1. Département de Chimie, CNRS UMR 8640 PASTEUR, Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris Cedex 05, France, and Department of Chemistry, University of Kansas, Lawrence, Kansas 66045-7582, and CNRS UMR 6510 SESO, Université de Rennes I, Campus de Beaulieu, 263 Av. du Général Leclerc, 35042 Rennes, France, and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215