Prepn: Russell et al., J. Am. Chem. Soc. 63, 2825 (1941); Woolf, Greenwood, J. Chem. Soc. 1950, 2200; Hoffman, Inorg. Synth. 4, 151 (1953); Kwasnik in Handbook of Preparative Inorganic Chemistry vol. 1, G. Brauer, Ed. (Academic Press, New York, 2nd ed., 1963) pp 197-198. Review: Kemmitt, Sharp, Adv. Fluorine Chem. 4, 208-209 (1965).