Diacetatodi-tert-butyltin(IV)

The title compound, [Sn(C4H9)2(CH3COO)2], was synthesized in order to study the influence of large organic groups on the molecular structure of diorganotin diacetates. The title compound exhibits the same structure type as other diorganotin(IV) diacetates characterized by an unsymmetrical bidentate bonding mode of the two acetate groups to tin. The influence of the t-butyl groups on this molecular structure is expressed in two significant differences: tin—carbon bond lengths are much more longer than in the other diacetates, as are the additional interactions of the acetate groups with the tin atom. Intermolecular interactions are restricted to C—H⋯O ones similar to those in the other diacetates, giving rise to a chain-like arrangement of the molecules with the tin atoms and acetate groups in the propagation plane.

The title compound, [Sn(C 4 H 9 ) 2 (CH 3 COO) 2 ], was synthesized in order to study the influence of large organic groups on the molecular structure of diorganotin diacetates. The title compound exhibits the same structure type as other diorganotin(IV) diacetates characterized by an unsymmetrical bidentate bonding mode of the two acetate groups to tin. The influence of the t-butyl groups on this molecular structure is expressed in two significant differences: tin-carbon bond lengths are much more longer than in the other diacetates, as are the additional interactions of the acetate groups with the tin atom. Intermolecular interactions are restricted to C-HÁ Á ÁO ones similar to those in the other diacetates, giving rise to a chain-like arrangement of the molecules with the tin atoms and acetate groups in the propagation plane.

Diacetatodi-tert-butyltin(IV) Martin Reichelt and Hans Reuter Comment
Diorganotin(IV) dicarboxylates, R 2 Sn(O 2 CR′) 2 , belong to the class of diorganotin compounds, R 2 SnX 2 , with univalent anions X, such as the halides (X = F, Cl, Br, I) or alkoxides (X = OR′). In contrast to these anions, that behave as unidentate substitutents, the carboxylate groups, O 2 CR′, can act via its two oxygen atoms as a bidentate ligand in a more or less symmetrical or unsymmetrical coordination mode giving rise to additional intra-or intermolecular interactions (Tiekink, 1991). In the case of diacetates, R′ = Me, this was formerly shown for R = phenyl (Alcock et al. 1992) and R = methyl (Lockhart et al. 1987, α-modification;Mistry et al. 1995, β-modification) both revealing in solid state the same molecular structure type with a strongly unsymmetrical bonding mode of the acetate groups. On this background it was interesting to see whether the larger t-butyl groups are compatible with that structure type or not.
The asymmetric unit of the title compound ( Fig. 1) consists of one formula unit with all atoms in general positions although the molecule displays a pseudo twofold rotation axis [midway C11/C21 -Sn -midway O11/O21]. In a first approximation, the tin atom is fourfold coordinated by the two t-butyl groups and an oxygen atom of each acetate group.
Both Sn-C bond lengths are almost equal as are both Sn-O bond lengths, too (see Table 1 (7)° between the t-butyl groups and 79.93 (6)° between the two oxygen atoms, the coordination polyhedron is compressed to a tetragonal disphenoid (Fig. 2).
Obviously, this distortion is typical for diacetates [C-Sn-C = 131.4°, R = Ph; 135.9 (2)°(1)°, The coordination sphere of the tin atom is completed by the other two oxygen atoms of the acetate groups that undergo a much more weaker interaction with the tin atom [d(Sn···O) = 2.689 (1) Å to O22, 2.647 (2) Å to O12], resulting in a very unsymmetrical bidentate coordination mode of the acetate groups (Fig. 2). This is also reflected in two different C-O distances for each acetate group (Table 1). Again, within the molecular structures of the other diacetates a similar coordination behaviour is observed but Sn···O interactions are considerably stronger [2.583 (4), 2.527 (5) Both t-butyl groups are well ordered with a mean value for the C-C bonds of 1.527 ( In the solid, molecules are arranged in chains with the tin atoms and acetate groups defining the propagation plane (Fig.   3). This arrangement is also characteristic for both modifications of the methyl compounds but not for the phenyl one. In the present case, the intermolecular O···Sn distances of 4.692 (1)  are so long that seems impossible that these interactions are responsible for the supra-molecular architecture. There are, however, O···HC interactions between the acetate groups and t-butyl groups of neighbouring molecules (Fig. 4) that are much more attractive (Table 2). Similar interactions are found in all other diorganotin(IV) diacetates and even in the phenyl compound.

Synthesis:
0.51 g (0.68 mmol) di-t-butyltin oxide are dissolved in 0.25 g (4.16 mmol) of acetic acid (Fluka). The solution is stirred for 6 h at ambient temperature before the solvent is allowed to evaporate slowly. After about 1 week colourless block-like crystals are grown.

Refinement
Hydrogen atoms were clearly identified in difference Fourier syntheses. Their positions were idealized and refined at calculated positions riding on the carbon atoms with C-H = 0.98 Å.

Crystal data
[Sn(C 4 H 9 ) 2 (C 2 H 3 O 2 ) 2 ] M r = 351.00 Monoclinic, P2 1 /n Hall symbol: -P 2yn a = 6.1039 ( 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.