Modification of Tetranuclear Zirconium‐Substituted Polyoxometalates – Syntheses, Structures, and Peroxidase‐Like Catalytic Activities

The introduction of hydrogen peroxide, dl ‐mandelic acid (H 2 Mal), 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: Na 4 (NH 4 ) 14 [Zr 4 (μ 3 ‐O) 2 (μ‐O 2 ) 2 (OAc) 2 (P 2 W 16 O 59 ) 2 ] · 51H 2 O ( 1 ), (NH 4 ) 16 [Zr 4 (μ 3 ‐O) 2 (Mal) 2 (H 2 O) 2 (P 2 W 16 O 59 ) 2 ] · 14H 2 O ( 2 ), and Na 7 (NH 4 ) 5 [{Zr 4 (OH) 6 (OAc) 2 }(SiW 10 O 37 ) 2 ] · 20H 2 O(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 [P 2 W 16 O 59 ] 12– building blocks, but they differ in the modifying ligands on the {Zr 4 } 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‐SiW 10 O 37 ] 10– moieties and decorated by two acetato ligands. The catalytic activities of 1 – 3 were evaluated on the basis of a catalytic oxidation reaction of the peroxidase substrate 3,3′,5,5′‐tetramethylbenzidine (TMB) by H 2 O 2 . Compound 1 exhibits the best catalytic activity, which suggests a new peroxidase‐like catalyst for the colorimetric detection of H 2 O 2 with a linear detection range from 100 to 1000 μ M ( r = 0.997) and a detection limit of 100 μ M .