A new oxoanion:: [IO4]3- containing I(V) with a stereochemically active lone-pair in the silver uranyl iodate tetraoxoiodate(V), Ag4(UO2)4(IO3)2(IO4)2O2

The hydrothermal reaction of elemental Ag, or water-soluble silver sources, with UO3 and I2O5 at 200 degreesC for 5 days yields Ag-4(UO2)(4)(IO3)(2)(IO4)(2)O-2 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 ribbon, formed by corner-sharing capped trigonal planar AgO4 polyhedra, AgO6 capped square pyramids. and AgO6 octahedra. The [IO4]3- anions in Ag-4(UO2)(4)(IO3)(2)(IO4)(2)O-2 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 Ag-4(UO2)(4)(IO3)(2)(IO4)(2)O-2 versus other uranyl iodate compounds with endotherms at 479 and 494 degreesC. Density functional theory (DFT) calculations demonstrate that the approximate C-2v 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 Ag-4(UO2)(4)(IO3)(2)(IO4)(2)O-2.