A new organic-inorganic heteropoly blue based on Dawson-type molybdosulfate and organic dye, (MB)(5)[(S2Mo1Mo17O62)-Mo-V-O-VI]center dot 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 C-H center dot center dot center dot O, C-H center dot center dot center dot S and C-H center dot center dot center dot N, and C-H center dot center dot center dot pi, pi center dot center dot center dot pi 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 chi T-M from 0.28 cm(3) mol(-1) at ambient temperature down to 0.13 cm(3) mol(-1) K at 2 K indicates the presence of antiferromagnetic interactions among the mono-electron reduction polyanions, (S2Mo1Mo17O625-)-Mo-V-O-VI. 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. (C) 2013 Elsevier Ltd. All rights reserved.