The uranyl iodates, UO2(IO3)2 (AU1 − 8) and UO2(IO3)2(H2O) (AU2 − 8) have been prepared from the reaction of UO3 with I2O5 under hydrothermal conditions. Equilibrium between AU1 − 8 and AU2 − 8 is established after 3 days at 400 °C, resulting in the isolation of an equimolar ratio of these compounds. Lowering of the reaction temperature to 180 °C or shortening of the reaction duration to 1 day allows for the isolation of AU2 − 8 in pure form. At 327 °C, AU2 − 8 undergoes dehydration and structural rearrangement to AU1 − 8, which is a reversible process. Single-crystal X-ray diffraction, bond valence sum calculations, EDX, DSC, TGA, and vibrational and fluorescence spectroscopy have been used to characterize these compounds. Crystallographic data are as follows:  AU1 − 8, monoclinic, space group P21/n, a = 4.2454(8) Å, b = 16.636(5) Å, c = 5.284(1) Å, β = 107.57(2)°, and Z = 2; AU2 − 8, orthorhombic, space group Pbcn, a = 8.452(2) Å, b = 7.707(2) Å, c = 12.271(3), and Z = 4. The structure of AU1 − 8 is pseudo-three-dimensional with one-dimensional uranyl iodate chains forming close I···O interchain contacts. Each one-dimensional chain consists of edge-sharing UO8 hexagonal bipyramids and chelating iodate anions that also bridge the UO2 2+ units through μ3-O atoms. AU2 − 8 has a corrugated layered structure containing pentagonal bipyramidal UO7 units that are formed from the binding of four oxygen atoms from four bridging iodates and the coordination of a water molecule to the UO2 2+ moiety. Both of these compounds fluoresce when irradiated with UV light (365 nm), yielding emission spectra characteristic of the uranyl dication.

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The hydrothermal reaction of elemental Ag, or water-soluble silver sources, with UO3 and I2O5 at 200 degrees C for 5 days yields Ag4(UO2)4(IO3)2(IO4)2O2 in the form of orange fibrous needles. Single-crystal X-ray diffraction studies on this compound reveal a highly complex network structure consisting of three interconnected low-dimensional substructures. The first of these substructures are ribbons of UO8 hexagonal bipyramids that edge-share to form one-dimensional chains. These units further edge-share with pentagonal bipyramidal UO7 units to create ribbons. The edges of the ribbons are partially terminated by tetraoxoiodate(V), [IO4]3-, anions. The uranium oxide ribbons are joined by bridging iodate ligands to yield two-dimensional undulating sheets. These sheets help to form, and are linked together by, one-dimensional chains of edge-sharing AgO7 capped octahedral units and ribbons formed by corner-sharing capped trigonal planar AgO4 polyhedra, AgO6 capped square pyramids, and AgO6 octahedra. The [IO4]3- anions in Ag4(UO2)4(IO3)2)(IO4)2O2 are tetraoxoiodate(V), not metaperiodate, and contain I(V) with a stereochemically active lone-pair. Bond valence sum calculations are consistent with this formulation. Differential scanning calorimetry measurements show distinctly different thermal behavior of Ag4(UO2)4(IO3)2(IO4)2O2 versus other uranyl iodate compounds with endotherms at 479 and 494 degrees C. Density functional theory (DFT) calculations demonstrate that the approximate C2v geometry of the [IO4]3- anion can be attributed to a second-order Jahn-Teller distortion. DFT optimized geometry for the [IO4]3- anion is in good agreement with those measured from single-crystal X-ray diffraction studies on Ag4(UO2)4(IO3)2(IO4)2O2.

The alkali metal and alkaline-earth metal uranyl iodates K(2)[(UO(2))(3)(IO(3))(4)O(2)] and Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O) have been prepared from the hydrothermal reactions of KCl or BaCl(2) with UO(3) and I(2)O(5) at 425 and 180 degrees C, respectively. While K(2)[(UO(2))(3)(IO(3))(4)O(2)] can be synthesized under both mild and supercritical conditions, the yield increases from <5% to 73% as the temperature is raised from 180 to 425 degrees C. Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O), however, has only been isolated from reactions performed in the mild temperature regime. Thermal measurements (DSC) indicate that K(2)[(UO(2))(3)(IO(3))(4)O(2)] is more stable than Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O) and that both compounds decompose through thermal disproportionation at 579 and 575 degrees C, respectively. The difference in the thermal behavior of these compounds provides a basis for the divergence of their preparation temperatures. The structure of K(2)[(UO(2))(3)(IO(3))(4)O(2)] is composed of [(UO(2))(3)(IO(3))(4)O(2)](2)(-) chains built from the edge-sharing UO(7) pentagonal bipyramids and UO(6) octahedra. Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O) consists of one-dimensional [(UO(2))(2)(IO(3))(2)O(2)](2)(-) ribbons formed from the edge sharing of distorted UO(7) pentagonal bipyramids. In both compounds the iodate groups occur in both bridging and monodentate binding modes and further serve to terminate the edges of the uranium oxide chains. The K(+) or Ba(2+) cations separate the chains or ribbons in these compounds forming bonds with terminal oxygen atoms from the iodate ligands. Crystallographic data: K(2)[(UO(2))(3)(IO(3))(4)O(2)], triclinic, space group P_1, a = 7.0372(5) A, b = 7.7727(5) A, c = 8.9851(6) A, alpha = 93.386(1) degrees, beta = 105.668(1) degrees, gamma = 91.339(1) degrees, Z = 1; Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O), monoclinic, space group P2(1)/c, a = 8.062(4) A, b = 6.940(3) A, c = 21.67(1), beta= 98.05(1) degrees, Z = 4.