1. H. Siegel, Angew. Chem. Intl. Edn. 8: 167 (1969).
2. O. N. Emanuel, A. M. Sakharov, and I. P. Skibida, Izv. Akad Nauk USSR ser. Chem. 2692 (1975).
3. N. D. Yordanov, unpublished results.
4. J. A. Bertrand and R. I. Kaplan, Inorg. Chem. 4: 1657 (1965); Z. Olejnic, R. Grobelny, and B. Jezowska-Trzebiatowska, Bull. Polish Acad. Sci. Chem. 24: 883 (1976).
5. Z. D. Raikov, P. M. Blagoeva, and N. D. Yordanov, Compt. rend. Acad. Sci. Bulg. 29: 709, 881 (1976).