1. Department of Applied Chemistry, Anhui University of Technology, Ma'anshan, Anhui 243002, P. R. China
2. Department of Physics, Harbin Institute of Technology, Harbin 150001, P. R. China
3. Department of Chemistry, Hong Kong Baptist University, Waterloo Road, Kowloon Tang, Hong Kong, P. R. China
4. Institut für Anorganische Chemie, Universität Karlsruhe (TH), 76128 Karlsruhe, Germany
5. Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, P. R. China