Competitive Coordination of the Uranyl ion by Perchlorate and Water - The Crystal Structures of UO2(ClO4)2·3H2O and UO2(ClO4)2·5H2O and a Redetermination of UO2(ClO4)2·7H2O (Z. Anorg. Allg. Chem.2003,629, 1012-1016)

AbstractUranyl-organic complexation in geologic fluids can have a profound impact upon uranium solubility and transport. Studies of uranyl organometallic crystal structures provide a basis for understanding complexation of the uranyl ion in solution.The crystal structures of several novel uranyl oxalates, synthesized under mild hydrothermal conditions, have been determined. These structures demonstrate new features little seen or not previously known in this chemical system, in particular polymerization into infinite sheets and direct linkage of uranyl polyhedra. Further work on the chemistry of this and other systems of hexavalent uranium and low molecular weight carboxylic acids, especially formic acid, is likely to turn up new insights.Although a hierarchical scheme exists for classifying inorganic uranyl compounds [1], no similar work has been done for organic compounds. Such a hierarchy would have practical benefits, in particular making structural information more accessible and understandable to workers studying related problems such as the environmental transport of hexavalent uranium as dissolved organic complexes. We offer a simple scheme that classifies uranyl oxalate structures by analyzing the long-range structural features and the coordination environments of uranyl ions, which leads to a structural symbol that can be used to easily identify uranyl oxalates with common structural features. This system is equally applicable to other carboxylate complexes with the uranyl ion, and could be extended to apply to any organic complex of the uranyl ion.

Download Full-text

Pollutant Identification by Selected Area Electron Diffraction

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100052675 ◽

1974 ◽

Vol 32 ◽

pp. 532-533

Author(s):

R. E. Ferrell ◽

G. G. Paulson ◽

C. W. Walker

Keyword(s):

Thermal Treatment ◽

Electron Diffraction ◽

Sample Preparation ◽

Crystal Structures ◽

Water Samples ◽

Environmental Samples ◽

Short Review ◽

Selected Area Electron Diffraction ◽

Multiple Component

Selected area electron diffraction (SAD) has been used successfully to determine crystal structures, identify traces of minerals in rocks, and characterize the phases formed during thermal treatment of micron-sized particles. There is an increased interest in the method because it has the potential capability of identifying micron-sized pollutants in air and water samples. This paper is a short review of the theory behind SAD and a discussion of the sample preparation employed for the analysis of multiple component environmental samples.

Download Full-text

The Imaging of Crystal Structures and Crystal Defects

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100069995 ◽

1978 ◽

Vol 36 (3) ◽

pp. 207-217

Author(s):

J.M. Cowley

Keyword(s):

Electron Microscope ◽

Crystal Structures ◽

Phase Contrast ◽

Crystal Defects ◽

Atom Density ◽

Lack Of Information ◽

Spatial Frequencies

The problem of "understandinq" electron microscope imaqes becomes more acute as the resolution is improved. The naive interpretation of an imaqe as representinq the projection of an atom density becomes less and less appropriate. We are increasinqly forced to face the complexities of coherent imaqinq of what are essentially phase objects. Most electron microscopists are now aware that, for very thin weakly scatterinq objects such as thin unstained bioloqical specimens, hiqh resolution imaqes are best obtained near the optimum defocus, as prescribed by Scherzer, where the phase contrast imaqe qives a qood representation of the projected potential, apart from a lack of information on the lower spatial frequencies. But phase contrast imaqinq is never simple except in idealized limitinq cases.

Download Full-text