1. Chemistry Department, Brookhaven National Laboratory Upton, New York 11973-5000 Department of Chemistry, University of MissouriSt. Louis St. Louis, Missouri 63121-4499 Shell Research and Technology Centre Amsterdam Postbus 38000, 1030 BN Amsterdam, The Netherlands Department of Inorganic Chemistry, University of Nijmegen Toernooiveld 1, 6525 ED Nijmegen, The Netherlands