Studies of titanocene and zirconocene pyridine-2,6-bis-thiocarboxylates exhibiting partial desulfurization

Article abstract of DOI:10.1016/j.ica.2012.11.014

Attempts to synthesize bent metallocene complexes of pyridine-2,6- bis(thiocarboxylate), Cp₂Ti(pdtc) and Cp₂Zr(pdtc) yielded partially desulfurized products. In the case of Cp₂Ti(IV) two types of products were obtained, in one case desulfurization was at one of the thiocarboxylate groups resulting in a carboxylate group while in the other case it was partial and from both the thiocarboxylate entities. In case of Cp ₂Zr(IV) similar partial desulfurization took place from both the thiocarboxylates. The complexes have been characterized by single crystal X-ray diffraction analysis. The ligands pyridine-2-carboxylate-6-thiocarboxylate, pyridine-2,6-dicarboxylate and pyridine-2,6-bis(thiocarboxylate) act as tridentate ligands. With both the metals binding of ligand is through the oxygen (and nitrogen) atoms leaving the sulfur free. Electronic absorption and emission spectra of the compounds have been studied experimentally and explained on the basis of DFT computations.

Full text of DOI:10.1016/j.ica.2012.11.014

Inorganica Chimica Acta 395 (2013) 230–236
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Studies of titanocene and zirconocene pyridine-2,6-bis-thiocarboxylates
exhibiting partial desulfurization
⇑
Suryabhan Singh, Subrato Bhattacharya
Department of Chemistry, Faculty of Science, 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:
Attempts to synthesize bent metallocene complexes of pyridine-2,6-bis(thiocarboxylate), Cp2Ti(pdtc) and
Cp2Zr(pdtc) yielded partially desulfurized products. In the case of Cp2Ti(IV) two types of products were
obtained, in one case desulfurization was at one of the thiocarboxylate groups resulting in a carboxylate
group while in the other case it was partial and from both the thiocarboxylate entities. In case of Cp2-
Zr(IV) similar partial desulfurization took place from both the thiocarboxylates. The complexes have been
characterized by single crystal X-ray diffraction analysis. The ligands pyridine-2-carboxylate-6-thiocarb-
oxylate, pyridine-2,6-dicarboxylate and pyridine-2,6-bis(thiocarboxylate) act as tridentate ligands. With
both the metals binding of ligand is through the oxygen (and nitrogen) atoms leaving the sulfur free. Elec-
tronic absorption and emission spectra of the compounds have been studied experimentally and
explained on the basis of DFT computations.
Received 7 September 2012
Received in revised form 30 October 2012
Accepted 9 November 2012
Available online 24 November 2012
Keywords:
Titanocene
Zirconocene
Pyridine-2,6-dicarboxylate
Pyridine-2,6-bis(thiocarboxylate)
Desulfurization
Ó 2012 Elsevier B.V. All rights reserved.
Hydrolysis
1. Introduction
complexes of Cp2Ti(IV) and Cp2Zr(IV). The significance of the pres-
ent study may be viewed not only in terms of the ligand’s ability to
Complexes of pyridine-2,6-dicarboxylate ligand have attracted
a lot of attention [1–5]. The ligand exhibits quite a few different
coordination modes leading to the formation of monomeric as well
as polymeric complexes. Conversely, studies on the complexes of
the corresponding thiocarboxylate [pyridine-2,6-bis(thiocarboxy-
late) (pdtc)] ligand are scanty. Though pdtcH2 is a natural product,
found in Pseudomonas bacteria [6] and have shown versatile liga-
tional ability in its dianionic form with a few transition metal ions,
yet its studies are limited largely to the complexes of Fe [7–9], Co
[10,11], Ni [10,11] and Pd [12]. The complexes of Ni(II) and Pd(II)
stabilize uncommon oxidation state (Ni3+) and unusual structural
motifs [19] (e.g. Ni-SH) but also because of the fact that simple
thiocarboxylates of these organometallic moieties have not been
characterized yet (there is only one report on the synthesis of Cp2-
Ti(III) thiocarboxylate [20] and possibly no reports on correspond-
ing Cp2M(IV) (M = Ti, Zr). Our attempts to isolate such complexes
with thiobenzoate and thioacetate were unsuccessful. Notably,
Cp2Ti(IV) carboxylates are known to be thermally unstable [21]).
2. Experimental
are dimeric (l2-S bridged) and undergo facile bridge cleavage reac-
tions with a number of nucleophiles. [Ni(pdtc)2]2ꢀ,1ꢀ were the first
pair of structurally characterized Ni(II) and Ni(III) complexes with
anionic sulfur ligands [11] which also threw light on factors that
lead to unusually low values of redox potentials for this couple
as found in [NiFe] hydrogenases. Pd(II) complexes show mesogenic
behavior when suitably substituted [13]. A search of the literature
revealed that other than the above mentioned late transition met-
als uranium is possibly the only metal whose complexes of pdtc
have been synthesized and characterized crystallographically
[14,15].
All the solvents were purified using standard methods. Pyri-
dine-2,6-bis(thiocarboxylic) acid was synthesized using reported
method [22].
IR spectra were recorded using Perkin-Elmer RX-1, FT-IR and
Varian-3100 FTIR instruments. NMR spectra were obtained using
a JEOL AL300 FT NMR spectrometer. Elemental analyses were per-
formed using an Exeter model E-440 CHN analyser. CHS analysis of
4 was carried out at National Chemical Laboratory, Pune, India.
Electronic absorption spectra were recorded using a Shimazdu
UV-1700 PhermaSpec Spectorphotometer. Solid state emission
spectra were recorded from VARIAN, CARY Eclipse Fluorescence
spectrometer.
Continuing our studies on thiocarboxylate complexes [16–18]
we here report the synthesis and characterization of the pdtc
Single crystal X-ray data of compounds were collected on
Xcalibur Oxford Diffractometer using graphite monochromated
Mo Ka radiation (k = 0.7107 Å). The SHELX program [23] was used
⇑
Corresponding author. Tel.: +91 542 6702451.
E-mail address: s_bhatt@bhu.ac.in (S. Bhattacharya).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.11.014

S. Singh, S. Bhattacharya / Inorganica Chimica Acta 395 (2013) 230–236
231
for structure solution and refinement. Data collections for all the
compounds were carried out at 293 K. Crystal data of complexes
are given in Table 1. While refining the structure of 2 and 4 it
was observed that the S atoms were disordered. On splitting them
in two parts it became clear that the parts closer to C are oxygen.
Further refinement was then made placing oxygen and sulfur
atoms based on the distances from the carboxylate carbon (assum-
ing that the sums of their occupancies equal to one).
2.1.4. Synthesis of [Cp2Zr(SCO)2Py] (4)
A similar procedure was followed as described for the synthesis
of 1, however, in place of Cp2TiCl2, Cp2ZrCl2 (0.292 g, 1.0 mmol)
was used. The red orange, rectangular crystals were obtained from
chloroform solution layered by petroleum ether (60–80 °C). Yield:
0.347 g (83%). Anal. Calc.: C, 50.75; H, 3.26; S, 7.81. Found: C, 50.35;
H, 3.71; S, 7.54% (This fits with the partially desulfurized product,
C
17H13O2N(S/O)2Zr in which 49% is thiocarboxylate and 51% has
desulfurized to carboxylate moity). IR spectra (KBr, cmꢀ1): 1670
m
(CO), 1387 m
(CS). 1H NMR (CDCl3, ppm) 6.25 (5H of cp, s), 6.27
(5H of Cp, s), 8.26(1H, m, J(H, H) 6.3 Hz), 8.30 (1H, m, J(H, H)
6.3 Hz), 8.70(1H, t, J(H, H) 8.7 Hz) (Py). 13C NMR (CDCl3, ppm)
114.4 (Cp), 114.4 (Cp), 125.5, 126.1, 128.0, 128.6, 142.9, 149.2
(Py), 165.3 (CO2), 207.2 (COS).
2.1. Syntheses
2.1.1. Synthesis of [Cp2Ti(SCOPyCO2)] (1)
To a solution of pyridine-2,6-bis(thiocarboxylic) acid (0.200 g,
1.0 mmol) in methanol was added triethyl amine (0.202 g,
2.0 mmol) and stirred for 5 min then bis-cyclopentadienyltitanium
dichloride (0.249 g, 1.0 mmol) was added with stirring. Precipita-
tion occurred (yellow) just after addition. The reaction mixture
was stirred further for an hour, the residue was then collected by
filtration which was washed with methanol (two times) and dried
under reduced pressure. The yellow residue was recrystallized
from its chloroform solution by slow evaporation of the solvent.
Yield: 0.254 g, (71%). Anal. Calc. for C17H13O3NSTi: C, 56.84, H,
3.65, N, 3.90. Found: C, 56.57, H, 3.59, N, 3.93%. IR spectra (KBr,
2.2. Computational details
The energy optimized geometries of 1 and 4 were calculated
using the B3LYP [24,25] exchange–correlation functional. The
effective core potential (ECP) standard basis set LANL2DZ [26–28]
was utilized for Ti and Zr atoms, where as the 6-31Gꢁꢁ [29] basis
set was used for C, H, O, N and S atoms. The energies and intensities
of the 20 lowest-energy spin allowed electronic excitations were
calculated by using TD-DFT at the same level of theory. The first
static hyperpolarizabilty (b0) for compounds 1 and 4 were calcu-
lated by using the finite field perturbation method by implement-
ing the PCM model [30,31]. The solvent parameters were those of
chloroform. X-ray coordinates were used for optimization of geom-
etries. The optimized coordinates were used for the calculation of
electronic excitations and hyperpolarizabilities. All the theoretical
calculations were performed using the GAUSSIAN 03W set of pro-
grams [32]. Molecular orbital plots were generated by using the
program MOLDEN [33].
cmꢀ1): 1656 (CS). 1H NMR (CDCl3, ppm) 6.23 (10H
m(CO), 1402 m
of Cp, s), 8.24(1H, m, J(H, H) 7.2 Hz), 8.70(2H, m, J(H, H) 7.5 Hz)
(Py). 13C NMR (CDCl3, ppm) 118.62 (Cp) 125.8, 126.3, 129.1,
142.7, 149.7 (Py), 167.0 (CO2), 198.7 (COS).
2.1.2. Synthesis of [Cp2Ti(OCS)2Py] (2)
A method similar to that for the synthesis of 1 was applied for
the synthesis of 2, however, toluene was used as the solvent in-
stead of methanol. Single crystals were grown from chloroform
solution by slow evaporation of the solvent. IR spectra (KBr,
cmꢀ1): 1658 (CS). 1H NMR (CDCl3, ppm) 6.20 (5H of
m(CO), 1405 m
3. Results and discussions
Cp, s), 6.24 (5H of Cp, s), 8.09(1H, d, J(H, H) 6.6 Hz), 8.42(1H, m,
J(H, H) 7.8 Hz), 8.53 (1H, d, J(H, H) 7.5 Hz) (Py). 13C NMR (CDCl3,
ppm) 118.5 (Cp), 118.7 (Cp), 128.1, 128.3, 128.6, 133.4, 134.3,
140.6 (Py), 186.1 (CO2), 205.9 (COS).
3.1. Syntheses and characterization
Complexes 1, 3 and 4 were obtained by the reaction between
Cp2MCl2 [M = Ti(IV) and Zr(IV)] and pyridine-2,6-bis(thiocarboxy-
lic) acid in presence of triethyl amine in methanol as shown in
Scheme 1.
2.1.3. Synthesis of [Cp2Ti(O2C)2Py] (3)
When a chloroform solution of 1 with few drops of water was
left for longer time (a week), yellow rectangular crystals of 3 were
obtained.
Complex 1 was formed when desulfurization (possibly in the
form of H2S) of one of the thiocarboxylate groups occurred during
the synthesis resulting in a carboxylate group. When a few drops of
Table 1
Crystal data and structure refinement of compounds.
1
2
3
4
Empirical formula
T (K)
C
293
17H13NO3STi
C17H13NO2E2Tia
293
C17H13NO4Ti
293
C17H13NO2E2Zra
293
Crystal system
Space group
a (Å)
b (Å)
c (Å)
orthorhombic
Cmca
10.4723(8)
12.2097(6)
24.1589(15)
90
3089.0(3)
8
orthorhombic
Pmn21
11.964(11)
8.167(4)
7.678(5)
90
750.2(9)
2
monoclinic
P21
orthorhombic
Pmn21
11.948(5)
8.280(5)
7.847(5)
90
776.3(8)
2
8.0004(13)
7.7109(10)
11.5957(14)
95.946(12)
711.49(17)
2
b (°)
V (Å3)
Z
l(Mo K
a
) (mmꢀ1
)
0.703
0.657
0.622
0.805
Reflections collected/unique
Rint
4852/1894
0.0245
2021/1432
0.0444
3194/2215
0.0340
2190/1148
0.0201
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0640, wR2 = 0.1635
R1 = 0.0931, wR2 = 0.1807
0.854
R1 = 0.0730, wR2 = 0.1744
R1 = 0.1392, wR2 = 0.2326
0.982
R1 = 0.0850, wR2 = 0.2254
R1 = 0.0925, wR2 = 0.2351
1.062
R1 = 0.0312, wR2 = 0.0656
R1 = 0.0504, wR2 = 0.0712
1.023
Goodness-of-fit on F2
a
E = S partially substituted with O.

232
S. Singh, S. Bhattacharya / Inorganica Chimica Acta 395 (2013) 230–236
Scheme 1.
water were added to a chloroform solution of 1 complete desulfur-
ization occurred and corresponding carboxylate complex 3 was ob-
tained. Since the bis-thiocarboxylate derivative could not be
isolated in methanol we attempted to isolate the same by carrying
out the reaction in toluene which can be dehydrated much easily.
However, the product obtained in this case contained Et3NHCl
which could not be separated completely by recrystalliztion. Crys-
tals of complex 2 could, however, be selected under microscope
and subjected to X-ray analysis. Desulfurization was also observed
in the cases of complexes 2 and 4 but it was partial and from both
the thiocarboxylate entities. Desulfurization of thiocarboxylate
complexes is quite uncommon, however, we have recently re-
ported [34] ready desulfurization of copper(II) thiocarboxylate
complexes leading to the formation of the corresponding carboxyl-
ate complexes. This reactivity may be rationalized in view of the
bonding modes of the ligands. As have been observed in the Cu(II)
complexes bonding of the thiocarboxylate groups in both 1, 2 and 4
is primarily through the oxygen atoms in contrast to possibly all
other structurally characterized transition metal thiocarboxylate
complexes (in which there is a strong M–S bonding).
It is however, interesting to note the difference between 1 and
2/4 in their desulfurization modes. While in 1 one of the thiocarb-
oxylate undergoes complete desulfurization leaving the other
group as such, 2 and 4 show partial desulfurization at both the
thiocarboxylate groups. To the best of our knowledge 2 and 4 pro-
vide the first examples of metal complexes in which some of the
molecules have changed from their original composition to a
new one in the same lattice. A search of the literature revealed that
such compositional change have earlier been reported only in the
case of triphenylphosphine sulfide [35].
1H and 13C NMR spectra of the complexes were recorded to
understand the nature of these in solution. In case of 1 a single
sharp peak was observed due to the cyclopentadienyl protons. In
addition there were two peaks with a proton ratio of 1:2, respec-
tively due to the protons at C4 and C3+C5 of pyridine. The peaks
appeared as multiplets since the environments at C2 and C6 are

S. Singh, S. Bhattacharya / Inorganica Chimica Acta 395 (2013) 230–236
233
Fig. 3. Thermal ellipsoid plot of 4 (at 30% probability level. Hydrogen atoms are
omitted for clarity). Selected metric data: Zr1–O1 2.186(6), Zr1–N1 2.278(13), Zr1–
Cp 2.238, O1–C1 1.285(14), C1–S1 1.586(12), C1–C2 1.454(17); O1–Zr1–O1
136.9(4), O1–Zr1–N1 68.5(2), Cp–Zr1–O1 98.00, Cp–Zr1–N1 114.34, O1–C1–S1
137.7(13).
Fig. 1. Thermal ellipsoid plot of 1 (at 30% probability level. Hydrogen atoms are
omitted for clarity). Selected metric data: Ti1–O1 2.122(4), Ti1–O3 2.145(4), Ti1–N1
2.191(4), Ti1–Cp 2.080, C7–S1 1.639(6), C7–O3 1.266(7), C1–O2 1.286(7), C1–O1
1.284(7), C1–C2 1.495(9), C7–C6 1.496(8); O1–Ti1–O3 141.48(16), O1–Ti1–N1
71.40(16), O3–Ti1–N1 70.08(16), Cp–Ti1–O1 98.57, Cp–Ti1–N1 114.72, Cp–Ti1–O3
97.29, Cp–Ti–Cp0 130.52, O1–C1–O2 126.0(6), O3–C7–S1 125.5(5).
3.2. Crystal and molecular structures
Table 2
Hydrogen bonding parameters.
Complex 1 was crystallized in orthorhombic system with space
group Cmca. Molecular structure of complex 1 is depicted in Fig. 1.
Ti(IV) is bonded to the two oxygen atoms, one from carboxylate
and the other from thiocarboxylate groups and the nitrogen atom
of pyridine ring. Thus in this complex the ligand behaves as a tri-
dentate ONO donor-chelating one. The two centroids of two cyclo-
pentadienyl groups occupied fourth and fifth coordination sites of
the central titanium atom.
Complex D–Hꢂ ꢂ ꢂA
Hꢂ ꢂ ꢂA
D–Hꢂ ꢂ ꢂA
(°)
Dꢂ ꢂ ꢂA Symm. Op.
(Å)
(Å)
1
4
C–H5ꢂ ꢂ ꢂS1
C–H3ꢂ ꢂ ꢂO1
2.925
2.569
145.48
146.40
138.23
122.94
122.56
3.727 x, 1 ꢀ y, 1ꢀz
3.383 ꢀx, ꢀ1/2 + y, 1.5 ꢀ z
3.393 ꢀx, ꢀ1/2 + y, 1.5 ꢀ z
3.422 1/2 + x, 2 ꢀ y, 1/2 + z
3.359 1/2 ꢀ x, 1 ꢀ y, ꢀ1/2 + z
C–H12ꢂ ꢂ ꢂO2 2.642
C–H3ꢂ ꢂ ꢂS1
C–H7ꢂ ꢂ ꢂS1
2.826
2.766
All the bond lengths are in their usual range. Geometry around
titanium atom can be described as distorted trigonal bipyramidal
with the two centroids of cyclopentadienyl rings and nitrogen
atom of pyridine ring occupying the three equitorial sites and
two oxygen atoms placed at axial positions. Bond angles Cp–Ti–
N1 and Cp–Ti–Cp0 being 114.72° and 130.52° are slightly deviated
from ideal angle of 120° whereas angle between O1–Ti–O3
(141.48°) is highly deviated from the ideal of axial positions. Nota-
bly, the S–M–S angles in Ni(II) and Pd(II) complexes vary in the
range of 172–180°.
There are three types of intermolecular hydrogen bonds, one
between a hydrogen of the pyridine ring and the sulfur atom of
thiocarboxylate (C–Hꢂ ꢂ ꢂS 2.925 Å), second one in between a hydro-
gen of pyridine and bonded oxygen of carboxylate group (C–Hꢂ ꢂ ꢂO
2.570 Å) and another one in between hydrogen of cyclopentadienyl
ring and oxygen of carboxylate (C–Hꢂ ꢂ ꢂO 2.643 Å). The C–Hꢂ ꢂ ꢂO/S
distances and angles (Table 2) are quite comparable to those re-
ported earlier [18,36,37]. CHꢂ ꢂ ꢂS interactions of two molecules
are such that they form a couple of molecule facing each other. Be-
Fig. 2. Thermal ellipsoid plot of 2 (at 30% probability level. Hydrogen atoms are
omitted for clarity). Selected metric data: Ti1–O1 2.154(8), Ti1–N1 2.184(12), Ti1–Cp
2.101, O1–C1 1.245(14), C1–S1 1.693(17), C1–C2 1.478(19); O1–Ti1–O1 143.3(5),
O1–Ti1–N1 71.7(2), Cp–Ti1–O1 97.16, Cp–Ti1–N1 113.45, O1–C1–S1 142(3).
sides these intermolecular hydrogen bondings a p–p interaction is
also present between pyridine ring and cyclopentadienyl ring of
two molecules with a centroid–centroid distance of 3.789 Å. Due
to presence of these weak interactions molecules are arranged in
the lattice forming a 3D network in a regular geometrical pattern
(Figs. S1 and S2, Supporting information).
Complex 2 crystallized in orthorhombic system with space
group Pmn21. The molecule possesses a plane of symmetry bisect-
ing the molecule through N1–Ti1. The molecular structure is de-
picted in Fig. 2. The overall geometry of the molecule is
comparable to that of 1.
slightly different owing to the presence of CO2 and COS groups,
respectively. The 13C NMR spectrum was also consistent with the
1H NMR features. There were five signals due to the five carbon
atoms of pyrindine indicating the chemical non-equivalence of
C2/C6 and C3/C4. NMR spectral patterns of 2 and 4 are similar. In
these cases two closely spaced singlets were observed due to the
protons (and carbons in 13C spectrum) of Cp groups which may
arise due to the presence of both carboxylate and thiocarboxylate
complexes in solution. The number of signals due to pyridine ring
protons and carbons are also consistent in the respective spectra.
As mentioned already partial desulfurization was noticed in
cases of complexes 2 and 4. In the case of 2 from single crystal
X-ray diffraction studies it appeared that sulfur atoms in both

234
S. Singh, S. Bhattacharya / Inorganica Chimica Acta 395 (2013) 230–236
bands at 225, 260 nm and two broad peaks at 318 and 388 nm.
Complex 4 showed (Fig. 4b) strong absorption bands at 225, 239,
246, 260, 311and 350 nm. Besides these another broad and weak
band was observed at 462 nm. The higher energy bands may be as-
signed as inter- or intraligand charge transfer bands where as the
lower energy bands are possibly due to ligand to metal or metal
to ligand charge transfers.
For unambiguous assignment of the spectral bands TDDFT cal-
culations have been carried out. Orbitals involved in selected tran-
sitions in 1 are shown in Fig. 5. Since 4 is a mixture containing both
carboxylate and thiocarboxylate ligands we have carried out calcu-
lations for both and the orbitals involved in selected transitions are
shown in Fig. 6a and b, respectively. From TDDFT calculations it’s
clear that higher energy band in both the cases of 1 and 4 are
due to transitions of ligand to metal and interligand charge transfer
transitions where as lower energy bands are due to inter/intrali-
gand charge transfer transitions.
3.4. Emission spectra
Emission spectrum of complex 1 recorded in solid state (Fig. 7).
It showed two strong emission bands at 408 and 528 nm when ex-
cited at 385 nm. Emission at 408 nm may be due to interligand
charge transfers however comparatively lower energy emission
band at 528 nm due to admixing of MLCT and ILCT. Conversely, 4
did not show any emission in this range.
3.5. Nonlinear optical properties
The nonlinear optical property of 1 and 4 (with thiocarboxy-
late form of ligand) was calculated by double numerical
differentiation of energies (finite-field perturbation method).
Fig. 4. Absorption spectra of (a) 1 (2 ꢃ 10ꢀ5 M) and (b) 4 (4 ꢃ 10ꢀ5 M).
the thiocarboxylate have 19% occupancy whereas in case of 4
(Fig. 3) sulfur atoms have 30% occupancy. Notably the elemental
analyses also suggested partial desulfurization to the extent of
51% in the latter. Crystals obtained from different batches also
showed similar composition. The molecular structures of 2 and 4
are quite similar.
There are two types of intermolecular hydrogen bonds in 4, one
between hydrogen of pyridine ring and sulfur and other in be-
tween hydrogen of cyclopentadienyl ring and sulfur (Table 2). Be-
sides these hydrogen bonds a
p–p interaction is also present
between pyridine ring and cyclopentadienyl ring of two molecules
with a centroid–centroid distance of 3.779 Å. Due to presence of
these interactions molecules are arranged along c-axis forming a
sheet (Fig. S3, Supporting information).
Complex 3 was crystallized in monoclinic system with space
group P21 and crystal data are given in Table 1. Since the molecular
structure has already been reported [38] earlier we refrain from
giving any further details of it. However, the earlier reported struc-
ture was solved in the space group P43212.
3.3. Electronic absorption spectra
Electronic absorption spectra of both 1 and 4 were recorded in
chloroform solution. Complex 1 showed (Fig. 4a) strong absorption
Fig. 5. Selected molecular orbitals for 1 (orbital contour value = 0.05).

S. Singh, S. Bhattacharya / Inorganica Chimica Acta 395 (2013) 230–236
235
Fig. 6. Selected molecular orbitals for 4 (orbital contour value = 0.05). (a) In pure carboxylate form and (b) in pure thiocarboxylate form.
Table 3
Calculated dipole moments and hyperpolarizabilities of 1 and 4.
System
l
bx
by
bz
b0
pNA
1
4
7.53
0.74
0.56
ꢀ13.70
0.03
1240.71
ꢀ2.99
0.04
0.82
2122.99
13.72
10.74
11.14
79.01
ꢀ1288.78
bx ¼ bxxx þ bxyy þ bxzz
¼ bzzz þ bzxx þ bzyy
;
by ¼ byyy þ byxx þ byzz
;
andbz
:
The solvent parameters used were those of chloroform. The b0
value calculated for one molecule of 1 and 4 (considering sulfur
containing pdtc ligand in the case of 4) was found to be
10.74 ꢃ 10ꢀ30 and 11.14 ꢃ 10ꢀ30 esu, respectively in chloroform,
which is less than p-nitroaniline (pNA, Table 3).
4. Conclusion
Fig. 7. Emission spectrum of 1 in solid state.
The organometallic complexes [Cp2Ti(SCOPyCO2)], [Cp2-
Ti(SCO)2Py] and [Cp2Zr(SCO)2Py] have been synthesized. Complex
[Cp2Ti(SCOPyCO2)] was formed when desulfurization (possibly in
the form of H2S) of one of the thiocarboxylate groups occurred dur-
ing the synthesis resulting in a carboxylate group. Similar desulfur-
ization was also observed in the case of complexes [Cp2Ti(SCO)2Py]
and [Cp2Zr(SCO)2Py] but it was partial and from both the
thiocarboxylate entities. Bonding of the thiocarboxylate groups in
both complexes is primarily through the oxygen atoms. Complexes
[Cp2Ti(SCO)2Py] and [Cp2Zr(SCO)2Py] are the first example of a me-
tal complex in which some of the molecules have changed from
their original composition to a new one in the same lattice.
Hyperpolarizability is given by the coefficients in the Taylor ser-
ies expansion of the energy in the external electric field [39]. If
the external electric field is weak and homogeneous the expan-
sion is (Eq. (1)).
E ¼ E0 ꢀ laFa ꢀ 1=2aabFaFb ꢀ 1=6ba FaFbFc
ð1Þ
b
c
In which E0 is the energy of unperturbed molecules, F is the
a
field of origin, and la
,
aab, and b
are the components of dipole
a
bc
moment, polarizability, and first hyperpolarizability, respectively.
The mean first hyperpolarizabilty is defined as shown in Eq. (2)
[40].
Acknowledgments
1=2
b0 ¼ ðb2x þ b2y þ b2z Þ
ð2Þ
The authors are grateful to Dr. G.J. Sanjayan, National Chemical
Laboratory, Pune, India for the elemental analysis of one of the
in which the bx, by, and bz components can be described by

236
S. Singh, S. Bhattacharya / Inorganica Chimica Acta 395 (2013) 230–236
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