1. a Faculty of Science, Department of Chemistry , Alexandria University , P.O. Box 426, Ibrahimia, 21321 Alexandria, Egypt
2. b Faculty of Science, Department of Chemistry , Fayoum University , Fayoum, Egypt
3. c Institut fuer Physikalische und Theoretische Chemie, Technische Universitaet Graz , Rechbauerstr. 12, A-8010 Graz, Austria