1. Departement of Chemistry and Biochemistry, Bern University, Freiestrasse 3, 3012 Bern, Switzerland
2. Departement of Chemistry, University of Basel, St.-Johanns-Ring 19, 4056 Basel, Switzerland, and Karlsuhe Institute of Technlogy (KIT), Institute for Nanotechnology, P.O. Box 3640, 76021 Karlsruhe, Germany