1. Contribution from the Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic, 250 68 Řež, Czech Republic, Faculty of Natural Sciences of Charles University, Hlavova 2030, 128 42 Prague 2, Czech Republic, Institute of Material Sciences, Campus UAB, 08193 Bellaterra, Spain, and Computer Chemistry-Center, Institute of Organic Chemistry, Universität Erlangen-Nürnberg, Henkestrasse 42, D-91054 Erlangen, Germany