* Corresponding authors

^a Department of Chemistry and Biochemistry, University of Namibia, 340 Mandume Ndemufayo Avenue, Windhoek, Namibia
E-mail: vuahengo@unam.na
Fax: +264 61 206 3465
Tel: +264 61 206 3465

^b Department of Chemical and Process Engineering, Jubail Industrial College, Jubail Industrial City 31961, Saudi Arabia

^c Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius, Réduit 80837, Mauritius

^d Department of Applied Chemistry, University of Johannesburg, Doornfontein Campus, Johannesburg 2028, South Africa

^e College of Chemistry and Molecular Sciences, Wuhan University, Wuhan, Hubei 430072, China