Hexa-μ2-acetato-hexa-n-butylhexa-μ3-oxido-tin(IV) toluene monosolvate

The title compound, [Sn6(C4H9)6(CH3COO)6O6]·C7H8, has one half-toluene molecule and one half-organotin molecule in the asymmetric unit. The latter is situated about an inversion centre and belongs to the class of hexameric monoorganooxotin carboxylates with a hexagonal prismatic or ‘drum-like’ motif of the central tin–oxygen core. Two Sn3O3 rings in a flat-chair conformation are linked via six Sn—O bonds and six bridging acetate groups. All Sn atoms have approximate octahedral coordination geometry. The Sn—O bonds which are trans to the alkyl group are significantly shorter than the others. One butyl group is disordered over two different sites, with occupancies of 0.9:0.1. Very large atomic displacement parameters of the toluene molecule indicate an unresolvable disorder about the twofold axis.

The title compound, [Sn 6 (C 4 H 9 ) 6 (CH 3 COO) 6 O 6 ]ÁC 7 H 8 , has one half-toluene molecule and one half-organotin molecule in the asymmetric unit. The latter is situated about an inversion centre and belongs to the class of hexameric monoorganooxotin carboxylates with a hexagonal prismatic or 'drum-like' motif of the central tin-oxygen core. Two Sn 3 O 3 rings in a flatchair conformation are linked via six Sn-O bonds and six bridging acetate groups. All Sn atoms have approximate octahedral coordination geometry. The Sn-O bonds which are trans to the alkyl group are significantly shorter than the others. One butyl group is disordered over two different sites, with occupancies of 0.9:0.1. Very large atomic displacement parameters of the toluene molecule indicate an unresolvable disorder about the twofold axis.
insoluble in non-complexing organic solvents results in the formation of monoorganooxotin carboxylates with "ladder"type structures of composition (RSn) 6 O 4 (O 2 CR′) 10 (Day et al.,1988) or, more frequently, to hexanuclear compounds [RSnO(O 2 CR′)] 6 . In the latter case, the structure is dominated by a hexagonal prismatic or "drum"-like arrangement of the tin-oxygen core as was demonstrated in the case of acetates (R′ = CH 3 ) for R = i Pr (Kuan et al., 2002), R = tmsm (Beckmann et al., 2004), and R = Me (Day et al.,1988). By dissolving n-butylstannonic acid of idealized formula n BuSnO(OH) in a mixture of toluene/acetic acid and removing the resulting water by use of a Dean-Stark apparatus we were able to obtain single crystals of the corresponding R = n-butyl hexamer as the 1:1 toluene solvate, [ n BuSnO(OAc)] 6 x C 7 H 8 .
The asymmetric unit of the title compound consists of a centrosymmetric hexamer ( Fig. 1) with i at (1/4,3/4,0) and a toluene molecule of site symmetry 2. As usual for the constitution (Fig. 2) of the drum, the six-membered tin-oxygen rings forming the bases are not planar but adopt a flat chair-conformation with the torsion angles listed in Tab In summary, all tin atoms are octahedrally coordinated by the n-butyl ligand, three oxygen atoms of the drum and two oxygen atoms of two different acetate groups (Fig. 2) µ 3 -oxygen atoms within the drum. They can be subdivided into those that are trans to the organic ligand and significantly shorter [2.080 (2) -2.085 (2) Å, mean value: 2.083 (3) Å] and those that are somewhat longer arising from the corresponding cis-oriented oxygen atoms [2.0882 (2) -2.0969 (2) Å, mean value: 2.092 (4) Å]. This strengthening although less marked is similar to the static trans-strengthening observed in the case of alkyl tin halides (Buslaev et al., 1989), Reuter & Puff, 1992).
Intermolecular interactions of the cylindrical hexamers are limited to van-der-Waals ones because the accessibility of the polar tin-oxygen core is restricted (Fig. 4). As a result of these weak interactions, molecules are arranged in planar hexagonal nets ( Fig. 5a) with two different orientations of the drum (Fig. 5b). Between these nets large apolar channels with large cavities exist ( Fig. 6a) which partially are fulfilled by the solvent molecules (Fig. 6b).

Experimental
1.24 g (6 mmol) n-butylstannonic acid (Gelest, Inc.) and 0.36 g (6 mmol) glacial acetic acid (Fluka) were dissolved in 120 ml toluene. The mixture was heated under reflux for 6 h. The water formed in the reaction was removed by a Dean-Stark apparatus. The reaction mixture was filtered and the solvent evaporated overnight at room temperature. After evaporation colourless block shaped crystals was obtained. A suitable single-crystal was selected under a polarization microsope and mounted on a 50 µm MicroMesh MiTeGen Micromount TM using FROMBLIN Y perfluoropolyether (LVAC 16/6, Aldrich).

Refinement
The n-butyl group at Sn3 is statistically disordered resulting in two different conformations with occupancies 0.9/0.1. In order to get a reliable structure model carbon-carbon bonds of the minor part were restraint to a common refined value of 1.516(x) Å and their anisotropic displacement parameters fit to those of the corresponding carbon atoms of the major part. Although the hydrogen atoms of the non-disordered carbon atoms could clearly identified in difference Fourier synthesis, all were idealized and refined at calculated positions riding on the carbon atoms with C-H distances of 0.98 Å (-CH 3 ), 0.98 (-CH 2 -) and 0.95 Å (H aromatic ). Carbon atoms of the solvent molecule show high anisotropic displacement parameters as a result of high thermal motion or more probably as a result of its statistic disorder about the twofold axis giving rise to unusual bond lengths and angles.  Ball-and-stick model of title compound with the atomic numbering scheme used; with exception of the hydrogen atoms, which are shown as spheres with common isotropic radius, all other atoms are represented as thermal displacement ellipsoids showing the 50% probability level of the corresponding atom; the statistically disordered n-butyl group of Sn3 is shown in case the major (90%) one at Sn3 and in case of the minor one (10%) at Sn3 i ; symmetry code: (i) -x + 1/2, -y + 3/2, -z.      Detail of the three-dimensional arrangement of the hexameric molecules, showing the stacking of the sheets and the open space between them (above, a) and its filling by the toluene molecules (below, b).

Hexa-µ 2 -acetato-hexa-n-butylhexa-µ 3 -oxido-tin(IV) toluene monosolvate
Crystal data Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors. R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (