Florian P. Pruchnik1, Francis Robert, Yves Jeannin, Suzanne Jeannin. 1. Faculty of Chemistry, University of Wroclaw, Joliot-Curie 14, 50-383 Wroclaw, Poland, and Laboratoire de Chimie des Metaux de Transition, Universite P. et M. Curie, 4, Place Jussieu, 75252 Paris Cedex 05, France.