1. Contribution from the Department of Chemistry and Biochemistry, The University of California, San Diego, 9500 Gillman Drive, La Jolla, California 92093-0358, UMR CNRS/ENSCM 5618, 8 rue de l'école normale, 34296 Montpellier Cedex 5, France, and Department of Chemistry, The University of Auckland, Private Bag 92019, Auckland, New Zealand