1. Department of Organic Chemistry, University of Geneva, 30 Quai E. Ansermet, CH-1211 Geneva 4, Switzerland
2. Department of Physical Chemistry, University of Geneva, 30 Quai E. Ansermet, CH-1211 Geneva 4, Switzerland
3. Laboratory of X-ray Crystallography, University of Geneva, 24 Quai E. Ansermet, CH-1211 Geneva 4, Switzerland