant with the help of a rheostat and hence H1 and H2 also remain constant. Hence,

X =α F + C/W

Where, for a given tube, α = 2 ℓ / (H12- H2

2) and C = V Km which are constants.

For a given substance, H1 and H2 are constants and therefore α is constant. If there is

no temperature variation in the pole gap during the measurement of the force, the

susceptibility of the medium (Km) in which the specimen is suspended is also constant. Thus

from the force ‘F’ on the specimen, mass susceptibility (Χ) can be measured when ‘α’ and

‘C’ are known.

DETERMINATION OF ‘C’:-

The value of ‘C’ is given by C = V. Km

Where, V is volume occupied by the specimen under investigation, Km is volume

susceptibility of air.

The volume susceptibility of air is known with accuracy; the value of ‘C’ could be

determined.

Determination of ‘Α’:-

It is difficult to measure the values of ℓ, H1 and H2 with great accuracy, hence ‘α’ is

determined by measuring the force exerted on a substance of known magnetic susceptibility.

For example, taking the susceptibility of conductivity water as - 0.712 x 10-6

c.g.s. and

determining the value of the force exerted on water and ‘C’ and the weight of water, the value

of ‘α’ is measured. Similarly a standard solid substance like potassium chloride (- 0.712 x 10-

6c.g.s.) was also used to determine the value of ‘α’. This is confirmed by determining the

value of magnetic susceptibility of different standard substances, whose susceptibilities are

known in the literature. Farquharson has measured the susceptibilities of several sulphur

compounds and compared them with their theoretically obtained values.

UV-Visible Spectroscopy:-

Introduction:-

Several molecules are studied by UV-Visible spectroscopy as they absorb

ultraviolet or visible light. Absorbance is directly proportional to the path length (b) and the

concentration (c) of the absorbing species. Beer-Lambert’s law states that,

A = abc

Where, ‘a’ is a constant of proportionality, called the molar absorbtivity.

An absorption spectrum will show a number of absorption bands corresponding to

structural groups within the molecule, as different molecules absorb radiation of different

wavelengths. For example, the absorption which is observed in the UV region for the

carbonyl group in acetone is of the same wavelength as the absorption from the carbonyl

group in diethyl ketone.



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Electronic Transitions:-

The outer electrons in the molecule are excited during the absorption of UV or

visible radiation. There are three types of electronic transitions

1) Transitions involving p, s, and n electrons

2) Transitions involving charge-transfer electrons

3) Transitions involving d and f electrons

When an atom or molecule absorbs energy, electrons are promoted from their ground

state to an excited state. In a molecule, the atoms can rotate and vibrate with respect to each

other. These vibrations and rotations also have discrete energy levels, which can be

considered as being packed on top of each electronic level.

Absorbing Species Containing, s and n Electrons :-

In organic molecules the absorption of ultraviolet and visible radiation is restricted to

certain functional groups (chromophores) which contain valence electrons of low excitation

energy. The complex spectrum is obtained for such molecules containing chromophores. This

is because the superposition of rotational and vibrational transitions on the electronic

transitions gives a combination of overlapping lines. This appears as a continuous absorption

band.



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σ →σ* Transitions:-

I n this transition an electron in a bonding s orbital is excited to the corresponding anti

bonding orbital. The energy required is large. For example, methane (which has only C-H

bonds, and can only undergo *transitions) shows an absorbance maximum at 125 nm.

Absorption maxima due to σ → σ* transitions are not seen in typical UV-Visible spectra

(200-700 nm).

n →σ* Transitions:-

The n →σ* transitions are possible in saturated compounds containing atoms with

lone pairs (non-bonding electrons). These transitions usually required less energy than σ→σ*

transitions. They can be initiated by the radiation whose wavelength is in the range of 150-

250 nm. Less number of organic functional groups exhibit n →σ* peaks in the UV region.

n→π * and π→π *Transitions:-

Most of organic compounds show transitions of n or electrons to the π * excited

state. This is because the absorption peaks for n→π * and π→π *transitions fall in an

experimentally convenient region of the spectrum (200-700 nm). These transitions need an

unsaturated group in the molecule to provide the π electrons.

Molar absorbtivities from n →σ*transitions are relatively low and range from 10 to

100 dm3 mol

-1cm

-1and the π→π* transitions normally give molar absorbtivities between 1000

and 10000 dm3 mol

-1 cm

-1.

The effect of solvent in which the absorbing species is dissolved is also the important

factor in the spectral studies. Peaks resulting from n→π *transitions are shifted to shorter

wavelengths (blue shift) with increasing solvent polarity. This arises from increased solvation

of the lone pair, which lowers the energy of the n orbital. Often (but not always), the reverse

(i.e. red shift) is seen for π→π* transitions. This is caused by attractive polarization forces

between the solvent and the absorber, which lower the energy levels of both the excited and

unexcited states. This effect is greater for the excited state and so the energy difference

between the excited and unexcited states is slightly reduced, resulting in a small red shift.

This effect also influences π→π* transitions but is overshadowed by the blue shift resulting

from solvation of lone pairs.

Charge-Transfer Absorption:-

Charge transfer absorption is observed in many inorganic species and such species

are called as charge-transfer complexes. These species have one component with electron

donating properties and another component with electron accepting properties. Absorption of

radiation then involves the transfer of an electron from the donor to an orbital associated with

the acceptor. Molar absorbtivities for charge-transfer absorption are large (more than 10000

dm3 mol

-1 cm

-1).

UV-Visible Spectrophotometer:-

The UV-Visible spectrophotometer is used in ultraviolet-visible spectroscopy. It

measures the intensity of radiation passing through a sample (I) and compares it to the

intensity of radiation before it passes through the sample (Io). The ratio I / Io is called the



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transmittance and is usually expressed as a percentage (%T). The absorbance (A) is based on

the transmittance

A = log10I0/It = - log10T

The UV-Visible spectrophotometer can also measure the reflectance. In this case,

the spectrophotometer measures the intensity of radiation reflected from a sample (I), and

compares it to the intensity of radiation reflected from a reference material (Io). The ratio I /

Io is called the reflectance and is usually expressed as a percentage reflectance (%R).

The basic parts of a spectrophotometer are source of radiation, holder for the

sample, diffraction grating in a monochromator or prism to separate the different wavelengths

of radiation and detector. The source of radiation is often a tungsten filament (300-2500 nm),

a deuterium arc lamp, which is continuous over the ultraviolet region (190-400 nm), xenon

arc lamps, which is continuous from 160-2000 nm; or more recently, light emitting diodes

(LED) for the visible wavelengths. The detector is typically photomultiplier tube, photodiode,

photodiode array or charge-coupled device (CCD). Photodiode detectors and photomultiplier

tubes are used with scanning monochromators which filter the radiation so that only radiation

of a single wavelength reaches the detector at one time. The scanning monochromator moves

the diffraction grating to ‘step-through’ each wavelength so that its intensity may be

measured as a function of wavelength. Fixed monochromators are used with CCDs and

photodiode arrays. As both of these devices consist of many detectors grouped into one or

two dimensional arrays, they are able to collect radiation of different wavelengths on

different pixels or groups of pixels simultaneously.

A spectrophotometer can be either single beam or double beam. In a single beam

instrument all of the radiation passes through the sample cell. Io must be measured by

removing the sample. This was the earliest design, but is still in common use.



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In a double-beam instrument, the radiation is split into two beams before it reaches

the sample. One beam is used as the reference; the other beam passes through the sample.

The reference beam intensity is taken as 100% transmission (or 0 absorbance)and the

measurement displayed is the ratio of the two beam intensities. Some doublebeam

spectrophotometers have two detectors (photodiodes) and the sample and reference beam are

measured at the same time. In other spectrophotometers, the two beams pass through a beam

chopper, which blocks one beam at a time. The detector alternates between measuring the

sample beam and the reference beam in synchronism with the chopper. There may also be

one or more dark intervals in the chopper cycle. In this case the measured beam intensities

may be corrected by subtracting the intensity measured in the dark interval before the ratio is

taken.

In UV-Visible spectrophotometry, most often samples used are liquids, although the

absorbance of gases and even of solids can also be measured. Samples are typically placed in

a transparent cell, known as a cuvette. Cuvettes are typically rectangular in shape, commonly

with an internal width of 1 cm. (This width becomes the path length, b, in the Beer-Lambert’s

law). Test tubes can also be used as cuvettes in some instruments. The type of sample

container used must allow radiation to pass over the spectral region of interest. The most

widely applicable cuvettes are made of high quality fused silica or quartz glass because these

are transparent throughout the UV, visible and near infrared regions. Glass and plastic

cuvettes are also common, although glass and most plastics absorb in the UV, which limits

their usefulness to visible wavelengths. Specialized spectrophotometers have also been made.

These include attaching spectrophotometers to telescopes to measure the spectra of

astronomical features. In simpler instruments the absorption is determined at one wavelength

at a time and then compiled into a spectrum by the operator. A complete spectrum of the

absorption at all wavelengths of interest can often be produced directly by a more

sophisticated spectrophotometer.

Microspectrophotometry :-

The microscopic samples are studied by UV-Visible spectroscopy by integrating

an optical microscope with UV-Visible optics, white sources of radiations, monochromator

and sensitive detector such as charge-coupled device (CCD) or photomultiplier tube (PMT).

These are single beam instruments because only a single optical path is available. Modern

instruments are capable of measuring UV-Visible spectra in both reflectance and

transmission of micron-scale sampling areas. The advantages of using such instruments is

that they are able to measure microscopic samples but are also able to measure the spectra of

larger samples with high spatial resolution. Such instruments are used in the forensic

laboratory to analyze the dyes and pigments in individual textile fibres, microscopic paint

chips and the colour of glass fragments. Micro spectrophotometers are used in the

semiconductor and micro-optics industries for monitoring the thickness of thin films after

they have been deposited. They are also used in the field of materials science and biological

studies and for determining the energy content of coal and petroleum source rock by

measuring the vitrinite reflectance.



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Infrared Spectroscopy:-

Introduction:-

For structural determination, infrared (IR) spectroscopy is one of the most widely

used spectroscopic techniques and simply, it is the absorption measurement of different IR

frequencies by a sample positioned in the path of an IR beam. The main objective of IR

spectroscopic analysis is to determine the chemical functional groups in the sample. Different

functional groups absorb characteristic frequencies of IR radiation. Using various sampling

accessories, IR spectrometers can accept a wide range of sample types such as gases, liquids

and solids. Thus, IR spectroscopy is vital and popular tool for structural elucidation and

compound identification.

IR Frequency Range and Spectrum Presentation:-

Infrared radiation is bound by the red end of the visible region at high frequencies and

the microwave region at low frequencies and it spans a section of the electromagnetic

spectrum having wave numbers roughly from 13000 to 10 cm–1

, or wavelengths from 0.78 to

1000 μm. The IR region is commonly divided into three smaller areas, near IR, mid IR, and

far IR.IR absorption positions are generally expressed as either wave numbers or

wavelengths. Wave number defines the number of waves per unit length. Thus, wave

numbers are directly proportional to frequency, as well as the energy of the IR absorption.

The wave number unit (cm–1

, reciprocal centimetre) is more commonly used in modern IR

instruments that are linear in the cm–1

scale. In the contrast, wavelengths are inversely

proportional to frequencies and their associated energy. At present, the recommended unit of

wavelength is μm (micrometers), but μ (micron) is used in some older literature.IR studies

are generally expressed in the form of a spectrum with wavelength or wavenumber as the x-

axis and absorption intensity or percent transmittance as the y-axis. Transmittance (T) is the

ratio of radiant power transmitted by the sample (I) to the radiant power incident on the

sample (Io). Absorbance (A) is the logarithm to the base 10 of the reciprocal of the

transmittance (T).

A = log10 (1 / T) = –log10T = –log10 (I / Io)

As transmittance ranges from 0 to 100%T whereas absorbance ranges from infinity to

zero, the transmittance spectra provide better contrast between intensities of strong and weak

bands.

Theory of Infrared Absorption:-

All the atoms in molecules are in continuous vibration with respect to each otherat

temperatures above absolute zero. When the frequency of a specific vibration of atoms in a

molecule is equal to the frequency of the IR radiation directed on the molecule, the molecule

absorbs the IR radiation. Each atom has three degrees of freedom, corresponding to motions

along any of the three Cartesian coordinate axes (x, y, z). A polyatomic molecule of n atoms

has 3n total degrees of freedom. However, 3 degrees of freedom are required to describe

translational motion, the motion of the entire molecule through space. Additionally, 3 degrees

of freedom correspond to rotation of the entire molecule. Therefore, the remaining (3n – 6)

degrees of freedom are true, fundamental vibrations for non-linear molecules. Linear

molecules possess (3n – 5) fundamental vibrational modes because only 2 degrees of freedom



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are sufficient to describe rotation. Among the (3n – 6) or (3n – 5) fundamental vibrations

(also known as normal modes of vibration), those that produce a net change in the dipole

moment may result in an IR activity and those that give polarizability changes may give rise

to Raman activity. Naturally, some vibrations can be both IR- and Raman- active. The total

number of observed absorption bands is generally different from the total number of

fundamental vibrations. It is reduced because some modes are not IR active and a single

frequency can cause more than one mode of motion to occur. Conversely, additional bands

are generated by the appearance of overtones (integral multiples of the fundamental

absorption frequencies), combinations of fundamental frequencies, differences of

fundamental frequencies, coupling interactions of two fundamental absorption frequencies

and coupling interactions between fundamental vibrations and overtones or combination

bands (Fermi resonance). The intensity of fundamental band is more than those of overtone,

combination and difference bands. The combination and blending of all the factors thus

create a unique IR spectrum for each compound.

Stretching and bending vibrations are the major types of molecular vibrations.

Infrared radiation is absorbed and the associated energy is converted into these types of

motions. The absorption involves discrete, quantized energy levels. However, the individual

vibrational motion is usually accompanied by other rotational motions. These combinations

lead to the absorption bands, not the discrete lines, commonly observed in the mid IR region.

Dispersive Spectrometers:-

It is introduced in the mid-1940s and widely used since, provided the robust

instrumentation required for the extensive application of this technique.

Spectrometer Components:-

It consists of three basic components, radiation source, monochromator and

detector. An inert solid heated electrically to 1000 to 1800°C is the common radiation source

for the IR spectrometer. Three popular types of sources are Nernst glower (constructed of

rare earth oxides), Globar (constructed of silicon carbide) and Nichromecoil. They all

produce continuous radiations, but with different radiation energy profiles.



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The monochromator is a device used to disperse a broad spectrum of radiation and

provide a continuous calibrated series of electromagnetic energy bands of determinable

wavelength or frequency range. Prisms or gratings are the dispersive components used in

conjunction with variable-slit mechanisms, mirrors, and filters. For example, a grating rotates

to focus a narrow band of frequencies on a mechanical slit. Narrower slits facilitate the

instrument to distinguish more closely spaced frequencies of radiation, resulting in better

resolution. Wider slits allow more radiation to reach the detector and provide better system

sensitivity. Thus, certain compromise is exercised in setting the desired slit width.

The detectors used in dispersive IR spectrometers can be classified into two

classes: thermal detectors and photon detectors. Thermal detectors include thermocouples,

thermistors and pneumatic devices (Golay detectors). They measure the heating effect

produced by infrared radiation. A variety of physical property changes are quantitatively

determined viz. expansion of a non absorbing gas (Golay detector), electrical resistance

(thermistors) and voltage at junction of dissimilar metals (thermocouple). Photon detectors

rely on the interaction of IR radiation and a semiconductor material. Non conducting

electrons are excited to a conducting state. Thus, a small current or voltage can be generated.

Thermal detectors give a linear response over a wide range of frequencies but exhibit slow

response time and lower sensitivities than photon detectors.

Spectrometer Design:-

In a typical dispersive IR spectrometer, radiation from a broad-band source passes

through the sample and is dispersed by a monochromator into component frequencies. Then

the beams fall on the detector, which generates an electrical signal and results in a recorder

response.

Most dispersive spectrometers have a double-beam design. Two equivalent beams

from the same source pass through the sample and reference chambers respectively. Using an

optical chopper (such as a sector mirror), the reference and sample beams are alternately

focused on the detector. Commonly, the change of IR radiation intensity due to absorption by

the sample is detected as an off-null signal that is translated into the recorder response

through the actions of synchronous motors.

Fourier Transform Spectrometer:-

For most of applications Fourier transform spectrometer has recently replaced

dispersive instruments due to its superior speed and sensitivity. It greatly extended the

capabilities of infrared spectroscopy and applied to many areas that are very difficult or

nearly impossible to analyze by dispersive instruments. Instead of viewing each component

frequency sequentially, as in a dispersive IR spectrometer, all frequencies are examined

simultaneously in Fourier transform infrared (FTIR) spectroscopy.



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Spectrometer Components:-

Radiation source, interferometer and detector are the three basic components in an FT

system. The same types of radiation sources are used for both dispersive and Fourier

transform spectrometers. However, to provide better power and stability, the source is more

often water-cooled in FTIR instruments.

To differentiate and measure the absorption at component frequencies a

completely different approach is taken in an FTIR spectrometer. The monochromator is

replaced by an interferometer, which divides radiant beams, generates an optical path

difference between the beams and then recombines them in order to produce repetitive

interference signals measured as a function of optical path difference by a detector. As its

name implies, the interferometer produces interference signals, which contain infrared

spectral information generated after passing through a sample. Michelson interferometer is a

most commonly used interferometer. It consists of three active components, moving mirror,

fixed mirror and beam splitter. The two mirrors are perpendicular to each other. The beam

splitter is a semi reflecting device and is often made by depositing a thin film of germanium

onto a flat KBr substrate. Radiation from the broadband IR source is collimated and directed

into the interferometer and impinges on the beam splitter. At the beam splitter, half the IR

beam is transmitted to the fixed mirror and the remaining half is reflected to the moving

mirror. After the divided beams are reflected from the two mirrors, they are recombined at

the beam splitter. Due to changes in the relative position of the moving mirror to the fixed

mirror, an interference pattern is generated. The resulting beam then passes through the

sample and is eventually focused on the detector. Thus, the detector response for a single-

frequency component from the IR source is first considered. This simulates an idealized

situation where the source is monochromatic, such as a laser source. As previously described,

differences in the optical paths between the two split beams are created by varying the

relative position of moving mirror to the fixed mirror. If the two arms of the interferometer

are of equal length, the two split beams travel through the exact same path length. The two

beams are totally in phase with each other; thus, they interfere constructively and lead to a

maximum in the detector response. This position of the moving mirror is called the point of

zero path difference (ZPD). When the moving mirror travels in either direction by the

distance λ/4, the optical path (beam splitter–mirror–beam splitter) is changed by 2 (λ /4) or λ

/2. The two beams are 180° out of phase with each other and thus interfere destructively. As



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the moving mirror travels another λ /4, the optical path difference is now 2 (λ /2) or . The two

beams are again in phase with each other and result in another constructive interference.

When the mirror is moved at a constant velocity, the intensity of radiation reaching

the detector varies in a sinusoidal manner to produce the interferogram output. The

interferogram is the record of the interference signal. It is actually a time domain spectrum

and records the detector response changes versus time within the mirror scan. If the sample

happens to absorb at this frequency, the amplitude of the sinusoidal wave is reduced by an

amount proportional to the amount of sample in the beam.

A more complex interferogram is obtained as an extension of the same process to

three component frequencies which is the summation of three individual modulated waves. In

contrast to this simple, symmetric interferogram, the interferogram produced with a

broadband IR source displays extensive interference patterns. It is a complex summation of

superimposed sinusoidal waves, each wave corresponding to a single frequency. When this

IR beam is directed through the sample, the amplitudes of a set of waves are reduced by

absorption if the frequency of this set of waves is the same as one of the characteristic

frequencies of the sample.

The interferogram contains information over the entire IR region to which the

detector is responsive. A mathematical operation known as Fourier transformation converts

the interferogram (a time domain spectrum displaying intensity versus time within the mirror

scan) to the final IR spectrum, which is the familiar frequency domain spectrum showing

intensity versus frequency. During the mirror scan, the detector signal is sampled at small and

precise intervals. The sampling rate is controlled by an internal, independent reference, a

modulated monochromatic beam from helium neon (He-Ne) laser focused on a separate

detector.

Deuterated triglycinesulfate (DTGS) and mercury cadmium telluride (MCT) are the

two most popular detectors for a FTIR spectrometer. The response times of many detectors

(e.g. thermocouple and thermistor) used in dispersive IR instruments are too slow for the

rapid scan times (1 sec or less) of the interferometer. The DTGS detector is a pyroelectric

detector that delivers rapid responses because it measures the changes in temperature rather

than the value of temperature. The MCT detector is a photon (or quantum) detector that

depends on the quantum nature of radiation and also exhibits very fast responses. DTGS

detectors operate at room temperature while MCT detectorsare maintained at liquid nitrogen

temperature (77 °K). In general, the MCT detector is faster and more sensitive than the

DTGS detector.

Spectrometer Design :-

The basic design of the instrument is quite simple. The IR radiation from a broadband

source is first directed into an interferometer, where it is divided and then recombined after

the split beams travel different optical paths to generate constructiveand destructive

interference. Next, the resulting beam passes through the sample compartment and reaches to

the detector.

Most benchtop FTIR spectrometers are single beam instruments. Unlike double beam

grating spectrometers, single beam FTIR does not obtain transmittance or absorbance IR

spectra in real time.



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A typical operating procedure is described as follows

A background spectrum is first obtained by collecting an interferogram(raw data),

followed by processing the data by Fourier transform conversion. This is a response curve of

the spectrometer and takes account of the combined performance of source, interferometer

and detector. The background spectrum also includes the contribution from any ambient

water (two irregular groups of lines at about 3600 cm–1

and about 1600 cm–1

) and carbon

dioxide (doublet at 2360 cm–1

and sharp spike at 667 cm–1

) present in the optical bench.

Next, a single beam sample spectrum is collected. It contains absorption bandsfrom

the sample and the background (air or solvent).

The ratio of the single beam sample spectrum against the single beam background

spectrum results in a ‘double beam’ spectrum of the sample. To reduce the strong background

absorption from water and carbon dioxide in the atmosphere, the optical bench is usually

purged with an inert gas or with dry, carbon dioxide–scrubbed air (from a commercial purge

gas generator). The alignment of spectrometer which includes optimization of the beam

splitter angle is required when a sample accessory is changed as part of a periodic

maintenance.

Thermal Analysis:-

The thermal analysis is concerned with the change in temperature. The change in

temperature always causes some changes in the substance concerned, e.g. water is

transformed from liquid to solid (ice) when it is deprived of heat of 80 cal per gram and from

solid to liquid when it is given same amount of heat. When it is heated to 100oC i.e.a heat of

540 cal/gm is further given, it is transformed into gas (vapours). These heats are latent heats

of fusion and latent heat of vapourization respectively. Heated or cooledmatters undergo

various changes, not only in the state but also in enthalpy, weight, dimensions and electric

resistance.

According to the ICTA (International Confederation on Thermal Analysis) the

thermal analysis is a group of techniques in which physical property of a substance is

measured as a function of temperature whilst a substance is subjected to controlled

temperature programmed.

In these methods, the change in physical and chemical properties of the material

subjected to the programmed heating or cooling at the pre-determined rate in the controlled

atmosphere are monitored as a function of temperature. Thermoanalyticaltechniques include

several methods which measures the properties such as mass, energy, dimension, modulus of

electricity, dielectric constant, etc. Each technique is identified with the physical parameter

measured.

If the mass of a substance is measured as a function of temperature, then the

technique is called as Thermogravimetry (TG) whereas if temperature difference between the

sample and the thermally inert reference material is measured as a function of temperature,

the technique is called as Differential Thermal Analysis (DTA). These techniques are

discussed in lucid manner in several books and monographs



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Table 2.1 Common Thermal Analysis Techniques

Technique Property Acronym

Thermogravimetry Mass TG

Thermomagnatometry Apparent mass Tm

Differential Thermal Analysis Temperature DTA / TA

Differential Scanning Calorimetry Heat/Heat Flux DSC

Thermodilatometry Dimensions TD

Thermomechanical Analysis Mechanical Properties TMA

Dynamic Mechanical Analysis DMA

Dielectric Thermal Analysis Electrical Properties DETA

Evolved Gas Detection Volatiles EGD

Evolved Gas Analysis EGA

Out of several thermo analytical techniques only two techniques namely, TG and

DTA were employed in the investigation hence are briefly illustrated in the following

sections.

Thermogravimetry (TG):-

It is a technique in which the mass of the sample is monitored against a time or

temperature of the sample when it is subjected to a programmed temperature change in a

specified atmosphere. The plot of a mass change versus temperature is termed as a

thermogravimetric or a TG curve.

The continuous recording of mass change offers special advantage; in that there is

much less possibility of missing the step corresponding to the formation of the weakly stable

intermediate in the multistep thermal decomposition reactions.



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TG curves describe some characteristic temperatures called the inception (Ti),

inflection (Tm) and final temperature (Tf). Inception temperature indicates the onset of the

mass change in the sample and generally corresponds to the temperature at which the

cumulative mass change exceeds the sensitivity of the thermogravimetric system. The

inflection temperature represents the temperature at which the rate of mass changewith

respect to temperature is maximum. The final temperature corresponds to the temperature at

which the mass loss / gain in the given step is complete. These temperatures for a given

sample size vary with several experimental parameters such as the sample size, heating rate,

type of sample holder, ambient atmosphere, etc. and sample characteristics such as particle

size, etc. Literature study gives many examples demonstrating the role of these experimental

parameters on the nature of the TG curve.

The thermo balance is used for monitoring the mass change as a function of

temperature. Such system can also be employed to monitor the mass change in the sample

isothermally. The thermo balance consists of a balance and a furnace as the main

components. The former monitors the mass change and the latter heats the sample at the

programmed rate or isothermally. The other important accessories of a thermo balance are the

gas and vacuum manifolds, temperature programmer and sample carrier. Several types of

thermo balances with different sensitivities and load capacities are available commercially.

Thermo balances have to be calibrated for mass and temperature using the standard materials

recommended by ICTAC.

Differential Thermal Analysis (DTA):-

Differential thermal analysis is one of the simplest and oldest thermal techniques.

It is employed to study the physical and chemical transformations in the materials associated

with the energy changes. The technique is associated with the measurement of temperature

difference between the sample and the thermally inert reference material when both are



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heated simultaneously at the predetermined constant heating rate in controlled atmosphere.

The sample as well as reference material kept in identical sample holders are located in the

uniform temperature zone of the furnace. The sample holders are made of silica, alumina or

platinum group metal alloys. The choice of the holder / container depends on several factors.

The system being investigated should be physically and chemically compatible with the

container material. The container should not crack due to dimensional incompatibility of the

product of transformation with it. Moreover, the sample under investigation undergoing

physical or chemical transformation like melting, vaporization or decomposition should not

promote any side reactions, which are often experienced when the container made up of

platinum group metal alloys are used.

The sensitivity of DTA instrument not only depends on the type of thermocouple

used but also on the sample container, its shape and the material from which it is fabricated.

The most commonly employed thermocouples in DTA are made either of base metal alloys

or platinum group metal alloys. The former, which includes chromel / alumel thermocouple,

can be used in inert or oxidizing atmosphere up to 1150oC and has an average sensitivity of

40 μV/oC. Platinum metal and their alloys are however known to vaporize at higher

temperature with the formation of their volatile oxides above 1200oC. This could result in the

loss of these precious metals on prolonged use. Continuous use of such thermocouples at high

temperatures could also result in the change in the sensitivity of these thermocouples due to

change in the composition of the alloy wire. In DTA, temperature difference between the

sample and the reference (ΔT) is plotted against the temperature T of either the sample or the

reference. The temperature difference ΔT is plotted on Y-axis and the temperature of the

sample is plotted on the X-axis.

The peaks obtained in a plot of ΔT vs T can either be exothermic or endothermic

depending on whether the energy is released or absorbed during the physical or chemical

process under consideration. Conventionally, the peak resulting due to exothermic process is

plotted above X-axis and that due to endothermic process below the X-axis. The initiation

temperature of the peak (Ti) indicates the temperature at which the process begins; the peak

temperature Tm, corresponds to the temperature at which rate of transformation of the

substance with respect to temperature is maximum and at the termination temperature (Tf)



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refers to the temperature at which the process is completed. These temperatures for first peak

are marked. The area under the DTA peak gives the measure of the energy / heat released or

absorbed during the process and is directly proportional to the active mass transformed. The

ratio of area traversed at any temperature ‘T’ on the DTA peak to the total area corresponds

to the fraction converted ‘α’.

In high sensitivity mode DTA can also be used for determination of glass transition

temperature (Tg). Just as conventional TG balance can be adopted for isothermal

measurements, DTA instrument also can be employed for following the temperature change

in the sample when the system comprising of the sample and the reference holder is

maintained at constant temperature and the process is initiated in the sample. Such approach

has been adopted in the study of the kinetics of solid state reactions, assuming that the

amount of heat absorbed / evolved is proportional to the amount of material transformed.

The DTA curve is highly influenced by several experimental parameters such as

sample size, heating rate, material and shape of container, ambient atmosphere, etc. The

knowledge of the influence of these factors on DTA curve is extremely important in the

interpretation of DTA curves.

X-Ray Diffraction:-

X-ray diffraction has been in use since the early part of twentieth century for the

fingerprint characterization of crystalline materials and the determination of crystal structures

and is one of the most important and useful techniques in solid state science. XRD was used

to confirm the formation of the metal oxides. Thus by matching the pattern recorded for the

sample with that in the standard X-ray diffraction file, the unknown can be identified.

Theory of X-Ray Diffraction:-

There are two categories of solid materials, crystalline and amorphous. When the

atoms or molecules are arranged in regular fashion in three dimensions, it is known as

crystalline state, while if atoms are arranged in irregular fashion then it is amorphous state.

The relatively random arrangement of molecules in non-crystalline materials makes them

poor scatters of X-rays, resulting in broad diffused maxima in their diffraction patterns. The

X-ray patterns of the amorphous materials are quite distinguishable from those of crystalline

specimen, which give sharply defined diffraction patterns. In crystalline materials, periodic

arrangement of atoms in all three dimensions is observed and is repeated over long distances.

Such arrangement gives rise to the lattice planes with fixed distance between adjacent planes.

The distance between the planes are related to the lattice parameters, the cell edges and inter

planer angles, which are the fingerprints for its identification. The distance‘d’ between the

two successive planes in the crystal is determined experimentally by X-ray diffraction.

X-rays are electromagnetic radiations of wavelength around 1Ao. They are

produced when a beam of electrons accelerated through ~30 kV is allowed to strike a metal

target such as Cu, Mo and Cr, etc. The high energy electrons knock off from the orbit close to

the nucleus and the electrons from higher level jump to the vacant levels and energy released

during the transition appears as X-rays. These are termed as characteristic X-rays. The

background or white radiations are also produced due to interaction of high energy electrons



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with matter and their subsequent deceleration. These background X-rays are suitably filtered

and X-rays with energy in the range 0.01 to 10 nm are employed in the X-ray diffraction

studies.

Principle of X-Ray Diffraction:-

The X-rays are scattered by the electrons or atoms without change in the wavelength,

the phenomenon is called as X-ray diffraction. In crystals the inter planer distance is of the

same order of magnitude as that of wavelength of X-rays and hence the crystal acts as a

grating for X-rays. The diffraction of X-rays by crystals obeys Bragg’s law

nλ = 2d sinθ

Where, n is the order of diffraction, is the wavelength of monochromatic X-rays and d

is the inter planer distance. It is clear that for the given values of and , the inter planer

distance ‘d’ can be evaluated.

When a narrow X-ray beam strikes the surface of a crystal like NaCl at a glancing

angle (θ) it meets an array of ions in parallel planes AA, BB separated by a inter planer

distance‘d’. The incident radiation LM is reflected as MN from the plane AA and the incident

radiation PQ is reflected as QR from the plane BB and so on. The second radiation PQR has

to travel a longer path than the first radiation LMN, the extra path being SQT, from the

geometry of the crystal planes and the laws of optical reflection is 2d sin (θ). If the two

reflected radiations are in phase then the path difference has to be an integral multiple of

� , the wavelength of the X-ray.

In powder method, a monochromatic beam of X-ray falls on the finally powdered

substances to be examined. The diffracted beam may be detected either by surrounding the

sample with a strip of photographic film or by using a movable detector, such as Geiger

counter, connected to a chart recorder such as diffractometer, which gives series of peaks on

a strip of chart paper. The peak positions and peak heights obtained from the chart are useful

for phase identification and phase analysis.

X-Ray Diffraction in Thermal Studies:-



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During the course of thermal analysis of solid materials the characterization of

materials is essential. X-ray diffraction has been used in solid state reactions and thermal

decomposition. In decomposition reactions, TG and DTA may be used to determine

individual decomposition steps, e.g. thermal decomposition of calcium oxalate monohydrate

CaC2O4.H2O + CaC2O4 CaCO3 CaO

The decomposition occurs in three steps giving intermediates as anhydrous calcium

oxalate and calcium carbonate and finally to calcium oxide at 800oC. The characterization of

these decomposition products is further supported by X-ray diffraction patterns, which are

characteristics of each compound. The products of solid state reactions are usually in the

form of a powder or a sintered polycrystalline material. X-ray diffraction technique is the best

for analyzing the product since this technique explains which crystalline material or mixture

of phases are present. X-ray diffraction technique also provides the information about the

completion of the reaction.

References:-

1. AMC Technical Briefs, Ed. Michael Thompson, Analytical Methods Committee,

AMCTB No 29, The Royal Society of Chemistry, 45 (2008)

2. R. Kellner, J.M. Mermet, M. Otto and H.M. Widmer, ‘Analytical Chemistry’,

Wiley-VCH, 433 (1997).

3. G. Raj, ‘Advanced Physical Chemistry’, Goel Publisher House, Meerut, 110 (1995).

4. J.N. Murrell and A.D. Jenkins, ‘Properties of Liquids and Solutions’,

Wiley-Interscience, New York, (1994).

5. M. Faraday, ‘Experimental Researches in Electricity and Magnetism’, (1949).

6. E. Muller, J. Electrochem., 45, 593 (1939).

7. W. Klemm, J. Electochem., 45, 503 (1939).

8. F.W. Gray and J.H. Cruickshank, Trans. Faraday Soc., 31, 1491 (1935).

9. P. Langevin, Ann. Chim. Phys., 4, 70 (1905).

10. F.E. Hoare and C.W. Brindly, Proc. Roy. Soc., London, 152 A, 342 (1935).

11. P. Curie and J. Wilson, Phys., 197, 263 (1895).

12. A.E. Oxley, Trans. Roy. Soc., London, 214 A, 109 (1914).

13. S.S. Bhatnagar and K.N. Mathur, ‘Physical Principles and Applications of

Magneto-chemistry’, Macmillan and Co. Ltd., London, (1935).

14. H. Decker, Ann. Phys., 79, 324 (1926).

15. L.G. Guoy, Compt. Rend., 109, 935 (1889).

16. G. Quincke, Ann. Phys., 24, 347 (1885).

17. J. Farquharson, Phil. Mag., 14, 1003 (1932).72

18. F.A. Cotton and G. Wilkinson, ‘Advanced Inorganic Chemistry’, John Wiley and

Sons, New York, (1966).

19. L.J. Bellamy, ‘The Infrared Spectra of Complex Molecules’, Chapman and Hall,

2 (1980).

20. G. Herzberg, ‘Molecular Structure and Molecular Spectra’, Van Nostrand,

London, 1 (1950).



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21. J.R. Ferraro and L.J. Basilo, ‘Fourier Transform Infrared Spectroscopy:

Applications to Chemical Systems’, Academic Press, 2 (1979).

22. J.O. Hill, ‘Better Thermal Analysis and Calorimetry’, 3rd Ed., International

Confederation for Thermal Analysis, (1993).

23. A. Blazek, ‘Thermal Analysis’, Reinhold, Van Nostrand, London, (1973).

24. W.W. Wendland, ‘Thermal Analysis’, Interscience, (1985).

25. P.D. Garn, ‘Thermoanalytical Methods of Investigation’, Academic Press,

New York, (1963).

26. P. Daniel, ‘Thermal Analysis’, Kogan Page Ltd., London, (1973).

27. C.J. Keattch and D. Dollimer, ‘An Introduction to Thermogravimetry’, Heydon,

London, (1975).

28. M.D. Judd and M.I. Pope, ‘Differential Thermal Analysis’, Heydon, London,

(1977).

29. G. Litplay, M. Berenyll and E. Sarkany, Hung. Sci. Inst., 15, 31 (1968).

30. M.D. Karkhanavala, A.B. Phadnis and V.V. Deshpande, J. Thermal Anal., 2, 259

(1970).73

31. S.R. Dharwadkar, A.B. Phadnis, S. Chandrashekharaiah and M.D. Karkhanavala,

J. Thermal Anal., 18, 185 (1980).

32. L.V. Azaroff, ‘Elements of X-ray Crystallography’, McGraw Hill Co., New York,

(1968).

33. L.S. Dentglasser, ‘Crystallography and its Applications’, Reinhold Co. Ltd.,

Van Nostrand, London, (1977)



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Chapter 3

Experimental



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Experimental

Chemicals :-

Mixed ligand Zn (II) complexes were prepared by using 8-hydroxyquinoline (HQ)

as a primary ligand and different amino acids (HL) such as L-valine, L-asparagine, L-

glutamine, L-arginine and L-methionine as secondary ligand.

For synthesis of the complexes, analytical grade zinc chloride dihydrate were used

as such without further purification. Amino acids, L-valine, L-asparagine, L-glutamine, L-

arginine and L-methionine and 8-hydroxyquinoline were obtained from S.D. Fine

Chemicals, Mumbai. Solvents like ethanol, dimethylformamide (DMF) and

dimethylsulphoxide (DMSO) and laboratory grade chemicals whenever used were distilled

and purified according to standard procedures.

Apparatus:-

Analytical balance was used for the samples weighing more than 50 mg, while

semi-micro balance was used for the samples weighing less than 50 mg. All glasswares used

were made of pyrex glass and they are calibrated by standard methods.

Synthesis of Mixed Ligand Zinc (II) Complexes:-

The zinc (II) complexes were synthesized from zinc (II) chloride dihydrate, 8-

hydroxyquinoline (HQ) as a primary ligand and different amino acids (HL) such as L-valine,

L-asparagine, L-glutamine, L-arginine and L-methionine as secondary ligand.

An aqueous solution (10 cm3) of zinc (II) chloride dihydrate (136.29 mg,

1mmol) was mixed with ethanolic solution (10 cm3) of 8-hydroxyquinoline (145 mg,

1mmol). The mixture was stirred and kept in a boiling water bath for 10 minutes. To this hot

solution, an aqueous solution (10 cm3) of amino acid (1 mmol) was added with constant

stirring. The reaction mixture (1:1:1 molar proportion) was taken in water bath and heated

for about 10 minutes till the temperature reached to 50oC. The pH of the mixture was raised

by adding dilute ammonia solution in the reaction mixture and complex was obtained. Then

the mixture was cooled and solid complex obtained was filtered, washed with water

followed by ethanol. The complexes thus synthesized were dried under vacuum.


The purity of the all ligands used for the synthesis of mixed ligand Zn (II)

complexes was ascertained by recording their exact melting points. The elemental analysis

of mixed ligand Zn (II) complexes for carbon, hydrogen and nitrogen was carried out on

Thermo Finnigan Elemental Analyzer, Model No. FLASH EA 1112 Series at Department of

Chemistry, I.I.T., Mumbai while copper and zinc in the complexes were estimated

complexometrically as per the methods described below.



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Complexometric Estimation of Zinc:-

i) Decomposition of the Zinc (II) Complex:-

The 20 cm3concentrated HNO3 was added to 0.35 gm of zinc (II) complex

(accurately weighed) and the mixture was evaporated to dryness in a beaker on a sand bath.

To the same mixture, few drops of HClO4 in 2 cm3concentrated HNO3 were then added and

the content of the beaker was again evaporated to dryness. The procedure was repeated till

the organic moiety was decomposed completely.

ii) Complexometric Titration:-

The 100 cm3 of dilute HCl was added by slow heating to the content of beaker

and the whole mixture was heated till boiling. In a conical flask 10 cm3

of above solution

was taken and 1 test tube distilled water and 10 cm3

of buffer solution of pH 10 was added to

it. The resultant solution was titrated with standard solution of EDTA by using Eriochrome

black T indicator till the colour change obtained from pink to light blue.

Physicochemical Studies:-

Conductance:-

All the mixed ligand zinc (II) complexes were found to be insoluble in water and

in common organic solvents viz. ethyl alcohol, acetone, chloroform, etc. but they are

partially soluble in DMF and DMSO. Hence 10-3

M solutions of all these complexes were

prepared by dissolving them in DMSO. The molar conductance of all mixed ligand zinc (II)

complexes were measured on an Equiptronics Autoranging Conductivity Meter Model No.

EQ-667 with a dip type conductivity cell fitted with platinum electrodes (cell constant = 1.0

cm-1

).

Magnetic Susceptibility:-

The Guoy’s method was applied to measure room temperature magnetic

susceptibility of all mixed ligand zinc (II) complexes. In this method Hg [Co(SCN)4] was

used as a calibrant. The room temperature magnetic susceptibility study was carried out at

Department of Chemistry, I.I.T. Mumbai. Then using Pascal’s constant5effective magnetic

moments were calculated after applying diamagnetic corrections for the ligand and metal

ions.

Electronic Spectra:-

The electronic spectra of all mixed ligand zinc (II) complexes in DMSO solution (10-4

M)

were recorded in the ultraviolet and visible region on Shimadzu UV / VIS-160

Spectrophotometer using a quartz cell of 1 cm optical path. Calibration of the instrument

was ensured with 0.0098% KMnO4.

Infra-red Spectra:-

Infra-red spectra of all the ligands and their mixed ligand zinc (II) complexes were

recorded in KBr disc on a Perkin-Elmer FTIR Spectrophotometer Model 1600 at

Department of Chemistry, I.I.T. Mumbai. The pellets were prepared by taking necessary



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precautions to avoid moisture. The instrument calibration with respect to wave number and

percent transmission was confirmed by recording the spectrum of standard polystyrene film.

From the spectra, the characteristic groups were assigned according to the different

frequencies.

Thermal Studies:-

Thermal studies (TG and DTA) of all mixed ligand zinc (II) complexes were

carried out in controlled nitrogen atmosphere on a Perkin-Elmer Diamond TG-DTA

instrument at Department of Chemistry, I.I.T., Mumbai by recording the change in weight of

the complexes on increasing temperature up to 900oC at the heating rate of 10

oC per minute.

X-Ray Diffraction:-

X-ray diffraction pattern of decomposed zinc (II) complexes were recorded on X-

ray diffractometer (SIEMENS Model D-500) at 900oC in controlled nitrogen atmosphere at

the scanning rate of (2 = 10) min-1

using monochromatized X-ray beam of wavelength

0.15405 nm at Department of Chemistry, I.I.T., Mumbai.

References:-

1. A.I. Vogel, ‘Textbook of Practical Organic Chemistry’, Longmans Green and

Co. Ltd., London, 5th Ed., (1989).

2. D.D. Perrin, D.R. Perrin and W.L.F. Armarego, ‘Purification of Laboratory

Chemicals’, Pergamon Press Ltd., 2nd

Ed., (1980).

3. A.I. Vogel, ‘Textbook of Quantitative Inorganic Analysis’, Longmans Green and Co.

Ltd., 5th Ed., United Kingdom, (1989).

4. A.I. Vogel, ‘Quantitative Inorganic Analysis’, 4th

Ed., ELBS, (1965).

5. P.W. Selwood, ‘Magnetochemistry’, Interscience, New York, 2nd

Ed., (1956).

6. S.P. Ross and D.W. Wilson, Spectrovision, 4, 10 (1961).

7. K. Nakanishi, ‘Infrared Absorption Spectroscopy-Practical’, Holden Day Inc.,

San Francisco, (1962).



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Chapter 4

Results and discussion



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Results and Discussion

In the present work, mixed ligand zinc (II) complexes have been synthesized by

using 8-hydroxyquinoline (HQ) as a primary ligand and N and / or O donor amino acids

(HL) such as L-valine, L-asparagine, L-glutamine, L-arginine and L-methionine as

secondary ligands. The mixed ligand zinc (II) complexes have been synthesized by the

reaction of zinc (II) chloride dehydrate with 8-hydroxyquinoline and amino acids in 1:1:1

molar proportion as per the following reactions.

ZnCl2∙2H2O + HQ + HL → [Zn (Q)(L).2H2O] + 2 HCl

Where, Q is deprotonated N and O donor primary ligand, 8-hydroxyquinoline and L

is deprotonated N and / or O donor secondary ligands, different amino acids.

All the complexes in general are non-hygroscopic, stable solids, insoluble in

water and in common organic solvents such as ethyl alcohol, acetone, chloroform, etc., but

partially soluble in DMF and DMSO. This insolubility of complexes hampered the

molecular weight determination. Therefore molecular weights were computed using

analytical data. All mixed ligand zinc (II) complexes are yellow in colour.

All the mixed ligand zinc (II) complexes are thermally stable at least up to

266oC. They do not melt but decompose at high temperatures. The higher temperature

indicates a strong metal-ligand bond in the complexes (Table 4.1 ).

The purity of all mixed ligand zinc (II) complexes are studied by thin layer

chromatography. The studies carried out on the metal complexes show single spot indicating

that they are pure and true mixed ligand metal complexes rather than a mixture of the two or

more complex species.



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Table 4.1 :- Empirical formula, molecular weight , decomposition temperature and

colour of Zn (II) complexes


Elemental analysis data (Table 4.2) shows that complexes of the type

[Zn(Q)(L)∙2H2O] are formed in 1:1:1 proportion by the reaction of metal salts, zinc (II)

chloride dihydrate with a primary ligand 8-hydroxyquinoline and secondary ligands L-

valine, L-asparagine, L-glutamine, L-arginine and L-methionine respectively.



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Table 4.2:- Elemental analysis data of Zn (II) complexes



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Conductance:-

All the mixed ligand Zn (II) complexes were found to be insoluble in water and in

common organic solvents viz., ethyl alcohol, acetone, chloroform, etc., but they were

partially soluble in DMF and DMSO. DMSO has a remarkable dissolving capacity. All the

complexes synthesized in the present work are partially soluble in DMSO. Thus 10-3

M

solutions of mixed ligand Zn (II) complexes were prepared in double distilled DMSO and

molar conductance values were measured. It is seen from the Table 4.3 that the molar

conductance values of these complexes in DMSO fall in the range 0.013 to 0.028 Mhos cm2

mol-1

, indicating their non-electrolytic nature.

Table 4.3:- Molar conductance of Zn (II) complexes



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Magnetic Susceptibility Measurements:-

In the Table 4.4 the results of the room temperature magnetic susceptibility

measurements of all the metal complexes are given. The following notations are used in all

the tables.

Χg = Specific magnetic susceptibility

Χm = Molecular magnetic susceptibility

By employing diamagnetic corrections, the magnetic moments of the mixed

ligand copper (II) complexes were calculated from the measured magnetic susceptibilities

which revealed their paramagnetic nature. The observed values for effective magnetic

moment (eff) expressed in B.M. (Table 4.4) are in the range 1.73 to 1.97. The magnetic

moment of the mixed ligand zinc (II) complexes were calculated from the measured

magnetic susceptibilities after employing diamagnetic corrections and revealed their

diamagnetic nature (Table 4.4).

Table 4.4:- Magnetic susceptibility data of Zn (II) complexes (c.g.s. units)



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Electronic Absorption Spectra:-

The electronic absorption spectra of mixed ligand Cu (II) and Zn (II) complexes

in DMSO solution were recorded in the ultraviolet and visible region (Figure 4.1 to 4.5) and

are summarized in Table 4.5. Electronic spectra of the metal chelates bear a close similarity

to those of the ligands and such type of results are reported by many researchers. Therefore

it is concluded that during complexation there is not much structural alteration of the

ligands. The electronic spectral studies of mixed ligand Zn (II) complexes show that the

bands in the range 272-280 nm (35714-36765 cm-1

) can be assigned to the π → π*transitions

of the aromatic chromophore of the ligand. The π → π* transitionsin the metal complexes

are observed at different positions indicating that the π electron system of the ligands

undergo alteration to a varying extent on coordination to different metal ions. The observed

bands in the range 333-339 nm (29499-30030 cm-1

) are attributed to the n → π*transitions

of the electrons of unshared electron pair on hetero atoms of the ligands. The electronic

spectra of the mixed ligand Zn (II) complexes also show charge transfer transitions in the

range 386-398 nm (25126-25907 cm-1

) in addition to the intra-ligand transition bands. These

bands may be attributed to the ligand to metal charge transfer (LMCT) transitions. As the

term implies, these transitions involve electron transfer from one part of the complex to

another which are fully allowed and hence give rise to much more intense absorption.

Table 4.5:- Electronic spectral data of Zn (II) complexes



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Figure 4.1:- UV –Visible Spectra of [Zn (Q) (Val.). 2H2O]

Figure 4.2:- UV –Visible Spectra of [Zn (Q) (Asp.). 2H2O]

Figure 4.3:- UV –Visible Spectra of [Zn (Q) (Glu.). 2H2O]



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Figure 4.4:- UV –Visible Spectra of [Zn (Q) (Arg.). 2H2O]

Figure 4.5:- UV –Visible Spectra of [Zn (Q) (Met.). 2H2O]



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Infrared Spectra:-

The FTIR spectra of the metal complexes recorded in KBr discs over the range

4000-400 cm-1. The IR spectra of the complexes were rather difficult to analyze due to

presence of many bands with fluctuating intensities. But on the basis of reported infrared

spectra of several N and / or O donor ligands, 8-hydroxyquinoline and their metal complexes

the important bands were assigned. It is observed that in the infrared spectra of all the metal

complexes there is absence of band due to O-H stretching vibrations of either the free –OH

group of 8-hydroxyquinoline or of the –COOH group of the amino acid. Therefore it can be

concluded that complexes are formed by the deprotonation of hydroxyl group of HQ and

carboxylic group of the amino acid moiety.A broad band observed in the region between

3300-3194 cm-1 due to asymmetric and symmetric O–H stretching modes and a weak band

in the range 1578-1570 cm-1due to H–O–H bending vibrations indicating presence of water

molecules furtherconfirmed by thermal studies.

In the infrared spectra of the metal complexes with 8HQ, there is the absence of

band 3440 cm-1due to the O-H stretching vibration of the free O-H group of HQ. Hence it

can be concluded that in the process of complex formation deprotonation of the hydroxyl

group of HQ moiety takes place to form M-O bond. The position of (CO) band in 8HQ

undergoes variation depending on metal complex under study. Charles et al. reported that for

several metal complexes with HQ, the (CO) band is observed at ~1120 cm-1. A strong (CO)

band observed in the range1111-1105 cm-1indicates the presence of oxine moiety in the

complexes coordinated through its nitrogen and oxygen atoms as uninegative bidentate

ligand.

The (C=N) mode observed at 1580 cm-1in the spectra of free HQ ligand is found

to be shifted to lower wave number in the range of 1500-1460 cm-1 in the spectra of

complexes, which indicates the coordination through tertiary nitrogen donor of HQ. The

coordination through ring nitrogen atom of HQ with the metal has been confirmed on the

basis of bands observed at the range of 508-504 cm-1 and 791-780 cm-1 that corresponds to

in plane and out of plane ring deformation modes respectively.

It is reported that, stability of amino acid complexes increases with the decrease in

the N-H stretching vibrational frequency. By comparing the spectra of free amino acids, it

has been proved that there is decrease in the N-H stretching frequency on complex

formation. Character and strength of the M-N bond has been correlated to the shift of N-H

stretching band. Broad band’s observed at range 3193-3086 cm-1 and 3060-3052 cm-1 are

assigned to N-H (asymmetric) and N-H (symmetric) vibrations respectively. In case of IR

spectra of free amino acid these bands appear at the range of 3040 and 2960 cm-1. This shift

of N-H vibrations to higher wave numbers, suggest that in the formation of metal

complexes, nitrogen atom of amino group coordinate to metal ion. Coordination through the

amino group of the amino acids has been further confirmed by the C-N symmetrical

stretching frequency. It is observed at 950 cm-1 in the spectra of free amino acids and found

to be shifted to lower wave numbers in the range of 914-910 cm-1in the spectra of the

complexes.

The coordination of carboxylic acid group via oxygen with the metal ion may be

indicated by the interpretation of the asymmetric and the symmetric mode of vibration of

(COO-) band. The asymmetric (COO-) band of free amino acids i.e. 1610-1590 cm-1 is



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shifted to higher wave number, in the range 1643-1602 cm-1 and the symmetric (COO-)

mode observed at 1400 cm-1 in the spectra of free amino acids is found to be shifted to

lower wave number in the range of 1373-1370 cm-1, in the spectra of complexes. Usually

the intense band is observed due to O-H stretching vibrations in the region 3650-3200 cm-1

indicates the presence of hydroxyl group in the molecule of carboxylic acid. In the spectra of

metal complexes, there is absence of bands due to O-H stretching vibrations indicating

bonding via oxygen atom of hydroxyl group to the metal ion. Some new bands of weak

intensity observed in the regions of 615-600 cm-1 and at 410 cm-1 may be ascribed to the

M-O and M-N vibrations respectively. It may be noted that these vibrational bands are

absent in the infra-red spectra of HQ as well as amino acids. The M-O bond has much less

covalent character than the M-N bond so the stretching bands of the former appear in low

frequency region.

The IR spectra of the complexes are shown in (Figure 4.6 to 4.10). Some of the

important IR bands and their assignments are shown in Table 4.6

Table 4.6:- Infra-red spectral bands (cm-1

) of Zn (II) complexes



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Figure 4.6:- FTIR Spectra of [Zn (Q) (Val.). 2H2O]

Figure 4.7:- FTIR Spectra of [Zn (Q) (Asp.). 2H2O]



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Figure 4.8:- FTIR Spectra of [Zn (Q) (Glu.). 2H2O]

Figure 4.9:- FTIR Spectra of [Zn (Q) (Arg.). 2H2O]



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Figure 4.10:- FTIR Spectra of [Zn (Q) (Arg.). 2H2O]

Thermal Studies:-

To understand the stages of decomposition, temperature range of decomposition

and decomposition products formed during the sequence of decomposition, the thermo-

gravimetric analysis (TG) and differential thermal analysis (DTA) was carried out for mixed

ligand zinc (II) complexes. The TG and DTA studies of the complexes have been recorded

in the nitrogen atmosphere at the constant heating rate of 10oC per minute upto 900

oC. TG

and DTA curves shown in Figure 4.11 to 4.20 and thermo analytical data is summarized in

Table 4.7 The thermal study indicates that the complexes show gradual loss in weight due to

decomposition by fragmentation with increasing temperature and they are thermally quite

stable.

Thermal Study on Zinc (II) Complexes:-

All the Zn (II) complexes show similar behaviour in TG and DTA studies. The

TG-DTA curves of these complexes show the loss in weight corresponding to two co-

ordinated water molecules in the temperature range 131-171oC, followed by simultaneous

weight loss due to amino acid and 8-hydroxyquinoline moieties in the range 245-560oC.

The DTA of the complexes display an endothermic peak in the range 131-171oC

which indicate the presence of two co-ordinated water molecules. As the temperature is

raised, the DTA curve shows a broad exotherm in the range 245-560oC attributed to

simultaneous decomposition of amino acid and 8-hydroxyquinoline moieties present in the

complexes. The formation of a broad exotherm is possibly due to simultaneous

decomposition of ligand moieties and their subsequent oxidation to gaseous products like

CO2, H2O, etc. Like most of the metal organic complexes, these complexes also decompose

to a fine powder of metal oxide i.e. ZnO . The constant weight plateau in TG after 610oC

indicates completion of the reaction. The ZnO formed was confirmed by X-ray diffraction

pattern of the decomposed product.



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Table 4.7:- Thermal data of Zn (II) complexes

Figure 4.11:- TG Curve of [Zn (Q) (Val.). 2H2O]



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Figure 4.12:- TG Curve of [Zn (Q) (Asp.). 2H2O]

Figure 4.13:- TG Curve of [Zn (Q) (Glu.). 2H2O]



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Figure 4.14:- TG Curve of [Zn (Q) (Arg.). 2H2O]

Figure 4.15:- TG Curve of [Zn (Q) (Met.). 2H2O]



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Figure 4.16:- DTA Curve of [Zn (Q) (Val.). 2H2O]

Figure 4.17:- DTA Curve of [Zn (Q) (Asp.). 2H2O]



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Figure 4.18:- DTA Curve of [Zn (Q) (Glu.). 2H2O]

Figure 4.19:- DTA Curve of [Zn (Q) (Arg.). 2H2O]



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Figure 4.20:- DTA Curve of [Zn (Q) (Met.). 2H2O]



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Figure 4.21:- XRD of decomposition Product of Zn (II) Complexes

On the basis of elemental analysis data and various physico-chemical studies,

Coordination number six is proposed for zinc (II) complexes. The proposed bonding and

structure for the zinc (II) complexes are shown in figure 4.22 to 4.26.

Figure 4.22:- Proposed structure of [Zn (Q) (Val.). 2H2O]

Figure 4.23:- Proposed structure of [Zn (Q) (Asp.). 2H2O]



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Figure 4.24:- Proposed structure of [Zn (Q) (Glu.). 2H2O]

Figure 4.25:- Proposed structure of [Zn (Q) (Arg.). 2H2O]

Figure 4.26:- Proposed structure of [Zn (Q) (Met.). 2H2O]

References:-

1. G.B. Ghosale, O.P. Sharma and R.B. Kharat, J. Ind. Chem. Soc., 55, 776 (1988).

2. S. Vatsala and G. Parmeswaran, Ind. J. Chem., 25, 1158 (1986).

3. W.J. Geary, Coord. Chem. Rev., 7 (1), 81 (1971).

4. E. Canpolat and M. Kaya, J. Coord. Chem., 55 (12), 1419 (2002).

5. R. Zhang, X. Yu Wu, F. Zhao and Y. Zhan, Polyhedron, 14 (5), 629 (1995).

M. Sonmez, Turk. J. Chem., 25, 181 (2001).

6. N.S. Bhave and R.B. Kharat, J. Inorg. Nucl. Chem., 42, 977 (1980).

7. K. Krishnakutty and P. Ummer, J. Ind. Chem. Soc., 66, 194 (1989).

8. A.B.P. Lever, ‘Inorganic Electronic Spectroscopy’, 2nd Ed., Elsevier Science

Publishers, Amsterdam, (1984).

9. M. Tumer, Synth. React. Inorg. Met. Org. Chem., 30 (6), 1139 (2000).

10. P.B. Chakrawarti and P. Khanna, J. Ind. Chem. Soc., 77, 23 (1985).

11. H. Beraldo, S.M. Kainser, J.D. Turner, I.S. Billeh, J.S. Ives and D.X. West,

‘Transition Metal Chemistry’, Ed. R. L. Carlin, Marcel Decker Inc., New York,



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22 (1997).

12. A.B. Lever, J. Chem. Edu., 51, 612 (1974).

13. J.E. Huheey, E.A. Keiter and R.L. Keiter, ‘Inorganic Chemistry’, 4th Ed., Harper

Collins College Publishers, New York, (1993).

14. A.B. Lever, ‘Inorganic Electronic Spectroscopy’, 2nd Ed., Elsevier, New York,

(1986).

15. S. Panda, R. Mishra, A.K. Panda and K.C. Satpathy, J. Ind. Chem. Soc., 66, 472

(1989). 148

16. V. Bhagwat, V. Sharma and N.S. Poonmia, Ind. J. Chem., 15 (A), 46 (1977).

17. M.S. Islam, M.S. Ahmed, S.C. Pal, Y. Reza and S. Jesmine, Ind. J. Chem., 34 (A),

816 (1995).

18. K. Nakamoto, Y. Morimoto and A.E. Martell, J. Am. Chem. Soc., 83, 4528

(1961).

19. K. Mohanan and N. Thankarajan, J. Ind. Chem. Soc., 7, 583 (1990).

20. A.K. Banerjee, D. Prakash and S.K. Roy, J. Ind. Chem. Soc., LII, 458 (1976).

21. N.V. Thakkar and J.R. Thakkar, Synth. React. Inorg. Met. Org. Chem., 30 (10),

1871 (2000).

22. B.V. Murdulla, G. Venkatnarayana and P. Lingaiah, J. Ind. Chem. Soc., 28 (A),

1011 (1989).

23. R.C. Charles, H. Freiser, R. Friedel, L.E. Hillard and W.D. Johnson, Spectrochim.

Acta., 8, 1 (1956).

24. V.S. Sharma, H.B. Mathur and A.B. Biswas, Spectrochim. Acta., 17, 895 (1961).

25. D.N. Sen, C. Mizushima, C. Curran and J.V. Quagliano, Spectrochim. Acta., 77,

211 (1955).

26. D. Segnini, C. Curran and J.V. Quagliano, Spectrochim. Acta., 16, 540 (1960).

27. M.M. Kennely, Spectrochim. Acta., 15, 296 (1959).

28. C.P. Prabhakaran and C.C. Patel, J. Inorg. Nucl. Chem., 37, 1901 (1975).

29. S. Hingorani, K. Singh and B.V. Agarwala, J. Ind. Chem. Soc., 71, 183 (1994).

30. J. Chacko and G. Parameswaran, J. Ind. Chem. Soc., 28 (A), 77 (1989).

31. S.E. Al-Mukhtar, Synth. React. Inorg. Met. Org. Chem., 30 (6), 997 (2000).

32. R. Thomas, J. Thomas and G. Parameswaran, J. Ind. Chem. Soc., 73, 529 (1996).149

33. K. Nakamoto, ‘Infrared and Raman Specta of Inorganic and Coordination

Compounds’, 4th Ed., John Wiley and Sons, New York, 233 (1986).

34. S.S. Patil, G.A. Thakur and M.M. Shaikh, Acta Pol. Pharm. Drug Res., 68 (6),

881 (2011).

35. S.S. Patil, G.A. Thakur and V.R. Patil, Acta Pol. Pharm. Drug Res., 66 (3), 271

(2009).



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Chapter 5

Biological activity



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Biological Activity

Introduction:-

In last few decades, Microbiology has emerged as key branch of life sciences and

it has played important role in the finding the solutions related to the problem of global

environment, the need of recycling the natural resources, technology of genetic engineering,

health and welfare of human beings. Microbiology deals with study of living organisms of

microscopic size, which includes bacteria, fungi, algae, protozoa and viruses. It deals with

their structures, reproduction, physiology, metabolism and classification. It also includes the

study of their distribution in nature, their relationship with each other and with other living

organisms, their ability to make physical and chemical changes in the environment and their

effects on human beings and animals. The microorganisms have important applications in

many areas such as industry, agriculture, food, shelter and clothing. Although relatively few

species of microorganisms are harmful to mankind and the animals, there are many species

which perform useful roles for the mankind. Microorganisms are useful for various

physiological and biochemical applications. Microorganisms are involved in processing of

domestic and industrial wastes, in making of yoghurt, cheese and wine and in the production

of penicillin and alcohol. Some microbes are helpful while some others are harmful to the

mankind or animals. Microorganisms can deteriorate materials, like iron pipes, glass lenses

and wood pilings. They can cause diseases like pneumonia, dysentery, cholera, typhoid,

tuberculosis, etc. and can cause decay of food.

Modern bacteriology has developed in quick succession from 1874 as a well-

organized science. Number of microbiologists work on bacteria with keen interest because

bacteria can be nourished, maintained inexpensively and safely in the test tubes except some

dangerous pathogens. Many bacterial species may be investigated as individual cells or as

populations that can multiply in a few hours from a single cell to thousands or millions

within a test tube. All bacteria are classified1as Gram-positive and Gram-negative

depending upon Gram staining property.

Gram Staining Method:-

In 1884, this method was introduced by Dr. Hans Christian Gram. In this

technique a fixed bacterial smear is subjected to staining reagents in the order of crystal

violet, iodine solution, alcohol and safranine or suitable counter stain. The bacteria which

retain the crystal violet and appear as deep violet in colour are termed as Gram-positive

bacteria while those which lose the crystal violet and are counterstained by safranine and

appear pink in colour are termed as Gram-negative bacteria.

Rationale:-

Antimicrobial agent is the one that interferes with the growth and metabolism of

the microbes. The term denotes ‘inhibition of growth’. Many antimicrobial agents show both

inhibitory (bacteriostatic) and lethal (bactericidal) activity depending on the concentrations

used. The biological activity of number of organic compounds used as antimicrobial agents



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depends on size, shape and structure of molecules. In fact antimicrobial activity is associated

with every functional group in the molecule or with the molecule as a whole. It is observed

that certain functional groups especially electron rich groups like aromatic or aliphatic

carboxyl, aldehyde, phenolic –OH, halogens, amino, etc. are responsible for antimicrobial

activity exhibited by them. The role of metal complexes as drugs in the biological systems

has been widely studied. Studies on the metal complexes and their biological activity have

been reported. The majority of the metal complexes possessing biological activity are

chelates. The activity of number of antimicrobial agents depends upon their ability to form

chelates. For example, 8-hydroxyquinoline (oxine) is a well-known chelating agent which

exhibits antimicrobial properties; on the other hand, 8-methoxyquinoline is not a chelating

agent hence does not show antimicrobial activity. Number of metal chelates of the transition

metals with sulphur containing ligands shows anticancer and antitumor activity. Many Schiff

base complexes are reported as antifungal agents.

Satpathy et al. have studied biological activity of the complexes of p,p’-bis (benzoyl

thiourea) benzene with Co(II), Ni(II) and Cu (II) salts. They concluded that complexes were

more active than the ligands due to complexation. In recent years, antimicrobial and

cytotoxic studies on some mixed ligand complexes have been studied.

Methodology

In the present work the antimicrobial activity of the ligands and their metal

complexes were studied. The methodology implemented for antibacterial activity is as

follows.

Antibacterial Activity:-

For the present work following bacterial strains were selected

1. Staphylococcus aureus: Gram-positive

2. Corynebacterium diphtheriae: Gram-positive

3. Salmonella typhi: Gram-negative

4. Escherichia coli: Gram-negative

Experimental Materials:-

Media:-

Nutrient agar and Muller Hinton broth.

Culture:-

Cultures in Muller Hinton broth (24 hrs. old).

The Culture Strains:-

Staphylococcus aureus: A pathogenic, enteric Gram-positive staphylococci, responsible for

boils, wound infection, pneumonia, etc.



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Corynebacterium diphtheriae: A pathogenic, nocardioform Gram-positive bacteria,

responsible for diphtheria in human.

Salmonella typhi: A pathogenic, enteric Gram-negative bacteria, is the agent of typhoid.

Escherichia coli: A pathogenic, enteric Gram-negative bacteria, a component of the normal

adult human intestinal flora. Diarrhea caused by toxin producing E coli is major cause of

infant mortality in the third world. It also causes urinary tract infection.

Assessment of Bacteriostatic Activity:-

Bacteriostatic activity can be measured in solid or liquid media. It depends on

several aspects like the agent concerned, time of contact, temperature, nutritional

environment and type of organism under study.

The exposure time have major importance since in some cases an organism may

initially be inhibited from growing but can multiply afterwards. Hence it is necessary to

standardize the period of incubation or a long incubation period is used. The antimicrobial

activity of the metal salts, ligands and their complexes has been tested against the selected

strains of microorganisms by agar cup and tube dilution methods.

Methods of Testing:-

Agar Cup Method:-

In this method, a single compound can be tested against number of organisms or

a given organism against different concentrations of the same compound. It was found

suitable for semisolid or liquid samples and was used in the present work. In agar cup

method, a plate of sterile nutrient agar with the desired test strain was poured to a height of

about 5mm, allowed to solidify and a single cup of 8 mm diameter was cut from the center

of the plate with a sterile cork borer. Thereafter the cup was filled with the sample solution

of 1000 µg/cm3concentration. The test solution was allowed to diffuse in surrounding agar

by keeping in refrigerator for 10 min and the plate was incubated at 37oC for 24 hrs. The

extent of inhibition of growth from the edge of the cup was considered as a measure of the

activity of the given compound. By using several plates simultaneously, the activities of

several samples could be qualitatively studied.

Tube Dilution Method:-

The test compounds were subjected to in vitro screening against

Staphylococcus aureus, Corynebacterium diphtheriae, Salmonella typhi and Escherichia

coli using Muller Hinton broth as the culture medium. The test compound (10 mg) was

dissolved in DMSO (10 cm3) so as to prepare a stock solution of concentration 1000 µg/cm

3.

From this stock solution, aliquots of 50, 100, 150, 200 to ……, 1000 µg/cm3 were obtained

in test broth. Bacterial inoculums were prepared in sterilized Muller Hinton broth and

incubated for 24 hrs. at 37oC. The aliquots were dispensed (5 cm

3) in each borosilicate test

tube (150 x 20 mm). The bacterial inoculums 0.1 cm3

of the desired bacterial strain (S.

aureus, C. diphtheriae, S. typhi and E. coli) containing bacteria/cm3 was inoculated in the

tube. The tubes were incubated at 37oC for 24 hrs and then examined for the presence or

absence of the growth of the test organisms. The lowest concentration which showed no

visible growth was noted as minimum inhibitory concentration (MIC).Tetracycline was used



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as standard drug against Gram-positive and Gram-negative bacteria by similar screening

procedure. The solvent DMSO was also tested as control to see that it did not affect the

growth of the culture. MIC of tetracycline was found to be MIC of tetracycline was found to

be 1.5 µg/cm3 against S. aureus, 2.0 µg/cm

3 against C. diphtheriae, 1.5 µg/cm

3 against S.

typhi and 2.5 µg/cm3 against E. coli.

The results of microbial studies are presented in Table 5.1 to 5.3.

Table 5.1:-Antibacterial activity (mm) of Zn (II) complexes by Agar Cup Method



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Table 5.2:-MIC of metal salts, ligand and tetracycline

Table 5.3:-Antibacterial activity of Zn (II) complexes



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Results And Discussion :-

All the metal complexes were screened against Staphylococcus aureus,

Corynebacterium diphtheriae, Salmonella typhi and Escherichia coli.The agar cup method

revealed that zinc (II) complexes are more active against S. aureus and S. typhi as compared

to C. diphtheria and E. Coli (Table 5.1 and 5.2).

The minimum inhibitory concentration (MIC) of metal complexes ranges between

50-250 µg/cm3. The results show that, as compared to the activity of metal salts and free

ligands the metal complexes (Table 5.3) show higher activity (Table 5.4 to 5.5). The activity

of metal complexes is enhanced due to chelation . The chelation reduces considerably the

polarity of the metal ions in the complexes, which in turn increases the hydrophobic

character of the chelate and thus enables its permeation through the lipid layer of

microorganisms.The tube dilution method revealed that zinc (II) complexes are more active

against S. aureu sand S. typhi as compared to C. diphtheria and E. Coli.

Compared to standard antibacterial compound tetracycline, all the complexes show

moderate activity against selected strains of microorganisms.

Conclusion:-

The microbial study of zinc (II) complexes shows that the potency of the

complexes depend on various factors such as the composition of ligand, type of

microorganism and the ability of metal ion to coordinate with ligand.

References:-

1. M.J. Pelczar Jr., E.C.S. Chan and N.R. Krieg, ‘Microbiology’, 5th Ed,

McGraw Hill, Singapore, 19, 24, 28, 30, 66 and 101 (1986).

2. W.A. Sexton, ‘Chemical Constitution and Biological Activity’, 2nd Ed., (1953).

3. H.W. Florey, ‘Antibiotics II’, Oxford Medical Publications, United Kingdom,

(1949).

4. S.L. Blessman and N.J. Doorenbos, Ann. Inter. Med., 47, 1036 (1957).

5. M.B. Chenouwert, Pharmaco. Revs., 8, 57 (1956).

6. G.L. Eichhorn, ‘Coordination Compounds in Natural Products’ in J.C. Bailar,

‘The Chemistry of the Coordination Compounds’, Reinhold, New York, (1956).

7. A.E. Martel and M. Calvin, ‘Chemistry of Metal Chelate Compounds’,

Prentice Hall, New York, (1952).

8. N.J. Doorenbos, ‘Medicinal Chemistry’, Alfred Berger (Ed.), Inter-science, New

York, (1960).

9. M. Ali Akbar and S.E. Livingstone, Coord. Chem. Rev., 133, 101 (1974).

10. T. Snamt and S. Umezari, Bull. Chem. Soc. Japan, 29, 975 (1956).

11. H. Theiss, H. Schomberger and K. Borach, Arch Pharma., 299, 1031 (1966).

12. K.C. Satpathy, H.P. Mishra and B.N. Patel, J. Ind. Chem. Soc., 59, 40 (1982).

13. V.S. Shivankar and N.V. Thakkar, Acta Pol. Pharm. Drug Res., 60 (1), 45 (2003).

14. M.S. Islam, M.A. Farooque, M.A.K. Bodruddoza, M.A. Mossadik and

A.M. Shahidul, J. Bio. Sci., 2 (12), 797 (2002).



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15. P.K. Panchal, H.M. Parekh and M.N. Patel, Tox. andEnv. Chem., 87 (3),

313 (2005). 164

16. N.B. Patel, G.P. Patel and J.D. Joshi, J. Macromol. Sci., 42 (7), 931 (2005).

17. P.K. Panchal and M.N. Patel, Synth. React. Inorg. Met. Org. Nano Met. Chem.,

34 (7), 1277 (2004).

18. P.P. Corbi, A.C. Massabni, A.G. Moreira, F.J. Medrano, M.G. Jasiulionis and

C.M. Costa-Neto, Can. J. Chem., 83 (2), 104 (2005).

19. S. Arandjelovic, Z. Tesic and S. Radulovic, Med. Chem. Rev., 2 (5), 415 (2005).

Galanski, Markus, Jakupec, A. Michael, Keppler and K. Bernhard, J. Med.

Chem., 12 (18), 2075 (2005).

20. J.R. Norris and D.W. Ribbons (Eds.), ‘Methods in Microbiology’, Academic

Press, London and New York, 7B, 214 (1972).

21. Z.H. Chohan, A.K. Misbahul and M. Moazzam, Ind. J. Chem., 27A, 1102 (1988).

22. R.V. Prasad and N.V. Thakkar, J. Mol. Cat., 92, 9 (1994).



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Chapter 6

Summary



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Summary

The research study on “Synthesis and Studies on Mixed Ligand Complexes of

Zinc (II) with Amino Acids” represents the synthesis and characterization of some mixed

ligand zinc (II) complexes. A microbial study of these complexes has also been carried out.

The thesis comprises of mainly five chapters.

CHAPTER 1:-

This chapter provides basic information regarding coordination chemistry. It

comprises a data on ligating properties of many polydentate ligands including amino acids

and 8-hydroxyquinoline. It also includes introduction to mixed ligand complexes, their role

in biological systems and stability and dynamics with reference to formation of binary and

ternary complexes. To decide the aim of this study thorough literature survey was carried

out which revealed the following conclusions –

Extensive research has been carried out for the study of mixed ligand complexes

and their importance in various biological processes. It has been found that many ternary

complexes of some metals are important for activation of enzymes and they are used for

storage as well as for transport of active materials. The correlation between the stability of

the metal-ligand complexes with their anti-microbial activity has been studied. Antitumor

activity of some mixed ligand complexes also have been reported . 2Complexes of many

metals with 8-hydroxyquinoline have been studied for their biological activity. Metabolic

enzymatic activities for many metal complexes of amino acids have been reported. Many

researchers have studied characterization, antimicrobial and toxicological activity of mixed

ligand complexes of transition metals and actinide metal ions. Synthesis and characterization

of some transition metal complexes derived from amino acids have been reported. It is well

known that the copper complexes play important role in various biological processes. The

antibacterial and anti-fungal properties of zinc (II) and copper (II) complexes have been

reported. Recently synthesis, structural characterization and antibacterial studies of some

biosensitive mixed ligand copper(II) complexes have been reported. Many complexes of

copper(II) and zinc (II) metal ion have been investigated for their chelation and biological

properties. Antioxidative and antitumour properties of copper(II) and zinc (II) metal

complexes have also been reported. The spectral, magnetic and biological properties of

ternary complexes of zinc (II) metal ion with amino acid as secondary ligand have been

studied.On the basis of above investigation, it was decided to undertake the study of

synthesis and characterization of some mixed ligand zinc (II) complexes of the type

[Cu(Q)(L)]∙2H2O, and [Zn(Q)(L)∙2H2O]respectively, where Q represents the deprotonated

primary ligand, 8-hydroxyquinolineand L represents deprotonated N and O donor amino

acids viz. L-valine, L-asparagine, L-glutamine, L-arginine and L-methionine as secondary

ligands. These complexes have been screened for their antibacterial activities.



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CHAPTER 2:-

The theoretical of techniques and methods used for the characterization of mixed

ligand complexes are discussed in this chapter. It includes elemental analysis and

introduction, basics and instrumentation of conductometry. The theory of diamagnetism,

theoretical calculations of magnetic susceptibility and different methods used in the present

investigation such as Guoy’s method for magnetic study also has been discussed. It explains

basics and instrumentation of UV-Visible and IR spectroscopy. It also describes thermal

techniques used, such as thermogravimetric analysis and differential thermal analysis to

interpret structure of the complexes. To confirm nature of metal oxide after decomposition

of the complex X-ray diffraction method was carried out.

CHAPTER 3:-

The chapter explains procedure for the synthesis of mixed ligand zinc (II) complexes with

different ligands. It includes experimental method for the synthesis of metal complexes.

Synthesis of Mixed Ligand Complexes:-

Zinc (II) complexes have been synthesized by using 8-hydroxyquinoline (HQ)

as a primary ligand and different amino acids (HL) such as L-valine, L-asparagine, L-

glutamine, L-arginine and L-methionine as secondary ligands.The mixed ligand zinc (II)

complexes were prepared from zinc chloride dihydrate respectively with primary ligand

(HQ) and secondary ligands (HL) in 1:1:1 proportion, according to the following reactions

ZnCl2∙2H2O + HQ + HL → [Zn (Q)(L) ∙ 2H2O] + 2HCl

It also explains various techniques employed for the characterization of the metal complexes

such as elemental analysis, conductometry, magnetic susceptibility, UV-Visible spectra, IR

spectra, TG-DTA and X-ray diffraction.

CHAPTER 4:-

Elemental analysis, electrical conductance, room temperature magnetic

susceptibility measurements, spectral and thermal studies are employed for characterization

of mixed ligand complexes.

Characterization of Mixed Ligand Complexes:-

The chapter emphases on the results obtained and their interpretation in

characterization of mixed ligand zinc (II) complexes of 8-hydroxyquinoline (HQ) as a

primary ligand and N and / or O donor ligands (HL) such viz. such as L-valine, L-

asparagine, L-glutamine, L-arginine and L-methionine as secondary ligands. All complexes

are non-hygroscopic and thermally stable solids. The complexes are insoluble in water and

common organic solvents but partially soluble in DMF and DMSO. Colour of zinc (II)

complexes varies from yellow to greenish yellow. The decomposition temperatures of the

complexes are found to be in the range of 246-266oC indicating that they are thermally



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stable with a strong metal-ligand bond. The elemental analysis data of zinc (II) complexes is

consistent with their general formulation as 1:1:1 of the type [Zn (Q)(L)∙2H2O] respectively.

The electrical conductance studies of the complexes in DMSO in 10-3

M concentration

indicate their non-electrolytic nature. Room temperature magnetic susceptibility

measurements specify that zinc (II) complexes are diamagnetic in nature. Electronic

absorption spectra of the complexes show intra-ligand and charge transfer transitions

respectively. FTIR spectra show bonding of the metal ion through N- and O- donor atoms of

the ligand molecules. The spectra also indicate the presence of water molecules in the

complexes. The far IR region shows presence of bands due to metal-nitrogen and metal-

oxygen stretching vibrations.

The TG and DTA studies of the complexes have been studied in the nitrogen

atmosphere at the constant heating rate of 10oC per minute. The TG of all the metal

complexes indicates that they are thermally stable to varying degree. The complexes show

gradual loss in weight due to decomposition by fragmentation with increasing temperature.

All the zinc (II) complexes show similar behavior in TG and DTA studies. The

TG-DTA curves of these complexes show the loss in weight corresponding to two co-

ordinated water molecules in the temperature range 131-171oC, followed by weight loss due

to amino acid and 8-hydroxyquinoline moieties in the range 245-560oC simultaneously.

Thermal decomposition of all the metal complexes in inert atmosphere produces finely

divided metal powder which gets transformed to metal oxide spontaneously even in the

presence of traces of oxygen present in nitrogen gas used in the experiment. The constant

weight plateau in TG of zinc (II) after 610oC indicates completion of the reaction. Each

metal oxides formed was confirmed by X-ray diffraction pattern of the decomposed product.

On the basis of elemental analysis data and various physico-chemical studies, it is

suggested that zinc (II) complexes has coordination number six.

CHAPTER 5:-

The chapter contains brief introduction about the microbiology and screening

procedures for agar cup method and tube dilution method. Both the methods were

implemented for study of antibacterial activity of the complexes against S. aureus, C.

diphtheriae, S. typhi and E.coli. The antibacterial study was carried out by using the

tetracycline as a standard antibacterial compound and it was found that, the complexes show

mild activity against selected strains of micro-organisms as compared to standard

tetracycline.

References:-

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