1. Istituto FRAE-CNR, Via Gobetti 101 I-40129 Bologna, Italy Dipartimento di Chimica “G. Ciamician” Università di Bologna Via Selmi 2, I-40126, Bologna, Italy Department of Physical Chemistry, University of Uppsala Box 532, S-75121 Uppsala, Sweden Laboratoire de Chimie Organo-Minerale Université Louis Pasteur, Faculté de Chimie 1 rue Blaise Pascal, F-67008 Strasbourg, France