1. Inorganic Chemistry, University of Duisburg–Essen, Universitaetsstrasse 5–7, 45117 Essen, Germany, Fax: +49‐201‐183‐2621
2. Laboratory of Industrial Chemistry, Ruhr University Bochum, Universitaetsstrasse 150, 44801 Bochum, Germany
3. Max‐Planck‐Institute for Coal Research, Kaiser‐Wilhelm‐Platz 1, 45470 Muelheim an der Ruhr, Germany