Frederic Poineau

Octachloro- and Octabromoditechnetate(III) and Their Rhenium(III) Congeners

The compound (n-Bu4N)2Tc2Br8 was prepared by the metathesis of (n-Bu4N)2Tc2Cl8 with HBr (g) in dichloromethane and characterized by X-ray absorption fine structure spectroscopy and UV-vis spectroscopy. Analysis of the data gives a Tc-Tc distance of 2.16(1) A and a Tc-Br distance of 2.48(1) A. The Tc(III) oxidation state was inferred by the position of the edge absorption, which reveals a shift of 12 eV between (n-Bu4N)2Tc2Br8 and NH4TcO4. The analogous shift between (n-Bu4N)2Tc2Cl8 and NH4TcO4 is 11 eV. The UV-vis spectrum of Tc2Br8(2-) in dichloromethane exhibits the characteristic delta --> delta* transition at 13,717 cm(-1). The M2X8(2-) (M = Re, Tc; X = Cl, Br) UV-vis spectra are compared, and the position of the delta --> delta* transition discussed.

Technetium Dichloride: A New Binary Halide Containing Metal–Metal Multiple Bonds

Technetium dichloride has been discovered. It was synthesized from the elements and characterized by several physical techniques, including single crystal X-ray diffraction. In the solid state, technetium dichloride exhibits a new structure type consisting of infinite chains of face sharing [Tc(2)Cl(8)] rectangular prisms that are packed in a commensurate supercell. The metal-metal separation in the prisms is 2.127(2) Å, a distance consistent with the presence of a Tc≡Tc triple bond that is also supported by electronic structure calculations.

Physical Properties of Superbulky Lanthanide Metallocenes: Synthesis and Extraordinary Luminescence of [Eu-II(Cp-BIG)(2)] (Cp-BIG=(4-nBu-C6H4)(5)-Cyclopentadienyl)

The superbulky deca-aryleuropocene [Eu(Cp(BIG))2], Cp(BIG) = (4-nBu-C6H4)5-cyclopentadienyl, was prepared by reaction of [Eu(dmat)2(thf)2], DMAT = 2-Me2N-α-Me3Si-benzyl, with two equivalents of Cp(BIG)H. Recrystallizyation from cold hexane gave the product with a surprisingly bright and efficient orange emission (45% quantum yield). The crystal structure is isomorphic to those of [M(Cp(BIG))2] (M = Sm, Yb, Ca, Ba) and shows the typical distortions that arise from Cp(BIG)⋅⋅⋅Cp(BIG) attraction as well as excessively large displacement parameter for the heavy Eu atom (U(eq) = 0.075). In order to gain information on the true oxidation state of the central metal in superbulky metallocenes [M(Cp(BIG))2] (M = Sm, Eu, Yb), several physical analyses have been applied. Temperature-dependent magnetic susceptibility data of [Yb(Cp(BIG))2] show diamagnetism, indicating stable divalent ytterbium. Temperature-dependent (151)Eu Mössbauer effect spectroscopic examination of [Eu(Cp(BIG))2] was examined over the temperature range 93-215 K and the hyperfine and dynamical properties of the Eu(II) species are discussed in detail. The mean square amplitude of vibration of the Eu atom as a function of temperature was determined and compared to the value extracted from the single-crystal X-ray data at 203 K. The large difference in these two values was ascribed to the presence of static disorder and/or the presence of low-frequency torsional and librational modes in [Eu(Cp(BIG))2]. X-ray absorbance near edge spectroscopy (XANES) showed that all three [Ln(Cp(BIG))2] (Ln = Sm, Eu, Yb) compounds are divalent. The XANES white-line spectra are at 8.3, 7.3, and 7.8 eV, for Sm, Eu, and Yb, respectively, lower than the Ln2O3 standards. No XANES temperature dependence was found from room temperature to 100 K. XANES also showed that the [Ln(Cp(BIG))2] complexes had less trivalent impurity than a [EuI2(thf)x] standard. The complex [Eu(Cp(BIG))2] shows already at room temperature strong orange photoluminescence (quantum yield: 45 %): excitation at 412 nm (24,270 cm(-1)) gives a symmetrical single band in the emission spectrum at 606 nm (νmax =16495 cm(-1), FWHM: 2090 cm(-1), Stokes-shift: 2140 cm(-1)), which is assigned to a 4f(6)5d(1) → 4f(7) transition of Eu(II). These remarkable values compare well to those for Eu(II)-doped ionic host lattices and are likely caused by the rigidity of the [Eu(Cp(BIG))2] complex. Sharp emission signals, typical for Eu(III), are not visible.

Physical Properties of Superbulky Lanthanide Metallocenes: Synthesis and Extraordinary Luminescence of [Eu[superscript II](Cp[superscript BIG])[subscript 2]] (Cp[superscript BIG]=(4-nBu-C[subscript 6]H[subscript 4])[subscript 5]-Cyclopentadienyl)

The superbulky deca-aryleuropocene [Eu(Cp(BIG))2], Cp(BIG) = (4-nBu-C6H4)5-cyclopentadienyl, was prepared by reaction of [Eu(dmat)2(thf)2], DMAT = 2-Me2N-α-Me3Si-benzyl, with two equivalents of Cp(BIG)H. Recrystallizyation from cold hexane gave the product with a surprisingly bright and efficient orange emission (45% quantum yield). The crystal structure is isomorphic to those of [M(Cp(BIG))2] (M = Sm, Yb, Ca, Ba) and shows the typical distortions that arise from Cp(BIG)⋅⋅⋅Cp(BIG) attraction as well as excessively large displacement parameter for the heavy Eu atom (U(eq) = 0.075). In order to gain information on the true oxidation state of the central metal in superbulky metallocenes [M(Cp(BIG))2] (M = Sm, Eu, Yb), several physical analyses have been applied. Temperature-dependent magnetic susceptibility data of [Yb(Cp(BIG))2] show diamagnetism, indicating stable divalent ytterbium. Temperature-dependent (151)Eu Mössbauer effect spectroscopic examination of [Eu(Cp(BIG))2] was examined over the temperature range 93-215 K and the hyperfine and dynamical properties of the Eu(II) species are discussed in detail. The mean square amplitude of vibration of the Eu atom as a function of temperature was determined and compared to the value extracted from the single-crystal X-ray data at 203 K. The large difference in these two values was ascribed to the presence of static disorder and/or the presence of low-frequency torsional and librational modes in [Eu(Cp(BIG))2]. X-ray absorbance near edge spectroscopy (XANES) showed that all three [Ln(Cp(BIG))2] (Ln = Sm, Eu, Yb) compounds are divalent. The XANES white-line spectra are at 8.3, 7.3, and 7.8 eV, for Sm, Eu, and Yb, respectively, lower than the Ln2O3 standards. No XANES temperature dependence was found from room temperature to 100 K. XANES also showed that the [Ln(Cp(BIG))2] complexes had less trivalent impurity than a [EuI2(thf)x] standard. The complex [Eu(Cp(BIG))2] shows already at room temperature strong orange photoluminescence (quantum yield: 45 %): excitation at 412 nm (24,270 cm(-1)) gives a symmetrical single band in the emission spectrum at 606 nm (νmax =16495 cm(-1), FWHM: 2090 cm(-1), Stokes-shift: 2140 cm(-1)), which is assigned to a 4f(6)5d(1) → 4f(7) transition of Eu(II). These remarkable values compare well to those for Eu(II)-doped ionic host lattices and are likely caused by the rigidity of the [Eu(Cp(BIG))2] complex. Sharp emission signals, typical for Eu(III), are not visible.

Synthesis and structure of technetium trichloride.

Technetium trichloride has been synthesized by reaction of Tc(2)(O(2)CCH(3))(4)Cl(2) with HCl(g) at 300 °C. The mechanism of formation mimics the one described earlier in the literature for rhenium. Tc(2)(O(2)CCH(3))(2)Cl(4) [P1̅; a = 6.0303(12) Å, b = 6.5098(13) Å, c = 8.3072(16) Å, α = 112.082(2)°, β = 96.667(3)°, γ = 108.792(3)°; Tc-Tc = 2.150(1) Å] is formed as an intermediate in the reaction at 100 °C. Technetium trichloride is formed above 250 °C and is isostructural with its rhenium homologue. The structure consists of Tc(3)Cl(9) clusters [R3̅m; a = b = 10.1035(19) Å, c = 20.120(8) Å], and the Tc-Tc separation is 2.444(1) Å. Calculations on TcX(3) (X = Cl, Br) have confirmed the stability of TcCl(3) and suggest the existence of a polymorph of TcBr(3) with the ReBr(3) structure.

Preparation of the binary technetium bromides: TcBr3 and TcBr4.

TcBr(3) (1) and TcBr(4) (2) were synthesized by reaction of Tc metal with elemental bromine at 400 degrees C. Single crystal XRD measurements indicate that TcBr(3) crystallizes in the orthorhombic space group Pmmn (a = 11.0656(2) A, b = 5.9717(1) A, c = 6.3870(1) A). The structure consists of infinite chains of face-sharing TcBr(6) octahedra with a regular alternation of short and long Tc-Tc distances (2.8283(4) A, 3.1434(4) A). TcBr(4) crystallizes in the orthorhombic space group Pbca (a = 6.3237(5) A, b = 12.1777(9) A, c = 14.7397(11) A). TcBr(4) contains infinite chains of edge-sharing TcBr(6) octahedra with no apparent metal-metal bond (Tc-Tc = 3.7914(4) A). Technetium tribromide is isomorphous with RuBr(3) and MoBr(3), while TcBr(4) is isomorphous with PtBr(4) and OsBr(4).

Speciation of heptavalent technetium in sulfuric acid: structural and spectroscopic studies

The speciation of Tc(vii) was studied in 12 M H(2)SO(4) by NMR, UV-visible and XAFS spectroscopy. Experimental results and density functional calculations show the formation of TcO(3)(OH)(H(2)O)(2).

Uranium/technetium separation for the UREX process - synthesis and characterization of solid reprocessing forms

Abstract In the context of the demonstration of the UREX (uranium extraction) process, a separation of uranium and technetium using an anion exchange resin was performed on a simulant solution containing 98.95 g/L of 238U and 130.2 mg/L of 99Tc. After sorption on the resin, TcO4− was eluted with NH4OH, the eluting stream was treated, and the technetium converted to Tc metal (yield=52.5%). The purity of the compound was analyzed: it contains less than 23.8 μg of 238U per gram of 99Tc. Tc metal was characterized by X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) spectroscopy; EXAFS analysis clearly confirms the hexagonal structure of the metal obtained after treatment. Uranium was converted to ammonium diuranate and to U3O8 in a yield of 88.2%, analysis indicates that the compound contains less than 0.16 μg of 99Tc per gram of ammonium diuaranate.

Crystal structure of octabromoditechnetate(III) and a multi-configurational quantum chemical study of the δ→δ* transition in quadruply bonded [M2X8]2− dimers (M = Tc, Re; X = Cl, Br)

The technetium(III) compound (n-Bu(4)N)(2)[Tc(2)Br(8)] was prepared by metathesis of (n-Bu(4)N)(2)[Tc(2)Cl(8)] with concentrated aqueous HBr in acetone and recrystallized from acetone-diethyl ether solution (2:1 v/v). The acetone solvate obtained, (n-Bu(4)N)(2)[Tc(2)Br(8)] x 4 [(CH(3))(2)CO] (1), crystallizes in the monoclinic space group P2(1)/n with a = 13.8959(8) A, b = 15.2597(9) A, c = 15.5741(9) A, beta = 109.107(1) degrees, R(1) = 0.028, and Z = 4. The Tc-Tc distance (2.1625(9) A) and the average Tc-Br distances (2.4734(7) A) are in excellent agreement with those previously determined by EXAFS spectroscopy. These and other experimental data on quadruply metal-metal bonded group 7 [M(2)X(8)](2-) dimers (M = Tc, Re; X = Cl, Br) are compared to the results of a set of multi-configurational quantum chemical studies. The calculated molecular structures of the ground states are in very good agreement with the structures determined experimentally. The theory overestimates the delta-->delta* transition energies by some 1000 cm(-1), but mimics the trends in delta-->delta* energies across the series.

Technetium(IV) halides predicted from first-principles.

We report the crystal structures of the novel technetium tetrahalides TcX(4) [X = F, I], as predicted from first-principles calculations. Isomorphous with TcCl(4) and TcBr(4) crystals, TcF(4) is orthorhombic with the centro-symmetric space group Pbca, while TcI(4) crystallizes in the monoclinic space group P2(1)/c. The structures, [TcX(2)(mu-X)(4/2)](infinity), consist of distorted edge-sharing octahedral groups of composition TcX(6) linked into endless cis chains. A possible explanation for the differences between these structures is offered in terms of varying degrees of bonding within the chains.