1. Department of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K., Department für Chemie und Biochemie, Universität Berne, CH-3000 Bern 9, Switzerland, School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, U.K., School of Physics and Astronomy, University of St. Andrews, St. Andrews, Fife KY16 9SS, U.K., Institute of Chemistry, Moldovan Academy of Sciences, Kishinev MD-2028, Moldova, and Laboratoire de Magnétisme Louis Néel, CNRS, BP 166, 38042 Grenoble Cedex...