1. Université de Toulouse, INSA, UPS, LPCNO, 135 avenue de
Rangueil, F-31077 Toulouse, France, and CNRS, F-31077 Toulouse, France
2. Department of Chemistry, University of California, Berkeley, California 94720-1460, United States
3. Institut Charles Gerhardt, CNRS UMR 5253, Université Montpellier 2, Place E. Bataillon, F-34095 Montpellier, France