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Keywords:

  • Polyoxometalates;
  • Zirconium;
  • Peroxido ligands;
  • Sandwich-type compounds;
  • Enzyme mimics

Abstract

The introduction of hydrogen peroxide, dl-mandelic acid (H2Mal), and acetate buffer into a reaction system containing zirconium(IV) ions and various trivacant polyoxometalates (POMs) led to the isolation of a series of new tetranuclear zirconium-substituted POMs modified by different O-donor ligands: Na4(NH4)14[Zr43-O)2(μ-O2)2(OAc)2(P2W16O59)2]·51H2O (1), (NH4)16[Zr43-O)2(Mal)2(H2O)2(P2W16O59)2]·14H2O (2), and Na7(NH4)5[{Zr4(OH)6(OAc)2}(SiW10O37)2]·20H2O(3) (3). All three compounds were characterized by elemental analyses, IR spectra, thermogravimetric (TG) analysis and single-crystal X-ray diffraction structural analyses. Compounds 1 and 2 possess similar sandwich-type polyoxoanion structures built from a tetranuclear Zr cluster and two [P2W16O59]12– building blocks, but they differ in the modifying ligands on the {Zr4} clusters, which are peroxido and mandelato for 1 and 2, respectively. The polyoxoanion of 3 contains a different tetranuclear Zr cluster, which is further sandwiched by two [α-SiW10O37]10– moieties and decorated by two acetato ligands. The catalytic activities of 13 were evaluated on the basis of a catalytic oxidation reaction of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2. Compound 1 exhibits the best catalytic activity, which suggests a new peroxidase-like catalyst for the colorimetric detection of H2O2 with a linear detection range from 100 to 1000 μM (r = 0.997) and a detection limit of 100 μM.