1. Institute of Nanoscience and Nanotechnology, N.C.S.R. “Demokritos”, 15310 Athens, Greece
2. Inorganic Chemistry Laboratory, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, 15771 Athens, Greece
3. Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany