Tsvetkov,E.N. et al. Bulletin of the Academy of Sciences of the USSR, Division of Chemical Science (English Translation), 1979 , vol. 28, p. 1722 - 1726 Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, 1979 , vol. 28, # 8 p. 1859 - 1862