1. Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48109-1055
2. Institute of Physical Chemistry University of Karlsruhe (TH), D-76128 Karlsruhe, Germany
3. Forschungszentrum Karlsruhe GmbH, Nanotechnology Institute, P.O. Box 3640, D-76021 Karlsruhe, Germany
4. Institute of Inorganic Chemistry University of Karlsruhe (TH), D-76128 Karlsruhe, Germany