1. Institute of Inorganic and Applied Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany, Institute of Optics and Quantum Electronics, Friedrich-Schiller-University, Max-Wien-Platz 1, D-07743 Jena, Germany, and Institute of Inorganic and Analytical Chemistry, Justus-Liebig-University Giessen, Heinrich-Buff-Ring 58, D-35392 Giessen, Germany