1. Laboratoire des Sciences Moléculaires, Institut de Chimie de la Matière Condensée de Bordeaux, UPR CNRS No. 9048, F-33608 Pessac, France, Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, B.C. V6T 1Z1, Canada, and X-ray Crystallographic Center, Department of Chemistry, 160 Kolthoff Hall, University of Minnesota, Minneapolis, Minnesota 55455