| Summary: | 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 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 (Sni and Sno) 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 carboxylate groups which exhibit μ2 (–COOi) and μ1 (–COOo) coordination modes, respectively. In summary, the following sequence of distances [mean values] is found: d(Sno—Oμ3)eq [2.024 (2) Å] < d(Sni—Oμ3)eq [2.044 (2) Å] < d(Sni—Oμ3)ax [2.158 (6) Å] < d(Sno—Oμ1-carb)ax [2.182 (6) Å] < d(Sni—Oμ2-carb)ax [2.250 (2) Å] ≃ d(Sno—Oμ2-carb)ax [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 molecule which exhibit gauche–anti and anti–gauche conformations. Weak intramolecular Sn...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...H—C interactions of which a nearly linear very short C—H...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).
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