Excision of uranium oxide chains and ribbons in the novel one-dimensional uranyl iodates K-2[(UO2)(3)(IO3)(4)O-2] and Ba[(UO2)(2)(IO3)(2)O-2](H2O)

The alkali metal and alkaline-earth metal uranyl iodates K-2[(UO2)(3)(IO3)( 4)O-2] and Ba[(UO2)(2)(IO3)(2)O-2](H2O) have been prepared from the hydroth ermal reactions of KCI or BaCl2 with UO3 and I2O5 at 425 and 180 degreesC, respectively. While K-2[(UO2)(3)(IO3)(4)O-2] can be synthesized under both mild and supercritical conditions, the yield increases from <5% to 73% as t he temperature is raised from 180 to 425 degreesC. Ba[(UO2)(2)(IO3)(2)O-2]H 2O), however, has only been isolated from reactions performed in the mild t emperature regime. Thermal measurements (DSC) indicate that K-2[(UO2)(3)(IO 3)(4)O-2] is more stable than Ba[(UO2)(2)(IO3)(2)O-2](H2O) and that both co mpounds 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[(UO2)(3-)(IO3)(4)O-2] is composed of (I)(infinity)(UO2)(3) (IO3)(4)O-2](2-) chains built from the edge-sharing UO7 pentagonal bipyrami ds and UO6 octahedra. Ba[(UO2)(2)(IO3)(2)O-2](H2O) consists of one-dimensio nal (1)(infinity)(UO2)(2)(IO3)(2)O-2](2-) ribbons formed from the edge shar ing of distorted U07 pentagonal bipyramids. In both compounds the iodate gr oups occur in both bridging and monodentate binding modes and further serve to terminate the edges of the uranium oxide chains. The K+ or Ba2+ cations separate the chains or ribbons in these compounds forming bonds with termi nal oxygen atoms from the iodate ligands. Crystallographic data: K-2[(UO2)( 3)(IO3)(4)O-2], triclinic, space group P (1) over bar, a = 7.0372(5) Angstr om, b = 7.7727(5) Angstrom, c = 8.9851(6) Angstrom, alpha = 93.386(1)degree s, beta = 105.668(1)degrees, gamma = 91.339(1)degrees, Z = 1; Ba[(UO2)(2)(I O3)(2)O-2](H2O), monoclinic, space group P2(1)/c, a = 8.062(4) Angstrom, b = 6.940(3) Angstrom, c = 21.67(1), beta = 98.05(1)', Z = 4.