Monoclinic- vs. triclinic-(NH4)2[Mg(H2O)6]2V10O28∙4H2O: Structural studies and variation in antibacterial activities with the polymorph type

•The monoclinic and triclinic polymorphs of (NH4)2[Mg(H2O)6]2V10O28∙4H2O were prepared and analyzed by single crystal XRD, FT-IR spectroscopy and thermal analysis.•The antibacterial activities of the polymorphs were determined against three bacterial strains (E. coli, P. aeruginosa and R. solanacearum).•The inhibitions against R. solanacearum given by the polymorphs are comparable to that obtained by the antibacterial standard. An increase in human and phytopathogenic bacterial diseases requires rapid development of new antibacterial agents. The formation of two polymorphs of bis(hexaaquamagnesium(II)) complex – decavanadate cluster compound, (NH4)2[Mg(H2O)6]2V10O28∙4H2O, was controlled by the addition of different organic molecules to the reaction medium. The two polymorphs {monoclinic (C2/c) and triclinic (P-1)} were characterized by single-crystal XRD analysis, elemental analysis and FT-IR spectroscopy. Additionally, their thermal decomposition mechanisms to a composite product of V2O5 and Mg(VO3)2 were elucidated. The antibacterial activities and the minimum inhibitory concentrations of the polymorphs were determined against two human pathogenic bacterial strains (E. coli O157:H7 and P. aeruginosa ATCC 9027) and a phytopathogenic bacterial strain (R. solanacearum). The inhibitory activity and the minimum inhibitory concentration (MIC) values of the tested compounds showed pronounced higher antibacterial activities of the triclinic polymorph against E. coli O157:H7 and P. aeruginosa ATCC 9027, while the monoclinic polymorph afforded higher inhibitory activity against R. solanacearum with MIC value of 1.125 mg/ml. Interestingly, the inhibitions against R. solanacearum given by the polymorphs are comparable to that obtained by the antibacterial standard.