1. I. Haiduc, Inuoduction to the Chemistry of Inorganic Cycles [in Rumanian], Ed. RPR, (Bucuresti, 1960).
2. V. V. Korshak and K. K. Mozgova. Usp. khimii28, 783 (1959).
3. A. A. Berlin and V. P. Parini, Usp. khimii18, 546 (1949).
4. A. A. Berlin and V. P. Parini, Khim. nauka i prom.1, 44 (1956).
5. A. Michel. Bull. Soc. Chim. France1956, 1103.