1. Department of Chemistry; University of Zululand; Private Bag X1001 Kwa-Dlangezwa 3886 South Africa
2. Department of Inorganic Chemistry; University of Yaoundé I; P.O. Box 812 Yaoundé Cameroon
3. School of Materials; University of Manchester; Oxford Road Manchester M13 9PL UK
4. Molecular Sciences Institute; School of Chemistry; University of Witwatersrand; P.O. WITS 2050 Johannesburg South Africa