Organic-inorganic heteropoly blue based on Dawson-type molybdosulfate and organic dye and its characterization and application in electrocatalysis

A new organic-inorganic heteropoly blue based on Dawson-type molybdosulfate and organic dye, (MB)5[S2Mo1VMo17VlO62]·CH3CN (MB = C16H18N3S), was synthesized under ambient conditions and characterized by IR, fluorescence spectrum, single crystal X-ray diffraction, magnetism measurement and X-ray photoelectron spectroscopy analysis. X-ray diffraction analysis shows that the polyoxoanions fill in the interspace formed by the MB cations and acetonitrile and interacted by Coulombic forces, complex hydrogen bonds, such as CH⋯O, CH⋯S and CH⋯N, and CH⋯π, π⋯π stacking interactions. The XPS data and magnetic measurements show that the polyanion was mixed valence as a result of one electron reduction. The monotonous decrease of χMT from 0.28 cm3 mol−1 at ambient temperature down to 0.13 cm3 mol−1 K at 2 K indicates the presence of antiferromagnetic interactions among the mono-electron reduction polyanions, S2Mo1VMo17VlO625−. Studies of the photoluminescent properties in acetonitrile solution suggest the presence of the formation of ion pairs of [S2Mo18O62]4− anion and MB cation or charge-transfer transitions between the cationic MB donor and the POM acceptor. Furthermore, the organic-inorganic heteropoly blue was used to fabricate a modified carbon paste electrode (1-CPE), which exhibits five pair redox peaks in the potential range −300 mV to 700 mV and more positive first redox potentials than P2Mo18O626−, higher stability and good electrocatalytic activity toward the reduction of nitrite, chlorate, bromate and hydrogen peroxide in acidic (1 M H2SO4) aqueous solution.