1. Freie Universität, Berlin, Takustrasse 3, D-14195 Berlin, Germany, Institute of Physics, St. Petersburg State University, 198904 St. Petersburg, Russian Federation, A. N. Nesmeyanov Institute of Organoelement Compounds, Laboratory of Organometalic Compounds, Vavilov Street, 28, 117813 Moscow, Russian Federation, and Laboratoire de Chimie de Coordination du CNRS (UPR 8241), 205, route de Narbonne, F-31077 Toulouse Cedex, France