1. Department of Chemistry, University of Glasgow, Glasgow G12 8QQ, Scotland, U.K., School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, Scotland, U.K., CLRC Daresbury Laboratory, Daresbury, Warrington, Cheshire, U.K. WA4 4AD, and Department of Chemistry, Imperial College of Science Technology and Medicine, South Kensington, London, U.K. SW7 2AY