Anne E. V. Gorden

Coordination Chemistry with f-Element Complexes for an Improved Understanding of Factors That Contribute to Extraction Selectivity

Here, we highlight some recent accomplishments in f-element coordination chemistry aimed at probing the fundamental chemical differences between the 4f elements, lanthanides, and the 5f elements, actinides. The studies of particular interest are those that target improving our knowledge of fundamental chemistry to aid in increased selectivity for extractions of actinides. Two components key to understanding the challenges of actinide separations are detailed here, namely, previously described separation methods and recent investigations into the fundamental coordination chemistry of actinides. Both are aimed at probing the critical features necessary for improved selectivity of separations. This is considered a critical goal in the safe remediation of contaminated sites and reprocessing of nuclear fuel sources used in either civilian and noncivilian energy production.

Allylic C-H activations using Cu(II) 2-quinoxalinol salen and tert-butyl hydroperoxide.

Using a Cu(II) 2-quinoxalinol salen complex as the catalyst and tert-butyl hydroperoxide (TBHP) as the oxidant, allylic activations of olefin substrates can be converted to the corresponding enones or 1,4-enediones. Excellent yields can be achieved (up to 99%) within a very short reaction time and with great tolerance for additional functional groups. Possible mechanistic pathways have been characterized using Raman spectroscopy, cyclic voltammetry, and theoretical calculations.

An Effective Method for Allylic Oxidation of Δ5-Steroids Using tert-Butyl Hydroperoxide

An allylic oxidation method for Delta(5)-steroids using TBHP as oxidant with a 2-quinoxalinol salen Cu(II) complex as catalyst is reported. A variety of Delta(5)-steroidal substrates are selectively oxidized to the corresponding enones. Excellent yields are achieved (up to 99% under optimized conditions) while significantly reducing reaction times required as compared to other current methods.

Monoprotonated Sapphyrin–Pertechnetate Anion Interactions in Aqueous Media

The addition of aqueous pH 7 solutions of 7.2×10-3 M pertechnetate to dilute aqueous 2.5% MeOH solutions containing a water-solubilized sapphyrin, 3,12,13,22-tetraethyl-8,17-bis[bis(hydroxyethyl)-amino)carbonylethyl]-2,7,18,23-tetramethylsapphyrin (1), gives rise to spectroscopic changes in the UV–Vis spectrum of 1 that are consistent with anion-binding and sapphyrin deaggregation. The spectroscopic changes induced by pertechnetate were found to differ dramatically from those induced by the addition of either pure water or dilute nitric acid; however, they were found to parallel those seen when sodium phosphate was added to solutions of 1 under analogous experimental conditions. Fits of the spectroscopic titration data to a 1:1 binding profile revealed that the effective K describing the interaction of pertechnetate anion with 1 was ca. 3900±300 M-1; this value compares to the effective K of 23000±3000 M-1 that describes the corresponding interaction of sodium phosphate with 1.

Hydroxypyridinone Extraction Agents for Pu(IV)

Abstract Twelve different extraction agents, based on the hydroxypyridinone (HOPO) chelating moieties 3,2‐HOPO, 3,4‐HOPO, and 1,2‐HOPO, have been synthesized and characterized for their ability to remove Pu(IV) from nitric acid solutions. Most of these, in particular those based on 1,2‐HOPO, displayed very rapid extraction kinetics and extracted Pu(IV) with large distribution ratios. They were also highly effective in removing Pu(IV) from solutions containing high concentrations of Fe(III) or ethylenediaminetetraacetic acid (EDTA). Stripping the bound Pu(IV) from the chelate complex proved challenging, as only ∼40% was removed even with concentrated (15.8 M) nitric acid.

Emission, Raman spectroscopy, and structural characterization of actinide tetracyanometallates.

Three new compounds, {U2(H2O)10(O)[Pt(CN)4]3}·4H2O, {Th2(H2O)10(OH)2[Pd(CN)4]3}·8H2O, and {(UO2)2(DMSO)4(OH)2[Ni(CN)4]}, in the actinide tetracyanometallate, Anx[M(CN)4]y, class of compounds have been synthesized and characterized by confocal Raman spectroscopy and single crystal X-ray diffraction. These compounds contain unique structures illustrating dimeric actinide species. The absence of intense charge transfer emission in the visible range for {U2(H2O)10(O)[Pt(CN)4]3}·4H2O, as compared to the platinum starting material, is unusual because of the presence of pseudo-one-dimensional Pt···Pt chains in this compound. Confocal Raman spectroscopy of the cyanide stretching region provides insight into the binding domain (mono-, bi-, tri-, tetradentate) of the tetracyanometallates in these novel structures.

Computational Study of Reduction Potentials of Th4+ Compounds and Hydrolysis of ThO2(H2O)n, n = 1, 2, 4

The stability of Th4+ to reduction in water is studied by DFT methods. The standard reduction potential (SRP) of homoleptic complexes including Th(H2O)94+, Th(H2O)104+, Th(NO3)4, Th(NO2)62-, Th(NO3)62-, Th(COT)2, Th(acac)4, ThCp4, ThF4, and ThCl4 have been investigated. The values vary widely (from -3.50 V for Th(OH)4 to -0.62 V for Th(NO3)4 depending on whether the ligands are redox active (noninnocent) or not. Several additional topics of thorium chemistry are explored, including the hydrolysis mechanism of ThO2(H2O)n, n = 1, 2, 4, and the solution phase nonzero dipole moment of ThCp4. Dinuclear complexes are also characterized, including Th2O4, Th2O2(OH)4, Th2O2(H2O)8, Th2(OH)8(H2O)4, and Th2(OH)2(NO3)6(H2O)4 and condensed thorium complexes as [Th4(OH)6(H2O)12]10+ and [Th6(OH)14(H2O)12]10+. For the Th2(OH)2(NO3)6(H2O)4 dinuclear complex, the first SRP is -0.82 V and the second is 1.59 V. The first SRP corresponds to the reduction of the ligand NO3-, and the second SRP corresponds to dissociative electron transfer to the NO32- ligand. The calculated formation constant of Th(EDTA)(H2O)4 is in reasonable agreement with experiment. The different stereochemistries of the bidentate ligands NO2-, NO3-, and acetylacetonate (acac) around the thorium center have very similar stabilities.

Actinide Selective Systems for Environmental Extraction and Sensing Applications

The potential environmental and health concerns surrounding actinides and the use of nuclear fuels limits the acceptance of nuclear power by the public. This in turn, hinders the capability of this country to take advantage of nuclear power. Expanding our fundamental knowledge of actinide coordination chemistry will allow for the development of improved actinide sensors, new separations methods, or new means of radioactive waste remediation. We have designed and optimized a solution-phase parallel method for the synthesis of a library of symmetrical 2-quinoxalinol salens, Schiff-base type ligands with a 2-quinoxalinol incorporated into the salen backbone. This combines the rigid salen coordination framework with the quinoxaline properties that impart properties for use in colorimetric or fluorescent sensors. These have now been incorporated into organic soluble resins for metal extraction. (authors)

Structural Characterization of a Plutonium Sequestering Agent Complex by Synchrotron X-Ray Diffraction

New ligands and materials are required that can coordinate, sense, and purify actinides for selective extraction and reduction of toxic, radioactive wastes from the mining and purification of actinides. The similarities in the chemical, biological transport, and distribution properties of Fe(III) and Pu(IV) inspired a bio-mimetic approach to the development of sequestering agents for actinides. A detailed evaluation of the structure and bonding of actinide coordinating ligands like these is important for the design of new selective ligand systems. Knowing the difficulty with working with the crystals resulting from these ligand systems and safe handling considerations for working with Pu, procedures were developed that utilize the Advanced Light Source of Lawrence Berkeley National Laboratory to determine the solid-state structures of Pu complexes by X-ray diffraction. (au0011tho.

Description and procedures for synchrotron radiation, smallmolecule, single crystal crystallography of plutonium complexes at ALSbeamline 11.3.1

Description and Procedures for Synchrotron Radiation, Small Molecule, Single Crystal Crystallography of Plutonium Complexes at ALS Beamline 11.3.1 (ALS and College of Chemistry Small Molecule Diffractometer) Anne E. V. Gorden 1,2 Kenneth N. Raymond 1,2 David K. Shuh 2 Department of Chemistry, University of California Actinide Chemistry Group, The Glenn T. Seaborg Center, Berkeley Lab Direct Determination of the Structural Parameters of Plutonium Complexes by Small Molecule, Synchrotron Radiation, Single Crystal X-ray Crystallography at the ALS A) The laboratory preparation and growth of the plutonium complexes (crystals) in the HERL is already covered under existing protocols of RWA 1117. The RWA 1117 procedure for mounting radioactive crystals follows. Radioactive Crystal Mounting Procedure: Equipment: Glove Box Parafilm test tube 15 gauge needle quartz capillary One end Sealed Quartz Capillary Tubes, 0.5mm crystal Rubber septa (Aldrich - size 18) vacuum grease Small Plastic bag Small Test tubes (10mm x 75mm) Watch Glass rubber septa Magnifying lenses parafilm Glass Fibers Vacuum Grease Epoxy Nail Clippers Putty Figure 1. Test tube/capillary/septa assembly Jar for transport Sally Hansen — Hard as Nails, a nylon based resin Good Pu-239 crystals: anticipate 1 mg crystals (0.06 mCi) maximum would be 4 mg crystals (0.25 mCi) Methodology: Prepare capillary tubes prior to working with hot materials. Place a square of parafilm on the top of the septa. Run the needle through the septa with the point of the needle up through the septa.