1. Institute of Organic Chemistry, RWTH Aachen, Professor-Pirlet-Str. 1, D-52056 Aachen, Germany, Technology and R+D-Management des Geschäftsbereichs Feinchemikalien, Degussa AG, Postfach 1345, D-62403 Hanau, Germany, Analytisch Technische Services, Infracor GmbH, Postfach 1345, D-62403 Hanau, Germany, and Institute of Inorganic Chemistry, Martin-Luther-University Halle-Wittenberg, Kurt-Mothes-Str. 2, D-06120 Halle, Germany