1. High Field Magnet Laboratory HFML, Radboud University Nijmegen, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, and Laboratoire de Chimie Organique et Organométallique, CNRS UMR 5802, Université Bordeaux I, 33405 Talence cédex, France