33
Chapter 2
2.1 Introduction:
The various experimental techniques used in research work reported in this thesis
have been discussed in this chapter. The theories of each instrument have also been
discussed briefly.
2.2 Materials:
All the salts were purchased from Merck or Loba chemie. The common organic
solvents were purchased from Merck. The glassy carbon electrodes and platinum electrodes
were purchased from CH instrument Inc., USA. Surfactants were purchased from Sigma-
Aldrich. Water used in all the experiments was purified by MilliQ(Millipore) water
purification system.
Table 2.1: Chemicals used with purchase information:
Chemicals used Manufacturer
1. Benzil LOBA CHEMIE
2. Ethylene diamine ,,
3. Sodium methoxide pure ,,
4. L Ascorbic acid ,,
5. Metal salts MERCK OR LOBA CHEMIE
6. Phthalic anhydride MERCK
7. Salicylaldehyde ,,
8. 1- Butanol ,,
9. Ethylene glycol ,,
10. Potassium superoxide ALDRICH
11. Dopamine hydrochloride SIGMA
12. CTAB, TX-100, SDS HIMEDIA
13. NBT HIMEDIA
14. Semicarbazide hydrochloride Sisco Research labortary
34
Chapter 2
2.3 Experimental technique used in the work:
The various electrochemical techniques used to carry out the works reported in this
thesis have been briefly described in the following sections.
2.3.1 Nuclear Magnetic Resonance Spectroscopy (NMR):
Nuclear Magnetic Resonance spectroscopy (NMR) is basically used for
determination of the structure of organic molecules. This technique also finds its use in
quality control and for determining the purity of a sample. Any nuclei having non zero
nuclear magnetic moment value (I) is NMR active. In this work we have reported NMR
spectra of H and 13
C, both of which have I value ½. On application of a magnetic field this
nuclear magnetic moment vectors splits according to their Iz values +1/2 and -1/2 (the
direction of applied magnetic field is considered as z axis). The magnetic nuclei can be
brought into the excited state from the ground state by application of radiation of
appropriate frequency, known as resonance. In practice the magnetic field is changed
gradually keeping the applied radiation fixed. Nuclei having different chemical
environment comes under resonance at different applied magnetic field resulting in
different peaks. Further a peak corresponding to a particular nuclei splits depending on the
nature and number of other nuclei with I ≠ 0 close to it.
The chemical shift of a nucleus, in NMR spectroscopy, is the difference between the
resonance frequency of the nucleus relative to a standard molecule which is quite often
tetramethylsilane (TMS, Si(CH3)4). Chemical shift is reported in ppm and given the symbol
delta (δ).
δ = (ʋ - ʋref) x106 / ʋref
Where ʋ and ʋref are the resonance frequencies of a sample nucleus and the nuclei of TMS.
The chemical shift value is diagnostic of a nucleus in a particular environment [1].
In our works all the 1H NMR and
13C NMR spectra were recorded on a Bruker
35
Chapter 2
Ultrashield 300MHz NMR spectrometer available in our own department. TMS has been
used as internal standard while either CDCl3 or d6-DMSO as solvents depending on the
nature of the sample. Generally two types of NMR instruments exist- continuous wave and
Fourier transform.
2.3.2 Ultraviolet/Visible Spectroscopy:
UV/Vis or electronic spectroscopy is based on the absorption of electromagnetic
radiation by a molecule in the range 200 nm to 900 nm, where the wavelength of 200 nm to
340 nm are referred as ultraviolet region and from 340 nm to 900 nm is the visible region
[2,3]. In organic molecules the absorption, upon irradiation, may be due to the transitions
between various electronic levels such as,
p p* ; n p* etc.
UV/Vis spectroscopy has been employed in this thesis mainly to analyse different
metal complexes where the transition is known as d-d transition. The combined effect of
ligand field and the electron-electron repulsion between electrons in d orbitals generates a
ground state energy level and a number of higher energy states. Selective transition
between ground state and a selection rule allowed higher energy state is possible providing
information about the structure of a particular metal complex [B N Figgis, Ligand field
theory].
In the UV/Vis spectroscopy the Beer-Lambert law is significant which states that
the absorbance of a sample solution is directly proportional to the concentration of the
absorbing species and the path length [4]. Thus for a fixed path length, UV/Vis spectra can
be analyzed to determine the concentration of the absorbing species in the solution. The
Beer-Lambert law is expressed by the following equation,
A=log10(I0/I) = ε.c.l (equation 2.1)
Where A is the measured absorbance, I0 is the intensity of the incident light at a given
36
Chapter 2
wavelength, I is the transmitted intensity, l the path length of the sample which is equal to
the length of the cuvette used to record the spectra which is 1 cm and c is the concentration
of the absorbing species. ε is the proportionality constant known as extinction coefficient
which is characteristic of a particular species. Beer-Lamberts law is best applicable in case
of dilute solutions having absorbance below 1.0.
Hitachi U-3210 UV-visible spectrophotometer and Shimadzu UV-1800
spectrophotometer have been used in our work.
The basic components of a UV/Vis spectrophotometer are the light source, holder
(for the sample), diffraction grating in a monochromator or a prism (to separate the
different wavelengths of light), and a detector. The radiation source is a Tungsten filament
(300-2500 nm), a deuterium arc lamp, which is continuous over the ultraviolet region (190-
400 nm), continuous Xenon arc lamps, (160-2,000 nm or more), light emitting diodes
(LED) for the visible wavelengths. The detector is typically a photomultiplier tube, a
photodiode, a photodiode array or a charge-couple device (CCD). Single photodiode
detectors and photomultiplier tubes are embedded with scanning monochromators, which
filter the light so that only light of a single wavelength can reach the detector at a time. A
spectrophotometer can be either a single beam or a double beam. In a single beam
instrument I0 must be measured by removing the sample, where as in the double beam
instrument, the light 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 zero absorbance), and the measurement displayed is in the
ratio of the two beam intensities. Some double beam instruments have two detectors
(photodiodes), and the sample and reference beam are measured at the same time [5, 6]
Samples for UV/Vis spectrophotometry was used as liquids, although the
absorbance of gases and even of solids can also be done. Samples are typically placed in a
transparent cell, known as cuvette. The cuvettes are typically rectangular in shape,
commonly with an internal width of one cm. and made of high quality fused silica or quartz
glass which is transparent throughout the UV, visible and near infrared regions.
37
Chapter 2
2.3.3 Fourier Transform Infrared Spectroscopy Studies (FTIR):
Fourier transform infrared spectroscopy is one of the most common spectroscopic
techniques used by chemists. It is the measurement of absorption band at different IR
frequencies for a sample positioned in the path of an IR beam. The main goal of FTIR
spectroscopic analysis is the determination of chemical functional groups in a compound.
Different functional groups absorb characteristic frequencies of IR radiations. The IR
region is commonly divided into three sub areas near IR, mid IR, and far IR, having wave
numbers in the electromagnetic spectrum 13,000-4,000 cm–1
, 4,000-200 cm–1
and 200-10
cm–1
respectively. The mid IR regions within the wavelength 400 cm–1
to 4000 cm–1
are
used in the present study [7-11]. The unit cm–1
is commonly used in modern IR. In the
contrast, wavelengths are inversely proportional to frequencies and their associated energy.
Above the absolute zero temperature, all atoms in molecules are in continuous
vibrational mode with respect to each other. When the frequency of a specific vibration
directed on the molecule is equal to the frequency of the IR radiations, absorption takes
place. The major types of molecular vibrations are stretching and bending. The IR
radiations are absorbed and the associated energy is converted into these types of motions.
The absorption produce discrete (quantized) energy levels. However, the individual
vibrational motion is usually accompanied by other rotational motions. All these
combinations lead to the absorption bands which are not discrete lines as commonly
observed in the mid IR region. The features of IR absorption are generally viewed in the
form of a spectrum with wavelengths or wave numbers along the x-axis and absorption
intensity or percent transmittance along the y-axis. Transmittance (T) is the ratio of radiant
power transmitted by the sample (I) to the radiant power incident on the sample (I0) [4, 7,
12]. Absorbance (A) is the logarithm to the base 10 of the reciprocal of the transmittance
(T).
A = log10 (1/ T) = –log10T = –log10 (I /I0) (equation 2.2)
Perkin-Elmer RX1- IR system and Shimadzu IR Affinity-1 spectrometers are used
38
Chapter 2
to analyze the metal complexes.
A FTIR spectrometer consists of three basic components such as radiation source,
monochromator and detector. The common radiation source for the IR spectrometer is an
inert solid heated electrically to 1000-1800° C. Three popular types of sources are Nernst
glower (made of rare-earth oxides), Globar (made of silicon carbide) and Nichrome coil [5,
6]. They can produce different continuous radiations. 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 ranges. The 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 enable the instrument to distinguish better
for the more closely spaced frequencies of radiations, thereby resulting in good resolution.
The wider slits allow more light to reach the detector and provide better system sensitivity.
Most detectors used in dispersive IR spectrometers can be categorized 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. Several changes of physical property are quantitatively
determined i.e. expansion of a non absorbing gas (Golay detector), electrical resistance
(thermistor) and voltage at junction of dissimilar metals (thermocouple). The photon
detectors rely on the interaction of IR radiation and a semiconductor material in which non
conducting electrons are excited to a conducting state producing small current or voltage.
Thermal detectors provide a linear response over a wide range of frequencies but exhibit
slower response times and lower sensitivities than photon detectors [13, 14, 15].
I The sample is mixed thoroughly with KBr using mortar and then pressed into a
transparent disk at sufficiently high pressure. To minimize band distortion due to scattering
of radiation, the sample should be ground to particles of 2 μm (the low end of the radiation
wavelength) or less in size. The IR spectra produced by the pellet technique often exhibit
bands at 3450 cm–1
and 1640 cm–1
due to absorbed moisture. Mulls are used as alternatives
for pellets and the common mulling agents include mineral oil or Nujol (high boiling
hydrocarbon oil), Fluorolube (a chlorofluorocarbon polymer) and hexachlorobutadiene. To
39
Chapter 2
obtain a full IR spectrum that is free of mulling agent bands, the use of multiple mulls such
as Nujol and Fluorolube are generally required. The sample (1 to 5 mg) is ground with a
mulling agent (1 to 2 drops) to give a two-phase mixture that has a consistency similar to
toothpaste. This mull is pressed between two IR-transmitting plates to form a thin film. In
the work reported in this thesis all the IR spectra were recorded as KBr pallets.
2.3.4 Liquid chromatography–mass spectrometry (LC-MS)
LC-MS is an analytical chemistry technique that combines the physical separation
capabilities of liquid chromatography with the mass analysis capabilities of mass
spectrometry. LC-MS is a powerful technique used for many applications which has very
high sensitivity and selectivity. It is used for determining masses of particles, for
determining the elemental composition of a sample or molecule, and for elucidating the
chemical structures of molecules. MS works by ionizing chemical compounds to generate
charged molecules or molecule fragments and measuring their mass-to-charge ratios [16].
In a typical MS spectrometer a sample is loaded onto the MS instrument which undergoes
vaporization which is then ionized by one of a variety of methods (e.g., by impacting them
with an electron beam), which results in the formation of charged particles (ions). The ions
are separated according to their mass-to-charge ratio in an analyzer by electromagnetic
fields and detected. The technique has both qualitative and quantitative uses like –
identification of unknown compounds, determination of the isotopic composition of
elements in a molecule and determination of the structure of a compound by observing its
fragmentation.
LC-MS / MS Agilent 1260 infinity spectrometer available at SIF, IIT-Guwahati and.
Agilent LCMS triple quad. 6410 series available at Guwahati biotech park,Guwahati are
used for our study.
MS instruments consist of three modules: An ion source, which can convert gas
phase sample molecules into ions (or, in the case of electron spray ionization, move ions
that exist in solution into the gas phase). A mass analyzer, which sorts the ions by their
40
Chapter 2
masses by applying electromagnetic fields. A detector, which measures the value of an
indicator quantity and thus provides data for calculating the abundances of each ion present.
2.3.5 ESI-Mass Spectroscopy:
Mass spectrometry is an analytical technique that can provide both qualitative
(structure) and quantitative (molecular mass or concentration) information on analyte
molecules after their conversion to ions. The technique has both qualitative and quantitative
uses. ESI uses electrical energy to assist the transfer of ions from solution into the gaseous
phase before they are subjected to mass spectrometric analysis. Ionic species in solution can
thus be analysed by ESI-MS with increased sensitivity. Neutral compounds can also be
converted to ionic form in solution or in gaseous phase by protonation or cationisation (e.g.
metal cationisation), and hence can be studied by ESI-MS.
The molecules of interest are first introduced into the ionisation source of the mass
spectrometer, where they are first ionised to acquire positive or negative charges. The ions
then travel through the mass analyser and arrive at different parts of the detector according
to their mass/charge (m/z) ratio. After the ions make contact with the detector, usable
signals are generated and recorded by a computer system. The computer displays the
signals graphically as a mass spectrum showing the relative abundance of the signals
according to their m/z ratio.
The transfer of ionic species from solution into the gas phase by ESI involves three
steps: (1) dispersal of a fine spray of charge droplets, followed by (2) solvent evaporation
and (3) ion ejection from the highly charged droplets tube, which is maintained at a high
voltage (e.g. 2.5 – 6.0 kV) relative to the wall of the surrounding chamber. LCQ Deca,
Thermo Fisher instrument available at TIFR, Mumbai was used in our study.
41
Chapter 2
2.3.6 Conductivity measurements:
The ease of flow of electric current through a body is called its conductance. In
metallic conductors it is caused by the movement of electrons, while in electrolytic
solutions it is caused by ions of electrolyte. The electrolyte conductance is possible through
movement of positive and negative ions, which originate through dissociation of
electrolyte.
Conductance is the reciprocal of resistance and its unit is Mho or Ohm-1
λ= 1/R
Where, λ is the conductance and R is the resistance.
Since a solution is a three-dimensional conductor, the exact resistance will depend
on the spacing (l) and area (A) of the electrodes. The resistance of a solution in such
situation is directly proportional to the distance between the electrodes and inversely
proportional to the electrode surface. Considering the two electrodes having a cross
sectional area of A m2 and separated by l m. The resistance (R) of the electrolyte solution
present between the two electrodes is given by the relation
R∞l
R∞1/A
R= ρ (l/A) (equation 2.3)
Or ρ=RA/l (equation 2.4)
Where ρ (rho) is proportionality constant is called resistivity (formerly called
specific resistance). It is a characteristic property of the material and it is the resistance
offered by a conductor of unit length and unit area of cross section.
Substituting the value of R
42
Chapter 2
Conductance, λ=1/ρ(l/A)=KA/l (equation2.5)
where K (kappa) is reciprocal of specific resistance called as specific conductance or
conductivity. It is measured in Ω-1
m-1
. This quantity may be considered to be the
conductance of a cubic material of edge length unity. Systronics Conductivity Meter 306
was used in our study.
2.3.7 Thermo gravimetric analysis (TGA):
Thermal methods of analysis may be defined as those techniques in which changes
in physical and /or chemical properties of a substance are measured as a function of
temperature. Thermogravimetric analysis determines the change in weight of the sample as
a function of temperature. This analysis is the act of heating a sample gradually to high
enough temperatures so that different components decompose into gas.
We carried out all the thermo gravimetric experiments mentioned in this thesis using
Mettler Toledo TGA/DSC instrument.
The analyzer usually consists of a high-precision balance with a pan (generally
platinum) loaded with the sample. That pan resides in a furnace and is heated or cooled
during the experiment. A different process using a quartz crystal microbalance has been
devised for measuring smaller samples on the order of a microgram (versus milligram with
conventional TGA)[17] The sample is placed in a small electrically heated oven with a
thermocouple to accurately measure the temperature. The atmosphere may be purged with
an inert gas to prevent oxidation or other undesired reactions. A computer is used to control
the instrument.
TGA is a process that utilizes heat and stoichiometry ratios to determine the percent
by mass of a solute. Analysis is carried out by raising the temperature of the sample
gradually and plotting weight (percentage) against temperature.
43
Chapter 2
2.3.8 Electron Paramagnetic Resonance spectroscopy (EPR):
The EPR spectra were recorded either in JEOL JES-FA200 (at IIT-Guwahati) or
Bruker EMX (at TIFR – Mumbai) or Bruker EMX EPR No. – 1444 (X-band 10-12) (at IIT
–Kanpur) spectrophotometer. The magnetic field was applied up to 30 seconds. Quartz
sample tubes of diameter 3 mm was used to record the spectra. DPPH was used to calibrate
the spectra.
To be EPR active the molecule must be paramagnetic that is it must have at least
one unpaired electron. The complexes reported in this thesis are of copper (II) ion having d9
electronic configuration and hence have one unpaired electron. The copper (II) ion has
nuclear magnetic moment value I = 3/2 and hence quadratic splitting of the EPR peak is
expected.
The EPR involves resonant absorption of electromagnetic radiation by electron
spins (s = ½) in which a splitting energy levels are induced by an applied magnetic field. In
the applied magnetic field, an unpaired electron which possesses both the spin and charge,
therefore a magnetic moment can occupy one of two energy levels. The levels are
characterized by a quantum number which has the values of -1/2 or +1/2. The phenomenon
of EPR occurs when the energy of the quantum equals to the difference between the two
energy levels given by the following relation:
∆E=hν =gμβBo (equation 2.6)
Where B0 is the applied magnetic field, ν the frequency of the applied microwave radiation,
h is the Plank’s constant μβ is the magnetic moment of the electron termed as Bohr
magneton. The g is a spectroscopic variable which is the characteristic of the
paramagnetism. When the spins interact with the incident microwave radiation, there is a
net absorption and this is detected as the EPR signal.
44
Chapter 2
2.3.9 Electrochemical Techniques:
In our work we mainly used two electrochemical techniques cyclic voltammetry
(CV) and Square Wave Voltammetry (SWV). All the electrochemical experiments were
performed in CHI 600B electrochemical analyzer (USA).We used a three electrode systems
and a brief introduction of the electrodes are given below.
Working electrode: In general, an electrode provides the interface across which a charge
can be transferred or felt the effects. The working electrode serves as the surface where the
reaction or transfer of charged species take place. The reduction or oxidation of a substance
at the surface of a working electrode at the appropriate applied potential can transport a
material to the other electrode surface for producing flow of current. The selection of a
working electrode material is critical to experiment. The most commonly used working
electrode is made of platinum, gold, carbon and mercury. Among these, platinum is likely
the most suitable metal electrode, due to good electrochemical inertness and ease of
fabrication into many forms. Electrolyte is usually added to the test solution to ensure
sufficient conductivity. The combination of solvent and electrolyte along with specific
working electrode can measure the potential range. In our experiment we mainly used
platinum and carbon electrode.
Reference electrode: The reference electrode should provide a reversible half-reaction
with Nernstian behaviour that may be constant over a period of time and easy to assemble
and maintain. The most commonly used reference electrodes for aqueous solutions are the
calomel electrode and the silver/silver chloride electrode with potential determined by the
reaction given below:
Hg2Cl2(s) + 2e – = 2Hg (l) + 2Cl
–
AgCl(s) + e– = Ag(s) + Cl
–
During our work the silver/silver chloride electrode was used.
Auxiliary electrode: Auxiliary electrode is also known as the counter electrode, can be any
material and serve as good conductor and does not react with the bulk solution. Reactions
occurring at the counter electrode surface are not so important as long as it continues to
45
Chapter 2
conduct current well. To maintain the observed current the counter electrode will often
oxidize or reduce the solvent or bulk electrolyte.
The Potentiostat: The potentiostat is an electronic device which controls the potential of
the working electrode and uses a dc power source to produce a potential which can be
maintained and accurately determined, while allowing small currents to be drawn into the
system without changing the voltage. It is designed to work with a three electrode cell in
such a way that all current flows between the counter and working electrodes, while the
potential of the working electrode is controlled with respect to the reference electrode. The
potentiostat ensures that the working electrode potential is not influenced by the reactions
which take place. The simplest potentiostat has a means of setting the starting potential and
the switching potential, a sweep rate adjustment, and outputs which monitor working
electrode potential and current flow
2.3.9.1 Cyclic Voltammetry(CV):
Cyclic Voltammetry is often the first experiment performed in an electro analytical
study. In particular, it offers a rapid location of redox potentials of the electropositive
species, and convenient evaluation of the effect of medium upon the redox process [18, 19].
A three electrode system has been used in our work namely – working electrode (WE),
reference electrode (RE) and auxiliary electrode (AE). In cyclic voltammetry (CV)
experiment the potential of the working electrode is cycled, with respect to the reference
electrode, between two values using a potentiostate and the corresponding current at each
potential is recorded. This plot of current versus applied potential is known as cyclic
voltammogram.
The electrochemical reactions take place on the surface of the WE. The role of the
AE is to complete the electrochemical circuit with the WE. Fig.2.I shows a typical cyclic
voltammogram for ferrocene in acetonitrile.
46
Chapter 2
Fig. 2.1: Cyclic Voltammogram of a single electron oxidation-reduction
In Fig.2.1, the reduction process occurs from (a) the initial potential to (d) the
switching potential. In this region the potential is scanned negatively to cause a reduction.
The resulting current is called reduction or cathodic current (ipc). The corresponding peak
potential occurs at (c), and is called the reduction or cathodic peak potential (Epc). The Epc
is reached when all of the substrate at the surface of the electrode has been reduced. After
the switching potential has been reached (d), the potential scans positively from (d) to
(g). This causes oxidation to occur and oxidation or anodic current (Ipa) results. The peak
potential at (f) is called the oxidation or anodic peak potential (Epa).
The average of the reduction peak potential (potential corresponding to miximum
47
Chapter 2
ip = 2.69 x 10
5 n
3/2ACD
½ ν
½
current in reduction process) and oxidation peak potential (potential corresponding to
miximum current in oxidation process) is the redox potential also known as mid-point
potential. The redox potential value has been written as E1/2 throughout the thesis. The
magnitude of the difference between the reduction peak potential and oxidation peak
potential should be 0.059 V for one electron transfer redox system while it is 0.030 V for
two electron redox system. For an electrochemical reversible process the ratio of reduction
and oxidation peak current should be approximately 1.0.
The oxidation or reduction peak current in a cyclic voltammogram is given by the
Randles-Sevcik equation (equation2.7):
Where, ip= peak current (ampere).
n = number of electrons transferred
A= electrode surface area (cm2)
C = concentration (mol cm-2
)
D = diffusion coefficient (cm2s
-1), ν = Sweep rate
(Vs-1
)
In our experiment we mainly used this system for qualitative information of the
compound prepared.
2.3.9.2 Square wave Voltammetry (SWV):
In SWV technique the entire potential range is applied as square waves and current
is plotted against the applied potential. A square wave is superimposed on the potential
staircase sweep (Fig.2.2). Oxidation or reduction of species is registered as a peak or trough
in the current signal at the potential at which the species begins to be oxidized or reduced.
The redox potential values could be obtained directly from the voltammogram as shown in
48
Chapter 2
Fig. 2.3 for ferrocene in acetonitrile solution. The current is measured at the end of each
potential change, right before the next, so that the contribution to the current signal from
the capacitive charging current is minimized. The differential current is then plotted as a
function of potential, and the reduction or oxidation of species is measured as a peak or
trough. In the SWV experiments reported in this thesis the applied square wave amplitude
was 25 mV, the frequency was 15 Hz and the potential height for base staircase wave front
was 4 mV.
Fig.2.2: Square wave potential sweep
The peak current in square wave voltammetry is given by:
ip = k n 2
D 2
∆EA Ca (equation 2.8)
Where ip is the peak current, k is a constant, n refers to the number exchanged electrons, D
is the diffusion coefficient of analyte, ΔEA is the pulse amplitude and Ca is the
concentration of the analyte.
49
Chapter 2
Fig.2.3: Square wave voltammogram of Ferrocene in acetonitrile using Platinum working
electrode with Ag-AgCl as reference. The peak position directly gives the redox potential.
2.3.10 Magnetic Susceptibility measurement:
Magnetic materials may be classified as diamagnetic, paramagnetic, or
ferromagnetic on the basis of their susceptibilities. Magnetic susceptibility measurements
were recorded at room temperature by the Gouy method using Cambridge Magnetic
Balance. The balance works on the basis of a stationary sample and moving magnets. The
pairs of magnets are placed at opposite ends of a beam so placing the system in balance.
Introduction of the sample between the poles of one pair of magnets produces a deflection
of the beam that is registered by means of phototransistors. A current is made to pass
through a coil mounted between the poles of the other pair of magnets, producing a force
50
Chapter 2
restoring the system to balance. At the position of equilibrium, the current through the coil
is proportional to the force exerted by the sample, and can be measured as a voltage drop.
The solid sample is tightly packed into weighed sample tube with a suitable length (l) and
noted the sample weight (m). Then the packed sample tube was placed into tube guide of
the balance and noted the reading (R) was noted. The mass susceptibility, χg, is calculated
using:
Where, = the sample length (cm)
m = the sample mass (g)
R = the reading for the tube plus sample
R0 = the empty tube reading
CBal = the balance calibration constant
Then molar susceptibility χm = χg × molecular formula of the complex. The
Molar susceptibility is corrected with diamagnetic contribution. The effective magnetic
moment, μeff, is then calculated using the following expression:
μeff = 2.83 T× χm
Magnetic moments of simple Cu (II) complexes are generally in the range of 1.70-2.20
B.M, regardless of stereochemistry and independent of temperature except at extremely low
temperature.
51
Chapter 2
2.3.11 X-ray Crystallography:
The X-ray data were collected at 293 K with Bruker Smart APEX II (3 circle X-ray
diffractometer). The SMART software was used for data collection, indexing the reflection
and determination of the unit cell parameters. Integration of the collected data was made
using SAINT XPREP software. Multi-scan empirical absorption corrections were applied
to the data using the program SADABS. The structures were solved by direct methods and
refined by full-matrix least-square calculations by using SHELXTL software. All non-
hydrogen atoms were refined in the anisotropic approximation against F2 of all reflections.
The hydrogen atoms attached were located in difference Fourier maps and refined with
isotropic displacement coefficients. The hydrogen atoms were placed in their geometrically
generated positions. Crystal parameters for the compounds are presented in the
experimental section of the respective chapter.
52
Chapter 2
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