1. Laboratory of Inorganic Chemistry, Department of Chemistry, Aristotle University of Thessaloniki, P.O. Box 135, GR-540 06 Thessaloniki, Greece, Institute of Materials Science, NCSR Demokritos, GR-153 10, Agia Paraskevi, Greece, and Department of Chemistry, St. Kliment Okhridskii University of Sofia, 1 James Bourchier av., 1126 Sofia, Bulgaria