1. Contribution from the School of Chemistry, University of Hyderabad, Hyderabad 500 046, India, France, Télécom, CNET, Laboratoire de Bagneux, Département d' Electronique Quantique Moléculaire, 196, avenue Henri Ravera, 92225 Bagneux, France, Institut für Anorganische Chemie, FB 8, Universität-GH Essen, Universitätsstrasse 5-7, D-45177 Essen, Germany, The Institute for Cancer Research, Fox Chase Cancer Center, 7701 Burholme Avenue, Philadelphia, Pennsylvania 19111