1. Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense, Madrid 28040, Spain
2. Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210-1185, United States
3. Institut Laue-Langevin, 6 rue Jules Horowitz, 38042 Grenoble Cedex 9, France