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Volatile and Thermally Stable Polymeric Tin Trifluoroacetates

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journal contribution
posted on 08.01.2020, 21:13 by Goran Bačić, Conor D. Rankine, Jason D. Masuda, Derek A. Wann, Seán T. Barry
Tin trifluoroacetates are effective vapor phase single-source precursors for F-doped SnO2, 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) (1) thermally decomposes into a 1:1 mixture of 1 and ditin­(II) μ-oxybis­(μ-trifluoroacetate) (2) during sublimation, which then polymerize into hexatin­(II)-di-μ3-oxyoctakis­(μ-trifluoroacetate) (3) upon solidification. Reversible depolymerization occurred readily upon heating, making 3 a useful vapor phase precursor itself. Tin­(IV) tetrakis­(trifluoroacetate) (5) was also found to be polymeric in the solid state, but it evaporated as a monomer over 130 °C lower than 3. 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.

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