Evaluation of Multidentate Ligands Derived from Ethyl 1,2,4-triazine-3-carboxylate Building Blocks as Potential An(III)-Selective Extractants for Nuclear Reprocessing.

Bis-1,2,4-triazine ligands are amongst the most promising soft N-donor ligands for the partitioning of trivalent actinides from trivalent lanthanides; a key separation proposed in the future reprocessing of spent nuclear fuels. In an effort to improve the extraction properties of these benchmark ligands, we propose herein a general ligand design approach that is inspired by the field of drug discovery, and we apply it to a new class of ligands in which the bidentate 3-(2-pyridyl)-1,2,4-triazine unit of the benchmark ligands is replaced by a bidentate 1,2,4-triazine-3-carboxamide unit. A series of nine novel ligands were synthesized by reactions of readily available ethyl 1,2,4-triazine-3-carboxylate building blocks with different polyamine cores and evaluated for their ability to extract and separate Am(III) and Cm(III) from Eu(III).

6-(6-Methyl-1,2,4,5-Tetrazine-3-yl)-2,2'-Bipyridine: A N-Donor Ligand for the Separation of Lanthanides(III) and Actinides(III).

Here, we report the synthesis of the 6-(6-methyl-1,2,4,5-tetrazine-3-yl)-2,2'-bipyridine (MTB) ligand that has been developed for lanthanide/actinide separation. A multimethod study of the complexation of MTB with trivalent actinide and lanthanide ions is presented. Single-crystal X-ray diffraction measurements reveal the formation of [Ce(MTB)(NO)], [Pr(MTB)(NO)HO], and [Ln(MTB)(NO)MeCN] (Ln = Nd, Sm, Eu, Gd).

New route to amide-functionalized N-donor ligands enables improved selective solvent extraction of trivalent actinides.

A new general synthetic route to selective actinide extracting ligands for spent nuclear fuel reprocessing has been established. The amide-functionalized ligands separate Am(III) and Cm(III) from the lanthanides with high selectivities and show rapid rates of metal extraction. The ligands retain the advantages of the analogous unfunctionalized ligands derived from camphorquinone, whilst also negating their main drawback; precipitate formation when in contact with nitric acid.

Thermodynamic and Structural Modelling of Non-Stoichiometric -Doped UO Solid Solutions = {La, Pr, Nd, Gd}.

Available data on the dependence of the equilibrium chemical potential of oxygen on degrees of doping, , and non-stoichiometry, , , in U O fluorite solid solutions and data on the dependence of the lattice parameter, , on the same variables are combined within a unified structural-thermodynamic model. The thermodynamic model fits experimental isotherms of the oxygen potential under the assumptions of a non-ideal mixing of the endmembers, UO, UO, UO, O, and UO, and of a significant reduction in the configurational entropy arising from short-range ordering (SRO) within cation-anion distributions. The structural model further investigates the SRO in terms of constraints on admissible values of cation coordination numbers and, building on these constraints, fits the lattice parameter as a function of , and .

Selective extraction of trivalent actinides using CyMeBTPhen in the ionic liquid Aliquat-336 nitrate.

The extraction of Am(iii), Cm(iii) and Eu(iii) by 2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-1,10-phenanthroline (CyMeBTPhen) from nitric acid solution was studied using the ionic liquid Aliquat-336 nitrate ([A336][NO]) as diluent. Results show a high selectivity of the solvent for Am(iii) and Cm(iii) over Eu(iii), but rather slow extraction kinetics. The kinetics of CyMeBTPhen were largely improved by the addition of 0.

Gamma radiolysis of hydrophilic diglycolamide ligands in concentrated aqueous nitrate solution.

The radiation chemistry of a series of hydrophilic diglycolamides (DGAs: TEDGA, Me-TEDGA, Me-TEDGA, and TPDGA) has been investigated under neutral pH, concentrated aqueous nitrate solution conditions. A combination of steady-state gamma and time-resolved pulsed electron irradiation experiments, supported by advanced analytical techniques and multi-scale modeling calculations, have demonstrated that: (i) the investigated hydrophilic DGAs undergo first-order decay with an average dose constant of (-3.18 ± 0.

Exploring the Subtle Effect of Aliphatic Ring Size on Minor Actinide-Extraction Properties and Metal Ion Speciation in Bis-1,2,4-Triazine Ligands.

The synthesis and evaluation of three novel bis-1,2,4-triazine ligands containing five-membered aliphatic rings are reported. Compared to the more hydrophobic ligands 1-3 containing six-membered aliphatic rings, the distribution ratios for relevant f-block metal ions were approximately one order of magnitude lower in each case. Ligand 10 showed an efficient, selective and rapid separation of Am and Cm from nitric acid.

Unprecedented Inversion of Selectivity and Extraordinary Difference in the Complexation of Trivalent f Elements by Diastereomers of a Methylated Diglycolamide.

When considering f elements, solvent extraction is primarily used for the removal of lanthanides from ore and their recycling, as well as for the separation of actinides from used nuclear fuel. Understanding the complexation mechanism of metal ions with organic extractants, particularly the influence of their molecular structure on complex formation is of fundamental importance. Herein, we report an extraordinary (up to two orders of magnitude) change in the extraction efficiency of f elements with two diastereomers of dimethyl tetraoctyl diglycolamide (Me -TODGA), which only differ in the orientation of a single methyl group.

Formation of Open Framework Uranium Germanates: The Influence of Mixed Molten Flux and Charge Density Dependence in U-Silicate and U-Germanate Families.

Seven novel open-framework uranyl germanates, K(UO)GeO, K(UO)GeO, α-Cs(UO)GeO, β-Cs(UO)GeO, Cs(UO)GeO, and A(UO)(GeO) (A = [NaKCl], [NaCsCl]), were grown from different mixed molten fluxes. The three-dimensional (3D) structure of K(UO)GeO with 8-ring channels can be built upon [UGe] pentamer secondary building units (SBUs). The 3D framework of K(UO)GeO with trapezoid (GeO) clusters consists of two types of [UGe] pentamers.

Porous Uranyl Borophosphates with Unique Three-Dimensional Open-Framework Structures.

Two novel alkali-metal uranyl borophosphates have been prepared and characterized for the first time, namely, K(UO)[BPO(OH)](OH)(HO) and K(UO)[B(HPO)](PO)(OH)(HO) denoted as KUPB1 and KUPB2, respectively. KUPB1 was obtained hydrothermally at 220 °C and crystallizes in a monoclinic structure in the chiral space group P2. The unit cell parameters of KUPB1 are a = 6.

Complexation of Actinide(III) and Lanthanide(III) with HTPAEN for a Separation of Americium from Curium and Lanthanides.

Previous studies have identified the TPAEN ligand as a potentially appropriate complexing agent in solvent extraction processes for the separation of americium (Am(III)) from the fission products including lanthanide (Ln(III)) and curium (Cm(III)) ions, a challenging issue for advanced nuclear fuel recycling. To get insight into the selectivity of this ligand, the complexation of selected trivalent Ln(III) and actinide (An(III)) cations with TPAEN was investigated in solution. First, the structure and stoichiometry of the TPAEN complex with Am(III) were characterized by extended X-ray absorption fine structure spectroscopy (EXAFS).

Gamma-radiolytic stability of new methylated TODGA derivatives for minor actinide recycling.

The stability against gamma radiation of MeTODGA (methyl tetraoctyldiglycolamide) and Me2TODGA (dimethyl tetraoctyldiglycolamide), derivatives from the well-known extractant TODGA (N,N,N',N'-tetraoctyldiglycolamide), were studied and compared. Solutions of MeTODGA and Me2TODGA in alkane diluents were subjected to (60)Co γ-irradiation in the presence and absence of nitric acid and analyzed using LC-MS to determine their rates of radiolytic concentration decrease, as well as to identify radiolysis products. The results of product identification from three different laboratories are compared and found to be in good agreement.

Morphotropy and temperature-driven polymorphism in A2Th(AsO4)2 (A = Li, Na, K, Rb, Cs) series.

A new alkaline thorium arsenate family was obtained and systematically investigated. The structures of A2Th(AsO4)2 (A = Li, Na, K, Rb, Cs) were determined from single crystal X-ray diffraction data. Li2Th(AsO4)2 and either isostructural K2Th(AsO4)2 and Rb2Th(AsO4)2 crystallize in the monoclinic crystal system.

High-temperature phase transitions, spectroscopic properties, and dimensionality reduction in rubidium thorium molybdate family.

Four new rubidium thorium molybdates have been synthesized by high-temperature solid-state reactions. The crystal structures of Rb8Th(MoO4)6, Rb2Th(MoO4)3, Rb4Th(MoO4)4, and Rb4Th5(MoO4)12 were determined using single-crystal X-ray diffraction. All these compounds construct from MoO4 tetrahedra and ThO8 square antiprisms.

Novel fundamental building blocks and site dependent isomorphism in the first actinide borophosphates.

Three novel uranyl borophosphates, Ag2(NH4)3[(UO2)2{B3O(PO4)4(PO4H)2}]H2O (AgNBPU-1), Ag(2-x)(NH4)3[(UO2)2{B2P5O(20-x)(OH)x}] (x = 1.26) (AgNBPU-2), and Ag(2-x)(NH4)3[(UO2)2{B2P(5-y)AsyO(20-x)(OH)x}] (x = 1.43, y = 2.

Plutonium(IV) complexation by diglycolamide ligands--coordination chemistry insight into TODGA-based actinide separations.

Complexation of Pu(IV) with TMDGA, TEDGA, and TODGA diglycolamide ligands was followed by vis-NIR spectroscopy. A crystal structure determination reveals that TMDGA forms a 1 : 3 homoleptic Pu(IV) complex with the nitrate anions forced into the outer coordination sphere.

Complexation of lanthanides, actinides and transition metal cations with a 6-(1,2,4-triazin-3-yl)-2,2':6',2''-terpyridine ligand: implications for actinide(III)/lanthanide(III) partitioning.

The quadridentate N-heterocyclic ligand 6-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2' : 6',2''-terpyridine (CyMe(4)-hemi-BTBP) has been synthesized and its interactions with Am(III), U(VI), Ln(III) and some transition metal cations have been evaluated by X-ray crystallographic analysis, Am(III)/Eu(III) solvent extraction experiments, UV absorption spectrophotometry, NMR studies and ESI-MS. Structures of 1:1 complexes with Eu(III), Ce(III) and the linear uranyl (UO(2)(2+)) ion were obtained by X-ray crystallographic analysis, and they showed similar coordination behavior to related BTBP complexes. In methanol, the stability constants of the Ln(III) complexes are slightly lower than those of the analogous quadridentate bis-triazine BTBP ligands, while the stability constant for the Yb(III) complex is higher.

Palladium-catalyzed cross-coupling of various phosphorus pronucleophiles with chloropyrazines: synthesis of novel Am(III)-selective extractants.

Palladium-catalyzed cross-coupling of (di)chloropyrazines with phosphorus pronucleophiles in the presence of a base gave the phosphorylated pyrazines in 81-95% yields. Based on this methodology a series of appropriately functionalized pyrazines was prepared as potential extractants of trivalent cations from highly acidic nuclear waste. A few hydrophilic derivatives exhibited a very good selectivity for Am(3+) over Eu(3+) with separation factors up to 40 at pH 1 at 0.

Highly efficient separation of actinides from lanthanides by a phenanthroline-derived bis-triazine ligand.

The synthesis, lanthanide complexation, and solvent extraction of actinide(III) and lanthanide(III) radiotracers from nitric acid solutions by a phenanthroline-derived quadridentate bis-triazine ligand are described. The ligand separates Am(III) and Cm(III) from the lanthanides with remarkably high efficiency, high selectivity, and fast extraction kinetics compared to its 2,2'-bipyridine counterpart. Structures of the 1:2 bis-complexes of the ligand with Eu(III) and Yb(III) were elucidated by X-ray crystallography and force field calculations, respectively.

Interaction of 6,6''-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2':6',2''-terpyridine (CyMe4-BTTP) with some trivalent ions such as lanthanide(III) ions and americium(III).

The new ligand 6,6''-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2':6',2''-terpyridine (CyMe4-BTTP) has been synthesized in 4 steps from 2,2':6',2''-terpyridine. Detailed NMR and mass spectrometry studies indicate that the ligand forms 1:2 complexes with lanthanide(III) perchlorates where the aliphatic rings are conformationally constrained whereas 1:1 complexes are formed with lanthanide(III) nitrates where the rings are conformationally mobile. An optimized structure of the 1:2 solution complex with Yb(III) was obtained from the relative magnitude of the induced paramagnetic shifts.