1. Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P. O. Box 9502, 2300 RA Leiden, The Netherlands , Fax: +31‐71‐5274451
2. Bijvoet Center for Biomolecular Research, Crystal and Structural Chemistry, Utrecht University, The Netherlands
3. Laboratory of Inorganic Chemistry, Department of Chemistry, University of Helsinki, P. O. Box 55, (A.I.Virtasen aukio 1), 00014 Helsinki, Finland