Bis(μ-benzoato-κ(2) O:O′)bis­(benzoato-κO)octabutyldi-μ(3)-oxido-tetra­tin(IV)

The asymmetric unit of the title compound, [{Sn(C(4)H(9))(2)(C(6)H(5)COO)}(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)°] in comparison with an ideal trigonal bipyramid. Sn—O bond lengths within the {R (2)SnO(3)} 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 μ(2) (–COO(i)) and μ(1) (–COO(o)) coordination modes, respectively. In summary, the following sequence of distances [mean values] is found: d(Sn(o)—Oμ(3))(eq) [2.024 (2) Å] < d(Sn(i)—Oμ(3))(eq) [2.044 (2) Å] < d(Sn(i)—Oμ(3))(ax) [2.158 (6) Å] < d(Sn(o)—Oμ(1)-carb)(ax) [2.182 (6) Å] < d(Sn(i)—Oμ(2)-carb)(ax) [2.250 (2) Å] ≃ d(Sn(o)—Oμ(2)-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).