Syntheses and structural studies of heterobimetallic thiocarboxylate complexes containing zinc and silver

Article abstract of DOI:10.1016/j.ica.2013.07.016

Novel heterobimetallic complexes, [(PPh₃)₂Ag(μ- SCOth)₂Zn(SCOth)(H₂O)] (1) and {[(PPh₃) ₂Ag(μ-SCOPh)₂Zn(SCOPh)(H₂O)][(PPh ₃)₂Ag(μ-SCOPh)Zn(SCOPh)₂]} (2) have been prepared and characterized by FTIR, ¹H, ¹³C and ³¹P NMR spectroscopy. Molecular structures of the complexes have been determined by single crystal X-ray diffraction technique. In these complexes the two metal atoms (Ag and Zn) are held together by bridging (μ-S or μ-O,S) thiocaboxylate groups. The terminal thiocarboxylate ligand binds monodentately (through S) in 1. Structure of 2 is unique as two different molecules, [(PPh₃)₂Ag(μ-SCOPh)Zn(SCOPh)₂] and [(PPh₃)₂Ag(μ-SCOPh)₂Zn(SCOPh)H ₂O] co-crystallize in the same lattice. The terminal thiocarboxylate ligand is monodentate (S) in the latter while bidentate (O,S) in the former molecule. Electronic spectral behaviors of the complexes have been explained by TDDFT calculations. Luminescence properties of both have been studied in solid state.

Full text of DOI:10.1016/j.ica.2013.07.016

Inorganica Chimica Acta 407 (2013) 31–36
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Syntheses and structural studies of heterobimetallic thiocarboxylate
complexes containing zinc and silver
1
⇑
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:
Novel heterobimetallic complexes, [(PPh3)2Ag(l-SCOth)2Zn(SCOth)(H2O)] (1) and {[(PPh3)2Ag
Received 12 April 2013
Received in revised form 9 July 2013
Accepted 10 July 2013
(l-SCOPh)2Zn(SCOPh)(H2O)][(PPh3)2Ag(l-SCOPh)Zn(SCOPh)2]} (2) have been prepared and characterized
by FTIR, 1H, 13C and 31P NMR spectroscopy. Molecular structures of the complexes have been determined
by single crystal X-ray diffraction technique. In these complexes the two metal atoms (Ag and Zn) are
Available online 26 July 2013
held together by bridging (
monodentately (through S) in 1. Structure of 2 is unique as two different molecules, [(PPh3)2Ag
-SCOPh)Zn(SCOPh)2] and [(PPh3)2Ag( -SCOPh)2Zn(SCOPh)H2O] co-crystallize in the same lattice. The
l-S or l-O,S) thiocaboxylate groups. The terminal thiocarboxylate ligand binds
Keywords:
Zinc
Silver
Thiocarboxylate
Heterobimetallic
Density functional calculations
(l
l
terminal thiocarboxylate ligand is monodentate (S) in the latter while bidentate (O,S) in the former
molecule. Electronic spectral behaviors of the complexes have been explained by TDDFT calculations.
Luminescence properties of both have been studied in solid state.
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
In view of these facts we have taken up the synthesis and char-
acterization of Zn/Ag thiocarboxylate complexes. We have chosen
Syntheses and studies of heterobimetallic complexes have
gained a lot of attention because of the exceptional physicochem-
ical properties and functions exhibited by these complexes arising
from a pair of different metal ions in close proximity [1–9]. Apart
from the tuned properties such heterobimetallic systems are extre-
mely useful as precursors of electronic materials [10–13]. During
recent years, heterobimetallic complexes containing sulfur donor
ligands are being utilized to prepare ternary metal sulfides by soft
chemical routes which are more energy efficient as compared to
conventional sintering methods [14,15].
Some times back we had reported [16] the synthesis and struc-
ture of the complex anion [In(SCOPh)4]À which has been used to
prepare a number of heterobimetallic complexes useful as single
source precursors of binary and ternary metal sulfides [14]. Very
recently, we have also used thiocarboxylate complexes containing
lead–copper and lead–silver metal ions to prepare the correspond-
ing ternary oxides [17].
thiophene-2-thiocarboxylate because of the fact that it contains
an additional sulfur atom which could affect the structure and
bonding of the complexes [22].
2. Experimental
2.1. Reagents and general procedures
All the solvents were dried according to standard procedures
and distilled before use. Thiophene-2-thiocarboxylic acid was pre-
pared by reported procedure [22]. Sodium salt of thiophene-2-
thiocarboxylic acid was obtained by reacting the acid with sodium
methoxide in stoichiometric ratio. Thiophene-2-carbonyl chloride
and thiobenzoic acid (Sigma–Aldrich) were used as received.
2.2. Instrumentation
A search of literature revealed the fact that though mononu-
clear Zn(II) thiocarboxylates [18–21] are known heterobinuclear
thiocarboxylate containing a Zn(II) metal are rare. Moreover, com-
plexes containing a pair of atoms one each from group 11 and 12
are limited and those with a sulfur ligand are scanty [14].
IR Spectra was recorded using Varian-3100 FTIR instruments.
NMR spectra (Figs. S1–S4, Supporting information) were obtained
using a JEOL AL300 FT NMR spectrometer. Electronic absorption
spectral measurements were carried out using
a Shimadzu
UV-1700 PharmaSpec Spectrometer. Absorption spectra of the
complexes have been recorded in chloroform solution
(2 Â 10À4 M). The solid state absorption spectra of 1 and 2 have
also been recorded. Elemental analyses were performed by the
EAT Exeter Analytical Inc. CE-440, elemental analyzer.
⇑
Corresponding author. Tel.: +91 542 6702451.
E-mail address: s_bhatt@bhu.ac.in (S. Bhattacharya).
1
Present address: IPC Department, IISc, Bangalore 560012, India.
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.07.016

32
S. Singh et al. / Inorganica Chimica Acta 407 (2013) 31–36
Table 1
Crystal data and structure refinement of complexes.
1
2
Empirical formula
(CCDC No.)
T (K)
C
51H41O4S6P2Zn1Ag1
C114H92O7S6P4Zn2Ag2
(772370)
150
(772371)
293
Crystal system
Space group
a (Å)
b (Å)
c (Å)
orthorhombic
Pccn
14.103(5)
39.571(5)
18.141(5)
90
10124(5)
8
1.215
monoclinic
P21/c
14.036(5)
39.376(5)
18.194(5)
91.500(5)
10052(5)
4
b (°)
V (Å3)
Z
l
(Mo K
a
) (mmÀ1
)
1.101
Reflections collected/
unique
28090/11524
47399/22942
Rint
0.0525
0.0590
Final R indices
[I > 2r(I)]
R indices (all data)
R1 = 0.1109,
wR2 = 0.2343
R1 = 0.1847,
wR2 = 0.2811
1.033
R1 = 0.0678,
wR2 = 0.1120
R1 = 0.1349,
wR2 = 0.1376
1.020
Goodness-of-fit (GOF)
on F2
2.3. Single crystal X-ray analysis
Fig. 1. Thermal ellipsoid plot of 1 at 30% probability level. Thiophene rings are
disordered. (Hydrogens and phenyl rings of triphenylphosphine are omitted for
clarity.)
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 for all com-
PBE1 level [29,30]. All the molecular orbital plots were generated
by MOLDEN program [31].
plexes were carried out at room temperature. Structures were
solved by the direct method and then refined on F2 by the full
matrix least square technique with SHELX-97 software [23] using
the WINGX program package [24]. Crystal data of complexes are gi-
ven in Table 1 The crystals of both the complexes showed some
disorders. In 1, all the three th rings were disordered. The disor-
dered atoms of the th rings were split in two parts and then some
geometrical restraints were applied (if necessary) for refinement.
Similarly disorders in rings of other structures were also refined.
2.5. Syntheses
2.5.1. Synthesis of [(PPh3)2Ag(SCOth)2Zn(SCOth)(H2O)], (1)
To the stirred methanolic solution (5.0 ml) of sodium thio-
phene-2-thiocarboxylate (0.240 g, 1.45 mmol) a methanolic solu-
tion (5 ml) of Zn(NO3)2Á6H2O (0.143 g, 0.48 mmol) was added to
get a light yellow colored solution of Na[Zn(SCOth)3]. In this stirred
reaction mixture added PPh3Ag(NO3) (0.208 g, 0.48 mmol) (pre-
pared by addition of 1:1 PPh3 and AgNO3 in acetonitrile) in 5 ml
of CH2Cl2 followed by PPh3 (0.126 g, 0.48 mmol) in 5 ml of CH2Cl2
then the reaction mixture was stirred for 2 h. The solvent was
evaporated under reduced pressure and the residue was dissolved
in CHCl3 (20 ml) and filtered off to separate out NaNO3. The filtrate
was evaporated under reduced pressure. The yellow colored
product was dried under vacuum for 1 h. Light yellow rod shaped
2.4. Computational details
All the calculations performed using GAUSSIAN 03W software [25].
As the final R indices for 1 were rather high the molecular geome-
try was optimized using B3LYP correlation functional. The opti-
mized atomic coordinates were used for TDDFT [26] calculations.
All time dependent calculations were performed using CEP-121G
basis set [27,28] for Ag atom and 6-31G⁄⁄ for rest of the atoms at
Zn(NO3)2.6H2O + 3RCOSH + 3NaOMe
Methanol
at ice bath
[(PPh3)Ag(NO3)]
PPh3
[(PPh3)2Ag(µ-SCOth)2Zn(SCOth)(H2O)]
(1)
Na[Zn(SCOR)3]
R = Ph and th
[(PPh3)Ag(NO3)] + PPh3
{[(PPh3)2Ag(µ-SCOPh)2Zn(SCOPh)(H2O)][(PPh3)2Ag(µ-SCOPh)Zn(SCOPh)2]}
(2)
Scheme 1.

S. Singh et al. / Inorganica Chimica Acta 407 (2013) 31–36
33
Table 2
m.p. 154–156 °C. Elemental Anal. Calc. for C51H41O4S6P2ZnAg: C,
53.48; H, 3.61. Found: C, 53.48; H, 3.70%. IR spectra (KBr, cmÀ1):
Selected bond lengths and bond angles of complexes.
1560, 1510
m(CO), 1228 m(th–C), 912, 870 m(C–S). NMR (CDCl3,
Complex
Bond length (in Å)
Bond angle (in °)
dppm): 1H NMR; 6.79–7.60 (Ph and th ring), 2.21 (H2O). 13C
NMR; 127.38–146.99 (Ph and th ring), 197.29 (COS). 31P NMR;
8.39.
1
Zn1–S1
Zn1–S3
Zn1–S5
Zn1–O2
Zn1–O4
Ag1–S1
Ag1–S3
Ag1–P1
Ag1–P2
2.369(3)
S1–Zn1–S3
S1–Zn1–S5
S3–Zn1–S5
S1–Zn1–O4
S3–Zn1–O4
S5–Zn1–O4
S1–Zn1–O2
S3–Zn1–O2
S5–Zn1–O2
O2–Zn1–O4
S1–Ag1–S3
S1–Ag1–P1
S1–Ag1–P2
S3–Ag1–P1
S3–Ag1–P2
P1–Ag1–P2
S1–Zn1–S3
S1–Zn1–O2
S3–Zn1–O2
S1–Zn1–O4
S3–Zn1–O4
O2–Zn1–O4
S1–Ag1–S2
S1–Ag1–P1
S1–Ag1–P2
S2–Ag1–P1
S2–Ag1–P2
P1–Ag1–P2
S4–Zn2–S5
S4–Zn2–S6
S5–Zn2–S6
S4–Zn2–O7
S5–Zn2–O7
S6–Zn2–O7
S4–Ag2–P3
S4–Ag2–P4
P3–Ag2–P4
89.14(11)
113.46(15)
98.73(12)
101.4(3)
147.0(3)
105.5(3)
125.5(4)
59.1(3)
114.6(3)
90.0(4)
84.07(10)
112.78(9)
106.65(9)
118.15(9)
93.46(9)
130.89(8)
116.50(6)
118.83(11)
112.72(12)
102.35(15)
105.59(15)
97.03(16)
81.98(5)
2.794(4)
2.319(4)
2.178(11)
2.071(10)
2.709(3)
2.722(3)
2.450(2)
2.475(2)
2.5.2. Synthesis of {[(PPh3)2Ag(
SCOPh)2Zn(SCOPh)(H2O)][(PPh3)2Ag(
l-
l-SCOPh)Zn(SCOPh)2]}, (2)
To the stirred methanolic solution (5.0 ml) of sodium thi-
obenzoate [PhCOSH (0.414 g, 3.0 mmol in 5 ml of MeOH) and
deprotonated by sodium methoxide (0.162 g, 3.0 mmol)], a metha-
nolic solution (5 ml) of Zn(NO3)2Á6H2O (0.297 g, 1.0 mmol) was
added to get a light yellow colored solution of Na[Zn(SCOPh)3].
In this stirred reaction mixture added PPh3Ag(NO3) (0.432 g,
1.0 mmol) (prepared by addition of 1:1 PPh3 and AgNO3 in acetoni-
trile) in 5 ml of CH2Cl2 followed by PPh3 (0.262 g, 1.0 mmol) in 5 ml
of CH2Cl2 then the reaction mixture was stirred for 2 h. The solvent
was evaporated under reduced pressure and the residue was dis-
solved in CHCl3 (20 ml) and filtered off to separate out NaNO3.
The filtrate was evaporated under reduced pressure. The yellow
product was dried under vacuum for 1 h. Light yellow colored
rod shaped crystals were obtained from chloroform solution
(15 ml) layered with diethyl-ether at room temperature. Yield:
1.047 g (93%). Elemental Anal. Calc. for C114H92O7S6P4Zn2Ag2: C,
61.21; H, 4.15. Found: C, 61.17, H, 4.19%. IR spectra (KBr, cmÀ1):
2
Zn1–S1
Zn1–S3
Zn1–O2
Zn1–O4
Ag1–S1
Ag1–S2
Ag1–P1
Ag1–P2
Zn2–S4
Zn2–S5
Zn2–S6
Zn2–O7
Ag2–S4
Ag2–P3
Ag2–P4
2.3461(16)
2.2979(15)
2.004(4)
2.061(4)
2.7440(14)
2.6530(15)
2.4487(14)
2.4814(14)
2.333(2)
2.341(2)
2.3733(18)
2.196(4)
113.25(5)
105.41(5)
124.23(5)
93.59(5)
128.08(5)
124.32(7)
111.74(7)
118.28(8)
115.04(12)
105.26(12)
68.03(11)
104.68(5)
120.42(5)
130.03(5)
2.6224(18)
2.4734(14)
2.4471(15)
1591, 1562
m(CO), 1203 m(Ph–C), 931, 910 m(C–S). NMR (CDCl3,
dppm): 1H NMR; 7.11–7.91 (Ph ring), 2.89 (H2O). 13C NMR;
127.53–140.19 (Ph ring), 205.45 (COS). 31P NMR; 8.63.
3. Results and discussion
3.1. Syntheses
Complex anions, tris(thiocarboxylato)zincate(II) was used as the
precursor for all the complexes reported here. For the synthesis of
heterobimetallic complexes these precursors were generated
in situ and used as such without any attempt for their purification
crystals were obtained from chloroform solution (15 ml) layered
with diethyl-ether at room temperature. Yield: 0.436 g, (79%).
Fig. 2. Thermal ellipsoid plot of 2 at 30% probability level (Hydrogens and phenyl rings of triphenylphosphine are omitted for clarity.)

34
S. Singh et al. / Inorganica Chimica Acta 407 (2013) 31–36
Fig. 3. Selected orbital transitions in 1 (orbital contour value 0.05).
or isolation. Both the complexes were synthesized by addition of
chloroform solution of triphenylphosphine silver to a methanolic
solution containing the thiocarboxylato zincate anion followed
by addition of one equivalent of triphenylphosphine (chloroform
solution) with stirring at room temperature (Scheme 1).
It may be noted that the complex 2 has two different molecules
in the solid state. However, in solution their individual identity is
not retained. As a result only one signal (at 8.63 ppm) is observable
in the 31P NMR spectrum of the complex.
nor) macrocyclic complex of Zn(II) is bounded to Ag(I) [32,33]
through the sulfur atoms present in the pendent arms of the mac-
rocyclic ligand.
Both the complexes were soluble in common organic solvents
such as chloroform, benzene etc. The compounds in solid state
were found to be fairly stable, under ambient conditions.
3.2. Crystal and molecular structures
It is also worth mentioning that Zn(II)/Ag(I) complexes are
uncommon and there are only a few such compounds that contain
a sulfur ligand. To the best of our knowledge the only structurally
characterized Zn(II)/Ag(I) complexes are those in which a (N-do-
Complex 1 crystallized in orthorhombic system with Pccn space
group. The molecular structure with atom labeling scheme is
depicted in Fig. 1 and slected bond lengths and bond angles are gi-

S. Singh et al. / Inorganica Chimica Acta 407 (2013) 31–36
35
similar to the thiocarboxylate complexes of Cd(II)/Ag(I) [15] and
Pb(II)/Ag(I) [17].
For unambiguous assignment of the absorption bands time
dependent density functional theory (TDDFT) calculations have
been performed at PBE1 level. The orbital transition plots of 1
are shown in Fig. 3. The calculated absorptions at 455 nm and
440 nm are due to electron transfers from lone pair of silver atom
to the p⁄ orbital of thiophene ring of the bridging thiocarboxylate.
This involves transitions (n ? p⁄) from HOMOÀ4 and HOMOÀ3 to
LUMO, LUMO+1 orbitals. Experimentally these transitions are
responsible for the broad absorption peak ranging from 400 to
450 nm (with an absorption maximum at 426 nm). Other absorp-
tion peaks at 372 and 345 nm are due to admixing of metal to li-
gand, intra-ligand and inter-ligand charge transfer transitions.
These peaks are observed experimentally at 368 and 342 nm
respectively.
3.4. Emission spectra
Fig. 4. Emission spectrum of 2 in solid state.
To the best of our knowledge there is no literature available on
the photoluminescence properties of Zn(II)/Ag(I) heterobimetallic
compounds. Emission spectra of complexes 1 and 2 have been re-
corded in solid state. When exited at 426 nm complex 1 showed
two weak emission bands at 469 and 522 nm (broad) (Fig. S9,
Supporting information). Complex 2 showed a strong and broad
emission band at 490 nm (Fig. 4) when it was exited at 400 nm.
In both the cases, no significant changes were observed in the
emission spectrum on changing the excitation wavelengths. The
emission bands observed are thus due to the excitation of electrons
by metal centered charge transfer transitions [17].
ven in Table 2. In this case all three thiophene rings and two phenyl
rings of triphenylphosphine are distorted.
The three thiocarboxylate ligands exhibit three different coordi-
nation modes. One of the ligands binds monodentately to Zn(II)
through the sulfur atom (S5) and the other two form bridges be-
tween Zn and Ag atoms. The bridging in one case is
is ( -O,S) in the other. The Zn(II) being harder as compared to
Ag(I) is bounded by O2 atom of the ( -O,S) bridging ligand. The
l-S while it
l
l
fourth coordination site of Zn is occupied by the oxygen atom of
a water molecule. A look at the various angles subtended at Zn1
by the donor atoms also reveals a distorted tetrahedral geometry
around it. However, the presence of S3 atom affects the geometry
to some extent by capping the S1, S5, O2 face of tetrahedron.
Geometry around Ag1 is also tetrahedral with significant distortion
which is possibly a consequence of large steric demands of the two
triphenylphosphine ligands.
Evidently, there is no Zn–Ag bonding in this complex as the two
atoms are separated by 3.723 Å which is even larger than the sum
of the van der Waals’ radii of these two atoms.
The structure of complex 2 revealed an unusual co-crystalliza-
tion of two different molecules in the same lattice (Fig. 2). Molec-
ular core in one of these (containing Zn1 and Ag1) is isostructural
to that of 1. In the second molecule, the two metals Zn2 and Ag2
4. Conclusions
Two new heterobimetallic complexes, [(PPh3)2Ag(
Zn(SCOth)(H2O)] (1) and {[(PPh3)2Ag( -SCOPh)2Zn(SCOPh)(H2-
O)][(PPh3)2Ag( -SCOPh)Zn(SCOPh)2]} (2) have been synthesized
l-SCOth)2-
l
l
and characterized by spectral and X-ray diffraction studies.
Structure of 2 is unique as two different molecules, [(PPh3)2Ag
(l-SCOPh)2Zn(SCOPh)] and [(PPh3)2Ag(l-SCOPh)2Zn(SCOPh)H2O]
co-crystallize in the same lattice. Electronic spectral behavior of
the complex 1 has been explained by TDDFT calculations. The
two complexes may further be explored for their application as
single source precursors for Ag/Zn sulfide nanoparticles.
are held together by the sulfur (l2-S) atom of a thiobenzoate
ligand. The Zn2 atom is coordinated by O7 besides the three S
atoms. The Ag2 is tricoordinated having bonded to one sulfur
and two phosphorus atoms. Notably, the Ag2 atom is tipped above
the P2S plane by 0.317 Å which is possibly a consequence of
Ag2Á Á ÁO6 interaction. [The Ag2–O6 distance is 2.757 Å which is
substantially shorter than the sum of the van der Waals’ radii of
the Ag and O atoms (3.24 Å).]
Acknowledgements
The authors are grateful to Professor R.J. Butcher, Howard Uni-
versity, USA for his help in refining the structures (particularly of
compound 1). Financial supports in the form of a research project
to S.B. by the university grants commission, India, SRF to S.S. and
J.C. by the Council of Scientific and Industrial Research, India are
gratefully acknowledged.
3.3. Electronic absorption spectra
Appendix A. Supplementary material
Absorption spectrum of 1 showed absorptions at 234, 239, 255
and 312 nm. In solid state the peaks at higher frequencies appeared
at 272 and 288 nm, while the lower energy absorptions were
observed at 321, 342, 368 nm and a broad peak at 426 nm. Simi-
larly, the complex 2 showed absorption peaks at 225, 234, 239,
246 and 314 nm in solution state whereas in solid state peaks were
observed at 252, 305, 326, 342 and 412 (broad) nm (Figs. S5–S8,
Supporting information). In general, lower energy peaks appear be-
cause of the metal to ligand (or ligand to metal) charge transfers
while peaks below 300 nm are due to the inter- or intra-ligand
charge transfers. Spectral behavior of both the complexes are very
CCDC 772371 and 772370 contains the supplementary crystal-
lographic data for 1 and 2. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2013.07.016.
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