1. Cotton, F. A.: Quart. Rev. Chem. Soc. 20, 389 (1966)
2. Cotton, F. A.: Acc. Chem. Res. 1, 257 (1968)
3. Kaesz, H. D.: Chem. in Britain 9, 344 (1973)
4. King, R. B.: Progr. Inorg. Chem. 15, 287 (1972)
5. Penfold, B. R.: Perspectives in Structural Chemistry 2, 71 (1968)