1. College of Chemistry, Fuzhou University, Fuzhou 350 002, P. R. China
2. Department of Post-Graduate Studies and Research in Chemistry, Gulbarga University, Gulbarga 585106, India
3. School of Chemistry, Sun Yat-sen University, Guangzhou 510 275, P. R. China
4. Department of Physics, Quaid Azam University, Islamabad 45320, Pakistan