Alfred P. Sattelberger

Reaction Sequence and Kinetics of Uranium Nitride Decomposition

The reaction mechanism and kinetics of the thermal decomposition of uranium dinitride/uranium sesquinitride to uranium mononitride under inert atmosphere at elevated temperature were studied. An increase in the lattice parameter of the UN(2)/alpha-U(2)N(3) phase was observed as the reaction temperature increased, corresponding to a continuous removal of nitrogen. Electron density calculations for these two compounds using XRD powder patterns of the samples utilizing charge-flipping technique were performed for the first time to visualize the decrease in nitrogen level as a function of temperature. Complete decomposition of UN(2) into alpha-U(2)N(3) at 675 degrees C and the UN formation after a partial decomposition of alpha-U(2)N(3) at 975 degrees C were also identified in this study. The activation energy for the decomposition of the UN(2)/alpha-U(2)N(3) phase into UN, 423.8 +/- 0.3 kJ/mol (101.3 kcal/mol), was determined under an inert argon atmosphere and is reported here experimentally for the first time.

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.

Synthesis and reactivity of technetium(VII) imido complexes

Abstract The synthesis, characterization and electrochemistry of a series of new technetium complexes, Tc(NAr)3X and Tc(NAr′)3X (X = OSiMe3, alkyl, I), is reported. These complexes are shown to be resistant to reduction and moderately air-sensitive. The siloxy complex Tc(NAr)3(OSiMe3) (1a) reacts with fluoride ion to give the tris(imido)oxo anion [TcO(NAr)3]−. Less sterically hindered M(Nar′)3(OSiMe3) complexes react with Ar′NCO in a net [2+2] fashion to give the urylene complexes M(NAr′) 2 (NAr′C(O)N Ar′) (OSiMe3) (2a, M = Tc; 2b, M = Re). The X-ray crystal structures of 1a, 2b and (Tc(NAr)3I (4a) suggest that the imido ligands moderate their level of electron donation to reflect the electronic requirements of the metal and the ancillary ligands.

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.

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).

New developments in actinide alkoxide chemistry

Abstract Much new information on the synthesis, physicochemical properties, solid state structures, and reaction chemistry of actinide alkoxide complexes has begun to emerge in the last decade. We have developed several new starting materials that facilitate easy entry into thorium and uranium alkoxide chemistry. Synthetic pathways employed in our laboratories to obtain alkoxide and aryloxide complexes of the actinides include (1) metathesis of the iodide ligands in Ul 3 (THF) 4 and Thl 4 (THF) 4 with potassium salts of the desired ligand, or (2) protonolysis of metal-nitrogen or metal-carbon bonds by alcohols or phenols. The rich structural and reaction chemistry of these new complexes is described along with prospects for future developments in the field.

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.