1. Department of Chemistry, University of Catania and INSTM UdR Catania, V.le A. Doria 6, 95125 Catania, Italy, Department of Chemistry, University of Modena and Reggio Emilia and INSTM UdR Modena, via G. Campi 183, 41100 Modena, Italy, and Department of Chemistry, University of Florence and INSTM UdR Florence, via della Lastruccia 3, 50019 Sesto Fiorentino, Italy