1. F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 5th Edit., Wiley Interscience, New York, 1988, p. 172.
2. N. P. Nies and G. W. Campbell in R. M. Adams (Ed.), Boron, Metallo-Boron Compounds and Boranes, Interscience, New York, 1964, p. 186.
3. R. Pizer and C. Tihal, Inorg. Chem., 26, 3639 (1987).
4. J. D. Lydon, L. M. Schwane and R. C. Thompson, Inorg. Chem., 26, 2606 (1987).
5. L. M. Schwane and R. C. Thompson, Inorg. Chem., 28, 3938 (1989).