1. Department of Inorganic Chemistry, Slovak Technical University, SK-812 37 Bratislava, Slovakia, Institute of Materials Science, Darmstadt University of Technology, D-64289 Darmstadt, Germany, Institute of Inorganic Chemistry, Vienna University of Technology, A-1060 Vienna, Austria, and Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg University, D-55099 Mainz, Germany