Designing polyoxometalate-based metal-organic framework for oxidation of styrene and cycloaddition of CO2 with epoxides

A photoactive polyoxometalate-based metal−organic framework (POMOF), NiW-DPNDI, was synthesized by combination of Ni(II) ions, [ZnW12O40]6‒ anions, and N,N'-bis(4-pyridylmethyl)naphthalene diimide (DPNDI) molecules into one single framework. NiW-DPNDI displays a three-dimensional structure by the strong anion⋅⋅⋅π interactions between the trapped [ZnW12O40]6‒ anions and the electron-deficient naphthalenic ring centroids and the π−π stacking interactions between DPNDI moieties. NiW-DPNDI displayed a highly efficient hole-electron separation and ordered electron transfer under irradiation, thus ensuing its excellent photocatalysis in oxidation of styrene to produce benzaldehyde. In addition, it gave a high efficiency for styrene oxide under thermocatalytic conditions. Because the carbonic anhydrase (CA)-mimicking Ni sites and the negative electron-enriched [ZnW12O40]6‒ anions are well aligned in the pores, it can promote the cycloaddition of CO2 with epoxides under mild conditions.