Novel heterobimetallic thiocarboxylato complexes: Synthesis, characterization and application as single source precursor for ternary chalcogenides

Article abstract of DOI:10.1039/c0dt00210k

Heterobimetallic complexes, (PPh₃)₂M(μ-SCOPh) ₂Pb(SCOPh) [where, M = Cu^I (1) or Ag^I (2)] have been synthesized and characterized by FTIR, ¹H, ¹³C and ³¹P NMR spectrosc

Full text of DOI:10.1039/c0dt00210k

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PAPER
www.rsc.org/dalton | Dalton Transactions
Novel heterobimetallic thiocarboxylato complexes: synthesis, characterization
and application as single source precursor for ternary chalcogenides†
Jyotsna Chaturvedi, Subrato Bhattacharya* and Rajendra Prasad‡
Received 26th March 2010, Accepted 26th June 2010
DOI: 10.1039/c0dt00210k
Heterobimetallic complexes, (PPh3)2M(m-SCOPh)2Pb(SCOPh) [where, M = CuI (1) or AgI (2)] have
been synthesized and characterized by FTIR, 1H, 13C and 31P NMR spectroscopy. Molecular structures
in solid state have been determined by single crystal X-ray diffraction. Electronic spectra of the
compounds have been recorded and explained on the basis of TDDFT calculations. Luminescence and
redox properties of the complexes have also been studied. Following the thermogravimetric analysis
data the compounds were pyrolysed and one of the decomposition products has been characterized as
Pb4Cu5O22.6 (3) by SEM-EDX and X-ray diffraction studies.
Introduction
Results and discussion
During the last two decades, synthesis and studies of heterobin-
uclear metal complexes have attracted a lot of attention because
of the unprecedented physicochemical properties and functions
exhibited by these complexes arising from a pair of dissimilar
metal ions in close proximity.1 Although the earlier studies
related to bi/polynuclear complexes were mainly confined to those
containing transition metals2 a few bimetallic or multimetallic
chalcogenide systems containing heavy main group metal and
transition metals have been explored for the unique physical or
chemical properties that these materials may possess.3 In view
of these, attempts are now being made to synthesize complexes
containing a transition metal and a main group metal.4
Syntheses
Complexes 1 and 2 were prepared by simple reactions of
tris(thiobenzoato)lead anions generated in situ with the nitrate
salts of bis(triphenylphosphine)copper(I) or silver(I) in stoichio-
metric ratios in methanol, as shown below in Scheme-1.
We have reported the synthesis of the [In(SOCPh)4]- complex
anion5 anda few heterobimetalliccomplexes have been synthesized
based on this anion.6 Some of these complexes have also been used
as single source precursors of binary and ternary metal sulfides,
thin films and nanoparticles.7,8 In contrast to the studies on the
thiocarboxylates of group 135,9 the chemistry of group 14 metal
thiocarboxylates is much less explored. Besides our reports5,10,11
on organotin(IV) thiocarboxylates there are only a few studies
on these [triorganotin/lead12 and binary M(II) (M = Pb/Sn)]
compounds.13–15 To the best of our knowledge no heterobinuclear
complex (containing a group 14 metal) of thiocarboxylate ligand
has yet been reported. Though a few complexes containing both
Pb/Cu and Pb/Ag are known,16–18 however, no such compound
with a sulfur donor ligand has yet been reported. Further, such
a compound can also act as a precursor of a ternary sulfide.
Therefore, we have taken up the synthesis of heterobimetallic
complexes containing Pb(II) along with either Cu(I) or Ag(I) and
studies on their structure, bonding and some physicochemical
properties.
Scheme 1 Synthesis of complexes 1 and 2.
The compounds are soluble in common solvents such as
chloroform and diethyl ether. The compounds in solid state
were found to be quite stable, and no apparent decomposition
occurred in several months on keeping under ambient conditions.
As mentioned above the two compounds are the first ones of
their kind containing Pb/Cu and Pb/Ag with a sulfur donor
ligand.
IR spectra of the complexes showed strong bands due to
C
O, C–S and Ph–C stretching vibrations. Frequencies of these
Department of Chemistry, Banaras Hindu University, Varanasi, 221005,
India. E-mail: s_bhatt@bhu.ac.in
† Electronic supplementary information (ESI) available: Fig. S1–S3 and
Tables S1 and S2. CCDC reference numbers 755191 and 755192. For ESI
and crystallographic data in CIF format see DOI: 10.1039/c0dt00210k
bands indicate the bonding of thiocarboxylate ligands mainly
through the sulfur atoms.11 13C spectra showed signals due to
phenyl and SCO carbon atoms, however, no structural inferences
are obtainable from these. 31P NMR spectra of complexes 1
and 2 showed single resonance signals at 0.17 and 9.05 ppm
‡ Present address: Department of Chemistry, Amarawati University, India.
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respectively, indicating the stereochemical equivalence of both the
PPh3 groups attached to a metal atom. The 31P signal appears at
-1.22 and 10.48 ppm in the case of [(PPh3)3Cu2(m-SCOPh)2] and
[(PPh3)Ag(m-SCOPh)]4 respectively.19,20
Molecular structures of 1 and 2
Both 1 and 2 are bimetallic complexes containing both lead and
copper/silver atoms with a P2MS3Pb core (M = Cu/Ag). The
complexes have comparable molecular structures (Fig. 1 and 2).
˚
˚
The M–Pb distances are 3.377 A in 1 and 3.787 A in 2 – both
being longer than the sum of the covalent radii of respective pairs
˚
˚
of atoms (3.04 A and 3.13 A) rule out the possibility of a Pb–M
bond. However, the sum of the van der Waals radii of Pb and
˚
Cu atoms (3.42 A) is slightly larger than the Pb–Cu distance and
indicates the possibility of a weak interaction between these atoms
in 1.
Fig. 2 Thermal ellipsoid plot of 2 (at 20% probability). Selected
metric data: Ag–S(2) 2.654(2), Ag–S(1) 2.684(2), Ag–P(1) 2.489(2),
Ag–P(2) 2.455(2), Pb–S(2) 2.678(2), Pb–S(1) 2.765(2), Pb–S(3) 2.686(2),
C(15)–S(3) 1.724(8), C(8)–S(2) 1.797(9), C(1)–S(1) 1.761(9), O(1)–C(1)
1.200(9), O(3)–C(15) 1.224(8), O(2)–C(8) 1.201(9), S(3)–Pb–S(1) 82.53(7),
S(2)–Pb–S(1) 85.98(6), P(2)–Ag–S(1) 121.09(7), P(2)–Ag–S(2) 115.77(7),
P(1)–Ag–S(1) 97.95 (7), P(1)–Ag–S(2) 108.48(7), P(1)–Ag–P(2) 120.04(7),
S(2)–Pb–S(3) 88.15(7), S(2)–Ag–S(1) 88.09(7), Ag–S(2)–Pb 90.53(7),
Ag–S(7)–Pb 88.04(6).
˚
to 0.23 A) than the sum of the covalent radii of Pb and S atoms.
The molecular structure of Pb(SCOPh)2 has been reported very
recently in which the Pb–S distances are even longer [3.022(4)
˚
and 3.173(4) A]. The report also describes intermolecular Pb–
˚
S interactions [3.665(4) A] imposing a five coordinate geometry
around Pb(II).14 The oxygen (O3) of the terminal thiobenzoate
˚
group in 1 is very close to the Pb atom (2.677 A) while the other
˚
two are at larger distances (2.842 and 2.882 A). The corresponding
Fig. 1 Thermal ellipsoid plot of 1 (at 20% probability). Selected
metric data: Cu–S(1) 2.427(2), Cu–S(2) 2.411(2), Cu–P(1) 2.272(2),
Cu–P(2) 2.290(19), Pb–S(1) 2.794(19), Pb–S(2) 2.794(2), Pb–S(3) 2.709(2),
Pb–O(3) 2.677(6), Pb–Cu 3.3774(9), S(3)–C(15) 1.747(8), S(1)–C(1)
1.779(8), S(2)–C(8) 1.784(8), O(3)–C(15) 1.242(10), O(1)–C(1) 1.227(8),
O(2)–C(8) 1.22(9), S(3)–Pb–S(2) 93.71(2), S(2)–Pb–S(1) 81.12(5),
S(3)–Pb–S(1) 82.94(6), O(3)–Pb–S(1) 139.09(14), O(3)–Pb–S(2) 89.64(13),
O(3)–Pb–S(3) -57.83(13), O(3)–Pb–Cu 133.70(13), P(1)–Cu–P(2)
118.03(7), P(1)–Cu–S(2) 114.47(7), P(2)–Cu–S(2) 105.20(7), P(1)–Cu–S(1)
110.01(7), P(2)–Cu–S(1) 109.73(7), S(2)–Cu–S(1), 97.37(7), Cu(1)–S(2)–Pb
80.56(6), Cu–S(1)–Pb(1) 80.28(5).
distances in 2 are also on the larger side (ranging between 2.902
˚
and 3.123 A).
The Pb–O3 distance in 1 though longer than the sum of the
covalent radii of Pb and O atoms (2.22 A) is quite short as
compared to the sum of their van der Waals radii (3.54 A). Notably,
˚
˚
the Pb–O bond lengths in the case of simple carboxylates of Pb(II)
fall in the range 2.32(2)–2.74(1).15 If the existence of a primary
bond is considered between Pb and O3, the coordination geometry
around Pb(II) should be described as either distorted tetrahedral
or trigonal bipyramidal containing a stereochemically active lone
pair at one of the equatorial coordination sites. However, a look
at the angles subtended by the three S and one O atoms at the
Pb centre are far from the angles expected. Possibly, the best
description would be as a trigonal pyramid with the Pb atom at
the vertex and three sulfur atoms at the corners of the triangular
base.
The M–S bond lengths in both the complexes are rela-
tively larger than the corresponding bond lengths found in
mononuclear as well as tetranuclear triphenylphosphine copper
or silver thiocarboxylate complexes where the Cu–S and Ag–
S bond lengths vary between 2.27–2.36 A and 2.46–2.57 A
respectively.
M(I) (M = Cu/Ag) is bonded with the phosphorous atoms
of two triphenylphosphine ligands and the sulfur atoms of two
thiobenzoate ligands acquiring a distorted tetrahedral geometry.
These two thiobenzoate anions are also bound to the Pb(II) centre
with their S atoms forming a bridge between the two metals. The
third thiobenzoate ligand binds with the Pb(II) atom only. As one
˚
would expect, the terminal S–Pb bond is shorter (by 0.085 A) than
the bridging S–Pb bonds in 1. On the contrary, one of the bridging
S–Pb bonds is the shortest one in the case of 2. It is interesting
to note that all the Pb–S distances are significantly longer (0.15
˚
˚
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Natural bond orbital analysis
As mentioned above, some of the structural features remain
unexplained from the X-ray crystallographic data. More detailed
studies are needed to make any unambiguous comments on the
observations such as the short Pb–Cu distance, long Pb–S bond
lengths and existence of Pb–O interactions. We have therefore
carried out theoretical calculations based on density functional
theory.21 The fully optimized molecular structures are quite similar
to those observed in the solid state (Fig. S1 and Table S1, ESI†).
As described above, the Pb–M distance in 1 was slightly shorter
than the sum of van der Waals radii of the two atoms and the same
in 2 was marginally larger than the sum of the corresponding van
der Waals radii. We have seen earlier that short bond distances
observed in the X-ray crystal structure may arise due to crystal
packing and are not always due to weak bond formation.22
However, in both 1 and 2 packing effects are possibly not playing
an important role as the Pb–M bond orders in Wiberg bond indices
were also found to vary according to the Pb–M distances (Pb–Cu =
0.04 and Pb–Ag = 0.01).
The results of second order perturbation theory analysis of Fock
matrix (NBO) reveal that there are significant intramolecular M–
Pb interactions in both cases (Table S2, ESI†). Electron transfers
from LpPb and Lp*Pb to various Lp*M and Ry*M orbitals
amount to 35.8 and 50.3 kcal mol-1 of energy lowering respectively
in 1 and 2. Though DFT is widely being used to optimize molecular
structures and also to calculate energies and other properties,
natural bond orbital analysis at ab initio level has also been found
to be very useful in some cases. In order to be more convinced
about the results of DFT calculations (NBO analysis) we have
repeated our NBO calculations at the Hartree–Fock level. The
results reveal that the CRCu to Lp*Pb and Lp*Cu to Ry*Pb charge
transfers are more favored (190.0 kcal mol-1) in 1. As a result the
Pb–Cu bond order (Wiberg) is significantly higher (0.1).
Fig. 3 Electronic absorption spectra of 1 and 2.
peak (at 263 nm) in the case of (Ph3P)2CuNO3.23 To understand
the effect of the thiobenzoate ligand and Pb(II) (if any) we have
studied the electronic spectra of two other related complexes,
(Ph3P)2Cu(SCOPh) and (Ph3P)3{Cu(m-SCOPh)}2.6 In these
complexes two other peaks were also observed. The dinuclear
complex absorbs at longer wavelengths (329 and 384 nm) as
compared to the mononuclear one (315 and 355 nm). In the solid
state one additional broad peak of lower intensity was observed
at 428 nm possibly due to some intermolecular charge transfer.
Similarly, 2 in CHCl3 solution shows three bands at 265, 299 and
320 nm (Fig. 3).
At first glance it seems surprising that in spite of such huge
amounts of energy lowering the molecular structures in neither
case are indicative of any strong Pb–M bond. However, it should
be kept in mind that the energy lowering is not associated with
overlap of any two particular orbitals, instead there are charge
transfers to all the Ry* orbitals available with the metal atoms.
In other words we can say that the interactions between the two
metals though very strong are more of ionic type.
The long Pb–S distances as compared to the sum of their
covalent radii agree with the calculated (PBE1) Pb–S bond orders
(Wiberg bond indices) which vary between 0.28 to 0.38 in 1 and
0.36 to 0.46 in 2. The Pb–O bond orders were found to be even
smaller (0.1 and 0.08 in 1 and 2 respectively), obviously due to
the lesser polarizability of oxygen than sulfur. The residual (NBO)
charge on Pb is +1.2 and +1.1 in 1 and 2 respectively (Table S2,
ESI†) which also corroborate the significant ionic character of the
lead-thiobenzoate bonds.
Electronic absorption and emission spectra
The electronic absorption spectra of compounds 1 and 2 were
recorded in solid state as well as in CHCl3 solutions. In the
solution spectrum of complex 1 three absorption bands were
observed at 268, 320 and 378 nm (Fig. 3). The highest energy
absorption is comparable to the intraligand (p–p*) charge transfer
Fig. 4 Selected orbital transition for 1 (contour value 0.05).
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For unambiguous assignment of the absorption bands we have
carried out time-dependent density functional calculations. In the
case of 1 the calculated spectrum shows absorption at 375 nm is
due to n → p* charge transfer from the lone pair of the lead atom
and the lone pairs of three sulfur atoms to the antibonding orbital
of the thiobenzoate ring.
The other absorptions are due to intraligand charge transfers
as shown in Fig. 4. In complex 2 the peak at 340 nm is due to
intraligand charge transfer where as the peaks at 327 nm, 312 nm,
308 nm, 299 nm and 265 nm are due to intraligand, interligand
(from one thiobenzoate to another and from triphenylphosphine
to bridging thiobenzoate) charge transfers Fig. 5.
Fig. 6 (a) Solid state emission spectra of complex 1 (lexcitation = 376 nm)
and (b) complex 2 (l.excitation = 320 nm).
bands at 350 nm and 525 nm when excited at 320 nm (Fig. 6(b))
while in the case of the emission study in solution state peaks of
very low intensities are observed. The emission band of higher
energy appears at 350 nm due to intraligand charge transfer, while
lower energy and lower intensity band appears at 525 nm due to
admixing of metal centered and intra-ligand transitions.25
Electrochemical study
The redox property of compound 1 was followed by cyclic
voltammetry (CV) using 0.1 M tert-butyl ammonium perchlorate
(TBAP) in acetonitrile as supporting electrolyte. Complex 1
exhibits two electron reversible oxidation corresponding to the
Pb(IV/II) redox couple at a half wave oxidation potential value
(E1/2ox in V vs. Ag/Ag+) of 1.14 V. The ipa/ipc ratio (1.6) was found
to be greater than 1 which represents the peak as a quasi-reversible
one at 1.14 V (35 mV). The electrode potential of the Cu+/Cu+2
couple under the experimental condition was 0.65 V vs. Ag/Ag+
showing irreversible oxidation of Cu(I) into Cu(II) (Fig. 7).
Fig. 5 Selected orbital transitions for 2 (contour value 0.05).
As compared to the other metal ion studies on the photolu-
minescence properties of lead-copper/silver containing bimetallic
complexes are rare.18 When excited at 376 nm complex 1 showed
a strong blue emission at 425 nm due to inter-ligand transition,
however, some low intensity emission bands are also observed at
460 nm, 485 nm and 513 nm (Fig. 6(a)). These may arise due to
metal-centered d to s orbital transition and ligand centered charge
transfer.24 However complex 2 in solid state, displays emission
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Table 2 EDX Composition of pyrolysed product of complex 1
Element
Wt (%)
At (%)
OK
CuK
PbL
23.89
21.29
54.82
Correction
71.34
16.01
12.64
ZAF
Matrix
From the residual weight percentage (Table 1) it appeared that
bimetallic sulfides along with a small quantity of some other
non-volatile solid (possibly carbon) was formed at the end of
decomposition.
For unequivocal characterization of the decomposition prod-
ucts we have carried out the pyrolysis of both compounds 1 and
2 and the products obtained (3 and 4) were then subjected to
SEM-EDX study (Fig. 9, Table 2).
Fig. 7 Cyclic voltammogram of 1 at 10 mV s-1 (vs. Ag/Ag+ in
dichloromethane).
Thermogravimetry and pyrolysis
The bimetallic sulfides of copper and lead having different
compositions show good optoelectronic and semi-conducting
properties.26 Thermal decompositions of 1 and 2 have been
investigated using TGA and are presented in Fig. 8 and the results
are summarized in Table 1. The decompositions of both 1 and 2
were found to be single step processes. However, in the case of
1, decomposition was preceded by loss of one acetone molecule
above 128 ◦C.
Fig. 9 EDX spectrum of pyrolysed product of complex 1.
The scanning electron micrographs of both the decomposition
products at higher magnification showed porous homogeneous
surface (Fig. S2 and S3, ESI†). Several metal thiocarboxylates
have been reported to be good precursors for metal sulfides,6
however, it is surprising to note that the products were ternary
oxides and no sulfide was formed in any of these cases. The
obtained decomposition product of 1 (compound 3) was found
to have the composition, Pb4Cu5O22.6. Powder X-ray diffraction of
this compound is given in Fig. 10. A search in the crystal structure
database27 revealed that the only Pb/Cu oxide reported so far28
is Murdochite, PbCu6O8 (JCPDS no. 07-0028) and 3 is a hitherto
unknown compound. In case of the decomposition product of 2
the results of EDX were non-reproducible as it absorbed varying
quantities of oxygen.
Fig. 8 Thermal decomposition patterns of complexes 1 and 2.
Table 1 Pyrolysis and TGA results for complexes 1 and 2
Residue wt.
Experimental section
T/◦C in observed
Expected product of
decomposition
Compound
TGA
(calcd.)(%) in TG
All manipulations were carried out under dry N2 atmosphere and
solvents were of reagent grade and were purified by standard
methods.29 Pb(NO3)2(CDH), Cu(NO3)2·3H2O (s. d. Fine chemi-
cals) and AgNO3 (RANKEM) were used as received. Thiobenzoic
1
2
128–148 95.0(95.4)
216–350 29.5(26.4)
238–378 32.7(32.3)
[(PPh3)2CuPb(SCOPh)3]
a
PbCuS2
a
PbAgS2
◦
acid (90%) (Sigma-Aldrich) was distilled (85–87 C/10 mm Hg)
a These have however, been found to be oxides by EDX.
before use. IR spectra were recorded using Varian 3100 FTIR
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Table 3 Crystal data and structure refinement of 1 and 2
1
2
Empirical formula
M
T/K
C60H51O4P2S3CuPb
1264.91
293(2)
C57H45O3S3P2AgPb
1251.11
293(2)
Crystal system
Space group
Monoclinic
P21/n
Monoclinic
P21/n
12.753(5)
17.287(6)
23.608(9)
99.079(8)
5140(3)
˚
a/A
16.0477(15)
13.0335(12)
26.548(3)
107.065(2)
5308.2(9)
4
3.794
R1 = 0.0505 wR2 =
0.1092
˚
b/A
˚
c/A
b/◦
3
˚
V/A
Z
4
m(Mo-Ka)/mm-1
3.880
R1 = 0.0561 wR2 =
0.1083
Final R indices [I > 2s(I)]
Reflections
34 210/13 027
33 881/12 821
collected/unique
R(int)
0.0559
0.0872
R indices(all data)
R1 = 0.0882
R2 = 0.1644
1.105
R1 = 0.1525
R2 = 0.1521
0.959
Fig. 10 X-Ray powder diffraction of 3.
GOF on F2
Instrument. NMR spectra were obtained from JEOL AL300
FTNMR spectrophotometer. Electronic spectra were recorded
using a Shimdzu UV-1700 Pharma Spect spectrophotometer
and fluorescence spectra were recorded in solid and solution
state using VARIAN, CARY Eclipse Fluorescence spectrometer.
Elemental analyses were performed by the Exeter Analytical
Inc.CE-440, Elemental analyzer. The SEM images and EDX
data were obtained from a FESEM-Quanta 200FEG and EDAX
instruments.
electrode as a working electrode. Electrochemical characteristics
of absorbed compound 1 was investigated by cyclic voltammetric
scanning of these electrodes in dichloromethane (1 ¥ 10-4 mmol
concentration) from 0.0 V to 2.0 V at scan rates of 100 and
10 mV s-1. The solution was purged with dry nitrogen gas for
10 min before starting the experiment.
Thermogravimetry and pyrolysis
Thermogravimetric analyses were carried out using Perkin Elmer,
X-Ray crystallography†
◦
Diamond TG/DTA with a heating rate of 10 C min-1 under
N2 atmosphere. Pyrolyses of the compounds in solid state were
Single crystal X-ray data of 1 and 2 were collected at room
performed at 350 ◦C in a furnace connected with a vacuum pump.
temperature on Bruker SMART APEX CCD diffractometer using
˚
graphite monochromated Mo-Ka radiation (l = 0.71073 A).
Data integration and reductions were processed with SAINT+
software.30 Structures were solved by the direct method and then
refined on F2 by the full matrix least square technique with
Synthesis of [(PPh3)2Cu(l-SCOPh)2Pb(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), an aqueous solution (5 ml) of
Pb(NO3)2 (0.331 g, 1.0 mmol) was added to get a green colored
solution of Na[Pb(SCOPh)3]. A solution of (PPh3)2Cu(NO3)38
(0.650 g, 1.0 mmol) in CHCl3 (~20 mL) was then added to
the reaction mixture with vigorous stirring at 10◦ C. Stirring
was continued for ~30 min maintaining the temperature below
SHELX-97 software31 using the WINGX program package.32
A
summary of the crystal data, experimental details, and refinement
results are listed in Table 3.
Theoretical calculations
All the calculations were performed using GAUSSIAN 03 W
software.33 Initial atomic co-ordinates were obtained from X-ray
crystallographic data which were used to optimize the molecular
structure of 1. For the NBO and TDDFT34 calculations optimized
structure was used for 1 while the atomic coordinates obtained
by X-ray crystallographic measurements were used as such for 2.
CEP-121G basis set35 was used at PBE1 level36 for the calculations.
However, d polarization functions and both d and p polarization
functions were augmented with the basis set respectively for O, P,
S, Ag and Cu, Pb atoms. All molecular orbital plots were generated
by MOLDEN program.37
◦
10 C. The solvent was then evaporated under reduced pressure
and the residue was extracted with CHCl3 (20 mL). Insolubles were
filtered off and solvent from the filtrate was evaporated under
reduced pressure. The yellow colored product was dried under
vacuum for 1 h. Recrystallized from a dichloromethane/acetone
solution at ~5 ◦C. Orange-yellow block shaped crystals were
obtained after a few days. (85% yield). Mp: 165 ◦C. Anal. Calcd.
for C57H45Cu1O3S3P2Pb1·CH3COCH3: C, 56.97; H, 4.06, Found:
C, 57.82; H, 4.124. 13C NMR (CDCl3, ppm); 127.5–141.6 (C6H5)
205.46 (COS), 31P NMR, +0.17. IR (KBr pellet, cm-1) 1568
n(C O), 1203 n(Ph–C), 913 n(C–S) and 692 d(SCO).
Electrochemical study
Synthesis of [(PPh3)2Ag(l-SCOPh)2Pb(SCOPh)] (2)
Electrochemical measurements were performed on a CHI 620c
electrochemical system with Ag/Ag+ electrode as reference elec-
trode, a platinum wire as counter electrode and a glassy carbon
To a freshly prepared solution of Na[Pb(SCOPh)3] [by mixing
thiobenzoic acid (0.207 g, 1.5 mmol), sodium metal (0.036 g,
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1.5 mmol) in MeOH (15 mL), and an aqueous solution (5 ml) of
Pb(NO3)2 (0.165 g, 0.50 mmol) with stirring at room temperature]
was added a chloroform (15 ml) solution of (PPh3)2Ag(NO3)
(0.347 g, 0.50 mmol) with stirring maintaining the temperature
below 10 ◦C. The resulting light yellow-green solution was stirred
for 30 min at 10 ◦C. The solvent was then evaporated and
the residue was extracted with dichloromethane. The insoluble
material (NaNO3) was filtered off and solvent from the filtrate was
evaporated under reduced pressure. The pale yellow product was
dried under vacuum for 1 h. Recrystallized by slow evaporation
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`
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◦
of a dichloromethane solution (91% yield); Mp: (179 C). Anal.
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`
Calcd for C57H45O3S3P2AgPb: C, 54.72; H, 3.63, Found: C, 54.72;
H, 3.63. 13C NMR (CDCl3, ppm); 127.5–141 (C6H5), 203.56
(COS),31P NMR, +9.05. IR (KBr pellet, cm-1): 1600 n(C O),
1198 n(Ph–C), 912 n(C–S) and 689 d(SCO).
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`
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Conclusions
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Novel Pb/M [where
M
=
Cu(I) and Ag(I)] contain-
ing heterobimetallic complexes of the type [(PPh3)2M(m-
SCOPh)2Pb(SCOPh)] have been synthesized and characterized
by various techniques including X-ray crystallography. Electronic
structures of the molecules have been studied by density functional
calculations. In both the molecules the Pb atom is at the vertex
of a trigonal pyramidal geometry while the other atom (Cu or
Ag) has a distorted tetrahedral environment. Pb ◊ ◊ ◊ M interactions
subsist in both the cases. In the electronic spectrum of complex 1
absorptions due to both metal to ligand charge transfer (MLCT)
and ligand to ligand charge transfer (LLCT) were observed while
in the case of 2 there was no absorption due to MLCT transition.
The complexes showed good photoluminescent behavior in solid
state. These compounds act as precursors for the corresponding
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◦
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.
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Acknowledgements
Authors are grateful to Prof. D. S. Pandey and Dr A. Mishra,
Department of Chemistry, Banaras Hindu University for electro-
chemical and fluorescence studies. Financial support (to S. B.)
from the UGC and CSIR, India are gratefully acknowledged.
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