1. Contribution from the Institute of Inorganic Chemistry, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany, Institute of Organic Chemistry, University of Erlangen-Nürnberg, Henkestrasse 42, 91054 Erlangen, Germany, and Institute of Inorganic Chemistry, Christian-Albrechts-University Kiel, Otto Hahn Platz 6/7, 24098 Kiel, Germany