Prepn from NbCl5 + HF: Ruff, Zedner, Ber. 42, 492 (1909); Ruff, Schiller, Z. Anorg. Allg. Chem. 72, 329 (1911); Kwasnik in Handbook of Preparative Inorganic Chemistry Vol. 1, G. Brauer, Ed. (Academic Press, New York, 2nd ed., 1963) p 254. Prepn from the elements: Fairbrother, Frith, J. Chem. Soc. 1951, 3051; Junkins et al., J. Am. Chem. Soc. 74, 3464 (1952). Review of transition metal pentafluorides: Peacock, Adv. Fluorine Chem. 7, 113-145 (1973).