Mukhametshina, Z. B.; Polyakov, O. G. Russian Journal of Inorganic Chemistry (Translation of Zhurnal Neorganicheskoi Khimii), 1994 , vol. 39, p. 1635 - 1638 Zhurnal Neorganicheskoi Khimii, 1994 , vol. 39, p. 1710 - 1713