Uranyl Bond Research Articles

Crystal structure of uranyl benzene 1,2,4,5-tetracarboxylate dihydrate: UO 2C 10O 8H 4 · 2H 2O

The crystal structure of the complex in the title was determined by X-ray crystallography from single-crystal diffractometer data. Crystal data: UO 2C 10O 8H 4 · 2H 2O, triniclic, P 1 ̄ , a = 6.355(6) A ̊ , b = 11.531(9) A ̊ , c = 5.548(5) A ̊ , α = 104.07 °, β = 109.06 °, γ = 81.85 °, M = 558.192, Z = 1, V =371.875 A ̊ 3 , d calc = 2.49 g cm −3, R ( F) = 0.106, R w = 0.134 for 3413 independent reflections. The hexagonal dipyramid around the uranium atom contains two carboxyl ligands and two water molecules in the equatorial plane of the uranyl ion. The U—O (uranyl bond) is 1.70(2) Å, 〈U—O〉 in the equatorial plane is 2.48 Å, and other distances and angles are similar to those in the literature.

Uranyl(VI) compounds. 3. Crystal structures of two forms of bis(urea)dioxouranium(VI) sulfate

The structures of the ..cap alpha.. and ..beta.. forms of the title compound UO/sub 2/SO/sub 4/.2CO(NH/sub 2/)/sub 2/ are similar. The uranium atom lies at the center of a pentagonal bipyramid formed by the oxygen atoms. Of the 5 equatorial oxygens, 3 belong to sulfate groups and two to urea molecules. The bridging tridentate sulfate groups join the bipyramids into infinite double chains in the same fashion as in uranyl sulfate hydrates. Selected interatomic distances and angles are listed. The distances and angles in UO/sub 7/ polyhedra are in close agreement with values reported for other related uranyl sulfates. The U-O (uranyl) bond distances in the ..cap alpha.. form are unusually long, exceeding 1.8 A. The U-O (urea) distances in the ..beta.. are slightly longer than in the ..cap alpha.. form. The orientation of the planar area molecules is different in the 2 forms. The urea molecules are involved in the hydrogen bonding within and between the chains. The main structural difference between the 2 forms lies in the packing of the chains. The packing efficiency is slightly greater in the ..cap alpha.. form as the unit cell volume is 2.3% smaller. 2 figures, 5 tables.

Electronic–vibrational mechanism of the reactivity and feasibility of laser control of chemical processes involving complex uranyl compounds

An analysis is made of the nature of the reactivity of complex uranyl compounds. Perturbation theory is used to estimate the enthalpy of activation reactions of dissociation and substitution of equatorial ligands. It is shown that feasibility of selective action of 10-μ CO2 laser radiation on these processes is due to the transfer of energy of vibrational excitation of the uranyl bond to the equatorial plane of a complex.

The crystal structures of α- and β-CdUO 4

The structural parameters of α- and β-CdUO 4 crystals are determined by X-ray powder diffraction technique. α-CdUO 4 is rhombohedral and cell parameters are a = 6.233(3) Å and α = 36.12(5)°. β-CdUO 4 crystallizes in a C-centered orthorhombic cell with a = 7.023(4), b = 6.849(3), c = 3.514 (2) Å. The space groups are R 3m for α-CdUO 4 and Cmmm for β-CdUO 4. α-CdUO 4: 1U in (000), 1Cd in ( 1 2 1 2 1 2 ), 2O(1) in ±( uuu), 2O(2) in ±( vvv); u = 0.113, v = 0.350, Z = 1. β-CdUO 4: 2U in ( 000; 1 2 1 2 0 ), 2Cd in ( 1 2 0 1 2 ; 0 1 2 , 1 2 ), 4O(1) in ( 0, ±y, 0; 1 2 , 1 2 ±y, 0 ), 4O(2) in ( ±x, 0, 1 2 ; 1 2 ±x, 1 2 , 1 2 ); x = 0.159, y = 0.278, Z = 2. β-CdUO 4 contains collinear uranyl UO 2+ 2 groups with a UO(1) distance of 1.91 Å, located either along or parallel to the c axis whereas the UO(1) bond length in α-CdUO 4 is 1.98 Å which is longer than the usual uranyl bond length.

Laser Raman Spectra and Normal Coordinate Analysis of Some Uranyl Tetrachloride Complexes

Laser Raman spectra of uranyl tetrachloride complexes [K2UO2Cl4, Rb2UO2Cl4, Cs2UO2Cl4, (NH4)2UO2Cl4] have been measured in the region from 3500 to 10 cm−1. Vibrational assignments as well as normal coordinate analyses have been carried out with the assumption that all the complexes contain discrete (UO2Cl4)2− ions belonging to a point group D4h. To understand the nature of the uranyl bonds in the complexes, approximate π-bonding energies of such bonds have been estimated from the U—O stretching force constants. The reliability of the values obtained are discussed in detail on the basis of Mulliken's magic formula.

RAMAN SPECTROSCOPIC STUDIES OF SOME URANYL NITRATE COMPLEXES

Abstract Laser Raman spectra of uranyl trinitrate complexes (KUO2(NO3)3, RbUO2(NO3)3, CsUO2(NO3)3, NH4UO2(NO3)3) have been measured in the region from 2000 cm−1 to 10 cm−1. Vibrational assignments have been made on the assumption that all the complexes contain discrete UO2X3 − (X = NO3) ions belonging to a point group of D3h. A brief discussion is made on the ligation effect of nitrate group on the uranyl bond order from a point of view of molecular orbital theory.

IR spectroscopic studies of some uranyl tetrachloride complexes

The IR spectra of dipotassium, dirubidium and diammonium uranyl tetrachloride hydrates (K 2UO 2Cl 4·3H 2O, Rb 2UO 2Cl 4·H 2O, (NH 4) 2UO 2Cl 4·4H 2O) have been measured in the region from 4000 down to 30 cm −1. A normal coordinate analysis of the (UO 2Cl 4) 2− ion apart from the K +, Rb + and NH 4 + ions has been made using Wilson's FG matrix method. The force constants associated with the UO and UCl bonds have been obtained on the basis of both the force models of modified Urey-Bradley and valence force fields. An effort has been directed towards the understanding of the uranyl bond weakening with coordination of the ligands. It has been suggested that this bond weakening is caused by charge transfer from the ligands to the uranium atom.

The crystal structures of α and γ SrUO4

Abstract On rhombohedral strontium monouranate which is metastable below ca. 770°C (α-phase) and stable above ca. 1230°C (γ-phase) in air, x-ray powder diffraction study was made with the samples of three different compositions, i.e. SrUO3.948(1), SrUO3.597(1) and SrUO3.777(1). Their structures were essentially identical with that of Zachariasen (1948) on SrUO4 with space group R[unk]m, Z = 1; 1 U in (000), 1 Sr in (½½½),2 O(1) in ±(uuu) and 2 O(2) in ± (vvv), and no more discrepancies were observed in the cell and the oxygen parameters between α and γ phases than those resulted from the oxygen non-stoichiometry: SrUO3.948(1) a = 6.551(3) Å, α = 34.82(2)°, u = 0.112(2), v = 0.357(2) SrUO3.597(1) a = 6.587(3) Å, α = 35.30(2)°, u = 0.110(2), v = 0.340(2) SrUO3.777<1) a = 6.542(3) Å, α = 35.54(2)°, u = 0.113(2), v = 0.340(2). In oxygen deficient crystals, oxygen vacancies were found to be formed in O(2) position but not in O(1). The U–O(2) bond length 2.30(1) ∼ 2.31(1) Å is reasonably consistent with the other alkali and alkaline-earth uranates, whereas the U–O(1) bond length lies in the range 2.04(4) ∼ 2.08(4) Å which is longer than the usual uranyl bond length of 1.8 ∼ 1.9 Å.

Neutron powder profile studies of the gamma uranium trioxide phases

Neutron powder profile studies show the existence of three phases in gamma uranium trioxide between 373°K and 77°K. The three phases are closely related and the transitions smooth and displacive. At 373°K, γ-UO 3 is tetragonal, with a = 6.9013 (5) and c = 19.9754 (18) Å, and space group I4 1 amd( D 19 4h) . At 323°K, γ-UO 3 becomes orthorhombic, space group F ddd (D 24 2 h ), with the cell dimensions (293°K) a = 9.787 (3), b = 19.932 (4) and c = 9.705 (3) Å. There is a further transition between 293°K and 77°K, and, at 77°K, the orthorhombic dimensions of the pseudocell are a = 9.8225 (7), b = 19.8487 (15), and c = 9.6318 (7) Å. The neutron diffraction studies show that, in all three phases, the coordination polyhedra of the two crystallographically distinct uranium atoms are octahedral and (dodecahedral-2) respectively. At 293°K, the shortest UO distance is 1.796 (6) Å, and thus there are no pure uranyl bonds, in agreement with the infrared spectrum. The UO distances are precise to about ± 0.006 Å, about ten times the precision of an earlier X-ray single-crystal study, in which the conclusions were in conflict with the infrared spectrum. The structure is made up of parallel chains of edge-fused U(2) octahedra, cross-linked by U(1) dodecahedra. The atomic shifts are not great in going from 373°K to 77°K; at 293°K the data will refine in the pseudotetragonal cell as well as the true orthorhombic cell, and the 77°K data will refine in the F ddd cell.

INFRARED SPECTROSCOPIC STUDIES OF SOME URANYL NITRATE COMPLEXES

Abstract The infrared spectra of ammonium, potassium, rubidium and cesium uranyl trinitrates (NH4UO2(NO3)3, KUO2(NO3)3, RbUO2(NO3)3 and CsUO2(NO3)3) have been measured in the region from 4000 cm−1 down to 30 cm−1. A normal coordinate analysis of the complexes has been made as a six-body problem (UO2 X3) (X=NO3) neglecting the outer cations. Force constants of U-O and U-X bonds in UO2X3 anion have been approximately obtained on the basis of a modified valence force field including an additional force constant of opposite U[sbnd]O bond-bond interaction. In addition, bond order of the uranyl bonds of the complexes has been determined from the U[sbnd]O stretching force constants and compared with those of other uranium compounds such as metal uranates and uranium oxides.

Uranates(VI) and tungstates(VI) within the system Li 2OUO 3WO 3

The system Li 2OUO 3WO 3, which was investigated between 300 and 1600°C at 1 atm O 2, contains the compounds Li 6WO 6Li 6UO 6, Li 4WO 5Li 4UO 5, Li 2WO 4Li 2UO 4, Li 2W 2O 7, Li 2W 4O 13, LiU 0.83O 3, Li 2U 3O 10, Li 2U 6O 19, UWO 6 and UW 3O 12. Lithium uranates(VI) and -tungstates(VI) with high Li 2O-content show an octahedral coordination of uranium and tungsten in closely related crystal structures and can form some solid solutions. At low Li 2O-content uranium forms strong uranyl bonds whereas tungsten prefers tetrahedral coordination with very little solid solution of uranium.

Infra-red spectra of some alkali metal uranates

Infra-red spectra (900-240 cm −1) of twelve alkali metal uranates are presented. Uranyl stretching vibrations of the monouranates occur between 700 and 800 cm −1, and of the diuranates between 750 and 850 cm −1. The infra-red results are correlated with X-ray diffraction data, and uranyl bond lengths of the compounds have been calculated.