1. Departments of Chemistry and Physics, Jadavpur University, Jadavpur, Calcutta 700 032, India, Laboratoire de Chimie de Coordination du CNRS, UPR 8241, 205 Route de Narbonne, 31077 Toulouse, Cedex 04, France, and Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan