1. Contribution from the Institute of Inorganic and Analytical Chemistry, University of Lausanne, BCH, CH-1015 Lausanne, Switzerland, Department of Chemistry, University of Adelaide, South Australia 5005, Australia, Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow V-334, Kosygina 4, Russia, and Institute of Inorganic Chemistry, University of Fribourg, Perolles, CH-1700 Fribourg, Switzerland