1. Dipartimento di Chimica e Chimica Industriale Università di Pisa Via G. Moruzzi 13 56124 Pisa Italy
2. Present address: Department of Chemistry University of Basel, BPR 1096 Mattenstrasse 24a 4058 Basel Switzerland
3. Institut des Sciences et Ingénierie Chimiques Ecole Polytechnique Fédérale de Lausanne (EPFL) CH-1015 Lausanne Switzerland
4. Institut für Anorganische Chemie Tammannstr. 4 37077 Göttingen Germany
5. Present address: Institut für Chemie und Biochemie Fabeckstr. 34–36 14195 Berlin Germany
6. Dipartimento di Chimica Industriale “Toso Montanari” Università di Bologna Viale Risorgimento 4 40136 Bologna Italy