1. Kekulé-Institute for Organic Chemistry and Biochemistry, University of Bonn, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany
2. Institute of Inorganic Chemistry, University of Bonn, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany
3. Department of Materials Chemistry and INSTM, University of Milano-Bicocca, Via R. Cozzi 53, I-20125 Milano, Italy
4. Institute of Physics II, University of Cologne, Zülpicher Str. 77, D-50937 Cologne, Germany
5. Mads Clausen Institute, University of Southern Denmark, Alsion 2, DK-6400 Sønderborg, Denmark
6. Physical Chemistry, University of Cologne, Greinstr. 4-6, D-50939 Cologne, Germany
7. Institute of Physics, University of Oldenburg, Carl-von-Ossietzky-Str. 9-11, D-26129 Oldenburg, Germany