1. Chemistry Department, Faculty of Science, Alexandria University, Egypt, Departament de Química Inorgànica, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain, Dipartimento di Chimica, Universitá degli Studi di Firenze, Via Maragliano 75−77, 50144 Firenze, Italy, Chemistry Department, Faculty of Science, Kuwait University, P. O. Box 5969, Safat, 13060 Kuwait, and Institut für Physikalische und Theoretische Chemie, Technische Universität Graz, A-8010 Graz, Austria