Effect of size of metal ion on MS4N2 chromophore: Synthesis, spectral and single crystal X-ray structural studies on (2,2′-bipyridine)bis(N-cyclohexyl-N-methyldithiocarbamato)M(II) (M = zinc, cadmium)

Article abstract of DOI:10.1016/j.poly.2009.11.008

Isomorphous complexes [Zn(S₂CN(Me)Cy)₂(bipy)] (1) and [Cd(S₂CN(Me)Cy)₂(bipy)] (2) (where Cy(Me)NCS₂^- = N-cyclohexyl-N-methyldithiocarbamate anion and bipy = 2,2′-bipyridine) have been synthesised. Their structures and spectroscopic properties have been studied by IR, ¹H and ¹³C NMR spectroscopy and single crystal X-ray analysis. IR spectrum of the complexes show the contribution of thioureide form to the structures. ¹H NMR spectra of the complexes showed the desheilding of methyl protons and H-1 of cyclohexyl group on complexation. The downfield shift of N¹³CS₂, methyl carbon and C-1 of cyclohexyl group carbon signals for 2 (205.5, 36.7 and 64.4 ppm) from the chemical shift value of 1 (204.2, 35.6 and 63.1 ppm) is attributed to the movement of more electron density from dithiocarbamate towards cadmium. Single crystal X-ray structures of 1 and 2 indicate that the central metal atom is in a distorted octahedral environment for both complexes. The presence of added 2,2′-bipyridine ligand in the coordination sphere of M(S₂CN(Me)Cy)₂ increases Zn-S distances and decreases S-Zn-S angles in 1 and slightly increases Cd-S distances in 2. S-Cd-S angles are not affected. This is due to the relatively larger size of the cadmium ion compared to zinc ion which alleviates the strain involved in transformation from tetrahedral to octahedral.

Full text of DOI:10.1016/j.poly.2009.11.008

Polyhedron 29 (2010) 1078–1082
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Effect of size of metal ion on MS4N2 chromophore: Synthesis, spectral
and single crystal X-ray structural studies on
(2,20-bipyridine)bis(N-cyclohexyl-N-methyldithiocarbamato)M(II)
(M = zinc, cadmium)
b
P.V. Subha a, P. Valarmathi a, N. Srinivasan a, S. Thirumaran a, , K. Saminathan
*
a Department of Chemistry, Annamalai University, Annamalainagar, Chidambaram 608 002, India
b Sophisticated Analytical Instrument Facility, Indian Institute of Technology Madras, Chennai, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 June 2009
Accepted 13 November 2009
Available online 23 November 2009
Isomorphous complexes [Zn(S2CN(Me)Cy)2(bipy)] (1) and [Cd(S2CN(Me)Cy)2(bipy)] (2) (where Cy(Me)
ꢀ
NCS2 = N-cyclohexyl-N-methyldithiocarbamate anion and bipy = 2,20-bipyridine) have been synthes-
ised. Their structures and spectroscopic properties have been studied by IR, 1H and 13C NMR spectroscopy
and single crystal X-ray analysis. IR spectrum of the complexes show the contribution of thioureide form
to the structures. 1H NMR spectra of the complexes showed the desheilding of methyl protons and H-1 of
cyclohexyl group on complexation. The downfield shift of N13CS2, methyl carbon and C-1 of cyclohexyl
group carbon signals for 2 (205.5, 36.7 and 64.4 ppm) from the chemical shift value of 1 (204.2, 35.6
and 63.1 ppm) is attributed to the movement of more electron density from dithiocarbamate towards
cadmium. Single crystal X-ray structures of 1 and 2 indicate that the central metal atom is in a distorted
octahedral environment for both complexes. The presence of added 2,20-bipyridine ligand in the coordi-
nation sphere of M(S2CN(Me)Cy)2 increases Zn–S distances and decreases S–Zn–S angles in 1 and slightly
increases Cd–S distances in 2. S–Cd–S angles are not affected. This is due to the relatively larger size of the
cadmium ion compared to zinc ion which alleviates the strain involved in transformation from tetrahe-
dral to octahedral.
Keywords:
Zinc
Cadmium
2,20-Bipyridine
Dithiocarbamate
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
MS4N2 chromophore, we report the synthesis, spectral and struc-
tural characterization of two new complexes 1 and 2.
Group XII dithiocarbamates have found wide practical applica-
tion as additives to pavement asphalt, as antioxidants and
lubricants and vulcanizing agents and as potent pesticides [1,2]. A
recent work has established that dithiocarbamates of zinc and cad-
mium are useful precursors for the synthesis of ZnS and CdS nano
particles, respectively [3,4] and have application as non-linear opti-
cal materials [5]. The affinity of 1,1-dithiolate ligands for metals
such as zinc and cadmium was indicated by the fact that the ligands
can be employed as scavengers for these elements in biological
media. Besides that, nitrogen donor adducts of dithiocarbamate
complexes are also widely used in the preparation of thin semicon-
ductor [6–8] and electroluminescent [9,10] films of transition metal
sulfides, the basis of electronic and solar cell technology [11].
In our previous publications we reported synthesis, spectral and
structural studies on bis(dialkyldithiocarbamato)M(II) complexes
with different nitrogenous bases [12,13]. In the present work, in
order to understand the influence of the size of metal ion on
2. Experimental
All reagents and solvents were commercially available high-
grade materials (Merck/Sigma–Aldrich/Sd fine/spectrochem) and
used as received.
2.1. Physical measurements
IR spectra were recorded on a Thermo NICOLET AVATAR 330
FT-IR Spectrophotometer (range: 400–4000 cmꢀ1) as KBr pellets.
The NMR spectra were recorded on a BRUKER-NMR500MHzBRU-
NMR Spectrometer operating at 500 MHz. CdS has been character-
ized by X-ray powder diffraction using X’Per PRO diffractometer
with Cu Ka radiation (k = 1.54 ÅA).
0
2.2. X-ray crystallography
Details of the crystal data and structure refinement for 1 and 2
* Corresponding author.
E-mail address: sthirumaran@yahoo.com (S. Thirumaran).
are summarized in Table 1. The intensity data were collected at
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.11.008

P.V. Subha et al. / Polyhedron 29 (2010) 1078–1082
1079
Table 1
Crystal data and structure refinement for 1 and 2.
Compound
1
2
Empirical formula
Formula weight
C26H36N4S4Zn
598.20
C26H36CdN4S4
645.23
Temperature (K)
293(2)
293(2)
Wavelength (Å)
0.71069
0.71073
Crystal system, space group
orthorhombic, Pbca
orthorhombic, Pcab
Unit cell dimensions
a (Å)
b (Å)
c (Å)
17.87(5)
9.50(5)
33.64(5)
90°
9.547(5)
17.735(4)
34.335(3)
90°
a
(°)
b (°)
90°
90°
c
(°)
90°
5714(4)
8, 1.391
1.174
90°
Volume (Å3)
5813(4)
8, 1.474
1.061
Z, Dcalc (mg/m3)
Absorption coefficient (mmꢀ1
F (0 0 0)
)
2512
2656
Crystal size (mm)
h Range for data collection
Limiting indices
Reflections collected/unique
Completeness to h = 25.00
0.22 ꢁ 0.20 ꢁ 0.16
0.20 ꢁ 0.16 ꢁ 0.16
1.21–25.00°
1.19–25.00°
ꢀ21 6 h 6 21, ꢀ11 6 k 6 9, ꢀ40 6 l 6 35
24281/5029 [R(int) = 0.0236]
99.9%
ꢀ11 6 h 6 11, ꢀ18 6 k 6 21, ꢀ22 6 l 6 40
27289/5102 [R(int) = 0.0227]
99.8%
Maximum and minimum transmission
Data/restraints/parameters
0.8465 and 0.7932
5029/0/327
1.10
0.8475 and 0.8196
5102/0/326
1.187
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0326, wR2 = 0.0765
R1 = 0.0422, wR2 = 0.0872
0.318 and ꢀ0.235
R1 = 0.0322, wR2 = 0.0602
R1 = 0.0429, wR2 = 0.0689
0.314 and ꢀ0.809
Largest difference in peak and hole (e Åꢀ3)
ambient temperature on a Bruker axs Kappa apex II CCD diffrac-
tometer using graphite monochromated Mo radiation
2.4. Preparation of CdS from (2)
K
a
0
(k = 0.71073 ÅA). The structure was solved by SIR 92 [14] and refined
by full matrix least squares with SHELXL-97 [15]. All non hydrogen
atoms were refined anisotropically and all hydrogen atoms were
fixed geometrically. Selected bond distances and angles are pre-
sented in Table 2.
One gram of [Cd(S2CN(Me)Cy)2(bipy)] was dissolved in 15 ml of
ethylenediamine in a flask, and then heated to reflux (117 °C), and
maintained at this temperature for 2 min. The yellowish CdS pre-
cipitate was filtered off and washed with ethanol.
Attempts to separate ZnS from [Zn(S2CN(Me)Cy)2(bipy)] were
not successful.
2.3. Preparation of the complexes (1) and (2)
2.4.1. [Zn(S2CN(Me)Cy)2(bipy)] (1)
IR(KBr)cmꢀ1: 1472 (
mC–N(thioureide)), 971 (
mC–S), 1594 (bipy
The bis(N-cyclohexyl-N-methyldithiocarbamato)M(II) (M = Zn,
Cd) complexes were prepared using the established procedure
[16]. Adducts were prepared by adding a hot solution of 2,20-bipyr-
idine (2 mmol) in ethanol to a hot solution of [M(S2CN(Me)Cy)2]
(1 mmol) in chloroform. The resulting solution was cooled and
then added with petroleum ether (boiling range 40–60 °C). Yellow
precipitate of the adducts were separated out.
(ring frequency)), 3055 (aromatic,
m
C–H). 1H NMR d (ppm); 1.05–
1.08 (m, axial H-4), 1.29–1.39 (m, H-3), 1.64 (d, equatorial H-4),
1.77–1.85 (m, H-2), 3.27 (s, –CH3), 4.92–4.99 (m, H-1),7.43 (t, H-
4 (bipy)), 7.89 (t, H-5 (bipy)), 8.21 (d, H-6(bipy)), 9.09 (d, H-
3(bipy)). 13C NMR d (ppm); 25.39 (C-4), 25.44 (C-3), 29.91 (C-2),
35.62 (CH3), 63.14 (C-1), 120.82 (C-6(bipy)), 124.84 (C-4(bipy)),
138.16 (C-5(bipy)), 149.16 (C-3(bipy)), 151.94 (C-10(bipy)),
204.23 (NCS2).
Table 2
Selected bond lengths (Å) and angles (°) for 1 and 2.
2.4.2. [Cd(S2CN(Me)Cy)2(bipy)] (2)
IR(KBr)cmꢀ1: 1471 (C–N), 968 (C–S), 1592 (bipy (ring fre-
quency)), 3055 (aromatic, C–H). 1H NMR d (ppm); 1.04–1.08 (m,
axial H-4), 1.25–1.37 (m, H-3), 1.62 (d, equatorial H-4), 1.74–1.85
(m, H-2), 3.29 (s, –CH3), 5.06–5.11 (m, H-1), 7.44 (t, H-4 (bipy)),
7.90 (t, H-5(bipy)), 8.13 (d, H-6 (bipy)), 9.00 (d, H-3 (bipy)). 13C
NMR d (ppm); 25.48 (C-4), 25.53 (C-3), 29.99 (C-2), 36.68 (CH3),
64.35 (C-1), 121.21 (C-60(bipy)), 125.39 (C-40(bipy)), 138.70 (C-
50(bipy)), 149.62 (C-30(bipy)), 150.61 (C-10(bipy)), 205.51 (NCS2).
Compound
1
2
C(7)–N(1)
C(14)–N(2)
C(7)–S(2)
C(7)–S(1)
C(14)–S(4)
C(14)–S(3)
N(6)–M(1)
N(8)–M(1)
S(1)–M(l)
S(2)–M(l)
S(3)–M(l)
S(4)–M(l)
S(2)–C(7)–S(1)
S(4)–C(14)–S(3
N(6)–M(1)–N(8)
S{3)–M(1)–S(4)
S(2)–M(l)–S(1)
S(3)–M(l)–S(4)
1.343(4)
1.329(3)
1.707(3)
1.714(3)
1.717(3)
1.718(3)
2.211(2)
2.219(2)
2.5767(11)
2.4811(8)
2.4691(9)
2.5199(8)
117.19(15)
116.42(15)
73.23(8)
71.62(3)
70.47(3)
71.62(3)
1.332(4)
1.328(4)
1.715(3)
1.717(3)
1.712(3)
1.724(3)
2.418(3)
2.424(3)
2.6214(11)
2.6515(10)
2.6487(10
2.6621(12)
118.6(2)
118.4(2)
66.84(9)
67.54(3)
68.07(3)
67.54(3)
3. Results and discussion
3.1. Infrared spectral studies
The vC–N has been used as a measure of the contribution of the
thioureide form to the complexes [17]. In the present study, com-
plexes 1 and 2 show thioureide vC–N band at 1472, 1471 cmꢀ1
,

1080
P.V. Subha et al. / Polyhedron 29 (2010) 1078–1082
Table 3
Band valence sums for zinc and cadmium complexes.
Compound
Coordination number
Vi (OK/B)
Vi (B/OK)
Referencesb
[Zn(S2CN(Me)Cy)2]
[Zn(S2CN(Me)Cy)2(bipy)]
[Cd(deadtc)2]2
[Cd(pipdfc)2]2
[Cd(S2CN(Me)Cy)2(bipy)]
4
6
1.96
1.85
1.95
2.05
2.06
2.02
1.89
2.00
2.10
2.10
[25]
this work
[26]
[27]
this work
4a
4a
6
a
Actual coordination number is five including a long M–S bond.
The crystal structure data of the complexes were obtained from the corresponding literature.
b
respectively, indicating the partial double bond character. The shift
in the electron density. The other cyclohexyl group carbon signals
in both the complexes are not greatly affected in complexation be-
cause of the relative distance from the thioureide p-system and the
in vC–N values to lower wave number compared to the parent
[Zn(S2CN(Me)Cy)2]
(v
C–N = 1488 cmꢀ1
)
and [Cd(S2CN(Me)Cy)2]
(v
C–N = 1482 cmꢀ1) is due to the change in coordination geometry
metal center. The 13C NMR peaks of the group N13CS2 are found in
both cases, at around 205 ppm, which indicates the bidentate char-
acter of the ligand [20]. The N13CS2, methyl carbon and C-1 carbon
of cychlohexyl group carbon signals for 2 are observed at 205.5,
36.7 and 64.4 ppm, respectively, with small downfield shift of
about 1 ppm compared to that of the corresponding signals in 1
(204.2, 35.6 and 63.1 ppm). The observed deshielding in 2 is attrib-
uted to the movement of more electron density from dithiocarba-
mate ligand towards the cadmium on complexation. This is due to
large size of cadmium ion in 2 experiences less steric effect in-
volved in transformation from tetrahedral to octahedral. Aromatic
carbon signals are observed in the downfield region 120.8–
152.0 ppm for the synthesized complexes. The observed small dif-
ferences in 1 and 2 compared to the free 2,20-bipyridine signals can
be attributed to charge delocalization which prevents the move-
ment of electron density from the adjacent carbons.
from tetrahedral to octahedral [18]. However, ring frequencies
associated with 2,20-bipyridine are observed in the 1600–1000
cmꢀ1. In the present study, complexes 1 and 2 show bands at
1594 and 1592 cmꢀ1, respectively. Other bands are masked by
those due to dithiocarbamate ligand.
3.2. 1H NMR spectral analysis
A singlet observed around 3.28 ppm and a multiplet observed in
the region of 4.92–5.11 ppm for the complexes 1 and 2 are due to
methyl protons and H-1 proton of cyclohexyl group, respectively.
The observed deshielding of the methyl protons and H-1 proton
of cyclohexyl group in both cases [19] is attributed to the release
of electrons on the nitrogen of the NR2 groups, forcing high elec-
tron density towards the sulfur (or the metal) via the thioureide
p-system. Although the magnitude of the deshielding decreases
with the increase in distance from the metal center or the thioure-
ide bond, the other proton signals of cyclohexyl group are also
slightly deshielded on complexation. The signals observed in the
downfield region of 7.43–9.09 ppm are assigned to the proton
present in the 2,20-bipyridine.
3.4. VBS analysis
Valence bond sum values were calculated by two procedures
OK/B [21] and B/OK [22]. The VBS values for 1 and 2 are also com-
pared with those whose structures have been reported in the liter-
ature. The valence bond sums of various complexes are given in
Table 3. VBS values (1.96) OK/B; 2.02 (B/OK)) are almost 2.0 for
parent [Zn(S2CN(Me)Cy)2] and the values are greater than the
sum of 1.85 (OK/B); 1.89 (B/OK) for 1. The decrease in VBS values
in the case of 1 can be ascribed to the increase in Zn–S distances
(which are longer than those observed in [Zn(S2CN(Me)Cy)2]),
due to the presence of an additional neutral ligand. In all the cad-
mium complexes, whether four coordinated or six coordinated, the
VBS has been found to be close to 2.0. It has already been reported
3.3. 13C NMR spectral studies
The signal for methyl and C-1 (cyclohexyl) carbon atoms adja-
cent to the nitrogen atom appear around 36 and 64 ppm. A down-
field shift of the methyl and C-1 (cyclohexyl) carbon signals in both
the complexes is an indication of the important consequence of the
dꢀ
d+. . .
complexation process, viz., a significant thioureide N
C
con-
•
tribution to the stability of the complexes and a resultant reduction
Fig. 1. ORTEP diagram of [Zn(S2CN(Me)Cy)2(bipy)].

P.V. Subha et al. / Polyhedron 29 (2010) 1078–1082
1081
Fig. 2. ORTEP diagram of [Cd(S2CN(Me)Cy)2(bipy)].
[23] that in the case of the cadmium dithiocarbamate complexes
and their adducts, no observable changes are seen in VBS values.
Due to larger size of cadmium ion compared to zinc ion, the Cd–
S distances are not much affected by the change in coordination
geometry from tetrahedral to octahedral.
with similar compounds is given in Table 4. No significant changes
in C–N, C–S bond lengths and S–C–S angles are observed. In com-
plex 1, Zn–S distances are longer and S–Zn–S angles are less com-
pared to those observed in parent [Zn(S2CN(Me)Cy)2] complex due
to the increased coordination around zinc. But in complex 2, accep-
tance of an additional neutral ligand causes only slight increase in
Cd–S distance. S–Cd–S angles are not affected. This is expected on
the basis of a relatively larger size of cadmium ion compared to
zinc ion, which alleviates the strain involved in the transformation
from tetrahedral to octahedral geometry. However, comparison of
the bond parameters of 2 is only possible with similar compounds
and not with the parent [Cd(S2CN(Me)Cy)2] because of the lack of
data.
3.5. Single crystal X-ray studies
The ORTEP of [Zn(S2CN(Me)Cy)2(bipy)] and [Cd(S2CN(Me)Cy)2
(bipy)] are shown in Figs. 1 and 2, respectively. The structures of
1 and 2 contain eight discrete monomeric units per unit cell. In
both complexes the metal atom is situated at the center of the dis-
torted octahedral arrangement of four sulfur atoms from the che-
lating dithiocarbamate groups and two nitrogen atoms from the
chelating 2,20-bipyridine ligand. The distinct asymmetry in M–S
distances is due to the steric effect exerted by 2,20-bipyridine, as
observed for similar adducts [19]. The C–S distances are symmet-
ric, indicating that the presence of an additional neutral ligand af-
3.6. X-ray powder diffraction studies on CdS
Fig. 3 shows the XRD pattern of the prepared CdS. The presence
of crystal planes of hexagonal CdS structure by this method is
fects only the M–S distances. The C–S distances are to
a
considerable extent shorter than the typical C–S single bond dis-
tance 1.81 Å. Therefore, all the C–S bonds in the present structure
are of partial double bond character as observed in most of the
dithiocarbamates [24]. Average C–N distance of 1 and 2 are
1.336(3) Å and 1.330(4) Å, which clearly indicates that the p-elec-
tron density is delocalized over the S2CN moiety and that this bond
has a strong double bond character. Comparison of bond parame-
ters (Table 2) of 1 and 2 shows that M–S and M–N bonds are longer
and S–M–S angles are smaller in 2 than that found in 1 due to the
larger size of cadmium compared to zinc. The 2,20-bipyridine and
cyclohexane rings show normal bond parameters. The cyclohexane
ring is in the chair conformation.
Of particular interest with respect to the dithiocarbamate–me-
tal bonding are the M–S, and C–S and C–N distances and the
related angles. A comparison of the bond parameters associated
Fig. 3. X-ray powder diffraction pattern of CdS.
Table 4
Comparative structural parameters.
Compound
Coordination number
S–M–S
S–C–S
M–S
C–S
S2C–N
References
[Zn(S2CN(Me)Cy)2]
4
6
78.11(3)
71.05(3)
68.36(2)
68.01(3)
67.80(4)
116.97(20)
116.81(15)
118.92(16)
118.7(3)
2.3445(10)
2.5115(9)
2.5967 (9)
2.5610(9)
2.6459(11)
1.733(3)
1.718(3)
1.730(3)
1.735(3)
1.717(3)
1.319(4)
1.336(3)
1.334(2)
1.326(4)
1.330(4)
[25]
this work
[26]
[27]
this work
[Zn(S2CN(Me)Cy)2(2,20-bipy)]
[Cd(deadtc)2]
4a
4a
6
[Cd(pipdtc)2]
[Zn(S2CN(Me)Cy)2(2,20-bipy)]
118.5(2)
The bond distances and angles are mean values.
a
It has been suggested thai the coordination number is essentially five.

1082
P.V. Subha et al. / Polyhedron 29 (2010) 1078–1082
consistent with the literature data of JCPDS card file No. 41-1049.
The presence of diffraction peak 2h = 28.5°, 52.2° correspond to
the crystal planes of wurtzite CdS structure. The absence of diffrac-
tion peak 2h = 31.5° indicates the lack of zinc blend structure in the
sample [28]. The broad peaks indicate that the particles are small
in size. The size of CdS particles estimated from the Scherrer for-
mula is 12 nm.
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1133.
4. Conclusion
Two crystalline isomorphous compounds 1 and 2 were pre-
pared and studied by means of IR, NMR spectroscopy, valence bond
sum parameter and single crystal X-ray diffraction. 13C NMR spec-
tral data give an insight into the direction of displacement of the
electron density which can be correlated with the size of the metal
ion. Comparison of bond parameters of 1 and 2 with those ob-
served in similar bisdithiocarbamates shows the following trends:
M–S distances increase, S–Zn–S angles decrease and S–Cd–S angles
are not affected on adduct formation. Comparison of bond param-
eters of 1 and 2 shows that M–S and M–N bonds are longer and S–
M–S angle is smaller in 2 than that found in 1 due to the larger size
of Cd2+ compared to Zn2+ (Cd2+: 109 pm; Zn2+: 88 pm). The obser-
vation is a manifestation of the size effects of the metal ions in-
volved. All other parameters including the thioureide bond
distances show very little differences for the 1 and 2.
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[22] N.E. Brese, M. O’Keeffe, Acta Crystallogr., Sect. B47 (1991) 192.
[23] S. Thirumaran, K. Ramalingam, G. Bocelli, A. Cantoni, Main group Met. Chem.
22 (1999) 423.
Supplementary data
[24] C. Husebye, Acta. Chem. Scand. 24 (1970) 2198.
CCDC 701407 and 701408 contain the supplementary crystallo-
graphic data for 1 and 2. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Center, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@
ccdc.cam.ac.uk
[25] M.Y. Chan, C.S. Lai, E.R.T. Tiekink, Appl. Organometal. Chem. 18 (2004) 298.
[26] Y. Zong, W. Zhang, J. Fan, M. Tan, C.S. Lai, E.R.T. Tiekink, Acta Crystallogr., Sect.
E60 (2004) m2633.
[27] A.V. Ivonov, V. Gerasimenko, A.A. Konzelko, M.A. Ivanov, O.N. Antzutkin, W.
Forsling, Inorg. Chim. Acta 359 (2006) 3855.
[28] W. Qingqing, X. Gang, H. Gaorong, J. Solid State Chem. 178 (2005) 2680.
Acknowledgments
We are thankful to SAIF, Indian Institute of Technolgy Madras
for the single crystal X-ray structural analysis and recording NMR
spectra of all compounds.