Bis(mu-benzoato-kappa O-2:O `)bis(benzoato-kappa O)octabutyldi-mu(3)-oxido-tetratin(IV)

Abstract

The asymmetric unit of the title compound, [{Sn(C4H9)(2)(C6H5COO)}(2)O](2), consists of two half molecules, completed by application of inversion symmetry. Both molecules adopt a ladder structure typical for this class of dimeric tetraorganodistannoxane dicarboxylates characterized by a centrosymmetric four-membered (Sn-O)(2) ring of rhomboidal shape that is extended on both sides by folded six-membered Sn-O-C rings. To a first approximation, both kinds of Sn atoms (Sn-i and Sn-o) are trigonal-bipyramidally coordinated. The bond angles between the n-butyl groups are widened [135.64 (7)-146.20 (7)degrees] in comparison with an ideal trigonal bipyramid. Sn-O bond lengths within the {R2SnO3} coordination sphere depend strongly on the position of the corresponding O atom -axial (ax) or equatorial (eq) -as well as on the functionality of the carboxylate groups which exhibit mu(2) (-COOi) and mu(1) (-COOo) coordination modes, respectively. In summary, the following sequence of distances [mean values] is found: d(Sn-o-O mu(3))(eq) [2.024 (2) angstrom] < d(S(n)i-O mu(3))(eq) [2.044 (2) angstrom] < d(Sni-O 3) ax [2.158 (6) angstrom] < d(Sno-O mu(1)-carb)(ax) [2.182 (6) angstrom] < d(Sn-i-O mu(2)-carb)(ax) [2.250 (2) angstrom] similar or equal to d(Sn-o-O mu(2)-carb)(ax) [2.247 (12) angstrom]. The n-butyl groups adopt an anti-anti conformation with exception of two disordered outer n-butyl groups of the second molecule which exhibit gaucheanti and anti-gauche conformations. Weak intramolecular Sn center dot center dot center dot O interactions between the different O atoms of the outer carboxyl groups with the inner, as well as outer, Sn atoms give rise to a strongly distorted octahedral coordination at these Sn atoms. Intermolecular interactions between the individual molecules are restricted to van der Waals and O center dot center dot center dot H-C interactions of which a nearly linear very short C-H center dot center dot center dot O contact between the H atom of the phenyl group of one of the molecules with the outer non-coordinating C=O group of the other molecule is the most prominent. It gives rise to a chain-like arrangement of the molecules along [111]. The two n-butyl groups attached to the outer Sn atom of one molecule are disordered over two sets of sites with occupancies of 0.806 (3)/0.194 (3) and 0.702 (3)/0.298 (3).