1. Dipartimento di Chimica Generale ed Inorganica, ChimicaAnalitica, Chimica Fisica, University of Parma, Viale G.P. Usberti 17/A, 43100 Parma, Italy, Fax: +39‐0521‐905557
2. Present address: Dipartimento di Chimica Inorganica, Metallorganica, Analitica, University of Milan, Via Venezian 21, 20133 Milan, Italy
3. Laboratory for Crystallography, van't Hoff Institute of Molecular Sciences, Faculty of Sciences, Universiteit van Amsterdam, Valkenierstraat 65, 1018XE Amsterdam, The Netherlands