Protactinium crystals

Actinide Peroxides. Many peroxo compounds of thorium, protactinium, uranium, neptunium, plutonium, and americium are known (82,89). The crystal stmctures of a number of these have been deterrnined. Perhaps the best known are uranium peroxide dihydrate [1344-60-1/, UO 2H20, and, the uranium peroxide tetrahydrate [15737-4-5] UO 4H2O, which are formed when hydrogen peroxide is added to an acid solution of a uranyl salt. 

Crystals of Potassium Protactinium Fluoride—KsPaFT. Left Dark field illumination X 60. 

Protactinium (of mass number 231) is found in nature iu all uranium ores, since it is a long-lived member of the uranium series. It occurs in such ores to the extent of about part per million parts of uranium. An efficient method for the separation of protactinium is by a carrier technique using zirconium phosphate which, when precipitated from strongly acid solutions, coprecipitates protactinium nearly quantitatively. Then the protactinium is separated from the carrier by fractional crystallization of zirconium oxychloride. 

Protactinium oxides can be stabilized in the tetravalent and pentavalent state. The most stable oxide phase obtained by the burning of metal or protactinium compoimds is the white pentoxide, Pa20s. The structme of the pentoxide is related to fluorite and has cubic symmetry. Pa02 is a black solid that crystallizes in the cubic fluorite structure. 

Protactinium pentaiodide crystallizes with orthorhombic symmetry (104) (Table III). The pentaiodide is extremely moisture-sensitive and hydrolyzes immediately on contact with water. It is slightly soluble in methyl cyanide, but insoluble in isopentane and carbon tetrachloride. 

Single crystal X-ray diffraction studies have shown that in NagPaFg each protactinium atom is surrounded by 8 fluorine atoms at the vertices of an almost perfect cube (Brown et al.). The Pa— F bond distance is 2.21 A with F—F approaches of 2.47 and 2.60, respectively (Fig. 10) ... 

A recent study of the alkali metal/uranium fluoride complex systems has shown that KriUFo, K3UF7, and K UFs are isomorphous (99), the crystal symmetry being unaffected by the fluoride ion absences. The structure of K PaFy has been determined only recently (39), and it has been shown that each protactinium atom is surrounded by nine fluorine atoms in what is effectively a trigonal prism with three added equatorial fluorine atoms the PaFo groups are linked in infinite chains by two fluorine bridges. 

The influence of unoccupied 5/band states on the Fermi surface of thorium metal has been evaluated from precise calculations of the Fermi surface areas and effective masses.Comparison of the results with those obtained from experiments showed agreement when the 5/electrons were treated as itinerant. The nature of the bonding, electronic configurations and degree of localization of 5/ electrons in the actinide elements have been described in terms of a phenomenal model constructed from a knowledge of the crystal structure, the metallic radii, melting points and enthalpies of sublimation of the elements. The 5/electrons in the elements between protactinium... 

The acetylacetonate PajacacjgClg has been prepared by direct reaction between protactinium pentachloride and acetylacetone in methylene dichloride. The addition of isopentane to this reaction mixture results in the formation of long, bright yellow needles of the complex, and single crystal studies have shown these to possess monoclinic symmetry, space group P2i/c with do = 8.01, = 23.42, Cq = 18.63 A, and... 

Penta(tropolonato)-protactinium and -uranium have been prepared using tropolone and the metal pentaethoxide in benzene. Uranium pentachloride reacts with an excess of tropolone in non-aqueous solvents to give chlorotetra(tropolonato)uranium. Enthalpies of formation of tri(tropolonato)- and tri(4-methyltropolonato)-aluminium (ill) have been determined at 298.15 K by solution calorimetry. The gas phase enthalpies of formation have been calculated and from these the A1—O bond energies derived. The crystal and molecular structure of a tetranuclear cobalt(ii)-tropolonate complex, [Co4(C7H502)s(H20)2] has been reported. Spectroscopic data (i.r., n.m.r.) of a mercury (ii) tropolonate indicates that it has an unsymmetrical structure with two approximately linear short Hg—O bonds and two longer ones. ... 

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