We report on a family of five new 4f- and 4d-doped sandwich-type germanotungstates with the general formula [(n-C4H9)(4)N](l/m)H-2[(M(H2O)(3))(gamma-GeW10O35)(2)]center dot 3(CH3)(2)CO [M(H2O)(3)(GeW10)(2)] (M = Ce-III, Nd-III, Gd-III, Er-III, l = 7; Zr-IV, m = 6), which have been synthesized at room temperature in an acetone-water mixture. Among the compound series, [Zr(H2O)(3)(GeW10)(2)](8-), which has been obtained in the presence of 30% H2O2, represents the first example of a 4d-substituted germanotungstate incorporating the intact dilacunary [gamma-(GeW10O36)-W-IV](8-) building block. All compounds were characterized thoroughly in the solid state by single-crystal and powder X-ray diffraction (XRD), IR spectroscopy, thermogravimetric analysis (TGA), and elemental analysis and in solution by NMR and UV-vis spectroscopy. The phosphoesterase activity of [Ce(H2O)(3)(GeW10)(2)](9-) and [Zr(H2O)(3)(GeW10)(2)](8-) toward the model substrates 4-nitrophenyl phosphate (NPP) and O,O-dimethyl O-(4-nitrophenyl) phosphate (DMNP) was monitored with H-1- and P-31-NMR spectroscopy revealing an acceleration of the hydrolytic reaction by an order of magnitude (k(corr) = 3.44 (+/- 0.30) x 10(-4) min(-1) for [Ce(H2O)(3)(GeW10)(2)](9-) and k(corr) = 5.36 (+/- 0.05) x 10(-4) min(-1) for [Zr(H2O)(3)(GeW10)(2)](8-)) as compared to the uncatalyzed reaction (k(uncat) = 2.60 (+/- 0.10) x 10(-5) min(-1)). [Ce(H2O)(3)(GeW10)(2)](9-) demonstrated improved antibacterial activity toward Moraxella catarrhalis (MIC 32 mu g/mL), compared to the unsubstituted [GeW10O36](8-) POM (MIC 64 mu g/mL).