The syntheses, crystal structures, and characterizations of two Mn^II/III-sandwiching polyoxometalate complexes based on [α-SeW₉O₃₃]⁸⁻ units

Two sandwich-type polyoxometalates (POM) based on [α-SeW₉O₃₃]⁸⁻ building blocks, K₈[{Mn^II(H₂O)}₂(WO)(SeW₉O₃₃)₂]·12H₂O (1) and K₆[{Mn^III(H₂O)}₂(WO)(SeW₉O₃₃)₂]·18H₂O (2), have been synthesized and characterized by elemental analyses, IR, diffuse reflectance UV–vis-NIR spectra, TG, X-ray photoelectron spectroscopy, and single-crystal X-ray diffraction. Electrochemical properties and photocatalytic activities have also been investigated. Single-crystal X-ray diffraction analysis shows that the polyoxoanions of 1 and 2 have similar sandwich structures composed of [α-SeW₉O₃₃]⁸⁻ units except for different oxidation states of Mn centers (II for 1, III for 2). Compound 2 is the first high-valent trinuclear-manganese (III)-substituted [α-SeW₉O₃₃]⁸⁻-based POM. Cyclic voltammograms of 1 and 2 show irreversible redox processes for Mn²⁺ and Mn³⁺, respectively. Compound 2 has better photocatalytic properties with photocatalytic degradation of Rhodamine-B (RhB) compared to 1.