1. Department of Inorganic Chemistry, University of Yaounde 1, Yaounde, Cameroon
2. Univ. Lille, CNRS, Centrale Lille, ENSCL, Univ. Artois, UMR 8181 - UCCS - Unité de Catalyse et Chimie du Solide, France
3. Department of Chemistry, University of Dschang, Dschang, Cameroon
4. Higher Teacher Training College, University of Yaounde 1, Yaounde, Cameroon
5. UFR de Physique, Université Lille, Lille, France