1. Department of Organic Chemistry, University of Geneva, quai Ernest Ansermet 30, CH-1211 Geneva 4, Switzerland, Istituto di Chimica dei Composti Organometallici, ICCOM-CNR, via Madonna del Piano 10, Sesto Fiorentino - (Fi), 50019 Italy, Department of Chemistry, National University of Ireland Maynooth, County Kildare, Ireland, and Laboratory of Crystallography, University of Geneva, quai Ernest Ansermet 24, CH-1211 Geneva 4, Switzerland