1. Institute of Chemistry, L. Eötvös University, Pázmány st 1/a., H-1117, Budapest, Hungary, Institute of Inorganic Chemistry I, University of Ulm, Albert-Einstein-Allee 11, D-89069 Ulm, Germany, Institute of Solid State Physics, Research Centre Jülich, D-52425 Jülich, Germany, and Institute of Material Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria