1. Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48, Vassileos Constantinou Ave., Athens 116 35, Greece
2. Institute of Materials Science, NCSR, Demokritos, Athens 153 10, Greece
3. Department of Inorganic Chemistry, Faculty of Chemistry, University of Athens, Panepistimioupoli Zografou 157 71, Athens, Greece