1. Contribution from the Materials Chemistry Research Group, Chemistry Department, University of Toronto, 80 St. George St., Toronto, Ontario, Canada M5S 3H6, and Davy Faraday Research Laboratory, Royal Institution of Great Britain, 21 Albemarle Street, London, WIX 4BS United Kingdom, and Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ United Kingdom