1. Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany, J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, CZ-18223 Prague, Czech Republic, Grenoble High Magnetic Field Laboratory, MPI-CNRS, 25, avenue des Martyrs, BP 166, F-38042 Grenoble Cedex 9, France, and Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India