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 dif ferent charges x and various shapes. Mixed valent compounds and polymeric c hains via cluster linkage promise outstanding physical and chemical propert ies. A summary of recent progress in synthesis, crystal structure, EXAFS in vestigations, chemical bonding, Raman spectroscopy, mass spectrometry, and chemical reactivity is given. The shapes of about 30 Zintl ions [E-9] are a nalysed. Finally, it is shown that a close relationship exists between the compounds with anionic nine-atom clusters of elements of the carbon group a nd the superconducting fulleride salts, which contain negatively charged po lyhedra of the lightest element in this group. (C) 2001 Elsevier Science B. V. All rights reserved.