Uranium crystal structure

Elemental uranium, crystal structures of, 25 409. See also Uranium (U) Elementary reaction, 21 336 Element/isotope ratios, in fine art examination/conservation, 11 419 Element mapping, in fine art examination/ conservation, 11 406 Element names/symbols, 17 386-387 transfermium, 17 387t Elements, in earth s crust, 26 23 a-Eleostearic acid, physical properties, 5 33t... 

Initially, the only means of obtaining elements higher than uranium was by a-particle bombardment of uranium in the cyclotron, and it was by this means that the first, exceedingly minute amounts of neptunium and plutonium were obtained. The separation of these elements from other products and from uranium was difficult methods were devised involving co-precipitation of the minute amounts of their salts on a larger amount of a precipitate with a similar crystal structure (the carrier ). The properties were studied, using quantities of the order of 10 g in volumes of... 

Reactions of UCI4 with [Li RC(NCy)2 (THF)]2 (R = Me, Bu ) in THF gave the tris(amidinate) compounds [RC(NCy)2]3UCl that could be reduced with lithium powder in THF to the dark-green homoleptic uranium(lll) complexes [RC(NCy)2]3U. Comparison of the crystal structure of [MeC(NCy)2]3U with those of the lanthanide analog showed that the average U-N distance is shorter than expected from a purely ionic bonding model. ... 

The crystal structures of a number of diphosphine disulphides (121) and (122) show a remarkable constancy in the bond lengths. Two types of molecule are observed in the crystal of the tetramethyl compound (121, X = Y = Me). The crystal structure of triphenylphosphine oxide (P—C 176 pm, P—O 164 pm) varies little from that observed in the uranium oxide complexes, and does not confirm P—O bond lengthening in complexes, as indicated by vp=.o (see Section 3C). 

Crystal Chemical Studies of the 5/-Series of Elements. VIII. Crystal Structure Studies of Uranium Silicides and of CeSia, NpSi3 and PuSia. Acta crystallogr. (London) 2, 94 (1949). 

Acta Cryst. B39 165-170 Pauling, L. Hendricks, S.B. (1925) The crystal structures of hematite and corundum. J. Am. Chem. Soc. 47 781-790 Pauling, L. (1929) The principles of determining the structure of complex ionic crystals. J. Amer. Chem. Soc. 51 289-296 Payne, J.E. Davis, J.A. Waite,T.D. (1996) Uranium adsorption on ferrihydrite — effect of phosphate und humic add. Radiochemica Acta 74 239-243... 

Between the two possible defects which may be responsible for hyperstoichiometry (i.e. uranium interstitials or oxygen vacancies) the latter is well evidenced by measurements of lattice parameter and densityand neutron diffraction Oxygen interstitials order in U4O9 to provide a crystal structure which can be derived from the fluorite structure of U02+x-... 

Samarskite.—TYna tantaloniobate mineral has a widely varying composition, and was first discovered in the Urals. The presence of uranium in this mineral renders it radioactive. The presence of lead and helium has been detected. The ratio of lanthanides to yttrium is approximataly 1 6. In its crystal structure samarskite resembles yttrotantalite. Native crystals are brown, or velvet black, and become yellow orange when crushed showing pleochroism. 

URANIUM. [CAS 7440-61-1], Chemical element symbol. U, at. no. 92, at. wt, 238,03, periodic table group (Actinides), mp 1,131 to i. 33°C, bp 3,818°C, density 18.9 g/cm3 (20UC). Uranium metal is found in three allotropic forms (1) alpha phase, stable below 668°C, orthorhombic (2) beta phase, existing between 668 and 774°C. tetragonal and (3) gamma phase, above 774°C, body-centered cubic crystal structure. The gamma phase behaves most nearly that of a true metal. The alpha phase has several nonmetallic features in its crystallography. The beta phase is brittle. See also Chemical Elements. 

In 1966, a catalyst based on a complex uranium antimonate system was developed and brought into commercial use (4, 87). Several physical methods of analysis were used in an attempt to clarify relationships between the structure and properties of the uranium antimonate system and its catalytic properties (20, 88, 89). X-Ray diffraction and infrared analysis demonstrated that the optimum selectivity for acrylonitrile formation coincided with the maximum concentration of the USb3O10 compound. The crystal structure of USb3O10 was shown to consist of layers of heavy atoms and oxygen ions alternated by layers of oxygen ions. Measurements by ESCA indicated that the surface layers contained U5+ and Sb5+ with intensities corresponding to the USb3O10 formula. 

Berthet, J.C., Miquel, Y., Iveson, P.B., Nierlich, M., Thuery, P., Madic, C., Ephritikhine, M. 2002. The affinity and selectivity of terdentate nitrogen ligands toward trivalent lanthanide and uranium ions viewed from the crystal structures of the 1 3 complexes. Journal of the Chemical Society, Dalton Transactions 3265-3272. 

The presence of two rather than three Cp rings around the trivalent uranium centers seems to provide an optimum stability to the complex. The synthesis of the Cp UI2(thf)3 and Cp 2UI(thf) was achieved in high yield upon treatment of UI3(thf)4 with the appropriate amount of Cp K (Scheme 17). Further functionalization of Cp UI2(thf)3 was obtained via a metathetic reaction with silazanate. The crystal structure of the resulting Cp U[N(SiMe3)2]2 showed the presence of agostic interactions between the U center and the methyl groups of the silazanate moiety (47). 

Only An(III) and An(IV) ions have been inserted into macrocyclic crown-ethers, e.g., in [UCl3(18-crown-6)]2[U02Cl3(OH)H20]. Hydrogen bond interactions between etheric oxygen and coordinated water molecules were only observed in the corresponding U02+ complexes [282]. The infrared spectrum and isotope effect of uranium-crown-ether complexes were reported [435], as well as the crystal structures... 

Coordination compounds of diphosphazane dioxides with uranyl or thorium ions were synthesized [475], The crystal structure of [U02(N03)2L1] [L, = Ph2P(0) N(Ph)P(0)Ph2] reveal the bidentate chelating mode of binding of the diphosphazane dioxide to these metals. The chemistry of other uranium organophosphorus and related compounds is described [476-479]. Some of the actinide complexes are presented in Table 5.16. 

---