1. a Department of Inorganic Chemistry , Indian Association for the Cultivation of Science , Calcutta, 700 032, India
2. b Department of Chemistry , Bengal Engineering College (Deemed University) , Howrah, 711 103, India
3. c Department of Physics , Krishnath College , Berhampore, Murshidabad, West Bengal, India
4. d Department of Pharmaceutical Sciences , Aston University , Aston Triangle, Birmingham, B4 7ET, UK