1. Contribution from the Institute of Inorganic & Physical Chemistry, University of Bremen, Leobener Strasse, D-28334 Bremen, Germany, Department of Chemistry, University of Tartu, Jakobi 2 str, 51014 Tartu, Estonia, and Hansa Fine Chemicals GmbH, Leobener Strasse, NW2 C, D-28359 Bremen, Germany