1. Department of Chemistry, Masaryk University, Kotlarska 2, CZ-61137 Brno, Czech Republic, Inorganic Chemistry Group, Department of Chemistry, St. Petersburg State University, University pr. 26, Old Peterhof 198504, Russia, and Institut für Anorganische Chemie, Universität Göttingen, Tammannstrasse 4, D-37077 Göttingen, Germany