1. Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria, Faculty of Chemistry, University of Sofia, 1126 Sofia, Bulgaria, Laboratoire Catalyse et Spectrochimie, CNRS-ENSICAEN, Université de Caen, 6 bd. Maréchal Juin, 14050, Caen Cedex, France, and Department Chemie, Technische Universität München, 85747 Garching, Germany