Yarmukhametova,D.Kh. et al. Bulletin of the Academy of Sciences of the USSR, Division of Chemical Science (English Translation), 1972 , vol. 21, p. 1556 - 1560 Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, 1972 , vol. 21, # 7 p. 1617 - 1621