1. Cotton, F. A. Chisholm, M. H.: Chem. Eng. News, June 28, 40, 1982
2. Muetterties, E. A.: Chem. Eng. News, Aug. 30, 28, 1982
3. Johnson, B. F. G.: Transition Metal Clusters. New York: John Wiley and Sons 1980
4. Burdett, J. K.: Molecular Shapes?Theoretical Models of Inorganic Stereochemistry. New York: John Wiley and Sons 1980
5. Corbett, J. D.: Prog. Inorg. Chem. 21, 129 (1976); Acc. Chem. Res. 14, 239 (1981)