1. Department of Chemistry, University College London, 20 Gordon Street, London WC1H OAJ, U.K., School of Chemical Sciences, The University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K., UMR 5803 CNRS - Université Bordeaux 1, Laboratoire de Physico-Chimie Moléculaire, Université Bordeaux 1, 33405 Talence Cedex, France, and Dipartimento di Chimica, Università di Perugia, 06123 Perugia, Italy