Crystal structure of bis(benzoato-κO)dibutyltin(IV), nBu2Sn(bzo)2

The title compound, [Sn(C4H9)2(C6H5COO)2], was synthesized in order to study the interaction between di-n-butyltin(IV) oxide and some carboxylic acids. Di-n-butyltin(IV) dibenzoate, nBu2Sn(obz)2, exhibits the same structural features as other diorganotin(IV) dibenzoates characterized by an unsymmetrical bidentate bonding mode [Δ(Sn—O) ≃ 0.4 Å] of the two benzoate groups to tin.


Chemical context
Organotin(IV) complexes have been studied extensively because of the diversity of structures that such compounds can form and their potential biological activities as well as their wide industrial and agricultural applications (Davies & Smith, 1982). As part of our interest in this type of complex (Corté s et al., 2011), we describe here the synthesis of the di-n-butyltin(IV) title complex with benzoic anions as ligands. The structures of some di-n-butyltin carboxylates have been reported previously by Kemmer et al. (2000) and Win et al. (2015). ISSN 2056-9890

Structural commentary
The asymmetric unit of the title compound ( Fig. 1) Allen et al. (1987), the somewhat shorter C-C bonds of the first n-butyl group are strongly influenced by some larger anisotropic displacement ellipsoids of the carbon atoms as a result of thermal motion or unresolved static disorder. Bond angles at the carbon atoms of the n-butyl groups range from 114.1 (2)-115.0 (3) , and 114.0 (2)-116.0 (2) , respectively. The two n-butyl groups, however, adopt different conformations: anti-gauche [166.0 (2)-63.9 (4) ] for the first one [n = 1] and gauche-gauche [65.0 (3)-56.3 (3) ] for the second one [n = 2], both with respect to the Cn11-Cn12 and Cn12-Cn13 bonds.
The two carboxylate ligands coordinate to the Sn IV atom asymmetrically. One oxygen atom of each carboxylate group reveals a very strong/short Sn-O bond of 2.122 (17) and 2.1405 (16) Å , respectively, which are of similar strength as the Sn-C bonds. With respect to these four strong bonds, the coordination polyhedron at the tin atom is compressed to a tetragonal disphenoid (Fig. 2) with a bond angle of 148.2 (1) between the two -carbon atoms of the n-butyl groups and of 82.01 (6) between the two oxygen atoms of the benzoate groups. On the carboxylate side, the corresponding C-O bonds are long The phenyl groups are almost planar with mean C-C bond lengths of 1.387 (5) Å and bond angles of 120.0 (5) . Again, the bond lengths are in good agreement with the literature data (Allen et al., 1987) of 1.387 (10) Å for C ar -C ar . The phenyl rings subtend dihedral angles of 6.7 (2) and 6.4 (3) with the planes formed by the three atoms of the carboxylate groups, while the dihedral angle between the phenyl rings is 17.7 (1) . As usual, the C-C single bonds between the carboxylate and phenyl groups are somewhat shorter [1.489 (3), 1.487 (3) Å ] than the C-C single bonds between sp 3 -hybridized carbon atoms (see above). The asymmetric unit of the title compound, showing the atom-labeling scheme and displacement ellipsoids for the non-H atoms at the 50% probability level.

Figure 2
Polyhedron model of the coordination sphere of the tin atom; n-butyl groups have been omitted for clarity, weak SnÁ Á ÁO interactions are indicated by dashed lines. Displacement ellipsoids are shown at the 50% probability level.

Supramolecular features
Besides the described intramolecular Sn-O interactions responsible for the distorted octahedral coordination of the tin atom, some weak intermolecular SnÁ Á ÁO interactions of 2.943 (2) Å exist and lead to the formation of centrosymmetric dimers and hence the coordination sphere of the tin atom is expanded from six, octahedral to seven, pentagonal-biypramidal (Fig. 3). Once the coordination sphere of the tin atom is completed, the solid-state packing of these dimers is due exclusively to intermolecular OÁ Á ÁH-C contacts [O11Á Á ÁH23 i = 2.64 Å ; symmetry code: (i) 1 À x, 1 À y, 1 À z] and van der Waals interactions (Fig. 4), respectively, whilestacking can be excluded (Fig. 5).

Synthesis and crystallization
The title compound was obtained by reacting 0.300 g (1.2 mmol) of di-n-butyltin oxide with 0.94 g (2.4 mmol) of benzoic acid in ethanol under reflux for 3.5 h. Colourless crystals suitable for X-ray analysis were grown by slow solvent evaporation. Elemental analysis calculated/found (  C-HÁ Á ÁO interactions (blue dashed lines) between neighboring dimers responsible for their chain-shaped arrangement along the a axis.

Figure 5
Perspective view of the crystal structure of the title compound viewed down the a axis.

Crystal data
[Sn(C 4 H 9 ) 2 (C 7 H 5 O 2 ) 2 ] M r = 475.13 Monoclinic, P2 1 /c a = 11.6801 (5)  Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.