1. J. P. Dahl and C. J. Ballhausen, Kgl. danske vid. sclkab. Mat.-fys. medd,33, 5, III. (1961).
2. E. M. Shustorovich and M. E. Dyatkina, Dokl. AN SSSR,128, 1234 (1959).
3. W. Kauzmann, Introduction to Quantum Chemistry [Russian translation] Izd. inostr. Ilt., M. (1960) p. 364?365.
4. A. V. Savitskii and Ya. K. Sytkin, Trudy po khimii i khim. tekhnol., Inst. khimii Gor'kovsk. gos. univ.,1, 165 (1961); A. V. Savitskii. Dissertation, M., IONKh AN SSSR (1961).
5. G. Wilkinson and F. A. Cotton, Progr. Inorg. Chem., 1, New York (1959) See also Uspekhi khimii31, 6 (1962).