1. Department of Organic and Nuclear Chemistry, Faculty of Science, Charles University, Hlavova 8, 128 43 Prague 2, Czech Republic, Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo náměstí 2, 166 10 Prague 6, Czech Republic, and Department of Inorganic Chemistry, Faculty of Science, Charles University, Hlavova 8, 128 43 Prague 2, Czech Republic