Supramolecular Organization and Evaporation of Polymeric Tin Trifluoroacetates
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Simple tin carboxylates make up a family of important industrial catalysts and precursors for deposition of SnO2 thin films. However, their structures remain disparately characterized, and tin trifluoroacetates have been particularly elusive. Here we report on a combined X-ray diffraction (XRD), gas phase electron diffraction (GED) and density functional theory (DFT) study into the structure and bonding of tin(II) and tin(IV) trifluoroacetates to understand their influence on thermal stability and volatility. Tin(II) bis(trifluoroacetate) (1′) eliminates trifluoroacetic anhydride upon sublimation to form the linear polymeric hexatin(II)-di-μ -oxy-octakis-μ-trifluoroacetate (1F ), which itself sublimes (1 Torr at 191 C) as a 1:1 mixture of 1 and ditin(II)-μ-oxy-bis-μ-trifluoroacetate (1′′). Tin(IV) tetrakis(trifluoroacetate) (2F) is also polymeric in the solid state, but evaporates as a monomer at low temperatures (1 Torr at 84 ◦C). Together they make a family of multifunctional Lewis acidic and basic building blocks for supramolecular organization of clusters and polymers in the solid state. Anomalous trends in the volatility of these trifluoroacetates and their hydrogenated derivatives can be rationalized by consideration of their modes of polymerization with respect to the thermodynamics of evaporation. Both 1F and 2F combine high thermal stability and volatility, and are demonstrated to be complementary, safe, and green potential precursors for chemical vapor deposition (CVD) or atomic layer deposition (ALD) of earth-abundant transparent conducting F-doped SnO2.