Thermal, UV and FTIR spectral studies of urea-thiourea zinc chloride single crystal

Article abstract of DOI:10.1007/s10973-010-0758-0

A single crystal of urea-thiourea was grown by slow evaporation of aqueous solution at room temperature. The bright and transparent crystals obtained were characterised by TG-DTA, UV and FTIR spectral analyses. A fitting decomposition pattern for the title compound was formulated on the TG curve which shows a two stage mass loss between 200 and 750 °C. DTA curve shows exothermic peaks supporting the formulated decomposition pattern in this temperature range. The UV and FTIR spectra show the characteristic absorption, vibration frequencies due to urea-thiourea zinc chloride crystals. Detailed structural analysis of the compound is under progress. Akademiai Kiado, Budapest, Hungary 2010.

Full text of DOI:10.1007/s10973-010-0758-0

J Therm Anal Calorim (2010) 100:763–768
DOI 10.1007/s10973-010-0758-0
Thermal, UV and FTIR spectral studies of urea–thiourea zinc
chloride single crystal
•
G. Madhurambal M. Mariappan
•
S. C. Mojumdar
CTAS2009 Special Chapter
´
´
ꢀ Akademiai Kiado, Budapest, Hungary 2010
Abstract A single crystal of urea–thiourea was grown by
slow evaporation of aqueous solution at room temperature.
The bright and transparent crystals obtained were charac-
terised by TG–DTA, UV and FTIR spectral analyses. A
fitting decomposition pattern for the title compound was
formulated on the TG curve which shows a two stage mass
loss between 200 and 750 ꢁC. DTA curve shows exother-
mic peaks supporting the formulated decomposition pattern
in this temperature range. The UV and FTIR spectra show
the characteristic absorption, vibration frequencies due to
urea–thiourea zinc chloride crystals. Detailed structural
analysis of the compound is under progress.
possesses large nonlinearity, high resistance to laser-
induced damage, low angular sensitivity and good
mechanical hardness [1–3]. Urea is representative of one
class of materials which are applicable to photonics and
served as a model compound and reference material in the
DMOS (Diffusive Mixing of Organic Solutions) experi-
ment in microgravity carried out by NASA [4]. Many
authors investigated various organic and organometallic
compounds due to their very important roles in chemical,
biological, electrical and environmental sciences and also
examined their various properties [5–30]. Recently, metal
complexes of thiourea have been explored. Example of
these complexes is zinc thiourea sulphate (ZTS), cadmium
thiourea chloride (CTC) and zinc thiourea chloride (ZTC).
These crystals have better nonlinear properties than KDP
[31–34]. Literature survey shows that urea metanitro
benzoic acid, urea hydrogen peroxide compounds have
been studied. However, there is no reference in literature
regarding the work of urea–thiourea zinc chloride (UTZC)
crystal. UTZC is one of the new semi organic nonlinear
crystals having good second harmonic generation (SHG)
efficiency. This article reports the synthesis, and charac-
terisation of UTZC crystal using UV and FTIR spectral and
TG–DTA studies. A detailed structural analysis of the
compound is under progress will be published in our next
article.
Keywords Solution growth ꢀ Urea–thiourea zinc
chloride single crystal ꢀ TG–DTA ꢀ UV ꢀ FTIR
Introduction
Nonlinear optical (NLO) materials have a significant
impact on laser technology, optical communication and
optical storage devices. The search for new frequency
conversion materials over the past decade has led to the
discovery of many organic materials. Organic material
G. Madhurambal
ADM College for Women, Nagapattinam, Tamil Nadu, India
Experimental details
M. Mariappan
EGS Pillay Engineering College, Nagapattinam, Tamil Nadu,
India
A single crystal of UTZC was prepared at room tempera-
ture by slow evaporation of aqueous solution containing
equimolar proportion of urea and thiourea (Merck,
Mumbai). Care was taken to minimise mechanical and
thermal variations. Colourless, bright and transparent crystal
S. C. Mojumdar (&)
Department of Engineering, University of New Brunswick,
Saint John, NB E2L 4L5, Canada
e-mail: scmojumdar@yahoo.com; mojumdar@unbsj.ca
123

764
G. Madhurambal et al.
DTA/mW/mg
Exo
with an average size of 0.9 9 0.8 9 0.8 mm was obtained.
The crystal was characterised as follows; the thermo-
gravimetric and differential thermal analyses of UTZC
was carried out using a NETZSCH STA 409C thermal
analyser in nitrogen atmosphere. The sample was heated
between 30 and 800 ꢁC at a heating rate of 10 K/min. UV
spectral analysis was carried out by using a double beam
spectrometer. A Burker IFS 66 V spectrometer was used to
record the FTIR spectra of the compound, employing KBr
pellet technique in the frequency range 400–4,000 cm-1. A
detailed structural analysis of the compound will be pub-
lished in future.
TG/%
100
1
0
90
80
70
60
50
–1
–2
–3
40
30
20
–4
–5
100 200 300 400 500 600 700 800
900
Temperature/°C
Fig. 1 TG–DTA curves of urea–thiourea zinc chloride
UV spectral analysis
Results and discussion
The UV spectra for urea, thiourea and UTZC are shown in
Figs. 2, 3, and 4. The observed bands have been given in
Table 1. In UTMC, the p–p* absorption band shifted to
longer wavelength compared to urea. This is because of the
formation of hydrogen bond between [C=O….N–H (of
urea, thiourea) increase the bond length of[C=O and thus
Thermal studies
The TG and DTA curves of UTZC are shown in Fig. 1.
The TG curve indicates a two step mass loss on heating the
compound between 30 and 800 ꢁC. The following
decomposition pattern is formulated for UTZC:
Step 1
2.000
Â
Ã
Zn HꢁHNꢁCOꢁNHꢁH. . .::S ¼ CðNH2Þ2 Cl2
! 2NH3 þ 2CO þ H2 þ 2S ¼ CðNH2Þ2
Step 2
2H2NꢁCSꢁNH2 ! 3H2S þ 2N2 þ 3C þ 2NH3
Two molecules of ammonia, carbon monoxide, carbon
dioxide and a molecule of hydrogen, thiourea is lost on
heating the compound from 180 to 400 ꢁC. This accounts
for 44.17% mass loss observed in TG curve. The theoret-
ical mass loss of urea is much closed to experimental mass
loss. The remaining portion of UTZC very slowly
decomposed to up to 750 ꢁC. High mass loss indicates the
presence of urea in UTZC. In UTZC, urea is stable up to
180 ꢁC. Above 180 ꢁC, urea in UTZC decomposes into
two molecules of ammonia, carbon dioxide and a molecule
of hydrogen. Urea is slowly vaporises at 400 ꢁC. After-
wards, thiourea in UTZC begins to split to hydrogen sul-
phide, ammonia and nitrogen and carbon residue. This
accounts for 30.25% mass loss observed in the TG. This is
consistent with the TG curve. The thermogravimetric study
thus confirms the formation of the title compound in the
stoichiometric ratio and the decomposition pattern of
UTZC. The DTA curve depicted in Fig. 1 shows exother-
mic peaks at 128.8, 237 and 311.6 ꢁC corresponding to the
first stage decomposition. The second peak and a broad
exothermic peak at 595 ꢁC are due to the decomposition of
thiourea in UTZC.
0.000
200
300
400
Wavelength/nm
Fig. 2 UV spectrum of urea
2.000
0.000
200
240
280
320
360
400
Wavelength/nm
Fig. 3 UV spectrum of thiourea
123

Urea–thiourea zinc chloride single crystal
765
2.000
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
0.000
25
200
240
280
320
360
400
20
15
10
Wavelength/nm
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers/cm–1
Fig. 4 UV spectrum of urea–thiourea mixed crystal
Fig. 6 FTIR spectrum of thiourea
Table 1 Comparison of absorption band of urea, thiourea with
UTMC
95
90
85
Crystals
Urea
Absorbance
Wavelength/nm
0.013
0.456
1.416
0.012
0.013
1.368
335
236
255
362
352
245
80
75
70
65
60
55
50
45
40
35
30
25
Thiourea
UTZC
smaller energy required for this transition and hence the
absorption shows the red end of the spectrum. Similarly,
n–p* transition also shifted to higher wavelength due to
less stable non-bonded electron in UTZC.
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers/cm–1
Fig. 7 FTIR spectrum of urea–thiourea zinc chloride
FTIR spectral studies
The frequencies at 3369.31 cm-1 are due to symmetric
stretching N–H vibration of UTMC. dsC=S and masC=S
bending and asymmetric stretching appear at 781.13 and
1455.32 cm-1, respectively. The weak band appearing at
1155.96 cm-1 is due to mCN symmetric stretching vibration.
The rocking mode of N=C=N found as a peak at
474.42 cm-1. FTIR spectra show the characteristic vibra-
tion frequencies of urea and thiourea. This conforms the
formation of UTZC.
The FTIR spectra for urea, thiourea and UTZC are shown
in Figs. 5, 6 and 7. The various absorption bands in FTIR
spectra and the corresponding assignments are given
below.
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
X-ray diffraction study
The X-ray diffraction data and XRD pattern of UTZC is
given below in Table 2 and Fig. 8. The American chemical
Society for Testing and Materials (ASTM) data of urea and
thiourea also represented.
From the ASTM values, the different planes absorbed
are identifies for all the mixed crystals and they are pro-
duced. Urea belongs to tetragonal and D2D2–P421M and
thiourea belongs to D2H16–P8MM1 orthorhombic. From the
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers/cm–1
Fig. 5 FTIR spectrum of urea
123

766
G. Madhurambal et al.
Table 2 X-ray diffraction data for urea–thiourea zinc chloride
˚
d of urea/A
˚
d of thiourea/A
˚
d of UTZC/A
hkl of urea
hkl of thiourea
hkl of UTZC
4.01
3.62
3.05
2.83
2.53
2.42
2.35
2.23
2.17
2.03
1.99
1.84
1.79
1.75
1.72
1.67
1.57
1.52
1.51
1.42
1.35
1.33
1.26
1.22
1.17
1.07
110
101
111
200
210
201
002
211
102
112
220
221
310
301
212
311
003
222
103
312
401
330
420
421
004
323
4.62
4.48
4.29
3.83
3.51
3.15
3.10
2.95
2.86
2.75
2.54
2.48
2.34
2.32
2.16
2.04
1.93
101
–
–
110
–
–
002
–
–
020
–
–
021
–
–
120
–
–
112
–
–
121
–
–
022
2.20
102
112
–
200
2.03
103
–
211
1.84
221
–
131
–
202
–
–
221
1.71
212
–
Indexed by BP
–
1.56
003
–
–
–
–
1.45
312
–
–
1.32
330
–
–
–
–
1.18,1.15
1.07
004
323
there-by-there is reorientation in the structure and this
brings at different morphology of the crystals itself. This is
very much striking phenomena observed and this mixed
combinations of mixed crystals will produce a wide range
of laser active crystals.
3000
2500
2000
1500
1000
500
SHG efficiency
The optical absorption of the crystalline sample was
recorded using Kurtz powder technique. The nonlinear
property in UTZC crystal was confirmed by shining
Nd:YAG laser (k = 1,046 nm) on thin plate of the grown
crystal. It is observed that green light is coming out of the
crystal. The crystal was ground into powder and densely
packed between two transparent glass slides. An Nd:YAG
laser beam of wavelength 1,046 nm was made to fall
normally on the sample cell. The transmitted fundamental
wave was absorbed by a copper sulphate solution and
second harmonic signal was detected by a photo multiplier
tube and displayed on a storage oscilloscope. A UTZC
crystal, powdered to the identical size was used as refer-
ence material in the SHG measurement. Although many
0
10
20
30
40
50
60
2θ/°
Fig. 8 X-ray diffraction pattern of urea–thiourea zinc chloride
Table 2, it is understood that the number of planes absor-
bed decreased and d values are also decreased. This may
be due to the overlapping of planes of urea crystals and
123

Urea–thiourea zinc chloride single crystal
767
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transparent crystal obtained was characterised. The TG and
DTA studies confirm a two stage decomposition of the
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spectral analysis confirms the formation of hydrogen bond
between urea and thiourea. The FTIR spectra show char-
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