1. Department of Chemistry, University of Florence, via Maragliano 75, 50144 Firenze, Italy, Department of Chemistry, University of Modena, via G. Campi 183, 41100 Modena, Italy, Laboratoire des Champs Magnetiques Intenses, CNRS, Grenoble, France, and A. N. Nesmeyanov Institute of Organoelement Compounds (INEOS), 28 Vavilov St., Moscow 117813, Russia