1. Department of Chemistry; Panchakot Mahavidyalaya; Sarbari Purulia 723 121 India
2. Department of Chemistry; University of Calcutta; 92 A. P. C. Road Kolkata 700 009 India
3. Departamento de Química Física y Analítica; Universidad de Oviedo; C/ Julián Clavería 8 33006 Oviedo Spain
4. Dipartimento di Scienze Chimiche; University of Trieste; Via L. Giorgieri 1 34127 Trieste Italy