Abstract The [As2W18U3O74]12 complex is formed by the ‘‘self-assembly’’ reaction of WO4 2;HAsO4 2 and UO2 2þ (uranyl nitrate) ions in acidic media. The anion complex is isolated as the potassium salt and characterized by elemental analysis, IR, UV–Vis, and X-ray single crystal analysis. The complex contains an anion in which three UO2 2þ ions are unsymmetrically sandwiched between two A-a- [AsW9O34]9 groups leading to a structure of C3v symmetry. Each uranium atom adopts pentagonal-bipyramidal coordination, achieved by three equatorial bonds to one [AsW9O34]9and two bonds to the other. The [As2W18U2V2O73]12and also [As2W18U3O74]12 complexes are formed also, by reaction of the [KAs2W18U2O72]13 with VO2+ and UO2 2þ ions in 1:1 mole ratio. The cyclic voltammogram of [As2W18U2VO73]12 in acetate buffer (pH 4.7) shows a reversible one-electron redox process for VIV/V

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