Bis(μ-benzoato-κ²O:O')bis-(benzoato-κO)octabutyldi-μ₃-oxido-tetra-tin(IV)

The asymmetric unit of the title compound, [{Sn(C₄H₉)₂(C₆H₅COO)}₂O]₂, consists of two half molecules, completed by application of inversion symmetry. Both mol-ecules adopt a ladder structure typical for this class of dimeric tetra-organodistannoxane di-carboxyl-ates 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 and Sn ) are trigonal-bipyramidally coordinated. The bond angles between the n-butyl groups are widened [135.64 (7)-146.20 (7)°] 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 carboxyl-ate groups which exhibit μ₂ (-COO ) and μ₁ (-COO ) coordination modes, respectively. In summary, the following sequence of distances [mean values] is found: d(Sn -Oμ₃) [2.024 (2) Å] < d(Sn -Oμ₃) [2.044 (2) Å] < d(Sn -Oμ₃) [2.158 (6) Å] < d(Sn -Oμ₁-carb) [2.182 (6) Å] < d(Sn -Oμ₂-carb) [2.250 (2) Å] ≃ d(Sn -Oμ) [2.247 (12) Å]. The n-butyl groups adopt an anti-anti conformation with exception of two disordered outer n-butyl groups of the second mol-ecule which exhibit gauche-anti and anti-gauche conformations. Weak intra-molecular Sn⋯O inter-actions 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 octa-hedral coordination at these Sn atoms. Inter-molecular inter-actions between the individual mol-ecules are restricted to van der Waals and O⋯H-C inter-actions of which a nearly linear very short C-H⋯O contact between the H atom of the phenyl group of one of the mol-ecules 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 mol-ecules along [111]. The two n-butyl groups attached to the outer Sn atom of one mol-ecule are disordered over two sets of sites with occupancies of 0.806 (3)/0.194 (3) and 0.702 (3)/0.298 (3).