1. Department of Chemistry, University of Bath, Claverton Down, Bath, U.K. BA2 7AY, School of Chemistry, University of Bristol, Cantock's Close, Bristol, U.K. BS8 1TS, Department of Chemistry, University of Leuven, Celestijueleua 200F, B-3001 Leuven, Belgium, and Department of Chemistry, University of Wales, Cardiff, P.O. Box 912, Park Place, Cardiff, U.K. CF1 3TB