1. Contribution from the Department of Chemistry, University of Florence, Via Maragliano 75/77, 50144 Florence, Italy, Department of Experimental Sciences, University Jaume I, Castellón, Spain, Institute of Chemical Sciences, University of Urbino, Via Stazione 4, 61029 Urbino, Italy, and Department of Inorganic Chemistry, University of Valencia, C/Dr. Moliner 50, 46100 Burjasot (Valencia), Spain