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CHAPTER 2

GROWTH AND CHARACTERIZATION OF

1H-IMIDAZOLINIUM HYDROGEN L-TARTRATE

SINGLE CRYSTALS

2.1 INTRODUCTION

Nonlinear Optical (NLO) materials are of current research interest

in materials science for their applications in second and third harmonic

generation, optical bistability, laser remote sensing, optical disk data storage,

laser driven fusion, medical and spectroscopic laser (Santhanu Bhattacharya

et al 1994). Organic molecules possess large second order molecular

polarizability (β) and more favorable physical properties like large optical

damage threshold and large birefringence. L-tartaric acid is a chiral

dihydroxycarboxylic acid and it is capable of initiating multidirectional

hydrogen bonding (Aakeröy et al 1994). The salts of tartaric acid belong to an

important class of materials because of their interesting physical properties

such as ferroelectricity, piezoelectricity and nonlinear optical properties

(Second Harmonic Generation).

The L-tartaric acid analogs were incorporated into organic salts and

their NLO properties were widely studied in recent experiments (Renuka

Kadirvelraj et al 1998). The nonlinear optical (NLO) properties of some

complexes of L-tartaric acid nicotinamide have attracted significant attention

because organic components contribute specifically to the process of second

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harmonic generation (Haja Hameed et al 2004). The 1H-Imidazolinium

Hydrogen L-tartrate single crystals are grown by slow evaporation solution

growth technique. Single crystal XRD and the theoretical factor group

analysis were carried out. The factor group analysis reveals the vibrational

modes. The IR spectrum has been recorded to confirm the functional groups

present in the material and the Second Harmonic Generation behaviour of

grown crystal was studied.

2.2 Growth of 1H-Imidazolinium Hydrogen L-tartrate single

crystals

The 1H-Imidazolinium Hydrogen L-tartrate was synthesized and

grown using two different solvents. Firstly the Imidazole and L(+)-tartaric

acid (equimolar ratio) were dissolved separately in ethanol and deionized

water, respectively and they were mixed together. The mixture of solutions

was found to be turbid and ethanol was added and stirred well for an hour by

using a motorized magnetic stirrer till a clear solution was obtained. The

solution was filtered using Whatman (grade no.1) filter paper in clean vessels

and the vessels containing the solution were closed with perforated polythene

cover and housed in the constant temperature bath (CTB) for growth at 32°C.

Single crystals were obtained within 12 days and one of the harvested crystals

is shown in Figure 2.1.

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Figure 2.1 As grown 1H-Imidazolinium Hydrogen L-tartrate single

crystal using ethanol as solvent

Secondly, the equimolar (1:1) ratio of Imidazole (C3N2H4)

(SRL-extra pure) and L (+) tartaric acid (C4H6O6) (Merck-extra pure) were

dissolved separately in deionised water. Then the solutions of the individually

prepared raw materials were mixed together and continuously stirred for six

hours. The solution was filtered using Whatman (grade No.1) filter paper in

clean vessels and the vessels containing the solution were closed with

perforated polythene covers and housed in the constant temperature (CTB)

bath at 32°C. The nucleation was observed in seven days and allowed to grow

for four weeks. The reaction is shown in the Figure 2.2. The crystal of size

15mm × 10mm × 5mm is obtained after four weeks (Figure 2.3).

N

NH

H

H

H

COOH

COOH

OH

OH

+N

NH

H

H

H

COOH

COOH

OH

OH

C3N2H4 + C4H6O6 C7N2H10O6

Imidazole L(+)-tartaric acid Imidazolinium Hydrogen L-tartrate

Figure 2.2 Reaction Scheme of 1H-Imidazolinium Hydrogen L-tartrate

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Figure 2.3 As grown 1H-imidazolinium Hydrogen L-tartrate single

crystal using water as solvent

2.3 CHARACTERIZATION OF 1H-IMIDAZOLINIUM

HYDROGEN L-TARTRATE SINGLE CRYSTALS

2.3.1 Single crystal XRD analysis

From the X-ray diffraction results, it has been found that IH-

imidazolinium Hydrogen L-tartrate belongs to the monoclinic crystal system

with space group P21 having two molecules in the unit cell. The single crystal

X-ray diffractometer (model Nonius CAD-4/MACH) with MoKα (0.71073Å)

radiation was used to obtain the accurate cell parameters of the grown

1H-Imidazolinium Hydrogen L-tartarate crystals at room temperature by the

least square refinement of the setting angles of 25 reflections. The obtained

lattice parameters are presented in Table 2.1, which are in good agreement

with the reported values (Aakeröy and Hitchcock 1993).

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Table 2.1 Crystallographic data of 1H-Imidazolinium Hydrogen

L-tartarate

Lattice

parametersPresent work

Reported

(Aakeröy and Hitchcock 1993)

a 7.555(4)Å 7.569(1) Å

b 8.989(4) Å 8.993(1) Å

c 6.961(4) Å 6.953(1) Å

α 90° 90°

β 101.43°(4) 101.55°(1)

γ 90° 90°

V 463.4(4) Å3 463.7 Å3

2.3.2 High Resolution X-ray Diffraction Studies on ImiLT Crystal

Good quality single crystals are much needed for device

fabrication. The defects are discrete entities and their location and degree of

disturbance produced in a lattice can be determined experimentally. The high

resolution X-ray diffraction technique (multicrystal X-ray diffractometer) is a

non-destructive analysis and can be used for direct observation of boundaries

and dislocations.

The high resolution X-ray diffraction analysis was carried out to

study the structural perfection of 1H-Imidazolinium Hydrogen L-tartrate. A

multicrystal crystal X-ray diffractometer (MCD) designed and developed at

National Physical Laboratory has been used to study the crystalline perfection

of the single crystal(s). Figure 2.4 shows the schematic diagram of the

multicrystal X-ray diffractometer. In this system a fine focus X-ray source

(Philips X-ray Generator; 0.4 mm × 8 mm; 2kWMo) energized by a well

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collimated and monochromated MoKα1 beam obtained from the three

monochromator Si crystals set in dispersive (+, -, -) configuration has been

used as the exploring X-ray beam. The specimen crystal is aligned in the

(+, -, -, +) configuration. Due to dispersive configuration, though the lattice

constants of the monochromator crystal(s) and the specimen are different, the

unwanted dispersion broadening in the diffraction curve of the specimen

crystal is insignificant.

Figure 2.4 Schematic of the Multicrystal X-ray diffractometer set up

Before recording the diffraction curve, the specimen surface was

prepared by lapping and polishing and then chemically etched by a non

preferential chemical etching using the etchant of the mixture of water and

acetone in 1:2 ratio. Figure 2.5 shows the high resolution X-ray diffraction

curve (rocking curve) recorded with high resolution X-ray diffractometer

using (100) diffracting planes for 1H-Imidazolinium Hydrogen L-tartrate

single crystal. Figure 2.5 shows the DC is quite sharp without any satellite

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-100 -50 0 50 1000

100

200

300

400

500

600

Dif

frac

ted

X-r

ay

inte

nsit

y[c

/s]

Glancing angle [arc s]

22"

peaks. The full width at half maximum (FWHM) of the diffraction curves is

22 arc sec, which is close to that expected from the plane wave theory of

dynamical X-ray diffraction. The single sharp diffraction curve with low

FWHM indicates that the crystalline perfection is quite good. The 1H-

Imidzolinium Hydrogen L-tartrate is a nearly perfect single crystal without

having any internal structural boundaries.

Figure 2.5 Rocking curve of ImiLT

2.3.3 Spectral Analysis

2.3.3.1 Factor group analysis

The factor group and the site group are important in the application

of group theoretical methods for the analysis of spectra of solids. Symmetry

analysis is made by applying all the symmetry operations of the factor group

to each atom in the unit cell, and reducing the representation thereby obtained

in order to determine the number of normal modes belonging to each

irreducible representation. An additional advantage of the factor group

method is that it provides a basis for the prediction of the IR and Raman

spectra of lattice vibration (Rousseau et al 1981).

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2.3.3.1.1 Vibrational analysis of 1H-imidazolinium hydrogen L-tartrate

1H-Imidazolinium Hydrogen L-tartrate crystallizes in the

monoclinic crystal system with the non-centrosymmetric space group P21 and

factor group symmetry22C . The factor group analysis of the unit cell of

1H-Imidazolinium Hydrogen L-tartrate is carried out using the character table

for the site symmetry group C1(2). The two molecules of the primitive unit

cell of 1H-Imidazolinium Hydrogen L-tartrate occupy general sites of C1 (2)

symmetry. A single molecule of 1H-Imidazolinium Hydrogen L-tartrate

crystal contains 25 atoms which in turn gives rise to 150 modes. Group

theoretical analysis of 1H-Imidazolinium Hydrogen L-tartrate gives 150

vibrational optical modes which decompose into Γ150 = 74A + 73B apart from

three acoustic modes (A + 2B). In monoclinic crystals like 1H-Imidazolinium

Hydrogen L-tartrate, the modes have associated polarizability tensors of the

form

0

0 0

0 0

xx xy

yy

zz

A

α α

α

α

� �� �

= � �� �� �

0 0

0 0

0 0 0

xz

yzB

α

α

� �� �

= � �� �� �

Here the polarizability tensors are depicted along the crystallographic

X-, Y- and Z-axes. Both phonon A and B are Raman and IR active. The

summary of the factor group analysis of 1H-Imidazolinium Hydrogen

L-tartrate is presented in Table 2.2.

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Table 2.2 Factor group analysis - Summary

Site symmetry

C1(2)

Factor

group

symmetry

22C Ext Int

C H N O Optical Acoustic Total

A 1T 3R 69 21 30 6 18 75 1 74

B 2T 3R 69 21 30 6 18 75 2 73

Total 3T 6R 138 42 60 12 36 150 3 147

Analysis of the vibrational spectra reveals the information

regarding the nature of bonding, structure of co-ordination compounds and

material confirmation. The molecular structure of 1H-Imidazolinium

Hydrogen L-tartrate enumerates that the title compound consist of C-H, N-H,

and O-H groups etc. The observed vibrations of 1H-Imidazolinium Hydrogen

L (+) tartrate could be due to lattice vibrations and internal vibration. The

bands observed between 4000 cm-1 and 400 cm-1 in Figure 2.6 arise from the

internal modes of 1H-Imidazolinium Hydrogen L-tartrate. The bands obtained

below 400 cm-1 arise from the deformational vibrations and the vibrational

and translational modes of anions and cations. Table 2.3 presents the

correlation scheme obtained by following the procedures of Fately et al

(1972). Each internal mode of 1H-Imidazolinium Hydrogen L-tartrate ions

split into two components of (A(Z), B(X) and B(Y)) are IR active and

A(αxx, αyy, αzz, αxy) and B(αxz, αyz) are Raman active.

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Table 2.3 Correlation Scheme of 1H-Imidazolinium Hydrogen L-tartrate

ActivitySite symmetry Factor group

symmetry Raman IR

74A αxx, αyy, αzz, αxy Z

A150

73B αxz, αyz X,Y

.

2.3.3.1.2 Internal Vibrations

As the 1H-Imidazolinium Hydrogen L-tartarate molecules do not

have any symmetry, the internal vibrations exhibited are of both IR and

Raman active exclusive of acoustic mode. The internal vibrations of

1H-Imidazolinium Hydrogen L-tartrate may be arising from the C-H, N-H

and O-H functional groups. These vibrations are strongly coupled between

themselves.

2.3.3.1.3 External vibrations

The bands observed below 400 cm-1 are mainly due to external

modes. The rotational modes are expected to have higher frequency and

intensity than translational modes in the Raman spectra. However, the

translational modes are more intense in IR spectra (Bhatacharjee 1990,

Hanuja and Fomitsev 1980) of 1H-Imidazolinium Hydrogen L-tartrate. It is

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found to have (A+2B) translational and (A+2B) rotational vibrations in the

title compound which can be achieved experimentally by polarized Raman

measurements.

2.3.4 Infrared Spectral Analysis

The mid Fourier Transform Infrared spectrum of 1H-Imidazolinium

Hydrogen L-tartrate was recorded at room temperature in the region

4000–400 cm-1 by JESCO 416 PLUS FT-IR spectrophotometer equipped

with LiTaO3 detector, KBr beam splitter and He-Ne Laser source boxcar

apodization used for 250 averaged interferogram collections for both the

sample and background using KBr pellet technique. The recorded FT-IR

spectrum of the title compound is shown in Figure 2.6 and the functional

group assignments were made using the standards (Martin Britto Dhas et al

2007a, Vijayan et al. 2004). The strong broad peak at 3491cm-1 is due to the

presence of O-H stretching in the carboxyl group. The N-H stretches of

Imidazole ring produce broad intense signals between 2000 and 3000 cm-1.

In the present case a very strong peak occurs at 3319 cm-1 which indicates the

functional groups of the title compound. The peak observed at 1726 cm-1

indicates the presence of C=O bond. The aromatic ring vibrations produce

their characteristic peaks at 1584 cm-1 and 1410 cm-1. The sharp peak at

1211 cm-1 is due to C-H bending vibrations of the aromatic ring. The weak

intensity peak at 842 cm-1 is assigned to the symmetric stretch, further it is

attributed to five membered Imidazole ring. The strong peak at 1262 cm-1 is

assigned to the breathing mode of imidazole ring in plane C-H deformation

(Juan Antonio Asensio et al 2002).

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Figure 2.6 FT-IR Spectrum of 1H - Imidazolinium Hydrogen L-tartrate

2.4 DIELECTRIC STUDIES

Dielectric properties are correlated with the electro-optic property

of the crystals (Boomadevi and Dhanasekaran 2004). The dielectric

measurements of the 1H-Imidazolinium Hydrogen L-tartrate were made using

HIOKI 3532 HiTESTER LCR meter. Good quality single crystals of 1H-

Imidazolinium Hydrogen L-tartrate were polished on soft tissue papers with

fine grade alumina powder. The sample was electroded on either side with

silver paste to make it behaves like a parallel plate capacitor. The studies were

carried out and the capacitance, dielectric loss (tanδ) and ac conductivity of

the sample were measured as a function of frequency (50 Hz to 5 MHz) and

temperature (in the range 35°C, 50°C and 100°C). A small cylindrical furnace

with dimensions 20 cm × 20 cm × 20 cm was used for the experiment and the

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temperature was controlled by Eurotherm temperature controller (±0.01°C).

The dielectric constant was calculated using the relation

0r

Cd

ε= (2.1)

where ε0 is the permittivity of dielectric region, C is the capacitance, d is the

thickness of the grown 1H-Imidazolinium Hydrogen L-tartrate crystal and A

is the area of cross section of the crystal used for experiment.

The frequency dependent dielectric constant is shown in Figure 2.7.

The dielectric constant decreases with increasing frequency and becomes

almost saturated beyond 10 kHz for all temperatures (35°C, 50°C and

100°C). The higher value of dielectric constant is due to higher space charge

polarization at lower frequency region. This may be explained on the basis of

the mechanism of polarization similar to the conduction process. The

electronic exchange of the number of ions in the crystal lattice gives local

displacement of the applied field, which gives the polarization. As the

frequency increases, at which the space charge cannot sustain and comply the

external field. Therefore the polarization decreases and exhibiting the

reduction in the value of dielectric constant with increasing frequency. The

magnitude of the dielectric constant depends on the degree of polarization

charge displacement in the crystals. The dielectric constant of materials is due

to the contribution of electronic, ionic, dipolar and space charge polarization

which depends on the frequencies (Dharmaprakash et al 1989). At low

frequencies, all these polarizations are active. The space charge polarization is

generally active at lower frequencies and high temperatures.

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Figure 2.7 Variation of Dielectric constant of ImiLT with frequency

The change of dielectric loss (tanδ) with frequency is represented

for the as grown crystal in Figure 2.8. It is observed that the dielectric loss

decreases with increasing frequency. The low value of dielectric loss indicates

good quality (Benet Charles and Gnanam 1994) of the crystal. The larger

value of dielectric loss (tanδ) at lower frequencies may be attributed to space

charge polarization owing to charged lattice defects (Smyth 1965). The low

values of dielectric loss indicate that the grown crystal contains minimum

defects.

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Figure 2.8 Variation of dielectric loss of ImiLT with frequency

The conductivity of 1H-Imidazolinium Hydrogen L-tartrate

increases with increase in temperature. The electrical conduction in dielectrics

is mainly a defect controlled process in the low temperature region. It is

inferred from Figure 2.9 that the electrical conductivity of 1H-Imidazolinium

Hydrogen L-tartrate is low at low temperature owing to trapping of some

carriers at defect sites. At any particular temperature, however the Gibb’s free

energy of a crystal is minimal when a certain fraction of ions leaves the

normal lattice. As the temperature increases, more and more defects are

created, and as a result, the conductivity, which is predominantly due to the

movement of defects produced by thermal activation, increases (Jain et al.

1964).

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1 2 3 4 5 6 7

0.00000

0.00002

0.00004

0.00006

0.00008

0.00010co

nd

uc

tiv

ity

(S/c

m)

log f

(35oC)

(50oC)

(100oC)

Figure 2.9 Variation of conductivity of ImiLT with frequency

2.5 OPTICAL STUDIES OF ImiLT Crystal

To determine the absorption range and hence to know the

suitability of 1H-Imidazolinium Hydrogen L-tartrate single crystals for optical

applications, UV-Vis spectrum was recorded with 2 mm thick crystal

between 200 – 800 nm using UV-VIS-NIR (PERKIN ELMER LAMBDA

35) Spectrometer which covers ultra violet (200-400 nm) and visible

(400-800 nm) region. The spectrum obtained is attributed to the promotion of

electrons in σ, π and n- orbital from the ground state to higher state. The

recorded UV-Vis spectrum of the title compound is shown in Figure 2.10.

The spectrum indicates the absorbance due to electronic transition between

338 nm and 800 nm. The cut off wavelength 338 nm may be assigned to the

electronic transitions in the aromatic ring of 1H-Imidazolinium Hydrogen

L-tartrate single crystals. Absence of absorbance in the region between

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400 and 800 nm is an advantage as it is a key requirement for materials

having NLO properties.

Figure 2.10 UV-Vis Spectrum of 1H-Imidazolinium Hydrogen

L-tartrate

2.6 TGA-DTA Analysis of ImiLT

Thermogravimetric and differential thermal analyses give

information regarding phase transition, water of crystallization and different

stages of decomposition of the crystal (Meng et al 1998). The

thermogravimetric analysis (TGA) was carried out on the 1H-Imidazolinium

Hydrogen L-tartrate crystals and TGA spectrum was recorded in Nitrogen

atmosphere between 50 and 500°C using NETZSCH STA 409 C/CD TGA

unit. The recorded 1H-Imidazolinium Hydrogen L-tartrate is shown in

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Figure 2.11. There is no weight loss between 50°C and 204°C. This indicates

that there is no inclusion of water in the crystal lattice, which was used as the

solvent for crystallization. The thermogram spectrum reveals that the major

weight loss (around 92%) starts at 204.4°C and it continues up to 250°C. The

nature of weight loss indicates the decomposition point of the material.

However, below this temperature no weight loss is observed. In the DTA

spectrum an irreversible exothermic peak observed around 204.4°C

corresponds to the decomposition temperature of the material.

Figure 2.11 TG and DTA curves of 1H-Imidazolinium Hydrogen

L-tartrate

2.7 SECOND HARMONIC GENERATION

A quantitative measurement of the Second Harmonic Generation

(SHG) conversion efficiency of 1H-Imidazolinium Hydrogen L-tartrate was

made by the Kurtz and Perry powder technique (1968). The schematic of the

experimental set up is shown in Figure 2.12. The finely powdered sample of

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1H-Imidazolinium Hydrogen L-tartrate was densely packed between two

transparent glass slides. A fundamental Laser beam of 1064 nm wavelength

from an Nd: YAG (DCR11) laser was made to fall normally on the sample

cell. The power of the incident beam was measured using a power meter. The

transmitted fundamental wave was passed over a monochromator (Czerny

turner monochromator) which separates 532 nm (second harmonic signal)

from 1064 nm, and absorbed by a CuSO4 solution F1 which removes the

1064 nm light. F2 is a BG-38 filter, which also removes the residual 1064 nm

light. F3 is an interference filter with bandwidth of 4 nm and central

wavelength 532 nm. The green light was detected by a photomultiplier tube

(Hamamatsu R5 109, a visible PMT) and displayed on a storage oscilloscope

(TDS 3052 B 500 MHz phosphor digital oscilloscope). KDP and Urea

crystals were separately powdered to identical particle size and were used as

reference materials in the SHG measurement. A bright green flash emission

from the title sample was observed which indicates the NLO behavior of the

material. The SHG of 1H-Imidazolinium Hydrogen L-tartrate crystal was

found to be 75 mV and that of 95 mV for KDP.

Figure 2.12 Experimental set up used for measuring the relative SHG

efficiency

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2.8 VICKER’S MICROHARDNESS STUDIES

The mechanical characterization of 1H- Imidazolinium Hydrogen

L-tartrate crystals has been done by microhardness testing at room

temperature. Transparent 1H-Imidazolinium Hydrogen L-tartrate crystals free

from cracks having the dimension of 3mm × 3 mm × 2 mm, with flat and

smooth faces are chosen for the static indentation tests. The crystal was

mounted properly on the base of the microscope. Now the selected faces have

been indented gently by applying loads varying from 10 to 50 g for a dwell

period of 3 second using Vickers diamond pyramid indenter attached to an

incident researcher microscope. The indented impressions are pyramidal in

shape. The shape of the impression is structure dependent, face dependent and

also material dependent. The length of the two diagonals has been measured

by a calibrated micrometer attached to the eyepiece of the microscope after

unloading and the average is found out. For a particular load five

well defined impressions were considered and the average of all the diagonals

(d) was considered. The Vickers hardness numbers (Hv) have been calculated

using the standard formula

2

1.8544v

PH

d= kg/mm2 (2.2)

where P is the applied load in kg and d in mm. Crack initiation and materials

clipping become significant beyond 50 g of the applied load. Hence hardness

test could not be carried out above this load. Figure 2.13 shows the variation

of Hv as a function of applied load ranging from 10 to 50 g. It is clear from

the Figure 2.13 that Hv increases with increase in load (5 to 50 g). This is

known as load dependent hardness and here its value is found to be

approximately 50 kg/mm2. Such a phenomenon of dependence of

microhardness of a solid on the applied load at low level of testing load is

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known as indentation size effect (ISE). The observed increase in hardness

with increasing load is usually termed as reverse indentation size effect

(Ramesh Babu et al 2006).

Figure 2.13 Plot between load and Hardness number

2.9 CONCLUSION

Bulk single crystals of 1H-Imidazolinium Hydrogen L-tartrate were

grown by slow evaporation solution growth technique. The optical studies

show the absence of absorption above 338 nm. The SHG efficiency is

comparable to that of the standard KDP crystal. From FT-IR spectrum, the

functional groups were identified. The occurrence of π-π* transition in the

carboxyl group accounts for the nonlinearity in the title compound. The

dielectric behaviour of 1H-Imidazolinium Hydrogen L-tartrate was analysed.

Group theoretical analysis of 1H-Imidazolinium Hydrogen L-tartrate reveals

Page 22: CHAPTER 2 GROWTH AND CHARACTERIZATION OF 1H …shodhganga.inflibnet.ac.in › bitstream › 10603 › 11300 › 7 › 07_chapter 2.pdf2.3.3.1 Factor group analysis The factor group

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that there are 150 vibrational optical modes which are seen to decompose into

Γ150 = 74A + 73B apart from three acoustic modes (A + 2B). The thermogram

of 1H-Imidazolinium Hydrogen L-tartrate crystal recorded in the present

work, reveals that the incipient melting occurs at 204.4°C. The hardness

study enumerates that grown crystals are moderately harder substance. Based

on these facts, it could be proposed that this material can be better

accommodated for optical applications.


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