1. Department of Materials Science and Technology, Tokyo University of Science, 2641 Yamazaki, 278‐8510 Chiba, Japan
2. Institute of Inorganic Chemistry, Saarland University, Building C4 1, 66123 Saarbruecken, Germany
3. Institute of Inorganic Chemistry, University of Siegen, Adolf‐Reichwein‐Str., 57068 Siegen, Germany
4. Institute of Inorganic Chemistry, University of Cologne, Greinstr. 6, 50939 Cologne, Germany, Fax: +49‐221‐470‐5899