The renaissance of homoatomic nine-atom polyhedra of the heavier carbon-group elements Si-Pb

Homoatomic nine-atom clusters of the elements Si, Ge, Sn, and Pb represent a fascinating class of molecules. The Zintl anions [E-9](v-) occur with different charges x and various shapes. Mixed valent compounds and polymeric chains via cluster linkage promise outstanding physical and chemical properties. A summary of recent progress in synthesis, crystal structure, EXAFS investigations, chemical bonding, Raman spectroscopy, mass spectrometry, and chemical reactivity is given. The shapes of about 30 Zintl ions [E-9] are analysed. Finally, it is shown that a close relationship exists between the compounds with anionic nine-atom clusters of elements of the carbon group and the superconducting fulleride salts, which contain negatively charged polyhedra of the lightest element in this group. (C) 2001 Elsevier Science B.V. All rights reserved.