1. J. A. Halfen, S. Mahapatra, E. C. Wilkinson, V. G. Young Jr., L. Que Jr., W. B. Tolman, Department of Chemistry, University of Minnesota, Minneapolis, MN 55455, USA.
2. S. Kaderli and A. D. Zuberbühler, Institute of Inorganic Chemistry, University of Basel, CH-4056 Basel, Switzerland.