1. J. Dirand, L. Ricard and R. Weiss, unpublished observations.
2. Y. A. Buslaev and R. L. Davidovich,Russ. J. Inorg. Cherry., 10, 1014 (1965).
3. See W. P. Griffith and T. D. Wickins,J. Chem. Soc. (A), 400 (1968).
4. Von R. Mattes, G. Müller and H. J. Becker,Z. Anorg. Allg. Chem., 389, 177 (1972).
5. L. Pauling,The nature of the Chemical Bond, 3rd Edit., Cornell University Press, Ithaca, N.Y., 1960, p. 260.