1. Department of Chemistry, University of Bremen P.O. Box 330 440, D‐2833 Bremen, Germany Fax: (internat.) +49(0)421 218 2871
2. Institute for Inorganic Chmistry, University of Munich Meiserstrasse 1, D‐8003 München, Germany fax: (internat.) + 49(0) 590 2451