1. Contribution from the Department of Organic Chemistry, University of Geneva, 30 Quai Ernest Ansermet, 1211 Genève 4, Switzerland, Department of Chemistry and Supercomputing Institute, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, Department of Physical Chemistry, University of Geneva, 30 Quai Ernest Ansermet, 1211 Genève 4, Switzerland, and Laboratory of X-Ray Crystallography, University of Geneva, 24 quai Ernest Ansermet, 1211 Genève 4, Switzerland