A New Oxoanion: [IO 4 ] 3- Containing I(V) with a Stereochemically Active Lone-Pair in the Silver Uranyl Iodate Tetraoxoiodate(V), Ag 4 (UO 2 ) 4 (IO 3 ) 2 (IO 4 ) 2 O 2 Amanda C. Bean, † Charles F. Campana, ‡ Ohyun Kwon, † and Thomas E. Albrecht-Schmitt* ,† Contribution from the Department of Chemistry, Auburn UniVersity, Auburn, Alabama 36849, and Bruker AXS, 5465 East Cheryl Parkway, Madison, Wisconsin 53711 ReceiVed May 15, 2001 Abstract: The hydrothermal reaction of elemental Ag, or water-soluble silver sources, with UO 3 and I 2 O 5 at 200 °C for 5 days yields Ag 4 (UO 2 ) 4 (IO 3 ) 2 (IO 4 ) 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 UO 8 hexagonal bipyramids that edge-share to form one-dimensional chains. These units further edge-share with pentagonal bipyramidal UO 7 units to create ribbons. The edges of the ribbons are partially terminated by tetraoxoiodate(V), [IO 4 ] 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 AgO 7 capped octahedral units and ribbons formed by corner-sharing capped trigonal planar AgO 4 polyhedra, AgO 6 capped square pyramids, and AgO 6 octahedra. The [IO 4 ] 3- anions in Ag 4 (UO 2 ) 4 (IO 3 ) 2 (IO 4 ) 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 (UO 2 ) 4 (IO 3 ) 2 (IO 4 ) 2 O 2 versus other uranyl iodate compounds with endotherms at 479 and 494 °C. Density functional theory (DFT) calculations demonstrate that the approximate C 2V geometry of the [IO 4 ] 3- anion can be attributed to a second-order Jahn-Teller distortion. DFT optimized geometry for the [IO 4 ] 3- anion is in good agreement with those measured from single-crystal X-ray diffraction studies on Ag 4 - (UO 2 ) 4 (IO 3 ) 2 (IO 4 ) 2 O 2 . Introduction Oxoanions of iodine display highly complex chemistry in both solution and the solid state owing to a series of equilibria among periodate, [IO 6 ], 5- and metaperiodate, [IO 4 ] - , species in aqueous media 1 and the thermal disproportionation of iodate to meta- periodate and iodine at moderate to high temperatures in the solid state. 2-6 As ligands, iodate and periodate display a number of unusual properties. The former anion, having C 3V symmetry and a stereochemically active lone-pair, has a propensity for yielding compounds with low-dimensional character. 7,8 Fur- thermore, these solids often crystallize in noncentrosymmetric space groups, especially with lanthanides, and therefore have been the subject of considerable physicochemical property measurements. 9-13 The latter anion has the ability to stabilize unusually high oxidation states for transition metals, including Cu(III), 14-16 Ag(III), 14,15,17 and Ni(IV). 18 Our recent efforts in the preparation of new solids containing oxoanions of iodine has focused on the hydrothermal syntheses of low-dimensional uranyl iodates. 7,8 The straightforward reac- tion of UO 3 with I 2 O 5 yields UO 2 (IO 3 ) 2 (H 2 O) or UO 2 (IO 3 ) 2 depending on whether mild (<250 °C) or supercritical (>374 °C) temperatures are employed. 7 However, the uranyl iodate framework is quite versatile, and a large number of cations can be incorporated to yield new compounds, including alkali metals, alkaline-earth metals, and main group elements. This has allowed for the isolation and structural elucidation of A 2 [(UO 2 ) 3 - (IO 3 ) 4 O 2 ] (A ) K, 7 Rb 19 , TI 19 ), Cs 2 [(UO 2 ) 3 Cl 2 (IO 3 )(OH)O 2 ]‚ 2H 2 O, and AE[(UO 2 ) 2 (IO 3 ) 2 O 2 ](H 2 O) (AE ) Sr, 19 Ba, 7 Pb 19 ). † Auburn University. ‡ Bruker AXS. (1) Buist, G. J.; Hipperson, W. C. P.; Lewis, J. D. J. Chem. Soc. A 1969, 2, 307. (2) Alici, E.; Schmidt, T.; Lutz, H. D. Z. Anorg. Allg. Chem. 1992, 608, 135. (3) Hoppe, R.; Schneider, J. J. Less-Common Met. 1988, 137, 85. (4) Hejek, B.; Hradilova, J. J. Less-Common Met. 1971, 23, 217. (5) Nassau, K.; Shiever, J. W.; Prescott, B. E.; Cooper, A. S. J. Solid State Chem. 1974, 11, 314. (6) Nassau, K.; Shiever, J. W.; Prescott, B. E. J. Solid State Chem. 1975, 14, 122. (7) Bean, A. C.; Peper, S. M.; Albrecht-Schmitt, T. E. Chem. Mater. 2001, 13, 1266. (8) Bean, A. C.; Ruf, M.; Albrecht-Schmitt, T. E. Inorg. Chem. 2001, 40, 3959. (9) Liminga, R.; Abrahams, S. C.; Bernstein, J. L. J. Chem. Phys. 1975, 62, 755. 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Soc. 2001, 123, 8806-8810 10.1021/ja011204y CCC: $20.00 © 2001 American Chemical Society Published on Web 08/15/2001