1. Contribution from the School of Chemistry, University of Leeds, Leeds, U.K. LS2 9JT, Department of Chemistry, University of MissouriSt. Louis, St. Louis, Missouri 63121, Department of Chemistry, University College Cork, Cork, Ireland, CCLRC Daresbury Laboratory, Daresbury, Warrington, U.K. WA4 4AD, and Department of Chemistry of the University of Newcastle, Newcastle upon Tyne, U.K. NE1 7RU