Volatile and Thermally Stable Polymeric Tin Trifluoroacetates.

Tin trifluoroacetates are effective vapor phase single-source precursors for F-doped SnO, but their structures have been poorly understood for decades. Here we undertook a comprehensive structural analysis of these compounds in both the solid and gas phases through a combined single-crystal X-ray crystallography, gas phase electron diffraction, and density functional theory investigation. Tin(II) bis(trifluoroacetate) () thermally decomposes into a 1:1 mixture of and ditin(II) μ-oxybis(μ-trifluoroacetate) () during sublimation, which then polymerize into hexatin(II)-di-μ-oxyoctakis(μ-trifluoroacetate) () upon solidification. Reversible depolymerization occurred readily upon heating, making a useful vapor phase precursor itself. Tin(IV) tetrakis(trifluoroacetate) () was also found to be polymeric in the solid state, but it evaporated as a monomer over 130 °C lower than . This counterintuitive improvement in volatility by polymerization was possibly due to the large entropy change during sublimation, which offers a strategic new design feature for vapor phase deposition precursors.