Cd(II)-NCS/NCO complexes of 1-alkyl-2-(arylazo)imidazole: Single crystal X-ray structure of [Cd(HaaiMe)2(SCN)2]

Article abstract of DOI:10.1016/j.ica.2005.10.019

The reaction of Cd(OAc)₂ ? 4H₂O and 1-alkyl-2-(arylazo)imidazole [RaaiR′ where R = H (a), Me (b); R′ = Me (1/3/5), Et (2/4/6)] and NH₄NCS/NaNCO in methanol in 1:2:2 mole ratio has afforded [Cd(RaaiR′)₂(NCS)

Full text of DOI:10.1016/j.ica.2005.10.019

Inorganica Chimica Acta 359 (2006) 695–700
www.elsevier.com/locate/ica
Note
Cd(II)–NCS/NCO complexes of 1-alkyl-2-(arylazo)imidazole:
Single crystal X-ray structure of [Cd(HaaiMe)2(SCN)2]
a
a
b
Kamal Krishna Sarker , Brojo Gopal Chand , Atish Dipankar Jana ,
b
a,
*
Golam Mostafa , Chittaranjan Sinha
a
Department of Chemistry, Jadavpur University, Jadavpur, Raja Suboth Mullick Road, Kolkata, West Bengal 700 032, India
Department of Physics, Jadavpur University, Jadavpur, Raja Suboth Mullick Road, Kolkata, West Bengal 700 032, India
b
Received 7 June 2005; received in revised form 1 October 2005; accepted 9 October 2005
Available online 29 November 2005
Abstract
The reaction of Cd(OAc)2 Æ 4H2O and 1-alkyl-2-(arylazo)imidazole [RaaiR0 where R = H (a), Me (b); R0 = Me (1/3/5), Et (2/4/6)] and
NH4NCS/NaNCO in methanol in 1:2:2 mole ratio has afforded [Cd(RaaiR0)2(NCS)2] (3,4) and [Cd(RaaiR0)2(NCO)2] (5,6) complexes.
The complexes are characterized by different physicochemical methods and in one case, the structure was confirmed by single crystal
X-ray diffraction study for title compounds.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Arylazoimidazoles; Cadmium(II) complexes; Octahedral; X-ray
1. Introduction
a surface modified extractant by anchoring imidazole to
polystyrene by azo group (–N@N–) and have been used
for the separation of heavy metals from drinking water,
environmental samples, medicinal samples and ores, min-
erals [18]. The fundamental property of interaction
between metal ions and organic ligands has been utilized
in the design of functional materials. Azoimidazoles is
one such system. It has also been used to extract anions
through protonation of imidazole motif and subsequent
interaction with anions via hydrogen bonding [19]. The
exo-bidentate behaviour of the ligand has been elimi-
nated by N(1)-alkylation. The coordination chemistry
of 1-alkyl-2-(arylazo)imidazoles (RaaiR0) has been stud-
ied by us [20–26] and others [27,28] using transition
metals.
We are interested to design imidazole-containing
ligands. There are two basic reasons to concentrate on
imidazole type systems: biochemical ubiquity and an
alternative to polypyridines. The metal complexes of
polypyridines have received much attention because of
rich electrochemistry, interesting optical properties, bioin-
organic chemistry and catalyses [1–7]. This has led to the
modification of the ligand system inserting different sub-
stituents, presence of other donor centers etc [7–13].
Ligand synthesis using imidazole as heterocyclic back-
bone is of much advantage because of the biochemical
importance of this molecule [14,15]. Imidazole carries
meta-related two N centers of different basicity and can
bind strongly heavy metal ions [16,17]. We have designed
In RaaiR0, the active function is the azoimine group
(–N@N–C@N–) which is isoelectronic with diimine func-
tion (–N@C–C@N–). The non-transition metal complexes
of arylazoimidazole has been reported recently by us [29–
32]. This ligand acts as a potential bidentate chelator with
*
Corresponding author. Tel.: +91 033 2414 6666x2453; fax: +91 033
2414 6584.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.10.019

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K.K. Sarker et al. / Inorganica Chimica Acta 359 (2006) 695–700
heavier transition metals [20–26]. It comprises with uni- or
bidenticity when coordinated with 3d block [20–22] and
non-transition metals [29–32]. The Group 12 (Zn, Cd,
Hg) metal complexes do not have CFSE and the stereo-
chemistry of the complexes has been controlled by steric
effect and the M–N bond strength. As a part of our
programme to explore the coordination chemistry of
Group 12 metal complexes of arylazoimidazoles, we wish
to report in this work the Cd(II)-thiocyanato/isocyanato
complexes of 1-alkyl-2-(arylazo)imidaz- oles (RaaiR0).
The X-ray structure of one of the complexes has been
described.
C26H28N10S2Cd: C, 47.53; H, 4.26; N, 21.32. Found: C,
47.44; H, 4.18; N, 21.24%.
2.4. Preparation of bis-isocyanato-bis-[1-methyl-2-
(phenylazo)imidazole] cadmium(II)
2.4.1. [Cd(HaaiMe)2(NCO)2] (5a)
Methanolic solution (15 ml) of 1-methyl-2-(pheny-
lazo)imidazole (HaaiMe, 0.22 g, 1.18 mmol) was added
dropwise to Cd(OAc)2 Æ 4H2O (0.15 g, 0.5 mmol) in the
same solvent (20 ml) at room temperature (298 K). Then
aqueous-methanolic solution of NaNCO (0.07 g,
1.08 mmol) was added dropwise. The mixture was stirred
for 15 min and filtered. Filtrate was kept undisturbed for
few days. Orange-red crystals were obtained and washed
with cold water and methanol. Finally they were dried in
vacuum. Isolated yield was 0.15 g, (53%).
2. Experimental
2.1. Materials
All other complexes were prepared by the same proce-
dure and yield varied 60–70%. Microanalytical data of
the complexes are as follows: [Cd(HaaiMe)2(NCO)2] (5a):
Anal. Calc. for C22H20N10O2Cd: C, 46.45; H, 3.52; N,
24.63. Found: C, 46.32; H, 3.60; N, 24.48%. [Cd(Mea-
aiMe)2(NCO)2] (5b): Anal. Calc. for C24H24N10O2Cd: C,
48.29; H, 4.02; N, 23.47. Found: C, 48.18; H, 3.94; N,
23.33%. [Cd(HaaiEt)2(NCO)2] (6a): Anal. Calc. for
C24H24N10O2Cd: C, 48.29; H, 4.02; N, 23.47. Found: C,
48.20; H, 3.90; N, 23.35%. [Cd(MeaaiEt)2(NCO)2] (6b):
Anal. Calc. for C26H28N10O2Cd: C, 49.97; H, 4.48; N,
22.42. Found: C, 49.81; H, 4.43; N, 22.35%.
Published methods [20] were used to prepare 1-alkyl-2-
(arylazo)imidazoles (RaaiR0 where R = H (a), Me (b);
R0 = Me (1,3,5), Et (2,4,6)). All other chemicals and
organic solvents used for preparation work were of reagent
grade received from SRL, India.
2.2. Physical measurements
Microanalyses (C, H, N) were performed using a Per-
kin–Elmer 2400 CHNO/S elemental analyzer. Spectro-
scopic measurements were carried out using the following
instruments: UV–Vis spectra, reflectance spectra, JASCO
UV–Vis/NIR model V-570; IR spectra (KBr disk, 4000–
200 cmꢀ1), JASCO FT-IR model 420.
2.5. X-ray crystal structure analysis of
[Cd(HaaiMe)2(NCS)2] (3a)
Crystal is growing (orange block, 0.3 · 0.3 · 0.2 mm3)
by slow evaporation of methanolic solution of mixture
containing Cd(OAc)2, HaaiMe and NH4CNS in 1:2:2
molar ratio. A summary of the crystallographic data
and structure refinement parameters are given in Table
1. Data were collected with Siemens SMART CCD dif-
fractometer using graphite-monochromatized Mo Ka
2.3. Preparation of bis-thiocyanato bis-[1-methyl-2-
(phenylazo)imidazole] cadmium(II)
2.3.1. [Cd(HaaiMe)2(NCS)2] (3a)
Methanolic solution (15 ml) of 1-methyl-2-(phenyl-
azo)imidazole (HaaiMe, 0.22 g, 1.18 mmol)was added drop-
wise to Cd(OAc)2 Æ 4H2O (0.15 g, 0.5 mmol) in the same
solvent (20 ml) at room temperature (298 K). Then aque-
ous-methanolic solution of NH4NCS (0.08 g, 1.05 mmol)
was added dropwise. The mixture was stirred for 15 min
and filtered. Filtrate was kept undisturbed for few days.
Orange-red crystals were obtained and washed with cold
water and methanol. Finally, they were dried in vacuo. Iso-
lated yield was 0.185 g, (62%).
All other complexes were prepared by the same procedure
and yield varied 60–70%. Microanalytical data of the com-
plexes are as follows: [Cd(HaaiMe)2(NCS)2] (3a): Anal. Calc.
for C22H20N10S2Cd: C, 43.96; H, 3.33; N, 23.31. Found: C,
43.90; H, 3.27; N, 23.38%. [Cd(MeaaiMe)2(NCS)2] (3b):
Anal. Calc. for C24H24N10S2Cd: C, 45.82; H, 3.81; N,
22.27. Found: C, 45.73; H, 3.74; N, 22.18%. [Cd(Haa-
iEt)2(NCS)2] (4a): Anal. Calc. for C24H24N10S2Cd: C,
45.82; H, 3.81; N, 22.27. Found: C, 45.76; H, 3.74; N,
22.18%. [Cd(MeaaiEt)2(NCS)2] (4b): Anal. Calc. for
˚
radiation (k = 0.71073 A) at 293(2) K. The intensity data
were corrected for Lorentz and polarisation effects and
an empirical absorption correction was employed using
SAINT program. A total of 16633 reflections [range
3.4 6 2h 6 56.74ꢁ] were collected and 3600 were assumed
observed applying the condition I > 2r(I). The structure
was solved by direct methods and followed by successive
Fourier and difference Fourier syntheses. Full matrix
least squares refinements on F2 were carried out for both
cases using SHELXL-97 with anisotropic displacement
parameters for all non-hydrogen atoms. The hydrogen
atoms were fixed geometrically and refined using the rid-
ing model. In the final difference Fourier map the resid-
3
˚
ual minima and maxima were ꢀ0.554 and 0.939 e/A .
Complex neutral atom scattering factors were used
throughout. All calculations were carried out using
SHELXS-97, SHELXL-97, PLATON-99, ORTEP programs.

K.K. Sarker et al. / Inorganica Chimica Acta 359 (2006) 695–700
697
Table 1
m(N@N) and m(C@N) appear at 1455–1460 and 1605–
1615 cmꢀ1. In the complexes, these are shifted to lower
frequency region which are in support of coordination of
azo-N and imine-N to Cd(II) centre.
Summarized crystallographic data for [Cd(HaaiMe)2(NCS)2] (3a)
[Cd(HaaiMe)2(NCS)2] (3a)
C22H20CdN10S2
601.03
293
monoclinic
P21/c (No. 14)
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
3.2.2. Electronic spectra
The solution electronic spectra of the complexes 3 and 4
show intense transition <400 nm and are assigned to ligand
centered transitions. Two weak (e ꢁ 103 dm3 molꢀ1 cmꢀ1
)
Unit cell dimensions
˚
a (A)
8.9960(9)
15.3217(15)
19.352(2)
91.445(2)
transitions are observed at >440 nm (Table 2). The ligands
are p-acidic and Cd2+ is a d10 system, thus the transition
may be assigned to d(Cd) ! p* (ligand) transition.
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A)
2666.5(5)
4
0.71073
1.006
1.497
316
16633
3600
0.0760
0.2644
1.03
1
3.2.3. H NMR spectra
Z
The 1H NMR spectra of [Cd(RaaiR0)2(NCS)2] (3,4) and
[Cd(RaaiR0)2(NCO)2] (5,6) were recorded in CD3CN. The
spectral data are collected in Table 3. The proton number-
ing pattern is shown in Scheme 1. The assignment has been
made on the basis of spin–spin interaction and on compar-
ing with reported data [30–32]. Imidazole protons (4- and
5-H) of [Cd(RaaiR0)2(NCS)2] (3,4) appear at ca. 7.5 and
7.3 ppm and are singlet in nature which may be due to
rapid proton exchange with solvent proton (CD3CN is
hydrolysed on exposure to air). In Cd(RaaiR0)2(NCO)2
(5,6) 4-H appears at ꢁ0.3 ppm (ca. 7.6 ppm) higher d than
5-H (ca. 7.3 ppm). It is concluded that 4-H is closer to the
metal centre. This is also supported from single crystal
X-ray structure (Fig. 2) where RaaiR0 is bounded to Cd(II)
through N(3) center only. Influence of anion ligand is also
reflected from the NMR data; being a better electron with-
drawing agent NCO than NCS, the chemical shift of the
coordinated ligands in 5, 6 are shifted to higher d by about
0.1 ppm. N(1)–Me appears at ca. 4 ppm; N(1)–CH2–CH3
shows quartet and triplet splitting signals at ca. 4.4
(J = 9.0 Hz) and ca. 1.6 (J = 7.5 Hz) ppm, respectively,
for –CH2, and –CH3 groups. The N(1)–CH2–Ph gives a sin-
glet response at ꢁ5.35 ppm. Aryl protons (7-11-H) appear
at usual position (7.4–7.8 ppm) and suffer shifting to down-
field position with reference to free ligand value.
˚
k (A)
l(Mo Ka) (mmꢀ1
)
Dcalc (mg mꢀ3
)
Refine parameters
Total collected data
Unique data [I > 2r(I)]
R1a[I > 2r(I)]
b
wR2
Goodness-of-fit
P
P
a
R = |Fo ꢀ Fc|/ Fo.
P
P
1=2
b
wR ¼ ½ wðF 2o ꢀ F c2Þ= wF 4oꢂ
are general but w ¼ 1=½r2ðF o2Þþ
2
ð0:1616PÞ þ ð0:0000PÞꢂ, where P ¼ ðF 2o þ 2F c2Þ=3.
3. Result and discussion
3.1. Synthesis and formulation
The reaction of Cd(OAc)2 Æ 4H2O, RaaiR0 and NH4CNS
in the mole proportion of 1:1:2 has synthesized l1,3-NCS
bridged cadmium polymer [30]. The reaction of Cd(ClO4)2
or Cd(NO3)2 salt with excess of RaaiR0, however synthesized
tetrahedral CdðRaaiR0Þ42þ compounds [32]. In this work we
are using different compositions of the metal:ligand:NCSꢀ.
Methanolic solution of Cd(OAc)2 Æ 4H2O and RaaiR0 in
the mole ratio of 1:2 followed by the addition of 2 equivalent
of NH4NCS or NaNCO at later stage has isolated complexes
of the composition [Cd(RaaiR0)2(NCS)2] (3,4) and [Cd-
(RaaiR0)2(NCO)2] (5,6), respectively. The microanalytical
data support the composition of the complexes. They are
non-electrolyte in nature.
3.3. Molecular structure
The molecular structure of [Cd(NCS)2(HaaiMe)2] (3a) is
shown in Fig. 1. Bond distances and angles are set out in
Table 4. The metric parameters (Table 2) and figure show
distorted CdN6 coordination sphere. The octahedral coor-
dination is satisfied by four N centers from two HaaiMe
ligands and other two N-centres from two NCS groups.
HaaiMe acts as bidentate N(imidazole), N(azo) chelator.
The chelating N–Cd–N bond angle is N(1)–Cd(1)–N(4),
67.2(2)ꢁ and lies in the limiting value of Group 12 com-
plexes of azoheterocycles [29–32]. Other chelate angle
N(5)–Cd(1)–N(8) is very low, 62.2(1)ꢁ. Very long Cd(1)–
3.2. Spectral studies
3.2.1. IR spectra
In the infrared spectra, the point of interest is the band
due to the thiocyanate (–NCS)/isocyanate (–NCO), azo
(–N@N–) and imine (–C@N–) groups in the complexes.
The spectra show very strong band at 2063–2067 cmꢀ1
for 3 and4 which are assigned to m(NCS) (Table 2). The
compounds 5, 6 show very strong band at 2190–
2208 cmꢀ1 and have been assigned to m(NCO). Moderately
intense stretchings at ca. 1595 and ca. 1445 cmꢀ1 are due to
m(C@N) and m(N@N), respectively. In free ligands [22,29]
˚
N(8) bond distance (2.919(2) A) may be due to the low che-
late angle. In pseudo-octahedral compounds of type
MX2(N,N0)2, five different isomers are possible: two
compounds having trans-MX2 configuration and three

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K.K. Sarker et al. / Inorganica Chimica Acta 359 (2006) 695–700
Table 2
UV–Vis spectraa, and IRb
Compound
UV–Vis spectral data (kmax/nm) (10ꢀ3 e Mꢀ1 cmꢀ1
)
IR spectra, cmꢀ1
m(NCS/NCO)
m(C@N)
m(N@N)
[Cd(HaaiMe)2(NCS)2] (3a)
[Cd(MeaaiMe)2(NCS)2] (3b)
[Cd(HaaiEt)2(NCS)2] (4a)
[Cd(MeaaiEt)2(NCS)2] (4b)
[Cd(HaaiMe)2(NCO)2] (5a)
[Cd(MeaaiMe)2(NCO)2] (5b)
[Cd(HaaiEt)2(NCO)2] (6a)
[Cd(MeaaiEt)2(NCO)2] (6b)
432(0.99), 386(2.81), 372(2.77), 232(1.33)
442(1.69), 384(3.74), 372(2.83), 234(1.22)
432(1.42), 390(3.45), 356(3.97), 236(1.67)
434(1.51), 386(3.29), 370(3.20), 244(1.09)
445(0.73), 395(2.65), 370(2.67), 238(1.40)
452(0.69), 398(3.45), 370(2.73), 236(1.32)
438(1.28), 396(3.55), 350(3.75), 240(1.74)
444(1.21), 392(3.16), 360(3.10), 244(1.26)
2060
2060
2055
2060
2190
2202
2208
2195
1590
1598
1585
1595
1600
1594
1605
1600
1440
1444
1445
1440
1448
1450
1455
1450
a
In CH3OH.
In KBr disk.
b
Table 3
1H NMR spectral data in CD3CN at room temperature
Compound
d, ppm (J, Hz)
4-Ha
5-Ha
7,11-Ha
8-10-H
9-Me
1-Me
1-CH2
(1-CH2)CH3
c
d
3a
3b
4a
4b
5a
5b
6a
6b
7.48(7.0)
7.50(7.0)
7.53(7.5)
7.51(7.5)
7.61(7.0)
7.64(7.5)
7.62(7.0)
7.59(7.0)
7.27(7.0)
7.27(7.0)
7.28(7.5)
7.32(7.5)
7.30(7.0)
7.32(7.5)
7.30(7.0)
7.29(7.0)
7.90(7.5)
7.92(7.5)
7.91(7.8)
7.89(7.5)
7.92(7.5)
7.95(7.8)
7.95(7.0)
7.92(7.0)
7.44b
4.09
4.11
7.34(7.5)a
7.46b
2.45
2.45
2.47
4.42 (12.0)
4.50 (12.0)
1.52 (7.5)
1.57 (7.5)
7.34(7.5)a
7.55b
4.10
4.13
7.37(7.0)a
7.51b
4.04 (10.0)
4.52 (10.0)
1.55 (7.0)
1.58 (7.0)
7.34(7.0)a
a
Doublet.
Multiplet.
Quartet.
Triplet.
b
c
d
5
4
N
N
R'
N
N
11
10
7
8
9
R
Scheme 1. RaaiR0: R = H (1,3,5); Me (2, 4, 6) R0 = Me (a), Et (b).
compounds having cis-MX2 configuration [25]. Sequence
of coordination of pairs of donor centers following pairs
of X, N and N0 donor centers the isomers are assigned as
trans–cis–cis, trans–trans–trans, cis–trans–trans, cis–trans–
cis, and cis–cis–cis. The orientation of donor centers in
the present complex about Cd(II) has constituted cis–cis–
cis type geometrical isomer. The atomic arrangements
Cd(1), N(1), C(1), N(3), N(4); Cd(1), N(5), C(12), N(7),
Fig. 1. ORTEP diagram of [Cd(HaaiMe)2(NCS)2] (with 50% probability
ellipsoids).
˚
N(8) constitute two chelate planes (deviation < 0.03 A)
arrangements Cd(1), N(4), N(5), N(8), N(9) (plane-1);
Cd(1), N(1), N(8), N(9), N(10) (plane-2); Cd(1), N(1),
N(4), N(5), N(10) (plane-3) constitute three molecular
and are inclined at dihedral ca. 70ꢁ. The pendant phenyl
groups are also planar and make dihedral of ca. 7ꢁ with
respective chelated azoimine fragment. Three atomic

K.K. Sarker et al. / Inorganica Chimica Acta 359 (2006) 695–700
699
are the longest in the series and they are not equivalent:
Cd(1)–N(4), 2.677(5) and Cd(1)–N(8), 2.919(2) A. It is
Table 4
˚
Selected bond distances and bond angles of 3a
˚
because the N(azo) requires considerably more room than
the other two types of N-donors. There are at least two ste-
ric reasons for this. First, the N(azo) belongs to exocyclic
N@N along with a pendant phenyl group; thus the van
der Waals repulsion will be greater than N(imidazole).
The lowering in overall symmetry is manifested by the
elongation of two Cd–N(azo) distances. However, the
Cd–N(azo) distances are less than the sum of the van der
Waals radii of Cd(II) (1.58 A) and N(azo) (1.55 A)
[33,34]. This implies covalent interaction of N(azo) and
Cd(II).
Three different types of non-covalent interactions (C–
H–S; C–H–p and p–p) are observed in the packing view
of the molecule (Figs. 2–4). Hydrogen bonding with non-
bonded S is scarce [35]. The coordinated M–NCS is
hydrogen bonded with H of N–CH3 group and 1-D
chain has been generated along the x-direction [C(22)–
Bond distance (A)
Bond angle (ꢁ)
Cd(1)–N(1)
Cd(1)–N(4)
Cd(1)–N(5)
Cd(1)–N(9)
Cd(1)–N(10)
S(1)–C(20)
S(2) –C(19)
N(9)–C(20)
N(10)–C(19)
N(3)-N(4)
2.086(6)
2.677(5)
2.202(5)
2.124(8)
2.044(6)
1.616(8)
1.608(7)
1.137(11)
1.120(9)
1.243(8)
1.253(7)
2.919(2)
N(1)–Cd(1)–N(4)
N(1)–Cd(1)–N(5)
N(1)–Cd(1)–N(9)
N(1)–Cd(1)–N(10)
N(4)–Cd(1)–N(5)
N(4)–Cd(1)–N(9)
N(4)–Cd(1)–N(10)
N(5)–Cd(1)–N(9)
N(5)–Cd(1)–N(10)
N(9)–Cd(1)–N(10)
Cd(1)–N(4)–N(3)
N(8)–Cd(1)–N(5)
N(8)–Cd(1)–N(9)
N(8)–Cd(1)–N(10)
N(8)–Cd(1)–N(1)
N(8)–Cd(1)–N(4)
67.2(2)
105.4(2)
111.2(3)
130.9(3)
171.81(17)
87.8(2)
86.5(2)
92.0(2)
˚
˚
101.3(2)
108.2(3)
111.4(4)
62.2(1)
154.1(7)
78.0(2)
N(7) –N(8)
Cd(1)-N(8)
79.1(3)
117.9(3)
˚
˚
planes and maximum deviation has been observed for
N(azo) (N(4/8)) and they make dihedral 75–88ꢁ.
There are three types of N-centres: N(imidazole) (N(1)/
N(5)), N(azo) (N(4)/N(8)) and N(thiocyanato) (N(9)/
N(10)). The Cd–N(thiocyanato) and Cd–N(imidazole)
distances do not differ widely. The Cd–N(azo) distances
H(22b)–S(1): C–H, 0.96 A; H–S(1), 2.76 A; C(22)–S(1),
˚
3.602(10) A; \C(22)–H(22B)–S(1), 164ꢁ; symmetry: x,
1/2 ꢀ y, 1/2 + z] (Fig. 2). It is proposed that S in M–
NCS is more electronegative and less polarisable than
sulfide-S and may exhibit an affinity to acidic-H. In fact,
this proton abstracting affinity in dilute acid solution is
Fig. 2. 1-D chain constituted by hydrogen bonding along x-direction.
Fig. 3. Sheet formation of 1D chain by C–H–p interaction.

700
K.K. Sarker et al. / Inorganica Chimica Acta 359 (2006) 695–700
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Fig. 4. Unit cell pack showing p–p interaction between inter-chain
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responsible for liberation of H2S from thiourea, thiocar-
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˚
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˚
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Acknowledgement
Financial supports (C.S.) from the Council of Scientific
and Industrial Research, New Delhi are gratefully
acknowledged. One of us (U.S.R.) also thanks the UGC
for a fellowship. Our sincere thanks are due to Prof.
T.-H. Lu, Department of Physics, National Tsing Hua
University, Taiwan, ROC for helpful discussion.
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