Solvent dependent crystallization of a few Hg(II) thiocarboxylates

Article abstract of DOI:10.1016/j.ica.2012.01.039

During the process of crystallization of newly synthesized heterobimetallic complexes [(Ph₃P)₂Cu(μ-SCOR)₂Hg(SCOR)] [R = Ph (1), th (thiophene) (2)] Hg(II) thiocarboxylate complexes were isolated. In chloroform/diethyl ether a phosphine migration led to the formation of Hg(Ph₃P)(SCOPh)₂ (3) and Hg(Ph₃P)(SCOth) ₂ (4) while in chloroform/n-hexane the binary Hg(II) complexes, Hg(SCOPh)₂ (5) and Hg(SCOth)₂ (6) were isolated. In another reaction a heterobimetallic complex, Hg(SCOPh)₂TiCl ₄ (7) was obtained as the end product. Molecular structures of 3, 4 and 6 were studied by single crystal X-ray diffraction. The crystals of 4 provided an interesting example of polytopal isomerism. Structures and electronic transitions have been explained on the basis of DFT calculations.

Full text of DOI:10.1016/j.ica.2012.01.039

Inorganica Chimica Acta 385 (2012) 112–118
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Inorganica Chimica Acta
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Solvent dependent crystallization of a few Hg(II) thiocarboxylates
⇑
Suryabhan Singh, Jyotsna Chaturvedi, Subrato Bhattacharya
Department of Chemistry, Banaras Hindu University, Varanasi 221005, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 July 2011
Received in revised form 16 January 2012
Accepted 20 January 2012
Available online 6 February 2012
During the process of crystallization of newly synthesized heterobimetallic complexes [(Ph3P)2Cu
(l-SCOR)2Hg(SCOR)] [R = Ph (1), th (thiophene) (2)] Hg(II) thiocarboxylate complexes were isolated.
In chloroform/diethyl ether a phosphine migration led to the formation of Hg(Ph3P)(SCOPh)2 (3) and
Hg(Ph3P)(SCOth)2 (4) while in chloroform/n-hexane the binary Hg(II) complexes, Hg(SCOPh)2 (5) and
Hg(SCOth)2 (6) were isolated. In another reaction a heterobimetallic complex, Hg(SCOPh)2TiCl4 (7) was
obtained as the end product. Molecular structures of 3, 4 and 6 were studied by single crystal X-ray
diffraction. The crystals of 4 provided an interesting example of polytopal isomerism. Structures and elec-
tronic transitions have been explained on the basis of DFT calculations.
Keywords:
Mercury
Thiocarboxylate
Triphenylphosphine
Polytopal isomerism
DFT
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Ligands containing both O and S donor sites exhibit interesting
coordination properties. Earlier studies on complexes of monot-
hiocarbamates [1] revealed the bonding features of the ligands
which can be explained on the bases of Pearson’s acid base theory
[2]. Though a bidentate bonding mode of a thiocarboxylate is less
favorable [3], yet thiocarboxylate ligands have been found to
exhibit rich coordination chemistry. Anionic thiocarboxylate
complexes [4] have been exploited as metalloligands and a good
number of bimetallic complexes have been prepared during recent
years which have also been used as precursors for ternary chalcog-
enides [5].
2.1. Reagents and general procedures
All the solvents were dried according to standard procedures and
distilled before use. Bis(triphenylphosphine)copper(I) nitrate [14]
and thiophene-2-thiocarboxylic acid was synthesised by a method
we have reported recently [15]. Sodium salt of thiophene-2-thio-
carboxylic acid was obtained by reacting the acid with sodium
methoxide in stoichiometric ratio. Thiobenzoic acid, triphenylphos-
phine and mercuric nitrate were purchased from Sigma–Aldrich and
used as received.
A few thiocarboxylate complexes of group 12 metals have been
prepared and structurally characterized by Vittal et al. [6–8].
Besides the neutral binary compounds [M(SCOR)2] {M = Zn, Cd,
Hg} [9] these metals form mono- and dianionic complexes
[M(SCOR)n]mÀ {n = 3; m = 1 and n = 4; m = 2} [6–8] also. In addition
Hg(II) has been reported to form unusual anionic complexes,
[MCl4Hg(SCOPh)2]2À {M = Cd(II)/Hg(II)} [10]. Very recently, we
have reported synthesis and structures of Pb/Cu and Pb/Ag hetero-
bimetallic complexes of thiobenzoate ligands which could be used
to prepare ternary oxides [11]. In view of these we have now taken
up the synthesis and characterization of thiocarboxylate complexes
containing Zn/Cu, Zn/Ag [12], Cd/Cu, Cd/Ag [13] and Hg/Cu. Here,
we report the results of our studies on the Hg(II) complexes.
2.2. Instrumentation
IR Spectra was recorded using Varian-3100 FTIR instruments.
NMR spectra were obtained using a JEOL AL300 FT NMR spectrom-
eter. Electronic absorption spectra were recorded using a Shimadzu
UV-1700 PharmaSpec Spectrometer. The electronic absorption
spectra of the 1–4 were recorded in chloroform solutions while of
5 and 6 were recorded in DMSO solutions. Since 1 and 2 dissociate
in solution we refrain from analyzing the solution spectral data of
these two. Solid state absorption spectra of 1–4 and 6 were also
recorded. Elemental analyses were performed by the EAT Exeter
Analytical Inc. CE-440, elemental analyzer.
Single crystal X-ray data of all complexes were collected on a
Xcalibur Eos, Oxford diffractometer using graphite monochromat-
ed Mo K
a radiation (k = 0.7107 Å). Data collections were carried
⇑
out at room temperature (293 K) using hemisphere mode. Struc-
Corresponding author. Tel.: +91 5426702451.
E-mail addresses: bhatt99@yahoo.com, s_bhatt@bhu.ac.in (S. Bhattacharya).
tures were solved by the direct method and then refined on F2 by
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2012.01.039

S. Singh et al. / Inorganica Chimica Acta 385 (2012) 112–118
113
Table 1
crystals of 3 were obtained after two days. Yield: 0.508 g (69%).
Anal. Calc. for C64H50O4S4P2Hg2: C, 52.13; H, 3.42. Found: C,
Crystal data and structure refinement of 3, 4 and 6.
52.09; H, 3.40%. IR spectra (KBr, cmÀ1): 1613, 1572
m(CO), 1197
3
4
6
m
(Ph–C), 906 m
(C–S). NMR (CDCl3, d ppm): 1H NMR 7.11–7.91
Empirical formula
T (K)
Crystal system
Space group
a (Å)
C
293
64H50O4S4P2Hg2 C84H63O6S12P3Hg3 C10H6O2S4Hg
(Ph). 13C NMR 128.19–138.83 (Ph), 198.39 (COS). 31P NMR 4.45,
11.94.
293
triclinic
P1
293
triclinic
P1
Monoclinic
P21/n
12.732(5)
17.069(5)
13.512(5)
90
109.324(5)
90
2771.0(17)
2
ꢀ
ꢀ
12.7085(8)
14.0629(9)
15.3760(11)
85.449(6)
82.363(6)
78.704(5)
2666.8(3)
1
6.6482(6)
14.1942(11)
14.7473(9)
73.609(6)
79.430(6)
86.273(7)
1312.30(18)
4
2.4.4. Attempt to crystallize 2: synthesis of Hg(PPh3)(SCOth)2
4
b (Å)
c (Å)
The complex 2 (1.217 g, 1.0 mmol) was dissolved in chloroform,
layered with diethyl ether and kept for crystallization. Single crys-
tals of 4 were obtained on the next day. Yield: 0.539 g (72%). Anal.
Calc. for C84H63O6S12P3Hg3: C, 44.88; H, 2.82. Found: C, 44.45; H,
a
(°)
b (°)
c
(°)
V (Å3)
2.81%. IR spectra (KBr, cmÀ1): 1606, 1570
m(CO), 1198 m(th–C),
Z
893 m
(C–S). NMR (CDCl3, d ppm): 1H NMR 7.00–7.74 (Ph and th).
l
(Mo K
Final R indices
[I > 2 (I)]
a
) (mmÀ1
)
5.792
0.0295
6.170
0.0727
12.348
0.0952
13C NMR 127.59–145.42 (Ph and th), 190.43 (COS). 31P NMR 2.62,
24.00.
r
R indices (all data)
Goodness-of-fit
(GOF) on F2
0.0428
0.982
0.0913
1.089
0.1431
1.000
2.4.5. Attempt to crystallize 1: synthesis of Hg(SCOPh)2
5
The complex 1 was dissolved in chloroform, layered with n-hex-
ane and kept for crystallization. Crystals of 5 settled down within
30 min. Yield: 0.421 g (89%). Anal. Calc. for C10H6O2S4Hg: C,
24.66; H, 1.24. Found: C, 24.62; H, 1.23%. IR spectra (KBr, cmÀ1):
the full matrix least square technique with SHELX-97 set of software
[16] using the WINGX program package. [17] Crystal data of com-
plexes 3, 4 and 6 are given in Table 1.
1624 m(CO), 1201 m(th–C), 1047 m
(C–S). NMR (DMSO, d ppm): 1H
NMR 7.41, 7.81 and 7.92 (th). 13C NMR 128.59, 133.38, 134.36
and 143.85 (th), 187.34 (COS).
2.3. Theoretical calculations
2.4.6. Attempt to crystallize 2: synthesis of Hg(SCOth)2
6
The atomic coordinates were obtained from X-ray crystallo-
graphic results for TDDFT calculations [18] and NBO calculation.
The calculations were performed at B3LYP level using 6-31G⁄⁄
basis set for C, H, O, P and S atoms while the CEP-121G basis set
was used for Hg. All the calculations were carried out using GAUSS-
IAN 03 program package [19].
The complex 2 was dissolved in chloroform, layered with n-hex-
ane and kept for crystallization. Well formed single crystals of 6
were obtained within 1 h. Yield: 0.418 g (86%). Anal. Calc. for
C
14H10O2S2Hg: C, 35.40; H, 2.12. Found: C, 35.37; H, 2.12%. IR spec-
tra (KBr, cmÀ1): 1624
m(CO), 1201 m(Ph–C), 906 m(C–S). NMR
(DMSO, d ppm): 1H NMR 7.48–7.98 (Ph). 13C NMR 128.13–138.52
(Ph), 196.03 (COS).
2.4. Syntheses
2.4.7. Synthesis of [TiCl4.Hg(SCOPh)2] 7
2.4.1. Synthesis of [(Ph3P)2Cu(l-SCOPh)2Hg(SCOPh)] 1
To a stirred solution of NaSCOPh prepared in situ by reacting
thiobenzoic acid (0.414 g, 3.0 mmol) and sodium metal (0.069 g,
3.0 mmol) in MeOH (15 mL) was added a methanolic solution
(5 mL) of HgCl2 (0.271 g, 1.0 mmol) to get a yellow colored solution
of Na[Hg(SCOPh)3]. A solution of TiCl4 (0.047 g, 0.25 mmol) in
methanol (10 mL) was then added to the reaction mixture with
vigorous stirring at 10 °C. Stirring was continued for 1 h maintain-
ing the temperature below 10 °C. The solvent was then evaporated
under reduced pressure and the residue was extracted with CHCl3
(20 mL). The insoluble particles were filtered off and solvent from
the filtrate was evaporated under reduced pressure. The product
was apparently a mixture of two compounds. Washed the mixture
with ethanol and diethyl ether to remove the colorless product.
The red colored crystalline compound was dried under vacuum
for 1 h. Yield (based on TiCl4): 0.158 g (95%). M+/e, 663. Anal. Calc.
for C14H10O2S2Hg1Ti1Cl4: C, 25.31; H, 1.52. Found: C, 24.80; H,
To a solution of sodium thiobenzoate (0.414 g, 3.0 mmol) (gen-
erated in situ by a reaction of thiobenzoic acid and sodium metal in
methanol) in 10.0 ml of methanol was added a solution of
Hg(NO3)2ÁH2O (0.342 g, 1.0 mmol) in methanol (5.0 ml) drop wise
with stirring in an ice bath. The reaction mixture was stirred for
15–20 min. then added a solution of (PPh3)2CuNO3 (0.650 g,
1.0 mmol) in 5.0 ml of dichloromethane. Then reaction mixture
was stirred for an hour and dried under reduced pressure. The light
yellow colored residue was dissolved in chloroform and filtered off
the insoluble NaNO3 formed. Solvent from filtrate was evaporated
under reduced pressure and then dried under vacuum. Yield:
1.092 g (91%). Anal. Calc. for C57H45O3S3P2HgCu: C, 57.04; H, 3.78.
Found: C, 57.45; H, 3.77%. IR spectra (KBr, cmÀ1): 1625, 1575
m
(CO), 1201 m(Ph–C), 905 m
(C–S). NMR (CDCl3, d ppm): 1H NMR
7.12–7.92 (Ph). 13C NMR 128.46–137.93 (Ph), 197.28 (COS). 31P
NMR 1.82.
1.65%. IR spectra (KBr, cmÀ1): 1625
m(CO), 1215 m(Ph–C), 908 m
(C–S). 1H NMR (CDCl3, d ppm): 7.3–7.8 (Ph). 13C NMR; 126–137
(Ph), 197.3 (COS).
2.4.2. Synthesis of [(Ph3P)2Cu(l-SCOth)2Hg(SCOth)] 2
A procedure similar to that described for the synthesis of 1 was
followed using sodium thiophene-2-thiocarboxylate (0.498 g,
3.0 mmol) in place of sodium thiobenzoate. Yield: 0.523 g (70%).
Anal. Calc. for C51H39O3S6P2Hg: C, 50.28; H, 3.23. Found: C, 50.43;
3. Results and discussion
H, 3.20%. IR spectra (KBr, cmÀ1): 1590, 1560
890
13C NMR 127.58–145.56 (Ph and th), 190.61 (COS). 31P NMR 3.43.
m
(CO), 1194
m(th–C),
3.1. Syntheses and characterization
m
(C–S). NMR (CDCl3, d ppm): 1H NMR 7.02–7.74 (Ph and th).
The anionic complexes, [Hg(SCOR)3]À were generated in situ by
reacting sodium salt of the thiocarboxylate with mercuric nitrate
in methanol. Reaction of the anion with bis(triphenylphos-
phine)copper(I) was carried out to isolate the heterobimetallic
2.4.3. Attempt to crystallize 1: synthesis of Hg(PPh3)(SCOPh)2
3
The complex 1 (1.198 g, 1.0 mmol) was dissolved in chloroform,
layered with diethyl ether and kept for crystallization. Single
complexes, [(Ph3P)2Cu(l-SCOR)2Hg(SCOR)] [R = Ph (1), th (2)]. In

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S. Singh et al. / Inorganica Chimica Acta 385 (2012) 112–118
the IR spectra of the compounds two CO stretching bands are
clearly observable in both the cases of 1 and 2. The peak at higher
frequency indicates a monodentate (through S) bonding mode
while the other band is indicative of a bidentate bonding mode
of the thiocarboxylate ligand. In absence of crystal structures it is
not possible to comment on the geometries of the molecules of 1
and 2. However, in view of the structures of analogous bimetallic
thiocarboxylates can be prepared by a direct reaction of the li-
gand’s sodium salt and Hg2+ in aqueous medium, yet it is rather
difficult to crystallize the product owing to its insolubility in suit-
able solvents. Notably, 5 and 6 were obtained as single crystals
from chloroform/n-hexane solutions of 1 and 2 respectively. The
crystals once formed were, however, insoluble in chloroform. Since
the Cu/Hg complexes dissociate in solution we thought it worth-
while to prepare a heterobimetallic complex in which an early
transition metal in higher oxidation state (hard metal) is present
along with Hg(II). One may expect the oxygen atom to bind with
the hard metal ion leaving the sulfur atom available for Hg(II).
Interestingly, when the anionic complex [Hg(SCOPh)3]À was trea-
ted with TiCl4 a complex, HgTiCl4(SCOPh)2 was isolated (see
Scheme 1).
Electronic absorption bands of 3 were observed at 298 and
261 nm where as in solid state observed at 327, 300, 265, and
231 nm. Electronic absorption bands of 6 were observed at 318
and 276 nm whereas in solid state it showed at 315, 299, 283
and 247 nm. These peaks may be assigned as intra/interligand
and ligand to metal charge transfer transitions (in a dithiocarba-
mate complex the LMCT transitions have been reported at 253
and 259 nm [22]) Absorption bands of the compounds are given
in supplementary file (Figs. S1–S6).
complexes such as [(Ph3P)2Cu(
l
-SCOPh)2Pb(SCOPh)] [11], [(Ph3
-SCOth)2Cd(SCOth)]
P)2Cu( -SCOPh)2Cd(SCOPh)] and [(Ph3P)2Cu(
l
l
[13] one may tentatively propose a similar structure for 1 and 2
in which Cu atom is bonded to the sulfur atoms of the bridging
thiocarboxylate groups. In contrast to the analogous highly stable
complexes of Cu/Zn and Cu/Cd, 1 and 2 dissociated in solution giv-
ing a variety (depending on the solvents) of Hg(II) thiocarboxylates
(see Scheme 1). In chloroform/diethyl ether a triphenylphosphine
migrated from Cu(I) to Hg(II) center and the products obtained
were Hg(Ph3P)(SCOR)2 [R = Ph (3) and th (4)] while in chloro-
form/n-hexane 1 and 2 dissociated completely into Hg(SCOR)2
[R = Ph (5), th (6)] and Cu(PPh3)2(SCOR).
Though quite a few triphenylphosphine complexes of Hg(II)
have been synthesized [20] yet this is the first example containing
a thiocarboxylate ligand. Triphenylphosphine migration has been
known from one metal to another in some cases and we have re-
cently studied one such example where the ligand migrates from
Cu(I) to Zn(II) [12], however, to the best of our knowledge no re-
port on phosphine migration to a Hg(II) center is available. Phos-
phine migration can be understood in view of the fact that metal
triphenylphosphine complexes are in general, known to dissociate
in solution. As a result various species exist in dynamic equilibrium
[21]. 31P NMR spectra of 3 and 4 showed two peaks at room
temperature indicating the existence of two different phosphine
containing species in solution. The spectra of other compounds
showed one peak which is possibly due to fast scrambling process
at room temperature [21].
For unambiguous assignment of the spectral bands TDDFT
calculations have been carried out. Orbitals involved in selected
transitions in the cases of 3 and 6 are shown in Figs. 1 and 2, respec-
tively. From TDDFT its clear that lower energy band in case of 3 due
to mixed transitions of ligand to metal and interligand charge trans-
fer transition where as higher energy bands are due to inter/intral-
igand charge transfer transitions. But in case of 6 all the absorption
bands are due to inter and intraligand charge transfer transitions.
3.2. Crystal and molecular structures
Complex 3 crystallized in monoclinic system with P21/n space
group. The asymmetric unit consists of a Hg(II) center coordinated
by two sulfur atoms of thiobenzoate ligands and a phosphorous of
triphenylphosphine. In the lattice the molecules are packed in such
Notably, a direct reaction of mercuric salt with sodium thi-
obenzoate in presence of triphenylphosphine, however, did not
yield 3, instead an insoluble product was isolated which is possibly
a mixture and could not be characterized. Although binary Hg(II)
Scheme 1. Synthesis of complexes.

S. Singh et al. / Inorganica Chimica Acta 385 (2012) 112–118
115
Fig. 1. Selected molecular orbitals for 3 (orbital contour value 0.05).
a way that two molecules join with each other by a pair of
l
-S
Mercury is bonded to two sulfur atoms of thiobenzoate and one
phosphorus atom of triphenylphosphine ligand. The two Hg–S
bond lengths are almost equal and are comparable to those
observed in the anionic mercury thiocarboxylates (2.402–
2.533 Å) and marginally longer than the sum of the covalent radii
of S and Hg atoms (2.37 Å). The oxygen atoms are quite away from
the Hg1 and the HgO distances (3.053 and 3.102 Å) are equal to the
sum of the van der Waals radii of the two atoms.
bridges as shown in Fig. 3. A closer look into the structure, how-
ever, reveals that the Hg–S and HgÁ Á ÁS distances are unequal and
one of them is too long (3.130 Å) to be considered as a covalent
bond. This is, however, shorter than the sum of the van der Waals’
radii of S and Hg atoms (3.35 Å) and is indicative of a weak inter-
action. To understand the nature of the Hg–S interaction we have
carried out DFT calculations. From the natural bond orbital (NBO)
analysis it became clear that there is no primary bonding between
the Hg–S atoms (with longer internuclear distance), however,
second order perturbation effect due to Lp(s) ? r⁄(Hg) electron
transfer plays an important role and leads to a stabilization of
21.4 kcal/mol.
The three donor atoms subtend 359.70° at Hg1 thus resulting in
a trigonal planar coordination environment. Trigonal planar coor-
dination of Hg(II) have been reported in anionic thiolate [23], phe-
nolate [24] and thiocarboxylate complexes, [5–7,25] and the
deviation from planarity is usually less than 0.07 Å. In the case of
3 also Hg1 is tipped above the S1S2P1 plane by 0.065 Å.
The thermal ellipsoid plot of a single molecule is depicted in
Fig. 4 and selected bond length and bond angles are given in Table
2.
ꢀ
Complex 4 crystallized in P1 space group with triclinic system.
The arrangement of two different structures in the same lattice

116
S. Singh et al. / Inorganica Chimica Acta 385 (2012) 112–118
Fig. 2. Selected molecular orbitals for 6 (orbital contour value = 0.05).
Fig. 3. A pair of molecules of 3 showing centrosymmetric P2S4Hg2 core.
Fig. 4. Molecular structure of 3 at 50% probability level (hydrogen atoms are
omitted for clarity).
offers an interesting example of polytopal isomerism. Molecular
structures are depicted in Fig. 5. Selected bond lengths and bond
angles are given in Table 2. Two types of isomers crystallized to-
gether in the same unit cell. Two discrete molecules are present
in the asymmetric unit. In one case the molecule is mononuclear
and Hg1 is bonded to one triphenylphosphine and two thio-
phene-2-thiocarboxylates through their sulfur atoms. Though a
weak interaction between Hg1 and O2 is evinced by the distance
between the two (2.875 Å) yet the sum of angles subtended by P,
S1 and S3 is 359.33° which render a trigonal planar geometry
around the metal center. Though two molecules are arranged in

S. Singh et al. / Inorganica Chimica Acta 385 (2012) 112–118
117
Table 2
the lattice giving a dimeric look, yet the intermolecular HgÁ Á ÁS dis-
tances (3.259 Å) are quite long and are comparable to the sum of
the van der Waals radii of the two atoms (3.35 Å). The other
molecule is a centro-symmetric dimer; a mercury atom (Hg2) is
bonded with one triphenylphosphine and two thiophene-2-thio-
carboxylates out of which one is terminal and other forms a bridge
with the second mercury atom via a weak interaction (HgÁ Á ÁS =
3.073 Å). The molecular core is isostructural to that of 3.
Selected bond lengths (Å) and bond angles (°).
Complex
Selected bond lengths (Å)
3
Hg1–S1
Hg1–P1
Hg1–S1
Hg1–O2
Hg2–S5
Hg2–P2
Hg1–S1
Hg1–O1
2.461(1)
2.501(1)
2.427(3)
2.875
2.445(3)
2.435(3)
2.353(4)
2.994
Hg1–S2
2.464(1)
4
Hg1–S3
Hg1–P1
Hg2–S7
Hg2–S–7
Hg1–S3
Hg1–O2
2.567(3)
2.431(3)
2.541(3)
3.073
2.357(4)
3.002
Though Hg(SCOPh)2 is known for a long time [6], to the best of
our knowledge no neutral binary mercury thiocarboxylate has yet
been structurally characterized. Crystals of both 5 and 6 could be
isolated from the solution of 1, and 2, respectively, however, those
of 6 were suitable for X-ray crystallography. Molecular structure of
6 is shown in Fig. 6 and selected bond lengths and bond angles are
given in Table 2. There are two molecules in the asymmetric unit.
There is no significant intermolecular interaction between the two
molecules and the internuclear distance between two Hg atoms of
the two molecules is 4.426 Å. Both have similar structures except
for the fact that the interplanar planar angles between the two
SCO units in each molecule are quite different. (31.58° and
5.13°). In both the cases, however, mercury atom is bonded to
two sulfurs of two thiophene-2-thiocarboxylate ligands and there
is no interaction between oxygen atoms and mercury. Thus the
geometry around Hg(II) is linear with slight distortion. This is in
sharp contrast to the case of Hg(II) monothiocarbamate complex
where the ligands bind to the metal through covalent Hg–S bonds
and weak intramolecular HgÁ Á ÁO interactions leading to the forma-
tion of a hexameric cluster and the coordination polyhedron
around each Hg atom is highly distorted octahedron [26].
6
Selected bond angles (°)
3
S1–Hg1–S2
S2–Hg1–P1
S1–Hg1–S3
S3–Hg1–P1
O1–Hg1–S3
S5–Hg2–S7
S7–Hg2–P2
S1–Hg1–S3
121.50(4)
128.00(4)
97.51(11)
123.07(11)
91.80
97.78(10)
125.86(10)
178.89(16)
S1–Hg1–P1
110.29(4)
4
S1–Hg1–P1
O1–Hg1–S1
O1–Hg1–P1
S5–Hg2–P2
Hg2–S7–Hg2
138.75(11)
57.07
103.57
134.33(10)
100.74
6
The molecules (containing Hg2) with higher inter-SCO torsional
angles form pairs due to intermolecular hydrogen bonding
(between oxygen of thiocarboxylate and hydrogen of thiophene
ring) in the lattice leaving a slit along the a-axis (intermolecular
hydrogen bonding [27] is evinced by short HÁ Á ÁO distance of
2.641 Å and C–HÁ Á ÁO angle of 129.86°).
The chain formed by the other molecules (containing Hg1) goes
parallel but does not have any interaction with the molecules con-
taining Hg2 (Fig. S7: Supplementary information).
FAB mass spectrum of 7 (Fig. 7) showed a molecular ion peak at
663 which corresponds to Hg(SCOPh)2TiCl4. In spite of our best ef-
forts single crystals of 7 could not be grown. One may expect the
Fig. 5. Molecular structure of 4 at 50% probability level (hydrogen atoms are
omitted for clarity).
thiobenzoate ligand to bridge (l-O,S) the Ti(IV) and Hg(II) centers.
It may be noted that there are two reported complexes of mercury,
[Ph4As]2[Hg2Cl4(SCOPh)2] and [Ph4As]2[CdCl4Hg(SCOPh)2] in
which the thiobenzoate ligands are bonded to the Hg atom in a
monodentate manner through their sulfur atoms constructing a
linear HgS2 skeleton [10]. The Hg(II) center is further connected
to the two Cl atoms forming
acceptor complex. Such a structure forming a Ti(Cl)2(
(SCOPh)2 type complex is also possible. Both the possible struc-
a
MCl42ÀÁ Á ÁHg(SCOPh)2 donor
l
-Cl)2 Á Á ÁHg
Fig. 6. Molecular structure of 6 at 50% probability level (hydrogen atoms are
omitted for clarity).
tures (Fig. 8) have been simulated using MM2 [28] force field.
Fig. 7. FAB mass spectrum of 7.

118
S. Singh et al. / Inorganica Chimica Acta 385 (2012) 112–118
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4. Conclusions
Three heterobimetallic complexes, [(Ph3P)2Cu(l-SCOR)2Hg(S-
COR)] [R = Ph (1), th (thiophene) (2)] and Hg(SCOPh)2TiCl4 (7) were
prepared and characterized by different spectroscopic techniques.
During crystallization of 1 and 2 in chloroform/diethyl ether
mixture the complexes disproportionated resulting in complexes,
Hg(Ph3P)(SCOPh)2 and Hg(Ph3P)(SCOth)2 respectively, whereas in
chloroform/n-hexane mixture they were dissociated resulting in
binary compounds Hg(SCOPh)2 and Hg(SCOth)2, respectively.
Structural investigations on representative molecules revealed
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Financial support in the form of fellowships (to S.S. and J.C.)
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Appendix A. Supplementary material
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Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2012.01.039.