1. Center for Education and Research on Macromolecules (CERM), University of Liège, B6, Sart- Tilman, 4000 Liège, Belgium, Department of Chemistry, University of Warwick, Coventry, CV4 7AL, U.K., Laboratoire de Structure et Réactivité des Espèces Paramagnétiques, UMR 6517 CBRL Centre de Saint Jérôme, Case 521, Av. Esc. Normandie Niemen, 13397 Marseille Cedex 20, France, and Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213