1. Department of Chemistry, 215 Glenbrook Road, University of Connecticut, Storrs, Connecticut 06269-4060, Gorlaeus Laboratories, Leiden University, 2300 RA Leiden, The Netherlands, Chemistry Division, Argonne National Laboratories, Argonne, Illinois 60439, Department of Chemistry, Northwestern University, Evanston, Illinois 60208, and Department of Chemistry, University of California, Riverside, California 92521