1. Department of Inorganic Chemistry, University of Yaoundé I , Yaoundé, Cameroon
2. Department of Chemistry, Kwame Nkrumah University of Science and Technology (KNUST) , Kumasi, Ghana
3. Department of Chemistry, University of Zululand, Private Bag X1001 , KwaDlangezwa 3880, South Africa
4. Department of Materials, University of Manchester, Oxford Road , Manchester M13 9PL, UK