Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “THORIUM”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 685 records · Page 38Linked to original sources
PubMed1997

Adsorption of Thorium on Amorphous Silica: An EXAFS Study

Wet samples of Th(IV) sorbed on colloidal amorphous silica particles (Aerosil OX 200) have been studied with extended X-ray absorption fine structure spectroscopy (EXAFS) at the Th LIII edge (16.3 keV). The samples were collected with sample surface coverages ranging from 3.8 to 230%. No fundamental changes in the structural environment of Th in terms of the types and distances of nearest neighbors with increasing surface loading were detected, but the results indicate an increasing degree of structural disorder with increasing surface coverage. The O shell around Th shows a distorted configuration with two O atoms at 2.33 A distance and four to six O atoms at 2.55 A. Only one Si shell is observed, with two Si atoms at a distance of 3.8-3.9 A. These results have been interpreted with a double corner-sharing surface complex of Th on silica, where the Th atom shares one O atom with each of two coordinated SiO4 tetrahedra, accounting for the first O coordination shell detected as well as the Th-Si distances. The longer Th-O distances result from coordinated water molecules from solution. No Th-Th interactions could be detected in the EXAFS spectra. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed2002

Application of thorium-normalized airborne radiospectrometric survey data of Wadi Araba area, North-eastern Desert, Egypt, as a guide to the recognition of probable subsurface petroleum accumulations.

A new exploration method has been developed by Saunders et al. (Geophysics 58(10) (1993) 1417) using surface and aerial gamma-ray spectral measurements in prospecting for petroleum in stratigraphic and structural traps. Wadi Araba area, North-eastern Desert, Egypt, was selected to apply this method on its recorded aerial gamma-ray spectrometric survey data, due to its distinct stratigraphic and structural setting as well as its situation in close connection with the Gulf of Suez, which represents one of the important sites of oil production in Egypt. The three variables (eU, eTh, and K) registered for the whole study area, in the form of three contour maps, were digitized along the flight paths every 1.0 km. The DRAD arithmetic means plus three standard deviations for the data set were computed. Any single profile value greater than this quantity should have a probability of 99.87% that it represents a valid anomaly and is not caused by random variations in the background values. The use of these criteria has identified one flight line which has a valid anomaly that is not caused by random variations in the background values. This might indicate a prospective possibility for petroleum accumulation in the Wadi Araba area. North-eastern Desert, Egypt.

Journal Article↗
PubMed2005

Structure and properties of the thorium vanadyl tellurate, Th(VO2)2(TeO6)(H2O)2.

The hydrothermal reaction of Th(NO3)4.xH2O with V2O5 and H6TeO6 at 200 degrees C under autogenously generated pressure results in the formation of Th(VO2)2(TeO6)(H2O)2 as a pure phase. The single-crystal X-ray data indicate that Th(VO2)2(TeO6)(H2O)2 possesses a three-dimensional structure constructed from ThO9 tricapped trigonal prisms, VO5 distorted square pyramids, VO4 distorted tetrahedra, and TeO6 distorted octahedra. Both of the vanadium polyhedra contain VO2+ vanadyl units with two short V=O bond distances. The tellurate octahedron is tetragonally distorted and utilizes all of its oxygen atoms to bond to adjacent metal centers, sharing edges with ThO9 and VO5 units, and corners with two ThO9, one VO5, and two VO4 polyhedra. Crystallographic data: Th(VO2)2(TeO6)(H2O)2, orthorhombic, space group Pbca, a = 12.6921(7), b = 11.5593(7), c = 13.0950(8) A, Z = 8 (T = 193 K). The UV-vis diffuse reflectance spectrum of Th(VO2)2(TeO6)(H2O)2 shows vanadyl-based charge-transfer absorption features. Th(VO2)2(TeO6)(H2O)2 decomposes primarily to Th(VO3)4 when heated at 600 degrees C in air.

Journal Article↗
PubMed1996

Specific Sequestering Agents for the Actinides. 29. Stability of the Thorium(IV) Complexes of Desferrioxamine B (DFO) and Three Octadentate Catecholate or Hydroxypyridinonate DFO Derivatives: DFOMTA, DFOCAMC, and DFO-1,2-HOPO. Comparative Stability of the Plutonium(IV) DFOMTA Complex(1).

The metal complex stability constants of Th(IV) with desferrioxamine B (DFO) and three octadentate derivatives [N-(2,3-dihydroxy-4-carboxybenzoyl)desferrioxamine B (DFOCAMC), N-(1,2-dihydro-1-hydroxy-2-oxopyridin-6-yl)carbonyl)desferrioxamine B (DFO-1,2-HOPO) and N-(2,3-dihydroxy-4-(methylamido)benzoyl)desferrioxamine B (DFOMTA)] have been determined. The formation constant of the Pu(IV)/DFOMTA complex has also been determined, and the formation constants have been estimated for the other Pu(IV) complexes of octadentate DFO derivatives. The DFO derivatives form 1:1 complexes with Th(IV) in aqueous solution. The solution chemistry of the Th(IV) complexes has been studied by spectrophotometric, potentiometric and proton NMR titrations. The Th(IV) formation constants are as follows (log K(f) values and esd's): DFO, 26.6(1); DFOMTA, 38.55(5); DFOCAMC, 37.2(3); DFO-1,2-HOPO, 33.7(4). The Pu(IV)/DFOMTA formation constant, determined by competitive spectrophotometric titration is (log K(f) value) 41.7(2). The estimation of the other Pu(IV) formation constants are as follows (log K(f) values): DFOCAMC, 40.4; DFO-1,2-HOPO, 36.9. The selectivity of DFO and the three derivatives for actinide(IV) ions is discussed.

Journal Article↗
PubMed1996

Synthesis and Structure of the Layered Thorium Telluride CsTh(2)Te(6).

The compound CsTh(2)Te(6) has been synthesized at 800 degrees C by the reaction of Th with a Cs(2)Te(3)/Te melt as a reactive flux. The compound crystallizes in the space group -Cmcm of the orthorhombic system with two formula units in a cell of dimensions a = 4.367(2) Å, b = 25.119(10) Å, c = 6.140(3) Å, and V = 673.5(5) Å(3) at T = 113 K. The structure of CsTh(2)Te(6) has been determined from single-crystal X-ray data. The structure comprises infinite, two-dimensional double layers of ThTe(8)-bicapped trigonal prisms. The structural motif of the trigonal prisms resembles that found in UTe(2). Cs(+) cations, disordered equally over two crystallographically equivalent sites, separate the layers and are coordinated by eight Te atoms at the corners of a rectangular parallelepiped. Short Te-Te distances of 3.052(3) and 3.088(3) Å form linear, infinite, one-dimensional chains within the layers. Simple formalisms describe neither the Te-Te bonding in the chain nor the oxidation state of Th. The compound shows weak semiconducting behavior along the Th/Te layers perpendicular to the Te-Te chain.

Journal Article↗
PubMed1996

Complexation of Thorium(IV) and Uranium(IV) by a Hexaacetic Hexaaza Macrocycle: Kinetic and Thermodynamic Topomers of Actinide Chelates with a Large Cavity Ligand.

The solution behavior of the Th(IV) chelate with a polyaza polycarboxylic ligand, HEHA (1,4,7,10,13,16-hexaazacyclooctadecane-N,N ',N ",N "',N "",N ""'-hexaacetic acid), is investigated by one- and two-dimensional NMR spectroscopy. [Th(HEHA)](2)(-) exhibits a very unusual irreversible topomerization process from a kinetically stable topomer of C(2) symmetry to a thermodynamically stable topomer of remarkably high symmetry (S(6)). The metal ion appears to be 12-coordinated in both geometries with a pseudoicosahedral arrangement of the chelating groups. The activation energy of the irreversible topomerization is exceedingly high (199 kJ.mol(-)(1)), and the slow kinetics of conversion is assigned to a complete reorganization of the chelate. U(IV) forms directly a stable entity of C(2) symmetry with HEHA and no reorganization of the complex is observed. The unusual topomerization phenomenon undergone by HEHA, is thus strongly dependant on the ionic radius of the encapsulated metal ion. The corresponding lanthanide chelates are totally asymmetric.

Journal Article↗
PubMed1998

Syntheses, Crystal Structures, and Physical Properties of the New Thorium Chalcogenides CuTh(2)Te(6) and SrTh(2)Se(5).

Single crystals of CuTh(2)Te(6) form by a stoichiometric reaction of the elements at 1000 degrees C. The compound crystallizes in the space group -P2(1)/m with unit cell parameters a = 6.170(2) Å, b = 4.332(1) Å, c = 10.424(3) Å, beta = 98.85(1) degrees, and Z = 1 at 113 K. The structure was solved from single-crystal X-ray data. It consists of layers of [Th(2)Te(6)(-)] double chains joined by Cu(+) cations. Each Th atom is coordinated to eight Te atoms in a bicapped trigonal prismatic arrangement. There are three crystallographically unique Te atoms. Each ThTe(8) unit is bridged through one distinct Te atom, such that the capping Te atom of one unit forms the vertex of its neighbor. The two nonbridging Te atoms form infinite Te-Te chains along the exterior of the [Th(2)Te(6)(-)] layer. Copper atoms are coordinated to these Te atoms in a tetrahedral arrangement. Owing to the existence of Te-Te bonds of intermediate length, the assignment of formal oxidation states in this compound is not possible. Four-probe dc electrical conductivity measurements of a single crystal of CuTh(2)Te(6) indicate the compound is a semiconductor along [010]. Magnetic susceptibility measurements in the range 2-300 K show CuTh(2)Te(6) to be paramagnetic with &mgr;(eff) = 2.06 &mgr;(B) at 300 K. Single crystals of SrTh(2)Se(5) form from the reaction SrSe + Th + 3Sn + 3Se at 1000 degrees C. EDAX experiments show no tin present in several crystals analyzed. Transparent red blocks of SrTh(2)Se(5) crystallize in the space group -P2(1)/c with unit cell parameters a = 8.704(2) Å, b = 7.861(2) Å, c = 12.458(4) Å, beta = 90.00(2) degrees, and Z = 4 at 113 K. The structure, which is related to that of U(3)S(5), is a three-dimensional framework with Sr cations located in one-dimensional channels. There are two distinct Th environments, bicapped trigonal prismatic and distorted monocapped octahedral. There are no Se-Se bonds and so formal oxidation states of Sr(2+), Th(4+), and Se(2)(-) may be assigned.

Journal Article↗
PubMed1999

Complexes of Triamidoamines with the Early Actinides. Synthetic Routes to Monomeric Compounds of Tetravalent Uranium and Thorium Containing Halide and Amide Ligands.

The reaction of the lithiated triamidoamine [Li(3)(NN'(3))(THF)(3)] [NN'(3) = N(CH(2)CH(2)NSiMe(2)Bu(t))(3)] with AnCl(4) (An = U, Th) followed by sublimation gives monomeric [An(NN'(3))Cl]. Reaction of these complexes with SiMe(3)X (X = Br, I) gives [An(NN'(3))X]. The amido derivatives [An(NN'(3))(NEt(2))] are prepared from H(3)(NN'(3)) and [U(NEt(2))(4)] and from [Th(NN'(3))Cl] and [Li(NEt(2))]. In each case, the complexes [U(NN'(3))X] (X = Cl, Br, I, NEt(2)) are shown by X-ray crystallography to contain a triamidoamine ligand disposed with 3-fold symmetry about the metal center. The structures are distorted from trigonal bipyramidal by displacement of the uranium atoms out of the equatorial plane of the three amido nitrogen atoms by ca. 0.8 Å. The ligand backbone is distorted in such a manner as to cause the tert-butyldimethylsilyl groups to encircle the equatorial plane of the metal atom rather than surround the apical coordination site as is observed in the transition metal complexes of this type. Variation of the auxiliary ligand has little effect on the orientation, bond lengths, and angles within the (triamidoamine)uranium fragment. The tert-butydimethysilyl-substituted triamidoamine ligand is thus ideally suited for coordination to large metals since it stabilizes the formation of 3-fold symmetric structures while also allowing reactivity at the fifth coordination site.

Journal Article↗
PubMed2000

Calix[4]arenes as selective extracting agents. An NMR dynamic and conformational investigation of the lanthanide(III) and thorium(IV) complexes.

The lanthanide and Th4+ complexes with calix[4]arene ligands substituted either on the narrow or at the wide rim by four coordinating groups behave totally differently as shown by an NMR investigation of the dia- and paramagnetic complexes. Solutions of complexes were prepared by reacting anhydrous metal perchlorate salts with the ligands in dry acetonitrile (CAUTION). Relaxation time T1 titrations of acetonitrile solutions of Gd3+ by calixarenes indicate that ligands subsituted on the narrow rim form stable 1:1 complexes whether they feature four amide groups (1) or four phosphine oxide functions. In contrast, a ligand substituted by four (carbamoylmethyl)-diphenylphosphine oxide moieties on the wide rim (3) and its derivatives from polymeric species even at a 1:1 ligand/metal concentration ratio. Nuclear magnetic relaxation dispersion (NMRD) curves (relaxation rates 1/T1 vs magnetic field strength) of Gd3+, Gd3+.1 and Gd3+.3 perchlorates in acetonitrile are analyzed by an extended version of the Solomon-Bloembergen-Morgan equations. A comparison of the calculated rotational correlation times tau r shows that ligand 3 forms oligomeric Gd3+ species. The chelates of ligand 1 are axially symmetric (C4 symmetry), and the paramagnetic shifts induced by the Yb3+ ion are accounted for quantitatively. The addition of water or of nitrate ions does not modify the geometry of the complex. The metal chelates of 3 and its derivatives adopt a C2 symmetry, and the paramagnetic shifts are interpreted on a semiquantitative basis only. Water and NO3- ions completely labilize the complexes of the heavy lanthanides. The very high selectivity of ligand 3 through the lanthanide series stems from a complex interplay of factors.

Journal Article↗
PubMed2000

Synthesis and structural characterization of quaternary thorium selenophosphates: A2ThP3Se9 (A = K, Rb) and Cs4Th2P5Se17.

Single crystals of A2ThP3Se9 (A = K (I), Rb (II)) and Cs4Th2PsSe17 (III) form from the reaction of Th and P in a molten A2Se3/Se (A = K, Rb, Cs) flux at 750 degrees C for 100 h. Compound I crystallizes in the triclinic space group P1 (No. 2) with unit cell parameters a = 10.4582(5) A, b = 16.5384(8) A, c = 10.2245(5) A, alpha = 107.637(1); beta = 91.652(1); gamma = 90.343(1) degrees, and Z = 2. Compound II crystallizes in the triclinic space group P1 (No. 2) with the unit cell parameters a = 10.5369(5) A, b = 16.6914(8) A, c = 10.2864(5) A, alpha = 107.614(1) degrees, beta = 92.059(1) degrees, gamma = 90.409(1) degrees, and Z = 2. These structures consist of infinite chains of corner-sharing [Th2Se14] units linked by (P2Se6)4- anions in two directions to form a ribbonlike structure along the [100] direction. Compounds I and II are isostructural with the previously reported K2UP3Se9. Compound III crystallizes in the monoclinic space group P2(1)/c (No. 14) with unit cell parameters a = 10.238(1) A, b = 32.182(2) A, c = 10.749(1) A; beta = 95.832(1) degrees, and Z = 4. Cs4Th2P5Se17 consists of infinite chains of corner-sharing, polyhedral [Th2Se13] units that are also linked by (P2Se6)4- anions in the [100] and [010] directions to form a layered structure. The structure of III features an (Se2)2- anion that is bound eta 2 to Th(2) and eta 1 to Th(1). This anion influences the coordination sphere of the 9-coordinate Th(2) atom such that it is best described as bicapped trigonal prismatic where the eta 2-bound anion occupies one coordination site. The composition of III may be formulated as Cs4Th2(P2Se6)5/2(Se2) due to the presence of the (Se2)2- unit. Raman spectra for these compounds and their interpretation are reported.

Journal Article↗
PubMed2004

Complexation of thorium(IV) with acetate at variable temperatures.

The complexation between Th(IV) and acetate in 1.05 mol kg(-1) NaClO4 was studied at variable temperatures (10, 25, 40, 55 and 70 degrees C). The formation constants of five successive complexes, Th(Ac)j(4-j)+ where Ac = CH3COO- and j = 1-5, and the molar enthalpies of complexation were determined by potentiometry and calorimetry. Extended X-ray absorption fine structure spectroscopy (EXAFS) provided additional information on the complexes in solution. The effect of temperature on the stability of the complexes is discussed in terms of the electrostatic model.

Journal Article↗