1. Department of Chemistry, McMaster University, Hamilton, Ontario L8S 4M1, Canada, Department of Chemistry, University of Jyväskylä, P.O. Box 35, FIN-40014, Finland, and Max-Planck-Institut für Chemische Physik fester Stoffe, Raum B1.2.11, Nöthnitzer Strasse 40, Dresden D-01187, Germany