Aluminum-Substituted Keggin Germanotungstate [Harh(2)O)Gew11o39](4-): Synthesis, Characterization, And Antibacterial Activity

We report on the new monosubstituted aluminum Keggin-type germanotungstate (C4H12N)(4)[HAIGeW(11)O(39)(H2O)]center dot 11H(2)O GAI(H2O)GeW11](4-)), which has been synthesized at room temperature via rearrangement of the dilacunary [gamma-GeW10O36](8-) polyoxometalate precursor. [Al(H2O)GeW11](4-) has been characterized thoroughly both in the solid state by single-crystal and powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and elemental analysis as well as in solution by cyclic voltammetry (CV) W-183, Al-27 NMR and UV-vis spectroscopy. A study on the antibacterial properties of [Al(H2O)GeW11](4-) and the known aluminum(III)-centered Keggin polyoxotungstates (Al-POTs) alpha-Na-5[AlW12O40] (alpha-[AlW12O40](5-)) and Na-6[Al(AlOH2)W11O39] ([Al(AIOH(2))W11O39](6-)) revealed enhanced activity for all three Al-POTs against the Gram-negative bacterium Moraxella catarrhalis (minimum inhibitory concentration (MIC) up to 4 mu g mL(-1)) and the Gram-positive Enterococcus faecalis (MIC up to 128 mu g mL(-1)) compared to the inactive Al(NO3)(3) salt (MIC > 256 mu g mL(-1)). CV indicates the redox activity of the Al-POTs as a dominating factor for the observed antibacterial activity with increased tendency to reduction, resulting in increased antibacterial activity of the POT.