1. Department of Chemistry, University College of Science, University of Calcutta, 92, A. P. C. Road, Kolkata 700009, India
2. School of Chemistry, The University of Reading, P. O. Box 224, Whiteknights, Reading RG 66AD, UK
3. Departament de Química Inorgànica, Universitat de Barcelona, Marti i Franques 1–11, 08028 Barcelona, Spain