Fedneva, E. M.; Alpatova, V. I.; Mikheeva, V. I. Zhurnal Neorganicheskoi Khimii, 1964 , vol. 9, p. 30 - 32 Zhurnal Neorganicheskoi Khimii, 1964 , vol. 9, p. 56 - 59 Gmelin Handbook: B: B-Verb.14, 3.6.1, page 53 - 57