The reaction Of UO3 with V2O5 and KIO4 under mild hydrothermal conditions produces K-2[(UO2)(2)(VO)(2)(IO6)(2)O].H2O (1) in the form of orange acicular crystals. The structure of 1 consists of UO6, VO6, and IO6 distorted octahedra that are assembled into a polar, open-framework structure. The distorted VO6 and IO6 octahedra edge-share to form chains that run down the c-axis. Each VO6 octahedron also shares a vertex with an adjacent vanadium atom to link the chains together into a ribbon. The IO6 units also partake in corner-sharing with the UO6 units to create interconnected elliptical tubes. The major channels in 1 are filled with K+ cations and water molecules, The polarity of this compound is caused by alignment of distorted vanadyl hexaoxoiodate ribbons and UO6 trapezoidal bipyramids resulting in a large second-harmonic generation response of 300 times that of alpha-quartz. Crystallographic data: 1, orthorhombic, space group Pba2, a = 9.984(2) Angstrom, b = 16.763(3) Angstrom, c = 4.977(l) Angstrom, Z = 4 (T = 193 K).