1. Institute of Organic and Biomolecular Chemistry, Georg-August-University of Göttingen, Tammannstrasse 2, D-37077 Göttingen, Germany, Institute of Inorganic Chemistry, Georg-August-University of Göttingen, Tammannstrasse 4, D-37077 Göttingen, Germany, and Institute of Biotechnology and Drug Research, D-67663 Kaiserslautern, Germany