Synthesis, optical nonlinearity and crystal structure of a novel mixed-chalcogen, thiolato-bridged complex [(η5-C5H5)2Mo 2(μ-S)(μ-Te)(μ-SPh)2]

Article abstract of DOI:10.1016/S0022-328X(99)00648-8

A novel dimolybdenum complex in which the metal atoms are bridged by two different chalcogens and two thiolato ligands has been synthesised and structurally characterised. This complex shows a large third-order optical nonlinearity as measured by degenerate four-wave mixing with picosecond excitation at 532 nm. A hyperpolarisability (γ) of 1.2×10^-30 esu has been obtained. The structure of the complex was established by the single-crystal X-ray diffraction method. It consists of a Mo-Mo unit, which is bridged by one S, one Te and two (SPh) groups. Each Mo atom also has a (η⁵-C₅H₅) group attached to it.

Full text of DOI:10.1016/S0022-328X(99)00648-8

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 595 (2000) 140–144
Synthesis, optical nonlinearity and crystal structure of a novel
mixed-chalcogen, thiolato-bridged complex
[(h5-C5H5)2Mo2(m-S)(m-Te)(m-SPh)2]
Pradeep Mathur a,*, Sanjukta Ghose a, Rajiv Trivedi a , Michael Gelinsky b,
Michael Rombach b, Heinrich Vahrenkamp b , Sudeep Banerjee c, Reji Philip c,
G. Ravindra Kumar c
a Chemistry Department, Indian Institute of Technology, Powai, Bombay 400 076, India
b Institut fu¨r Anorganische und Analytische Chemie, Uni6ersita¨t Freiburg, Albertstrasse 21, D-79104 Freiburg, Germany
c Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400 005, India
Received 11 May 1999; received in revised form 8 July 1999
Abstract
A novel dimolybdenum complex in which the metal atoms are bridged by two different chalcogens and two thiolato ligands has
been synthesised and structurally characterised. This complex shows a large third-order optical nonlinearity as measured by
degenerate four-wave mixing with picosecond excitation at 532 nm. A hyperpolarisability (k) of 1.2×10−30 esu has been
obtained. The structure of the complex was established by the single-crystal X-ray diffraction method. It consists of a Mo–Mo
unit, which is bridged by one S, one Te and two (SPh) groups. Each Mo atom also has a (h5-C5H5) group attached to it. © 2000
Elsevier Science S.A. All rights reserved.
Keywords: Molybdenum; Sulfur; Tellurium; Thiolato; Complex
nonresonant excitation [3,4]. Some of the chalcogen-
bridged clusters synthesised by us display interesting
1. Introduction
NLO properties [5].
The strategy of using certain main group elements as
bridges in cluster growth reactions has been successfully
used for obtaining a large number of transition metal,
nonmetal cluster compounds [1]. Group 16 elements
have been widely used for such purpose and the com-
pounds [Fe2(CO)6(m-EE%)] and [Fe3(CO)9(m3-E)(m3-E%)]
(E, E%=S, Se or Te) have been recognised as conve-
nient starting materials for synthesis of numerous
chalcogen bridged cluster compounds [2]. In recent
times, optical properties of some inorganic clusters have
attracted attention, both in the linear and nonlinear
regimes, not only for the fundamental aspects of optical
excitation in these materials but also due to their poten-
tial for device applications. Interest in the nonlinear
regime has stemmed from possibilities for obtaining
materials with large nonlinear susceptibilities under
Although chalcogens are now recognised to serve as
important ligands towards systematic cluster growth,
their influence as stabilising ligands is also being in-
vestigated with interest. From the thermolysis of
[Fe3(CO)9(m3-E)(m3-E%)] and [Cp2Mo2(CO)6], mixed Fe/
Mo carbonyl clusters with one to three bridging chalco-
gen ligands can be isolated [6]. One such type of cluster,
[Cp2Mo2Fe2(CO)7(m3-E)(m3-E%)], contains a tetrahedral
metal framework in which two faces are bridged by
chalcogen ligands. Our studies indicate that this cluster
undergoes fragmentation reaction under facile condi-
tions to produce chalcogen bridged dimolybdenum
compounds, [Cp2Mo2(CO)2(m-E)(m-X)] (E=S or Te,
X=O; E=Te, X=NPh) [7]. Also, we recently re-
ported that thermolysis of [Cp2Mo2Fe2(CO)7(m3-S)(m3-
Te)] with PhSH, forms the m3-hydride, m-thiolato
bridged
dichalcogenide
mixed
metal
cluster
* Corresponding author. Fax: +91-22-577-4089.
[Cp2Mo2Fe2(CO)5(m3-S)(m3-Te)(m-SPh)(m3-H)] [8].
E-mail address: mathur@ether.chem.iitb.ernet.in (P. Mathur)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00648-8

P. Mathur et al. / Journal of Organometallic Chemistry 595 (2000) 140–144
141
Scheme 1.
Transition metal complexes containing thiolato lig-
ands continue to be the focus of considerable research
activity. Mitsudo and co-workers [9,10] have reported
on the use of a thiolato complex of ruthenium,
[Cp*RuCl(m-SPh)]2, as a promising catalyst for the
transformation of sulfur-containing organic com-
pounds. The reactions of cationic class of compounds
Mo(IV)/sulfide clusters containing Mo and a Group 8
metal are particularly interesting as models for hy-
drodesulfurisation (HDS) catalysts. Moreover, there is
a continuing importance of molybdenum complexes
containing thiolate, thioether or sulfide as models for
the molybdenum centre in nitrogenase [11–13]. Re-
cently, Baker et al. [14] have reported on the synthesis
and crystallographic characterisation of a series of new
16-electron dithiolate complexes [W(SPh)2(CO)2(PEt3)2]
and [M{S(CH2)nS}(CO)2(PEt3)2] (M=Mo or W, n=2;
M=W, n=3). In continuation of our interest in the
synthesis of chalcogen-bridged species, we report here
on the synthesis and structure of a dimolybdenum
compound containing different bridging chalcogens and
thiolato bridges.
Fig. 1. Molecular structure of Cp2Mo2(m-S)(m-Te)(m-SPh)2 (1).
,
length of 2.6263(18) A is slightly longer than the Mo–
Mo bond distances in Cp2Mo2S4 derivatives, which are
,
normally in the range 2.59–2.61 A [15], but is compara-
,
ble with the metal–metal distance of 2.635(1) A in
[(CpMo)2(S2CH2)-(S2CCH3)Br] [16]. It is, however,
shorter than the Mo–Mo bond distance in the pre-
cursor
[Cp2Mo2Fe2(CO)5(m3-S)(m3-Te)(m-SPh)(m3-H)]
,
(2.669(1) A) or in [Cp2Mo2Fe2(CO)7(m3-S)(m3-Te)]
(2.783(1) A) and is considerably shorter than the bond
distance of 3.073(1)
,
,
A
observed in [{CpMo-
(S)(S2C6H5)}]2 [6,8]. The Mo–Mo bond length in 1 is
longer than the MoꢀMo double-bonded distances re-
ported for the trans/anti and trans/syn isomers of (h5-
,
RC5H4)2M2(CO)2(m-SePh)2 (2.609(1) and 2.598(1) A,
respectively) [17], as also for the trans/anti and trans/
syn isomers of Cp2Mo2(CO)2(m-SPh)2 (2.616(2) and
2. Results and discussion
2.1. Synthesis and characterisation of
[Cp2Mo2(v-S)(v-Te)(v-SPh)2]
,
2.569(6) A, respectively) [18,19] and in [Mo2Cp2(m-
SMe)2(m-h2:h2-C4H2(CF3)2SCH3)](BF4) (2.604(1) A)
,
,
[20]. The average Mo–S(1)–Ph distance (2.484 A) and
,
Mo–S(2)–Ph distance (2.495 A) is comparable to other
When a benzene solution containing [Cp2Mo2Fe2-
(CO)5(m3-S)(m3-Te)(m-SPh)(m3-H)] [8] and a large excess
of PhSH was subjected to reflux for 9 h, the new blue
compound [Cp2Mo2(m-S)(m-Te)(m-SPh)2] (1) was ob-
tained in 53% yield (Scheme 1). There was substantial
decomposition in the reaction mixtures and the fate of
any Fe-containing products is unknown.
such Mo–SR bond distances found in literature, for
,
instance, Mo–S–Me (2.411(4) A) in [Cp2Mo2(S2CH2(m-
SMe)(m-Cl))] or the average Mo–S–Me distance (2.453
A) in [CpMo(CO)2(S2CH2)(m-SMe)] or the Mo–S(Pr)i
+
,
i
,
distance (2.536 A) in [Mo2Ru2(m3-S)2(m-SPr )2(CO)4(h-
C5H5)2] [16,21]. The Mo–S and Mo–Te distances in 1
are unexceptional.
1H-NMR spectroscopy confirmed the presence of
(h5-C5H5) and (C6H5) groups in 1. Also, the presence of
tellurium was confirmed by observation of a single peak
in the 125Te-NMR spectrum. Its unambiguous struc-
tural assignment is based on a single-crystal X-ray
structure analysis.
The molecular structure of 1 is shown in Fig. 1. It
consists of a Mo–Mo unit, which is bridged by one S,
one Te and two (SPh) groups. Each Mo atom also has
a (h5-C5H5) group attached to it. The Mo–Mo bond
The formation of the blue compound, 1, may be
envisaged to occur from decarbonylation and fragmen-
tation of the parent compound under the thermolytic
conditions. Several other compounds were observed
during chromatographic work-up, but they could not
be characterised completely due to insufficient yields.
Compound 1 was also obtained by a different route
in a slightly lower yield of 34% together with the parent
compound [Cp2Mo2Fe2(CO)5(m3-S)(m3-Te)(m-SPh)(m3-

142
P. Mathur et al. / Journal of Organometallic Chemistry 595 (2000) 140–144
than those reported for other frequently cited, promis-
ing materials like phthalocyanine, for which DFWM
data under nonresonant excitation are available [23,24].
Among clusters, compound 1 has hyperpolarisability
that is four orders of magnitude larger than the well
known fullerene, C60, data for which were obtained
under similar nonresonant excitation conditions.
It is worthwhile comparing the magnitude of nonlin-
earity of compound 1 with that of the starting materials
from which it was synthesised (Table 1). It is evident
that the nonlinearity in either starting material is an
order of magnitude lower than in the final compound 1.
The large nonresonant third-order hyperpolarisability
of 1 indicates that it is a promising nonlinear optical
material.
Fig. 2. DFWM signal variation with pump pulse energy. The solid
curve is a cubic polynomial fit to the data. The inset shows the linear
absorption spectrum of 1.
3. Experimental
3.1. General procedures
Table 1
All reactions and other manipulations were carried
out using standard Schlenk techniques under an inert
atmosphere of argon. All solvents were deoxygenated
immediately prior to use. Infrared spectra were
recorded on an Impact 400 FTIR spectrophotometer,
as hexane solutions in 0.1 mm path length cells. Ele-
mental analysis was performed using a Carlo–Erba
Comparison of the nonlinear response of the clusters
Cluster
Absorption
coefficient
(cm−1) at
532 nm
k (molecular
hyperpolarisability)
(esu)
Cp2Mo2(m-S)(m-Te)(m-SPh)2 (1)
Cp2Mo2Fe2STe(m-SPh)(m3-H)(CO)5 1.05
Cp2Mo2Fe2STe(CO)7
C60 (Ref. [26])
0.24
1.21×10−30
5.31×10−31
3.64×10−31
1
automatic analyser. H- and 125Te-NMR spectra were
1.3
recorded on a Varian VXR-300S spectrometer in
CDCl3. The operating frequency for 125Te-NMR spec-
trum was 94.705 MHz with a pulse width of 9.5 ms and
a delay of 1 s. The spectrum was referenced to Me2Te
(l=0). The starting materials [Cp2Mo2Fe2-(CO)5(m3-
S)(m3-Te)(m-SPh)(m3-H)] and [Cp2Mo2Fe2STe(CO)7]
were prepared as reported in literature [8,6]. Thiophe-
nol was purchased from Fluka and used as such.
6 (at 1064 nm) 3×10−34
H)] (yield 41%) when
[Cp2Mo2Fe2(CO)7(m3-S)(m3-Te)] and a large excess of
PhSH was subjected to reflux for 9 h.
a
benzene solution of
2.2. Nonlinear optical properties of 1
3.2. Reaction of [Cp2Mo2Fe2(CO)5(v3-S)(v3-Te)-
(v-SPh)(v3-H)] with PhSH
We find the value of 3 for compound 1, as measured
using the degenerate four-wave mixing (DFWM) tech-
nique [22] to be large. Fig. 2 shows the DFWM signal
at 532 nm as a function of input pulse energy. The inset
in the Figure shows the linear absorption spectrum. It
is evident that there is insignificant absorption at 532
nm and hence the nonlinearity is mainly nonresonant.
The DFWM signal shows the expected cubic depen-
dence on the energy of one of the pump pulses. From
these data, and taking the refractive indices of n-hexane
A benzene solution of [Cp2Mo2Fe2(CO)5(m3-S)(m3-
Te)(m-SPh)(m3-H)] (0.80 g, 0.095 mmol) and PhSH (0.4
ml, 3.6 mmol) was refluxed with constant stirring for 9
h. The solvent was removed in vacuo and the residue
was subjected to chromatographic work-up using silica
gel TLC plates. On elution with hexane–benzene mix-
ture (50:50, v/v), compound 1 was separated (36.1 mg,
53%), together with unreacted [Cp2Mo2Fe2(CO)5(m3-
S)(m3-Te)(m-SPh)(m3-H)] and some other compounds
that could not be characterised completely due to in-
sufficient yields. IR for 1 [hexane, w cm−1]: 1523 (m,
br), 1465 (m, br), 1383 (sh), 1231 (vs), 1225 (vs), 1202
(vs), 1024 (m, br), 930 (s), 913 (vs), 806 (s), 767 (vs), 725
3
and CS2 to be 1.372 and 1.628, respectively, a  of
4.5×10−13 esu was obtained for 1. From this value
and the concentration of the solution, the molecular
hyperpolarisability k was found to be 1.21×10−30 esu.
This value is at least one order of magnitude larger
1
(vs). H-NMR [CDCl3]: l 6.51 (s, C5H5), 6.92–6.94 (m,

P. Mathur et al. / Journal of Organometallic Chemistry 595 (2000) 140–144
143
C6H5). 125Te-NMR [CDCl3]: l 761. Anal. Calc. for
C22H20Mo2S3Te·CH2Cl2: C, 36.8; H, 3.10. Found: C,
36.5; H, 3.34%.
ꢀ–2q-scan mode using graphite monochromatised
Mo–Ka radiation, 4710 were independent (Rint
=
0.0746). These data were corrected empirically for ab-
sorption (with maximum 0.5071 and minimum 0.3543
transmission). Hydrogen atoms were fixed on calculated
positions. Full-matrix least-squares refinement, based
on F2, of the positional, isotropic, and anisotropic
thermal parameters converged at R1=0.0640 (wR2=
0.1404) for 2432 data with I=2|(I) and R1=0.1810
(wR2=0.1848) for all data. Despite correction for ab-
sorption there are still some rest electron residues near
the heavy atoms Te and Mo1 and Mo2. Solution of the
structure was performed using direct methods and
refinement carried out by least-squares procedures.
SHELXS-86 and SHELXL-97 were used as the computing
systems. Selected bond lengths and bond angles for 1
are given in Table 2.
3.3. Thermolysis of [Cp2Mo2Fe2(CO)7(v3-S)(v3-Te)]
with PhSH
A benzene solution (50 ml) of [Cp2Mo2Fe2(CO)7(m3-
S)(m3-Te)] (0.15 g, 0.19 mmol) and thiophenol (0.4 ml,
3.6 mmol) was refluxed with constant stirring for 9 h.
The solvent was removed in vacuo and the residue was
subjected to chromatographic work-up using silica gel
TLC plates. Using hexane–benzene (50:50, v/v) mixture
as eluent, the new blue compound [Cp2Mo2(m-S)(m-
Te)(m-SPh)2] (1) (0.046 g, 34%) could be isolated to-
gether with the red [Cp2Mo2Fe2-(CO)5(m3-S)(m3-Te)-
(m-SPh)(m3-H)] (0.066 g, 41%).
3.4. Structural characterisation of 1
3.5. Study of nonlinear optical properties of 1
Crystal data: C22H20Mo2S3Te.H2O, monoclinic, P21/
DFWM measurements were performed with 35 ps
pulses at 532 nm provided by an Nd–YAG laser at a
repetition rate of 10 Hz. The standard backward
DFWM geometry [22,25], with strong, equal intensity,
counterpropagating pump beams and a weak probe
beam, was adopted. The beams were focused to ap-
proximately 3 mm diameter spots on the sample. The
emitted signal was steered and collected 2 m away from
the sample, to eliminate background optical noise. The
signal was measured by a sensitive photodiode (Hama-
matsu) and fed to a digital storage oscilloscope (Tek-
tronix TDS320). A part of the input laser beam was
split off and measured by a similar photodiode, to
monitor the input laser energies as well as the fluctua-
tions in them. Both input and emitted light signals were
typically averaged over 100 pulses to obtain each data
point. The sample dissolved in n-hexane, was contained
in an optically polished cuvette of 1 mm path length
and its concentration was 2.2×10−4 M giving a linear
transmission of 95%. The solvent did not produce any
signal under the conditions of our experiment. The
,
c, a=10.938(2), b=10.926(2), c=20.337(4) A, i=
3
,
,
99.24(3)°, U=2398.9(8) A , wavelength=0.71073 A,
Z=4, v(Mo–Ka)=2.510 mm−1, Dcalc=1.988 Mg
m,−3 number of reflections collected/unique=4849/
4710. Dark-blue crystals of 1 were grown from
dichloromethane–hexane solvent mixtures at −5°C. A
dark-blue opaque single crystal was mounted using glue
to a thin glass fibre. Diffraction data were collected on
Nonius Turbo CAD4 four-circle diffractometer. Of a
total of 4849 data collected in the q-range of 2.65–
26.0°, (−13BhB13, −13BkB0, −25BlB0) in
Table 2
,
Selected bond distances (A) and bond angles (°) for 1
Bond distances
Mo(1)–S(1)
Mo(2)–S(1)
Mo(1)–S(3)
Mo(1)–Te
Mo(1)–Mo(2)
S(2)–C(17)
2.480(4)
2.485(4)
2.331(4)
2.702(2)
2.626(2)
1.80(2)
Mo(1)–S(2)
Mo(2)–S(2)
Mo(2)–S(3)
Mo(2)–Te
S(1)–C(1)
2.499(4)
2.490(4)
2.322(4)
2.700(2)
1.81(2)
3
signals were calibrated with respect to CS2 whose  is
Bond angles
taken to be 1.62×10−12 esu [22].
S(3)–Mo(1)–S(1)
S(1)–Mo(1)–S(2)
S(1)–Mo(1)–Mo(2)
S(3)–Mo(1)–Te
S(1)–Mo(1)–Te
S(3)–Mo(2)–S(1)
S(1)–Mo(2)–S(2)
S(1)–Mo(2)–Mo(1)
S(3)–Mo(2)–Te
S(2)–Mo(2)–Te
Mo(1)–Mo(2)–Te
C(1)–S(1)–Mo(1)
76.32(13) S(3)–Mo(1)–S(2)
115.64(14) S(3)–Mo(1)–Mo(2)
58.15(10) S(2)–Mo(1)–Mo(2)
116.35(10) Mo(2)–Mo(1)–Te
71.21(10) S(2)–Mo(1)–Te
76.39(13) S(3)–Mo(2)–S(2)
115.79(13) S(3)–Mo(2)–Mo(1)
57.98(10) S(2)–Mo(2)–Mo(1)
116.75(10) S(1)–Mo(2)–Te
72.05(10) Mo(1)–S(1)–Mo(2)
75.52(13)
55.48(9)
58.08(10)
60.88(5)
71.89(10)
75.84(14)
55.80(10)
58.40(10)
71.18(10)
63.86(10)
58.17(4)
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 119753 for compound 1.
Copies of the information may be obtained free of
charge from The Director, CCDC, 12, Union Road,
Cambridge CB2 1EZ, UK (fax: +44-1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.
cam.ac.uk).
60.95(5)
116.5(5)
Mo(2)–Te–Mo(1)
C(1)–S(1)–Mo(2)
108.3(5)
C(17)–S(2)–Mo(2) 113.4(6)
Mo(2)–S(2)–Mo(1) 63.52(10) Mo(2)–S(3)–Mo(1)
C(17)–S(2)–Mo(1) 111.3(6)
68.73(10)

144
P. Mathur et al. / Journal of Organometallic Chemistry 595 (2000) 140–144
[8] P. Mathur, S. Ghose, M.M. Hossain, C.V.V. Satyanarayana,
Acknowledgements
J.E. Drake, J Organomet. Chem. 557 (1998) 219.
[9] (a) K. Fujita, M. Ikeda, T. Kondo, T. Mitsudo, Chem. Lett.
(1997) 57. (b) U. Koelle, C.R. Tjoe, T. Wagner, U. Englert,
Organometallics 14 (1995) 703. (c) T. Kondo, N. Suzuki, T.
Okada, T. Mitsudo, J. Am. Chem. Soc. 119 (1997) 6187. (d) T.
Kondo, N. Hiraishi, Y. Morisaki, K. Wada, Y. Watanabe, T.
Mitsudo, Organometallics 17 (1998) 2131.
Grateful acknowledgement is due to the Commission
of the European Community for support through a
joint research grant to P.M. and H.V. S.G. would like
to thank the Council for Scientific and Industrial Re-
search, Government of India, for the award of a Senior
Research Fellowship. We are also grateful to Dr Udo
Brand and A. Tro¨sch for assistance with
crystallography.
[10] T. Kondo, S. Uenoyama, K. Fujita, T. Mitsudo, J. Am. Chem.
Soc. 121 (1999) 482.
[11] J. Kim, D.C. Rees, Science 257 (1992) 1677.
[12] W.H. Orme-Johnson, Science 257 (1992) 1639.
[13] J. Kim, D.C. Rees, Nature (London) 360 (1992) 553.
[14] P.K. Baker, A.I. Clark, M.G.B. Drew, M.C. Durrant, R.L.
Richards, Inorg. Chem. 38 (1999) 821.
[15] W.K. Miller, R.C. Haltiwanger, M.C. VanDerveer, M.
Rakowski DuBois, Inorg. Chem. 22 (1983) 2973.
[16] (a) D.E. Coons, R.C. Haltiwanger, M. Rakowski Dubois,
Organometallics 6 (1987) 2417. (b) D.S. Tucker, S. Dietz, K.G.
Parker, V. Carperos, J. Gabay, B. Noll, M. Rakowski Dubois,
Organometallics 14 (1995) 4325.
[17] L.-C. Song, J.-Q. Wang, Q.-M. Hu, R.-J. Wang, T.C.W. Mak,
Inorg. Chim. Acta 256 (1997) 129.
[18] S.E. Nefedov, A.A. Pasynskii, I.L. Eremenko, G.A. Papoyan,
L.I. Rubinshtein, A.I. Yanovskii, Y.u.T. Stuchkov, Zh. Neorg.
Khim. 38 (1993) 76.
[19] I.B. Benson, S.D. Killops, S.A.R. Knox, A.J. Welch, J. Chem.
Soc. Chem. Commun. (1980) 1137.
[20] J.-F. Capon, P. Schollhammer, F.Y. Pe´tillon, J. Talarmin,
Organometallics 18 (1999) 2055.
[21] H. Adams, N.A. Bailey, S.A. Gay, L.J. Gill, T. Hamilton, M.J.
Morris, J. Chem. Soc. Dalton Trans. (1996) 2403.
[22] R. Fisher ((Ed.), Optical Phase Conjugation, Academic Press,
New York, 1983.
[23] J.S. Shirk, J.R. Lindle, F.J. Bartoli, Z.H. Kafafi, A.W. Snow, in:
S.R. Marder, J.E. Sohn, G.D. Stucky (Eds.), Materials for
Nonlinear Optics — Chemical Perspectives, ACS Symposium
Series, 455, American Chemical Society, Washington DC, 1991,
p. 629.
References
[1] P. Mathur, Adv. Organomet. Chem. 41 (1997) 243.
[2] (a) K.H. Whitmire, J. Coord. Chem. 17 (1988) 95. (b) L.C. Roof,
J.W. Kolis, Chem. Rev. 32 (1993) 1037. (c) P. Mathur, D.
Chakrabarty, M.M. Hossain, R.S. Rashid, V. Rugmini, A.L.
Rheingold, Inorg. Chem. 31 (1992) 1106. (d) P. Mathur, M.M.
Hossain, S.B. Umbarkar, C.V.V. Satyanarayana, S.S. Tavale,
V.G. Puranik, Organometallics 14 (1995) 959.
[3] (a) S. Shi, W. Ji, S.H. Tang, J.P. Lang, X.Q. Xin, J. Am. Chem.
Soc. 116 (1994) 3615. (b) S. Shi, W. Ji, S.H. Tang, J.P. Lang,
X.Q. Xin, J. Phys. Chem. 98 (1994) 3750.
[4] W. Ji, S. Shi, H.J. Du, P. Ge, S.H. Tang, X.Q. Xin, J. Phys.
Chem. 99 (1995) 17297.
[5] (a) S. Banerjee, G.R. Kumar, P. Mathur, P. Sekar, Chem.
Commun. (1997) 299. (b) P. Mathur, S. Ghose, M.M. Hossain,
C.V.V. Satyanarayana, S. Banerjee, G.R. Kumar, P.B. Hitch-
cock, J.F. Nixon, Organometallics 16 (1997) 3815. (c) P. Mathur,
S. Ghose, M.M. Hossain, C.V.V. Satyanarayana, R.K. Chadha,
S. Banerjee, G.R. Kumar, J. Organomet. Chem. 568 (1998) 197.
[6] (a) P. Mathur, M.M. Hossain, S.B. Umbarkar, C.V.V. Satya-
narayana, A.L. Rheingold, L.M. Liable-Sands, G.P.A. Yap,
Organometallics 15 (1996) 1898. (b) P. Mathur, S. Ghose, M.M.
Hossain, C.V.V. Satyanarayana, M.F. Mahon, J. Organomet.
Chem. 543 (1997) 189.
[24] R. Philip, G.R. Kumar, M. Ravikanth, unpublished results.
[25] G.R. Kumar, F.A. Rajgara, S. Rangwala, Chem. Phys. Lett. 245
(1995) 287.
[26] Z.H. Kafafi, J.R. Lindle, R.G.S. Pong, F.J. Bartoli, L.J. Lingg,
J. Milliken, Chem. Phys. Lett. 188 (1992) 492.
[7] (a) P. Mathur, S. Ghose, M.M. Hossain, P.B. Hitchcock, J.F.
Nixon, J Organomet. Chem. 542 (1997) 265. (b) P. Mathur, S.
Ghose, M.M. Hossain, H. Vahrenkamp, J. Organomet. Chem.
538 (1997) 185.
.
.