1. Humboldt Universität zu Berlin, Department of Chemistry, Brook‐Taylor‐Str. 2, 12489 Berlin, Germany, Fax: +49‐30‐20937387
2. Institut für Anorganische Chemie, Karlsruhe Institute ofTechnology (KIT), Engesserstr., 76131 Karlsruhe, Germany
3. Department of Theoretical Chemistry, Lund University, Chemical Centre, P. O. Box 124, 22100 Lund, Sweden
4. Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), P. O. Box 3640, 76021 Karlsruhe, Germany