1. EPSRC c.w. EPR Service Centre, Chemistry Department, The University of Manchester, Manchester, M13 9PL, U.K., Chemistry Department, Imperial College of Science, Technology and Medicine, London, SW7 2AY, U.K., School of Chemistry, University of Tasmania, GPO Box 252-75, Hobart Tasmania 7001, Australia, and Lehrstuhl für Anorganische Chemie III, Fachbereich Chemie, Universität Dortmund, 44221 Dortmund, Germany