1. Contribution from the Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, Institute of Inorganic Chemistry, Academy of Science of the Czech Republic, 25068 Rež near Prague, Czech Republic, Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, and Department of Organic Chemistry, Charles University, Albertov 2030, 12840 Prague 2, Czech Republic