1. Department of Chemistry, Laboratory of Inorganic Chemistry, P.O. Box 55, University of Helsinki, FIN-00014 University of Helsinki, Finland, Optics and Molecular Materials, Helsinki University of Technology, Rakentajanaukio 2 C, FIN-02150 Espoo, Finland, and NMR Laboratory, Finnish Institute for Verification of the Chemical Weapons Convention (VERIFIN), P.O. Box 55, University of Helsinki, FIN-00014 University of Helsinki, Finland