1. See for instance: Cotton,F.A., Wilkinson,G.: Advanced inorganic chemistry, p. 719. New-York: Interscience Publishers 1968.
2. Demuynck,J., Coutiere,M.-M., Veillard,A.: to be published.
3. Griffith,W.P.: Quart. Rev. 16, 188 (1962).
4. Jørgensen,K.: private communication.
5. Lloyd,D.R, Schlag,E.W.: Inorg. Chemistry 8, 2544 (1969).