1. Department of Chemistry, University of Dschang, P.O. Box 67, Dschang, Cameroon
2. Institut für Anorganische Chemie und Strukturchemie, Heinrich-Heine-Universität Düsseldorf, Universitätsstraße 1, 40225 Düsseldorf, Germany
3. Division of Thermal Systems and Buildings, Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstrasse 2, 79110 Freiburg, Germany
4. CRM2, CNRS Université de Lorraine, Vandoeuvre-lès-Nancy, CEDEX BP 70239, France
5. Department of Higher Teacher’s Training College, University of Yaoundé I, P.O.
Box 47, Yaoundé, Cameroon