1. Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P. O. Box 9502, 2300 RA Leiden, The Netherlands, Fax: +31‐715274671
2. Department of Chemistry, Laboratory of Inorganic Chemistry, P. O. Box 55 (A. I. Virtasenaukio 1), 00014 University of Helsinki, Helsinki, Finland
3. Université Bordeaux 1, Centre de Recherche Paul Pascal – CNRS UPR 8641, 115 avenue du dr. A. Schweitzer, 33600 Pessac, France