Ac. Bean et al., 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), INORG CHEM, 40(16), 2001, pp. 3959-3963
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.