1. Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, Centre de Recherche Paul Pascal, UPR-CNRS 8641, 115 avenue du Dr. A. Schweitzer, 33600 Pessac, France, and Laboratoire Louis Néel, CNRS, BP-166, 38042 Grenoble Cedex 9, France