Role of Steric Hindrance in the Crystal Packing of Z′ = 4 Superstructure of Trimethyltin Hydroxide

The room-temperature crystal structure of trimethyltin hydroxide, (CH3)3SnOH, has been described by Anderson et al. [Cryst. Growth Des. 2011, 11, 820–826] as a 2a × 2b × 8c, 32-fold superstructure. We report a a × b × 8c, eight-fold superstructure with orthorhombic P21 cn symmetry and Z′ = 4. Structured diffuse scattering observed at the positions of presumed superlattice reflections along a* and b* might have appeared as Bragg reflections in the experiment by Anderson et al. Alternatively, Anderson et al. and the present work might have studied different polymorphs of (CH3)3SnOH. Crystalline (CH3)3SnOH constitutes polymeric chains arranged parallel to c. In the eight-fold superstructure at 220 K, the polymeric chains possess a distorted zigzag arrangement of linked linear O–Sn–O units with bent angle at oxygen of ∼139.2°. This structure is essentially different from the 83-helical arrangement in the published 32-fold superstructure model. The origin of the distorted zigzag structure is explained by steric hindrance between hydrogen atoms of adjacent hydroxy groups and (CH3)3Sn groups. Frustration in the packing of the chains is determined by steric hindrance between methyl groups of neighboring chains, which prevents the formation of interchain C–H···O hydrogen bonds.