Geometrically unprecedented 3-, 5- and 7-membered Hg(II)-Cu(I) and Hg(II)-Ag(I) thiolate clusters: Precursors to intermetallics

Article abstract of DOI:10.1039/c4dt03500c

The syntheses of three polynuclear heterobimetallic complexes through the use of a homoleptic mercuric thiolate anion as a template for the assembly of coinage metal are presented. The complexes, [(PPh₃)₃Ag₃(μ-SPh)₇

Full text of DOI:10.1039/c4dt03500c

Dalton
Transactions
PAPER
Geometrically unprecedented 3-, 5- and
7-membered Hg(II)–Cu(I) and Hg(II)–Ag(I) thiolate
clusters: precursors to intermetallics†
Cite this: Dalton Trans., 2015, 44,
8932
Geetika Gupta, Jyotsna Chaturvedi and Subrato Bhattacharya*
Received 14th November 2014,
Accepted 31st March 2015
The syntheses of three polynuclear heterobimetallic complexes through the use of a homoleptic mercuric
thiolate anion as a template for the assembly of coinage metal are presented. The complexes,
[(PPh3)3Ag3(μ-SPh)7Hg2] (1), [Hg(µ-SPh)4{Cu(PPh3)2}2] (2) and [(dppe)2Cu5(μ-SPh)7Hg2(SPh)2] (3) were
utilized as precursors for the fabrication of Hg–Ag and Hg–Cu intermetallics.
DOI: 10.1039/c4dt03500c
www.rsc.org/dalton
active for various chemical transformations, have also been
Introduction
synthesized via low temperature solution chemistry.12 In spite
Synthetic strategies are rapidly being developed to address the of these developments, the synthesis of intermetallics by solu-
demand for intermetallic compounds1 as they exhibit interest- tion chemistry routes have not flourished and still remain a
ing physical and chemical properties owing to the synergistic largely unexplored area of research. This is in contrast to many
effects among their constituent metals. These atomically other classes of materials, such as the sol–gel synthesis of
ordered compounds span a wide range of compositions as well metal oxides,13 the low temperature synthesis of binary and
as crystal structures and so find use in a myriad of appli- ternary chalcogenides using single molecule precursors,14 and
cations, including catalysis,2 hydrogen storage,3 ferromagnet- the spin coating of polymer and chalcogenide films,15 where
ism,4 electrocatalytic activity,5 superconductivity,6 shape- solution routes are rather well-established.
memory effects,7 corrosion resistance,8 etc.
It is well known that thiols are oxidized easily into
Intermetallic compounds are often prepared by using co- disulfides.16–18 Transition metal salts and oxides have been
reduction, wet-impregnation or co-precipitation methods and used as catalysts in this oxidation process. However, to the
annealing to temperatures near or above 1000 °C in a reducing best of our knowledge, such a process has not yet been
atmosphere. However, heating at such high temperatures exploited to prepare intermetallic compounds. Thiolate
causes particle sintering. During the past decade, Schaak and ligands are expected to be advantageous over polyols due to
co-workers’ seminal low-temperature solution chemistry their ease of binding with various types of metal ions, as well
approach towards the synthesis of various intermetallic nano- as their propensity to be oxidized under ambient conditions.
structures9 became particularly relevant and topical by offering The effectiveness of thiolate sulfur is further established as a
several advantages over traditional high-temperature good bridging ligand preventing undesirable fragmentation of
methods;10 for instance, low temperature solution chemistry heteronuclear frameworks. Herein, we present the first report
strategies for synthesizing intermetallic nanoparticles offer on the syntheses and structural characterizations of high
better control over particle size, size dispersity, shape, compo- nuclearity mercury–copper/silver complexes with thiolate
sition, and crystal structure.11
ligand and their use as single molecular precursors for the syn-
On the one hand, the polyol process has been used to thesis of Hg–Cu and Hg–Ag intermetallic compounds.
prepare bulk intermetallic powders and, on the other hand,
the nano-scale mixing of nanoparticles has been utilized to
synthesize multi-metallic nanoparticles with novel properties.9
Results and discussion
Supported intermetallic nanoparticles, which are catalytically
Syntheses
Department of Chemistry, Faculty of Science, Banaras Hindu University,
The dissolution of HgO in a methanolic solution of sodium
phenyl thiolate provides homogeneous pale yellow solutions.
The use of mercuric oxide rather than the corresponding
Varanasi 221005, India. E-mail: s_bhatt@bhu.ac.in
†Electronic supplementary information (ESI) available: EDS analysis data, PXRD
spectra, results of DFT calculations, crystallographic data. CCDC 1016719 (1)
halide completely eradicates the presence of potentially ligat-
ing halide ions.19 Following an earlier report,20 HgO was
and 1016721 (3). For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c4dt03500c
8932 | Dalton Trans., 2015, 44, 8932–8937
This journal is © The Royal Society of Chemistry 2015

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Paper
Table 1 Crystal data and structure refinement of 1 and 3
1
3
Empirical formula
Formula weight
Temperature (K)
C
100H84Ag3Cl3Hg2P3S7 C106H93Cu5Hg2P4S9
2315.22
293 K
2498.1
293 K
Crystal system
Space group
Triclinic
P1
Monoclinic
P21/c
ˉ
a/Å
b/Å
c/Å
α/°
β/°
γ/°
17.0142(14)
17.3392(15)
20.1081(14)
68.901(7)
71.772(7)
61.000(9)
4770.5(7)
2
4.076
2268
0.882
R1 = 0.0676
wR2 = 0.155
R1 = 0.1319
wR2 = 0.1686
24.3852(6)
16.4533(4)
26.4195(9)
90
105.248(3)
90
10226.80 (87)
4
4.303
4952
1.014
R1 = 0.0774
wR2 = 0.1517
R1 = 0.1801
wR2 = 0.1969
Scheme 1 Syntheses of 1, 2 and 3.
V/Å3
Z
dissolved in a methanolic NaSPh solution in 1 : 4 molar ratio, μ (mm−1
)
F (000)
which was then treated with two equivalents of a coinage
GOF on F2
metal complex, [Ag(PPh3)3]+, [Cu(PPh3)2]+ or [Cu(dppe)]+
Final R indices [I >
resulting in successful isolation of heterobimetallic poly- 2σ(I)]
R indices (all data)
nuclear complexes [(PPh3)3Ag3(μ-SPh)7Hg2] (1), [Hg(µ-SPh)4-
{Cu(PPh3)2}2](2)and[(dppe)2Cu5(μ-SPh)7Hg2(SPh)2](3),respecti-
vely, as shown in Scheme 1.
Zhang and co-workers recently synthesized heterobimetallic
Cd(Hg)/Cu(Ag)/S(Se) complexes using homoleptic, neutral
−
[Hg(EPh)2] and anionic [Cd(EPh)4]2 (E = S, Se) complexes as
precursors to coordinate with the [M(PPh3)2Q] (M = Cu, Ag; Q =
Cl−, NO3−) species.21 In the present case, one may expect the
formation of a neutral tri-nuclear species like [Hg(µ-SPh)4-
{M(PPh3)2}2], but such a product was formed only when
Cu(PPh3)2NO3 was used. Clearly, some additional coordination
vacancies were created that facilitate the preparation of
complexes 1 and 3 of higher nuclearity.
The 31P NMR spectra of complexes 1 and 2 showed two
resonances, whereas 3 showed one signal only. Evidently the
structures of the complexes observed in the solid state are
not retained in their solutions. The labile nature of the phos-
phine ligands often lead to their scrambling, which was earlier
detected in copper thiocarbamates and thiocarboxylates.22 The
peaks observed at lower fields are possibly due to cationic
species like [Ag(PPh3)]+, [Cu(PPh3)]+ and [Cu(dppe)]+, while
those at high fields are due to the neutral complexes. However,
due to the rapid nature of the scrambling processes, the struc-
tures of the different species formed in solutions have not
been studied in detail.
Crystal and molecular structures
Compound 1 crystallizes in a triclinic system with the space
Fig. 1 Molecular structure of 1. Selected bond lengths (Å) and angles
ˉ
group P1 (Table 1) and as a discrete unit along with benzene (°): Hg1 S5 = 2.416(3), Hg1 S1 = 2.425(3), Hg1 S4 = 2.456(2), Hg2 S6 =
2.376(3), Hg2 S3 = 2.526(3), Hg2 S7 = 2.684(2), Hg2 S2 = 2.772(2), Ag3
S2 = 2.585(3), Ag3 S5 = 2.639(3), Ag3 S3 = 2.646(2), Ag1 S4 = 2.574(3),
Ag1 S7 = 2.596(3), Ag1 S3 = 2.712(2), Ag2 S2 = 2.590(3), Ag2 S7 = 2.606
(2), Ag2 S1 = 2.643(3); S5 Hg1 S1 = 125.60(8), S5 Hg1 S4 = 117.08(9), S1
and chloroform solvent molecules in the lattice. The molecular
structure of compound 1 is given in Fig. 1. The molecule con-
sists of three Ag(I) and two Hg(II) metal atoms held together by
six bridging (three μ2 and three μ3) thiolate ligands and the
Hg1 S4 = 117.07(9), S6 Hg2 S3 = 145.80(10) S6 Hg2 S7 = 119.13(11), S3
seventh thiolate ligand bonded terminally to Hg2. In addition, Hg2 S7 = 86.51(8), S6 Hg2 S2 = 119.63(10), S3 Hg2 S2 = 84.45(8), S7 Hg2
S2 = 80.83(7), P3 Ag3 S2 = 124.30(9), P3 Ag3 S5 = 108.04(10), S2 Ag3
S5 = 104.35(9), P3 Ag3 S3 = 118.26(9), Ag3 S3 = 85.92(8), S5 Ag3 S3 =
114.36(8), P2 Ag1 S4 = 124.37(9), P2 Ag1 S7 = 113.53(10), S4 Ag1 S7 =
113.55(8), P2 Ag1 S3 = 117.40(8), S4 Ag1 S3 = 94.87(8), S7 Ag1 S3 = 84.57(8),
the three Ag atoms are bonded to a phosphine ligand each.
There are no metal–metal bonds; the shortest M–M (Ag3–Hg1)
distance being 3.534 Å is pretty longer than the sum of the
covalent radii of the two atoms (2.77 Å).23 The coordination
P1 Ag2 S2 = 117.98(9), 1 Ag2 S7 = 120.50(10), S2 Ag2 S7 = 85.83(8), P1
geometry around all the metals except Hg1 is tetrahedral with Ag2 S1 = 118.65(9), S2 Ag2 S1 = 108.55(9), S7 Ag2 S1 = 99.67(8).
This journal is © The Royal Society of Chemistry 2015
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Fig. 2 Optimized structure of 2. Selected bond lengths (Å) and angles
(°): Hg(14)–S(8) = 2.705, Hg(14)–S(18) = 2.745, Hg(14)–S(7) = 2.812, Hg
(14)–S(20) = 2.775. Cu(2)–S(8) = 2.621, Cu(2)–S(7) = 2.478, Cu(2)–P(1) =
2.478, Cu(2)–P(6) = 2.449, Cu(23)–S(18) = 2.536, Cu(23)–S(20) = 2.534,
Cu(23)–P(26) = 2.509, Cu(23)–P(28) = 2.425; P(28)–Cu(23)–P(26) =
113.905, P(28)–Cu(23)–S(20) = 18.410, P(26)–Cu(23)–S(18) = 101.032,
S(18)–Cu(23)–S(20) = 96.845, S(7)–Cu(2)–S(8) = 91.858, S(7)–Cu(2)–
P(1) = 11.018, P(1)–Cu(2)–P(6) = 115.856, S(8)–Cu(2)–P(6) = 100.498,
S(20)–Hg(14)–S(18) = 86.778, S(7)–Hg(14)–S(18) = 115.873, S(7)–Hg(14)–
S(8) = 83.243, S(20)–Hg(14)–S(8) = 123.198.
Fig. 3 Molecular structure of 3. Selected bond lengths (Å) and angles
(°): Hg1 S7 = 2.44(5), Hg1 S2 = 2.661(2), Cu1 S1 = 2.379(3), Cu1 S2 =
2.429(3), Cu2 S3 = 2.345(3), Cu3 S9 = 2.278(3), Cu4 S4 = 2.341(3), Cu5
S4 = 2.377(3), Cu5 S8 = 2.564(3), Cu1 P4 = 2.238(3), Cu4 P3 = 2.220(3),
Cu2 P1 = 2.232(3); S7 Hg1 S6 = 151.5(6), S7 Hg1 S2 = 102.9(5), S6 Hg1
S2 = 104.54(8), S5 Hg2 S9 = 134.0(4), S5 Hg2 S4 = 111.9(4), S9 Hg2 S4 =
113.93(9), P4 Cu1 S1 = 104.94(10), P4 Cu1 S8 = 129.40(10), P4 Cu1 S2 =
122.92(9), S1 Cu1 S2 = 107.08(9), S8 Cu1 S2 = 94.85(9), P4 Cu1 Cu4 =
102.37(8), P1 Cu2 S3 = 121.55(10), P1 Cu2 S2 = 128.18(10), S3 Cu2 S2 =
99.73(9), P1 Cu2 S8 = 114.47(10), P1 Cu2 Cu5 = 103.01(8), S3 Cu2 Cu5 =
49.67(6), S9 Cu3 S3 = 111.10(10), S9 Cu3 S1 = 119.04(11), S9 Cu3 S6 =
108.63(10), S3 Cu3 S6 = 113.90(10), S1 Cu3 S6 = 104.97(10), P3 Cu4 S4 =
130.60(10), P3 Cu4 S1 = 120.70(10), S4 Cu4 S1 = 96.94(9), P3 Cu4 S8 =
113.02(10), S4 Cu4 S8 = 96.47(9), S1 Cu4 S8 = 89.81(8), P3 Cu4 Cu1 =
102.53(8), S4 Cu4 Cu1 = 126.59(8), P2 Cu5 S3 = 116.42(10), P2 Cu5 S4 =
123.84(10), S3 Cu5 S4 = 105.06(9), P2 Cu5 S8 = 120.02(11), S3 Cu5 S8 =
89.90(8), P2 Cu5 Cu2 = 103.10(8), S4 Cu5 Cu2 = 132.86(8).
different degrees of distortion. The latter atom has a trigonal-
planar geometry and the Hg1 lies in the plane constituted by
the S1, S4 and S5 atoms (the deviation is only 0.071 Å).
The structure refinement could not be carried out up to a
desired level in the case of complex 2, as the crystals were
twinned. Thus, we refrain from giving the structural details
here. However, the structure of the molecule appeared analo-
21
gous to Cu2Cd(SPh)6 reported earlier. Using the atomic co-
ordinates obtained from the crystallographic data, we
optimized the molecular structure by DFT calculations, and
this is shown in Fig. 2.
Complex 3 crystallizes in a monoclinic system with the
space group P21/c. The molecular structure of the complex is
depicted in Fig. 3. The complex is a neutral heptanuclear
Decomposition studies of 1 and 2
molecule consisting of five Cu(I) and two Hg(II) atoms bridged In view of the labile nature of the phosphine ligands bonded
by the PhS− ligands. In spite of being in close proximity to one to the coinage metal centres in conjunction with the known
another, M–M bonds are not conspicuous. There are four ease of oxidation of the thiophenol moiety, we reasoned that
copper atoms in a basal plane, with a fifth copper atom Cu3, the Hg–Cu and Hg–Ag heterobimetallic complexes 1 and 2
at the apex and the sixth position capped by a µ4-SPh. There would serve as good sources of ‘intermetallics’. In order to
are two fused six-membered rings in twisted boat confor- achieve this, solvent-assisted thermal decompositions were
mations, each consisting of two Cu, three S and one Hg atoms, carried out on 1 and 2. When a solution of 1 was refluxed in
and three nearly planar four-membered rings constituted dodecanethiol for 3 h, a colloidal solution resulted, from
by S8Cu1S2Cu2, S8Cu1S1Cu4 and Cu4S4Cu5S8. The geometry which a grey-black powder (1a) was isolated. Under similar
around each mercury atom is trigonal planar. Each copper conditions, 2 also yielded a similar powder (2a), along with a
atom except Cu3, is ligated to two µ3-SPh, one µ4-SPh and one few small mercury droplets. It is quite obvious that the
P atom of dppe ligand with a highly distorted tetrahedral reduction of mercuric ion to its elemental state24 was assisted
geometry; explicitly tangible by the S–Cu–S bond angle in the by the oxidation of benzenethiol to the corresponding
range of 89.80(9)°–119.04(11)°. Cu3 is bonded to two µ2-SPh disulfide. Identical results were obtained when 4-methyl-
and two µ3-SPh moieties. The bond lengths follow the expected pyridine was used as the decomposition solvent instead of
decreasing order: M–µ4S > M–µ3S > M–µ2S.
dodecanethiol.
8934 | Dalton Trans., 2015, 44, 8932–8937
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Paper
The powders 1a and 2a isolated from the colloids were sub-
jected to XRD analysis (Fig. S1 and S2†). 1a is a Hg–Ag inter-
metallic compound with the composition Ag2Hg3.02 (JCPDS
no. 71-0529), along with traces of sulphur (1.77%). 2a is an
Hg–Cu intermetallic, Cu7Hg6 (JCPDS no. 45-1474), along with
traces of HgS (JCPDS no. 06-0256) and CuS (JCPDS no.
06-0464). The powder diffraction pattern of the product
obtained by decomposing 3 is comparable to that of 2a, which
indicates that the phosphine ligands do not affect the
decomposition pathway/decomposition products to any signifi-
cant extent.
Powder patterns of the residues after the thermal treatment
of 1 and 2 up to 800 °C show distinctly different results. The
products obtained from 1 and 2 are 1b and 2b, respectively.
The PXRD pattern of 1b (Fig. S3†) shows intense peaks,
perfectly matching the cubic phase of Ag metal (JCPDS no.
04-0783). Silver, being a noble metal, is exempted from oxi-
dation, whereas the change in the visual appearance of 2b
from brown to orange can be attributed to the propensity of
the copper metal to undergo surface oxidation upon exposure
to the ambient atmosphere at room temperature.25
Fig. 4 SEM images of 1a, 1b, 2a and 2b.
To obtain evidence that initially 2b was metallic copper,
X-ray powder diffraction was performed immediately after
sample preparation, and showed all the possible peaks of
copper at 2θ value of 43.3° and 50.4°, representing the (111)
and (200) planes of the fcc structure of copper with the space
were performed using an Exeter model E-440 CHN analyzer.
Scanning electron microscopic images were taken on a JEOL
model JSM-6390LV.
ˉ
group of Fm3m (JCPDS no. 85-1326). Thus, 2b is largely Cu
Synthesis of 1
metal, along with minor products such as Cu2O and CuO
(JCPDS no. 05-0667 and 48-1548). As a result, the diffraction
peaks of the residue 2b (Fig. S4†) can be identified by compar-
ison with the peak patterns of Cu and Cu2O. It is worth men-
tioning here that the segregation of certain intermetallic
phases into the constituent metal phases at higher tempera-
tures has been noted earlier also. For example, PtRu alloy
separates into pure Pt and Ru phases only at 220 °C.12
The surface morphologies of all the decomposed products
were studied using scanning electron microscopy (Fig. 4). SEM
micrographs of all the compounds showed the presence of
uniform granular crystallites.
Sodium metal (0.023 g, 1.0 mmol) was dissolved in MeOH
(5 cm3), and thiophenol (102 µL, 1.0 mmol) was added to it,
followed by the addition of solid HgO (0.054 g, 0.25 mmol).
The solid slowly dissolved with stirring and slight warming to
produce a pale yellow solution. After 30 min, a solution of
Ag(PPh3)2NO3 (0.347 g, 0.50 mmol) in chloroform (10 cm3) was
added to yield a slightly turbid yellow solution. The reaction
mixture was stirred for further 3 hours. The solvent was then
evaporated under reduced pressure and the residue was
extracted with CHCl3 (20 cm3) and the solution was layered
with benzene. After two days, plate-like pale yellow crystals
were formed, which were then dried under vacuum (0.1 mmHg/
2
h). Yield: 58% (based on Ag(PPh3)2NO3). NMR 1H:
6.8–7.7 (Ph); 13C: 128.5–133.8 (Ph); 31P: 29.8 and 4.9. IR spectra
(KBr, cm−1): 692.9 ν(C–S), 1080 ν(P–C). Anal. calcd for (1):
C96H80Ag3Hg2P3S7: Calcd: C, 50.66; H, 3.54; Found: C, 50.70; H,
3.60.
Experimental section
Materials and methods
All solvents used were purified using standard methods.26
Diphenylphosphinoethane (Sigma-Aldrich), 4-methylpyridine
Synthesis of 2
(Sigma-Aldrich) and thiophenol (Avra) were used as received.
28
The precursors Cu(dppe)Cl,27 Cu(PPh3)2NO3 and Ag(PPh3)2- The same procedure was followed as mentioned in the case of
NO3 were prepared following the methods described in the 1, except in place of (PPh3)2AgNO3, (PPh3)2CuNO3 (0.324 g,
29
literature. The sodium salt of thiophenol was obtained by 0.50 mmol) was used. A yellow crystalline product was
reacting thiophenol with sodium methoxide in a stoichio- obtained from a chloroform solution that was dried under
metric ratio. IR spectra were recorded using a Varian-3100 vacuum (0.1 mmHg/3 h). Yield: 88% (based on Cu(PPh3)2NO3).
FTIR instrument. NMR spectra were obtained using a JEOL NMR 1H: 6.7–7.7 (Ph); 13C: 124.3–134.2 (Ph); 31P: 29.9 and
AL300 FT NMR spectrometer. 31P NMR spectra were recorded −1.6. IR spectra (KBr, cm−1): 692.6 ν(C–S), 1079.3 ν(P–C). Anal.
on a Jeol ECX500 NMR spectrometer using orthophosphoric calcd for (2): C96H80Cu2Hg1P4S4: Calcd: C, 63.58; H, 4.45;
acid as the external standard (δ = 0.0 ppm). Elemental analyses Found: C, 63.50; H, 4.50.
This journal is © The Royal Society of Chemistry 2015
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Synthesis of 3
Powder X-ray diffraction data were collected on a Bruker D8
Advance X-ray diffractometer equipped with a graphite mono-
chromator using Cu Kα (0.154 nm) radiation.
A similar procedure was followed as mentioned in the case of
1 and 2. However, in this case the coinage metal complex used
was Cu(dppe)Cl. An orange crystalline product was obtained
from a chloroform solution that was dried under vacuum
(0.1 mmHg/3 h). Yield: 52% (based on Cu(dppe)Cl). NMR
1H: 6.7–7.7 (Ph); 2.2 (–CH2); 13C: 125.4–136.9 (Ph); 20.8,
21.2, 21.6, 22.0 (–CH2); 31P: 34.9. IR spectra (KBr, cm−1): 693.9
ν(C–S), 1084.9 ν(P–C). Anal. calcd for (3): C106H93Cu5Hg2P4S9:
Calcd: C, 50.96; H, 3.75; Found: C, 51.00; H, 3.75.
Theoretical calculations
As mentioned, the structure of 2 was optimized by DFT calcu-
lations at the B3LYP level32 using the LANL2DZ basis set. The
calculations were carried out using GAUSSIAN 03 program
package.33 The final atomic coordinates are given in Table S1.†
Conclusions
Synthesis of 1a and 2a
A 100 mL round-bottomed three-necked flask equipped with a
reflux condenser was charged with 0.500 g of 1 and 10 mL of
dodecanethiol. The solution was degassed for 5 minutes by
purging with a stream of N2 gas and then refluxed for 3 h
under a continuous flow of nitrogen. Compound 1 slowly dis-
solved in dodecanethiol giving a yellow clear solution which
turned into a colloidal solution at 150 °C with the concomitant
formation of a grey solid and Hg metal droplets. The solution
was cooled to room temperature and the nanocrystals of 1a
were precipitated by the addition of ethanol and were then
collected by centrifugation. For the synthesis of 2a, a similar
methodology described above was followed except the precur-
sor 2 was used instead of 1. A greyish black powder (2a) was
obtained in this case.
The great affinity of thiols for soft acids prompted us to exploit
anionic mercury thiolates as metalloligands for complexation
with other soft metal centers such as Cu+ and Ag+. The syn-
thetic concept used in this study represents a very good model
for the synthesis of polynuclear heterobimetallic thiolate
complexes. The reductive elimination of thiolate ligands on the
one hand leads to the formation of intermetallics when
refluxed in solvents such as dodecanethiol or 4-methylpyridine.
On the other hand, coinage (single) metals (Cu/Ag) can be
obtained by carrying out decompositions at higher (800 °C)
temperatures. This illustrates that due to the facile reductive
elimination involved, complexes such as 1 and 2 may be used
as suitable precursors to obtain related Hg(II)–Cu(I)/Ag(I) inter-
metallics. Further studies on other heterobimetallic thiolate
complexes are expected to demonstrate the general applicability
of this methodology.
Synthesis of 1b and 2b
The precursors 1 and 2 were (individually) subjected to pyrol-
ysis under an inert atmosphere up to 800 °C. In case of 1, a
white solid (1b) was obtained, while the decomposition of 2
resulted in a brown solid (2b) with a metallic lustre; both were
kept at room temperature under ambient conditions. After a
day, no visual difference was found in the case of 1b. On the
other hand, 2b was tarnished, leading to the change in appear-
ance from brown to orange. The same results were obtained
when 1a and 1b were decomposed under similar conditions.
Acknowledgements
The authors thank the Council of Scientific and Industrial
Research, New Delhi (scheme number 01(2680)/12/EMR-II) for
financial assistance. Thanks are due to Mr Pramod Kumar and
Mr Nayab Ahmed, IIT Kanpur, India for 31P NMR spectra.
Notes and references
X-ray crystallography
Single crystals of 1 were grown from chloroform/benzene (3 : 1)
mixture, while those of 3 were grown from its chloroform solu-
tion by slow evaporation of the solvent. The diffraction data
were collected on an Xcalibur Eos Oxford CCD diffractometer
using graphite monochromated Mo-Kα radiation. Data
integration and reductions were carried out using Crysalis Pro
software. The structures were solved by direct methods
(SHELXS-97)30 and refined by full-matrix least squares
methods against F2 (SHELXL-97)31 using a WinGX platform.
All non-hydrogen atoms were refined with anisotropic dis-
placement parameters, while the hydrogen atoms were refined
isotropically on their calculated positions using a riding
model. Disordered moieties were refined using bond length
restraints, wherever required. The crystallographic data and
structure determinations of 1 and 3 are summarized in
Table 1.
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