Trimethyltin Hydroxide: A Crystallographic and High Z′ Curiosity

The remarkable room temperature structure of trimethyltin hydroxide comprises a total of 32 crystallographically independent SnMe3OH units arranged in four independent coordination polymer strands. We suggest that a Z' = 4 value is more appropriate than Z' = 32, reflecting the polymeric structure of the compound. DSC, single crystal and XRPD studies show that on cooling below ca. 160 K the structure undergoes a first order phase change to a symmetric Z' = 1 structure with just one crystallographically unique SnMe3OH unit. The phase change is reversible, and on warming past 176 K the high Z' structure is regenerated, in an endothermic transition. The Z' = 1 and 4 structures are an enantiotropic pair, and trimethyltin hydroxide represents a case where the higher Z' structure is the most stable form at high temperature with the high Z' value possibly arising from a consideration of the dynamics of the crystal as a whole.