1. Institute of Chemistry; Martin-Luther University Halle-Wittenberg; Kurt-Mothes Str. 2 06120 Halle/Saale Germany
2. Department of Chemistry; Faculty of Science; Cairo University; P.O. 12613 Giza Egypt
3. State Key Laboratory for Mechanical Behavior of Materials; Xi'an Jiaotong University; Xi'an 710049 P.R. China