P. Singh et al. •Arsenic(III), Antimony(III) and Bismuth(III) Thiobenzoates
1481
As the size of the central atom increases the solid state (Sb - S': 3.802 A) in contrast to
an expansion of the coordination shell can
be expected as verified e. g. for the series of
compound 4b where two additional Sb -S interac-
tions with neighbouring sulfur atoms are establised
tris(ethyldithiocarbamato)arsenic, -antimony and (Sb---S 3.769 A) as depicted in Fig. 5.
-bismuth complexes. The arsenic compound is a
molecular compound with C3 point group sym-
metry [29] while in the antimony and bismuth
complexes weak intermolecular metal sulfur con-
tacts are established expanding the coordination
to a dodecahedron [31]. Although the molecular
symmetry of Bi(SOC-/?-Tol)3 is comparable to that
of Bi(S2CNEt2)3, the intermolecular interaction is
quite different since the stacking of the molecules
leads to a trigonal prism for the BiSö core.
One may envisage that the lone pairs of electrons
at As(III), Sb(III) and Bi(III) are directed along the
three fold axis of the molecules. However, the bond
angles S-M-S are all close to 90°, anditthusappears
that the lone pair has a high degree of s-character
and is therefore not stereochemically active.
While the molecular structure of PhSb(SOCPh)2
4b and PhSb(OSCMe)2 [10] are very similar - 4b
has somewhat longer Sb-S and C=0 bonds, while
the S-C bond lengths are identical - the main struc-
tural differences are significant Sb-O contacts in the
thioacetate (Sb -O: 2.808, 2.818(6)A), leading to a
square pyramidal geometry with an apical phenyl
The differences in the packing in the crystal are
most likely due to the greater space requirements of
the phenyl groups compared to the methyl groups
allowing a close packing of the SbS2 units.
The best molecule to be compared with 2a is
the antimony(III) thioacetate Sb(S(0 )CMe)3 [10].
Its Sb-S bonds are somewhat longer than in 2a but
shorter than in the xanthates Sb(S2COR)3 [25 - 27]
(2.511 - 2.546 A) or Sb(S2CNEt2")3 (2.57 A) [31].
It is particularly noteworthy that the intermolecu-
lar Sb- S distances are shorter than those of As-- S.
We attribute this to the particularly strong Lewis
acidic character of Sb(III) compounds compared to
As(III) compounds [11]. In the antimony(III) ac-
etate, xanthates and diethyldithiocarbamate the lig-
ands are bonded asymmetrically as in 2a. In case
of Sb(S2COMe)3 [25] there are also intermolecu-
lar Sb-S contacts which generate a dimeric unit in
contrast to the stacks of 2a.
Acknowledgements
P. S. and S. S. are grateful to the GATE-UGC and
group. These molecular units join to a dimer in CSIR, New Delhi, India respectively for fellowships.
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