1. Contribution from the Department of Organic Chemistry II, University of Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany, Department of Inorganic Chemistry, University of Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany, Department of Physical Chemistry, University of Kaiserslautern, Erwin Schrödinger-Strasse, D-67663 Kaiserslautern, Germany, and Department of Chemistry, Physical Chemistry, University of Munich, Butenandtstrasse 11, D-81377 München, Germany