1. Department of Chemistry, Indian Institute of Chemical Biology (Unit of C.S.I.R), Jadavpur, Calcutta 700 032, India, Faculty of Chemistry and Institute of Physics, Nicolaus Copernicus University, 87-100 Toruń, Poland, Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, Department of Chemistry, Adam Mickiewicz University, 60-780 Poznań, Poland, and School of Chemistry, University of Hyderabad, Hyderabad 500 046, India