Indian Journal of Pure & Applied Physics
Vol. 40, February 2002, pp. 85-88
Vibrational studies of gel grown antimony thiourea chloride and
bismuth thiourea chloride crystals
A Jayarama , S Govinda Bhat & S M Dharmaprakash
Department of Ph ysics, Mangalore University, Mangalagangothri 574 199
Received 14 June 2001; revised 20 November 2001 ; accepted 11 January 2002
Single crystals of antimony thi ourea chloride (ATC) and bismuth thiourea chloride (BTC) have been grown in gels at
ambient temperature using a controlled chemical reaction method. The laser Raman and FTIR spectra of the gel grown
ATC and BTC crystals have been recorded. The presence of thi ourea ion, water molecules and normal mode vtbratiOnal
frequencies are identified and discussed . The basic ideas regarding the normal modes of vtbratwn, selectiOn rules for
Raman and IR spectra and hydrogen-bonding effect are constdered tn bnef. Molecules of water of crystalltzatton are
weakly bonded in antimony thiourea chloride crystal and do not take part tn hydrogen bond formatiOn.
1 Introduction
The non-linear optical properties of some of the
complexes of thiourea have attracted significant
attention in the last few years l.2, because both
organic and inorganic components in it contribu~e
specifically to the process of second harmomc
generation. Thiourea molecule is an interesting
inorganic matrix modifier due to its large dipole
moment 3 and its ability to form an extensive
network of hydrogen bonds. Most of the thiourea
complexes form metal-sulphur bonding in the metal
structured centre4 • Spectroscopic investigations in
different region s of the electromagnetic spectrum
provide
information
regarding
translational ,
rotational , vibrational and electronic energy levels
of molecules . Vibrational spectroscopy deals with
the interaction of electromagnetic radiation with
molecular vibrations and thi s is one of the most
useful spectroscopic tools for basic research .
Information
regarding
molecular
structure,
stereochemi stry of complex molecules, hydrogen
bonding and inter-and-intra molecular processes can
be obtained from the vibrational spectra. In this
paper, a detailed analysis of the Raman and FTIR
vibrational spectra of the gel grown A TC and BTC
crystals has been presented . Vibration spectroscopic
studies of these crystals were carried out in order to
check similarities if any, with other thiourea adducts
and to establish the bonding in the crystal.
2 Experimental Details
In order to grow ATC single crystals, sodium
meta silicate (SMS) solution of density 1.04 gm/cc
was acidified by 0 .8 N acetic acid and mixed with
7 .8% of thiourea solution (All analaR). The mixed
solution was taken in one end opened corning test
tube of length 200 nm and diameter 20 nm. The
medium for crystal growth was set in 36 hr. The
13% a timony dioxide by weight, was dissolved in
100 ml of concentrated HCI, and poured over the gel
medium in the tube. Similar experiment was also
performed to grow BTC single crystals. Single
crystals of ATC 5 and BTC~ begin to grow just inside
the gel medium in about four day s. The suitabl e
conditions for the growth of ATC and BTC single
crystals are: pH of the gel solution 4.8, gelling time
36 hr, growth temperature 30 "C and the den sity of
the SMS solution 1.04 glee. Well grown crystals
were harvested in about 15 days, washed and dri ed
in air.
The FTIR spectra of ATC and BTC crystals in
the micro-crystalline form have been recorded on a
BRUKER IFS FTIR spectrometer in the region of
400-4000 cm- 1 using KBr pellet technique. Laser
Raman spectra of ATC and BTC polycrystalline
samples were recorded using BRUKER IFS 66V
FTIR spectrometer-FRA I 06 Raman module with
YAG laser.
INDIAN J PURE & APPL PHYS , VOL 40, FEBRUARY 2002
86
3 Results and Discussion
Figs I and 2 give the FTIR and Raman spectra
of the ATC crystal s. The ass ignments of different
vibrations are given in Table I. Table 2 shows the
assignments for different vibrations of the BTC
crystals.
The existence of molecular units such as
thiourea and water in the crystal facilitates the
analysis of the vibration spectra in terms of the
vi brations of these molecular groups, particularly in
the internal mode region. A number of studies are
available on the infrared and Raman spectra of
thiourea. The normal coordinate analysis of thiourea
molecules has also been reported. The structure of
thiourea has been investigated 7 • At room
temperature the crystals belong to the orthorhombic
centrosymmetric space group D 2h with four
molecules per unit cell. The asymmetric crystal unit
consists of half of one molecule, the carbon and
sulphur atoms lying in the mirror plane and the
molecules were found to be planar. No hydrogen
bonding was observed presumably becau se of large
thermal motion . The ATC crystal crystallize in the
orthorhombic form with a = 14.0266( I 0) A, b =
14.825(4) A, c = 6.044(5) A, space group Pnma
having four molecules in the unit cell . BTC crystals
crystallize in hexagonal fo rm with a == 13.5335 ( I 0)
A, b = 13.5335( I 0) A, c = 7 .I 093(1 0) A, y = 120"
space group P3 having three molecules in the unit
80
60
~
Q)
u
c
40
E
1/l
c
20
0
0
>....
.....
0
-20
4 0 00
3500
30 00
2500
2000
Wavenumber
Fig. I -
1500
1000
em_,
FfiR spectra of ATC crystals
0 .5
0.4.
lfl
.....
0.3 ..
·~
:::>
·c
0
0 .2
E
0
a::
0.1
o .o
3500
3000
2500
2000
1500
Wavenumber cm-
1
Fig. 2 - Laser Raman spectra of ATC crystals
1000
500
500
JAYARAMA et al.:GEL GROWN CRYSTALS
cell. The thiourea molecule in its free state has C2 •
symmetry and the irreducible representation of the
mode is :
Table I -Spectral ass ignment of ATC crystals
Infrared lines cnf 1
Raman lines
cm· 1
(y and Yl)
3287
3293
3252
3224
3206
2800 to 1700 cm· 1
1387
1096
1049
1624
1516
1424
1393
1114
1061
(NH) 8
H20 bending (y2)
(SCN) bending
(1114+306)
(CS) y, andy._,
(NH)p
(41Ix2 +236)
Librational mode
of H 20
706
(C-N) y,
(SCN)~
613
(305x2)
Wagging mode of
H20
(Librational)
605
577
467
410
(Yas and y, )
vibrations of
NH
Combinations and
overtones
713
702
624
observed in the ATC and BTC crystals . Thi s
indicates that the hydrogen atoms of NH 2 take part
in inter-molecular/intra-molecular hydrogen bonds.
Another possible reason for the bands in this region
is the existence of thiourea in the resonance
configurationR_ The vibration between about 1700 to
about 2800 cm· 1 is considered as overtones/
combination.
H20 stretching
3576
3558
1650
1620
1502
Assignments
87
477
305
235
160
116,96
(CN) 8
(NH 2) torsion
(Sb-S) stretching
(Sb-Cl) stretching
(S-Sb-Cl)bending
Lattice vibrations
Of which, sixteen vibrations with symmetries
A 1• 8 1 and 8 2 are allowed in theIR spectrum by the
selection rules and all eighteen vibrations are
allowed in the Raman spectrum. Thiourea, like other
thioamides, thiosemicarbazones and dithioamides
exhibit bands in the region 940-1140, 1260-1420
and 1375-1570 cm· 1• These bands arise because of
the strong coupling between C=S and C=N
vibrations.
In the high wave number region 3000 3400cm 1, there are several peaks due to N-H
stretching. NH 2 stretching modes are observed at
lower wave number than for free ion. This effect is
Table 2 - Spectral Assignment of BTC crystals
Infrared lines
cm· 1
Raman lines
cm· 1
Assignments
3398
3307
3298
3194
3204
Yas andy, vibrations of
(NH )
2750 to 1750
cm· 1
1619
1497
1429
1381
1099
781
706
519
465
Combinations and
overtones
1614
1506
1384
1098
706
598
460
386
241
199
126
93
(NH) 8
(SCN) bending
(CS) y..,
(CS) y,
(NH) p
(CS) y..,
Bi-S vibration
(SCN) bending
Combination
(Bi-S) stretching
(Bi-CI) stretching
S-Bi-CI bending
Torsion
Earlier workers 9 - 10 did infrared studies on metal
coordination compounds of thiourea. All metals
except Ti form complexes via sulphur. (Ti forms
bond via nitrogen). It is expected that on formation
of metal-sulphur bond, the vibration at 1412 and
730 cm 1 would be down-shifted. A comparison of
our results with the infrared spectra of thiourea and
Zn(Tu) 3S04 is made in Table 3. These studies
corroborate the crystal structure data of thiourea
complexes, establishing the metal complexation via
sulphur atoms.
The stretching frequencies of H20 in A TC
crystals are slightly down-shifted and the bending
frequencies are slightly uplifted . This shows that the
water of crystallization do not take part in forming
hydrogen bonds 11 • This inference is in support of the
structure analysis of the crystals 12 • The free H20
molecule vibrations are compared with that of the
INDIAN 1 PURE & APPL PHYS, VOL 40, FEBRUARY 2002
88
water of crystallization of ATC crystals in Table 4 .
The comparison result shows that the H 2 0
mol ecules are weakly bonded in ATC crystals .
Table 3 - Compari son of vibrations of thiourea with met al
complexes
Species
Thiourea
cm-1*
y(N II ) 2
o(N II 2)
y, (CS)
P(NII 2)
y, (C N)
3385
1618
141 2
1087
730
Zn (tu h
so4.
cnf 1+
3329
1635
1408
1083
713
BTC
ATC
cm· 1 **
cm-1**
3398
1622
1099
1099
706
3287
1650
1387
1049
713
* Re f. (9)
+ReL ( IO)
** Present work
undertaken. The presence of thiourea ion, water
molecules and normal mode vibrational frequencies
are identified.
During complex formation it is observed that
thiourea is coordinated to the an timony through
sulphur in ATC and bismuth in BTC crystals. Intermolecular/intra-molecular hydrogen bonds are
observed in these crystals. Molecules of water of
crystallization are weakly bonded in the ATC
crystals and they do not take part in hydrogen bond
formation.
Acknowledgements
The authors are grateful to the Department of
Science and Technology, New Delhi, India for the
research grant.
References
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Yenkataramanan V, Dhanraj G, Wadhawan V K et al., J
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Bhat S G & Dharmaprakash S M, Mater Res Bull, 3:
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Table 4 - Comparison of H20 mode vibrations
Free H20 molecule
vibrations
cm· 1
(AI) 3657 Y1
(8 2) 3756 Yo
(AI) 1595 Y2
H 20 mode vibrations in the
grown crystals
cm· 1
ATC
3558
3578
1620
Raman spectra obtained at lower wave number
region help in assigning the vibrations, which
involve heavy atoms. The vibrations of metalsulphur stretching mode appear around 273 cm· 1 in
Zn thiourea complexes. On complex formation with
various legends, the metal-sulphur vibration wave
number was not found to change appreciably 13 • The
Sb/Bi-S stretching and bending modes were
compared with that of the study made on antimony
su lphobromide and antimony sulphochloride 14 , on
the atomic mass, the bond distance and the bond
angle, the vibration frequ encies vary.
4 Conclusions
The Laser Raman and FTIR spectral studies of
the gel grown antimony thiourea chloride and
bi smuth thiourea chloride crystals have been
7
Yoshida T & Mashiyana H, J Korean Phys Soc, 32 ( 1998
920.
8
Marcy H 0, Warren L F, Web M S et al. , Appl Opt , 3
( 1992) 5051.
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Nakamoto K. Infrared and Raman spectra of inorganic an
coordination compounds, Part A & B, (John Wiley an
Sons, New York) , 1997.
I0
Venkataramanan V, PhD thesis, Indian Institute of Scienc1
August 1994.
II
Pillai V P M, Nayar V U & Jordanovska V 8 , J Solid Sta1
Chem, 133 ( 1997) 407.
12
Govind Bhat S, PhD thesis, Mangalore University, 200 I.
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Flint C D & Goodgame M, J Chem Soc, 38A ( 1996) 753 .
14
Marshall J, Indian J Phys, 32 ( 1997) 589.