Lewis acid. Prepd from SnCl4 and HF: Ruff, Plato, Ber. 37, 673 (1904); or from stannous fluoride and chlorine or bromine: Forbes, Anderson, J. Am. Chem. Soc. 67, 1911 (1945); from stannous oxide or sulfide and fluorine: Haendler et al., J. Am. Chem. Soc. 76, 2179 (1954). Review: Kemmitt, Sharp, Adv. Fluorine Chem. 4, 185-186 (1965).