Comparative Analysis of Tetravalent Actinide Schiff Base Complexes: Influence of Donor and Ligand Backbone on Molecular Geometry and Metal Binding.

A series of isostructural early actinide An complexes was synthesized in order to investigate the influence of a conjugated framework in the ligand backbone on An bonding. Therefore, the An complexes [An(pyrophen)] (An = Th, U, Np, and Pu) with the pure N-donor ligand bis(2-pyrrolecarbonylaldehyde)-o-phenylenediamine referred to as pyrophen, were synthesized and characterized. Solid state analysis via single-crystal X-ray diffraction (SC-XRD) reveals two sets of ligands binding in an almost orthogonal arrangement to the actinide center.

Structure, Covalency, and Paramagnetism of Homoleptic Actinide and Lanthanide Amidinate Complexes.

Isostructural trivalent lanthanide and actinide amidinates bearing the -bis(isopropyl)benzamidinate (PrBA) ligand [Ln/An(PrBA)] (Ln = La, Nd, Sm, Eu, Yb, Lu; An = U, Np) have been synthesized and characterized in both solid and solution states. All compounds were examined in the solid state utilizing single crystal X-ray diffraction (SC-XRD), revealing a notable deviation in the actinide series with shortened bond lengths compared to the trend in the lanthanide series, suggesting a nonionic contribution to the actinide-ligand bonding. Quantum-chemical bonding analysis further elucidated the nature of these interactions, highlighting increased covalency within the actinide series, as evidenced by higher delocalization indices and greater 5 orbital occupation, except for Th(III) and Pa(III), which demonstrated substantial 6 orbital occupancies.

Triply Bonded Pancake π-Dimers Stabilized by Tetravalent Actinides.

Aromatic π-stacking is a weakly attractive, noncovalent interaction often found in biological macromolecules and synthetic supramolecular chemistry. The weak nondirectional nature of π-stacking can present challenges in the design of materials owing to their weak, nondirectional nature. However, when aromatic π-systems contain an unpaired electron, stronger attraction involving face-to-face π-orbital overlap is possible, resulting in covalent so-called "pancake" bonds.

Fate of Oxidation States at Actinide Centers in Redox-Active Ligand Systems Governed by Energy Levels of 5 f Orbitals.

We report the formation of a Np complex from the complexation of Np O with the redox-active ligand tBu-pdiop =2,6-bis[N-(3,5-di-tert-butyl-2-hydroxyphenyl)iminomethyl]pyridine. To the best of our knowledge, this is the first example of the direct complexation-induced chemical reduction of Np O to Np . In contrast, the complexation of U O with tBu-pdiop did not induce the reduction of U O , not even after the two-electron electrochemical reduction of [U O (tBu-pdiop)].

Deconvoluting Cr states in Cr-doped UO nuclear fuels via bulk and single crystal spectroscopic studies.

Cr-doped UO is a leading accident tolerant nuclear fuel where the complexity of Cr chemical states in the bulk material has prevented acquisition of an unequivocal understanding of the redox chemistry and mechanism for incorporation of Cr in the UO matrix. To resolve this, we have used electron paramagnetic resonance, high energy resolution fluorescence detection X-ray absorption near energy structure and extended X-ray absorption fine structure spectroscopic measurements to examine Cr-doped UO single crystal grains and bulk material. Ambient condition measurements of the single crystal grains, which have been mechanically extracted from bulk material, indicated Cr is incorporated substitutionally for U in the fluorite lattice as Cr with formation of additional oxygen vacancies.

Comparative Analysis of Mononuclear 1:1 and 2:1 Tetravalent Actinide (U, Th, Np) Complexes: Crystal Structure, Spectroscopy, and Electrochemistry.

Six mononuclear tetravalent actinide complexes (-) have been synthesized using a new Schiff base ligand 2-methoxy-6-(((2-methyl-1-(pyridin-2-yl)propyl)imino)methyl)phenol (). The is treated with tetravalent actinide elements in varied stoichiometries to afford mononuclear 1:1 complexes [MCl-THF] (-) and 2:1 complexes [MCl-] (-) (M = Th ( and ), U ( and ), and Np ( and )). All complexes are characterized using different analytical techniques such as IR, NMR, and absorption spectroscopy as well as crystallography.

MOFs with 12-Coordinate 5f-Block Metal Centers.

We have constructed an unprecedented MOF platform that accommodates a range of 5f-block metal ions (Th, U, Np, Pu) as the primary building block. The isoreticular actinide metal-organic frameworks (An-MOFs) exhibit periodic trends in the 12-coordinate metal environment, ligand configuration, and resulting ultramicroporosity. It holds potential in distinguishing neighboring tetravalent actinides.

Structure and Thermodynamics of Eu(III) and Cm(III) Complexes with Glucuronic Acid.

Complexation by small organic ligands controls the bioavailability of contaminants and influences their mobility in the geosphere. We have studied the interactions of Cm, as a representative of the trivalent actinides, and Eu, as an inactive homologue, with glucuronic acid (GlcA) a simple sugar acid. Time-resolved laser-induced luminescence spectroscopy (TRLFS) shows that complexation at pH 5.

Coordination of trivalent lanthanum and cerium, and tetravalent cerium and actinides (An = Th(IV), U(IV), Np(IV)) by a 4-phosphoryl 1-pyrazol-5-olate ligand in solution and the solid state.

Structural investigations of three actinide(iv) 4-phosphoryl 1H-pyrazol-5-olate complexes (An = Th(iv), U(iv), Np(iv)) and their cerium(iv) analogue display the same metal coordination in the solid state. The mononuclear complexes show the metal centre in a square antiprismatic coordination geometry composed by the two O-donor atoms of four deprotonated ligands. Detailed solid state analysis of the U(iv) complex shows that dependent on the solvent used altered arrangements are observable, resulting in a change in the coordination polyhedron of the U(iv) metal centre to bi-capped trigonal prismatic.

Systematic comparison of the structure of homoleptic tetradentate NO-type Schiff base complexes of tetravalent f-elements (M(IV) = Ce, Th, U, Np, and Pu) in solid state and in solution.

A series of tetradentate N2O2-type Schiff base complexes with tetravalent 4f- and 5f-block metals, [M(salpn)2] (H2salpn = N,N'-disalicylidene-1,3-diaminopropane; M = Ce, Th, U, Np, and Pu), were prepared to systematically investigate their solid state structure, and their complexation behaviour in solution with the goal to investigate the subtle differences between 4f- and 5f-elements. X-ray diffraction revealed that all investigated metal cations form [M(salpn)2] complexes. All the complexes show the same ligand arrangement with meridional conformation, amongst which only Ce(iv) exhibits unique behaviour upon crystallisation.

Series of Tetravalent Actinide Amidinates: Structure Determination and Bonding Analysis.

Two series of isostructural tetravalent actinide amidinates [AnX(()-PEBA)] (An = Th, U, Np; X = Cl, N) bearing the chiral (,)-,'-bis(1-phenylethyl)benzamidinate (()-PEBA) ligand have been synthesized and thoroughly characterized in solid and in solution. This study expands the already reported tetravalent neptunium complexes to the lighter actinides thorium and uranium. Furthermore, a rare Ce(IV) amidinate [CeCl(()-PEBA)] was synthesized to compare its properties to those of the analogous tetravalent actinide complexes.

Bonding Trends in Tetravalent Th-Pu Monosalen Complexes.

The synthesis of three complex series of the form [AnCl (salen)(Pyx) ] (H salen=N,N'-bis(salicylidene)ethylenediamine; Pyx=pyridine, 4-methylpyridine, 3,5-dimethylpyridine) with tetravalent early actinides (An=Th, U, Np, Pu) is reported with the goal to elucidate the affinity of these heavy elements for small neutral N-donor molecules. Structure determination by single-crystal XRD and characterization of bulk powders with infrared spectroscopy reveals isostructurality within each respective series and the same complex conformation in all reported structures. Although the trend of interatomic distances for An-Cl and An-N (imine nitrogen of salen or pyridyl nitrogen of Pyx) was found to reflect an ionic behavior, the trend of the An-O distances can only be described with additional covalent interactions for all elements heavier than thorium.

Enantiomerically Pure Tetravalent Neptunium Amidinates: Synthesis and Characterization.

The synthesis of a tetravalent neptunium amidinate [NpCl((S)-PEBA) ] (1) ((S)-PEBA=(S,S)-N,N'-bis-(1-phenylethyl)-benzamidinate) is reported. This complex represents the first structurally characterized enantiopure transuranic compound. Reactivity studies with halide/pseudohalides yielding [NpX((S)-PEBA) ] (X=F (2), Br (3), N (4)) have shown that the chirality-at-metal is preserved for all compounds in the solid state.

Interdisciplinary Round-Robin Test on Molecular Spectroscopy of the U(VI) Acetate System.

A comprehensive molecular analysis of a simple aqueous complexing system-U(VI) acetate-selected to be independently investigated by various spectroscopic (vibrational, luminescence, X-ray absorption, and nuclear magnetic resonance spectroscopy) and quantum chemical methods was achieved by an international round-robin test (RRT). Twenty laboratories from six different countries with a focus on actinide or geochemical research participated and contributed to this scientific endeavor. The outcomes of this RRT were considered on two levels of complexity: first, within each technical discipline, conformities as well as discrepancies of the results and their sources were evaluated.

Complex formation between UO and α-isosaccharinic acid: insights on a molecular level.

Cellulosic materials present as tissue, paper, wood, or filter materials in low and intermediate level waste will degrade under alkaline conditions if water ingresses in a cementitious backfilled repository. The main degradation product is isosaccharinic acid. Complex formation with isosaccharinic acid may adversely affect the retention of radionuclides by the sorption or formation of solid phases.

Recovery of gallium from wafer fabrication industry wastewaters by Desferrioxamine B and E using reversed-phase chromatography approach.

Gallium (Ga) is a critical element in developing renewable energy generation and energy efficient systems. The supply of Ga is at risk and needed recycling technologies for its availability in future. This study demonstrated the recovery of Ga from low gallium concentrated wafer fabrication industry wastewaters using the siderophores desferrioxamine B (DFOB) and desferrioxamine E (DFOE).

NMR and TRLFS studies of Ln(iii) and An(iii) C5-BPP complexes.

C5-BPP is a highly efficient N-donor ligand for the separation of trivalent actinides, An(iii), from trivalent lanthanides, Ln(iii). The molecular origin of the selectivity of C5-BPP and many other N-donor ligands of the BTP-type is still not entirely understood. We present here the first NMR studies on C5-BPP Ln(iii) and An(iii) complexes.

Neptunyl(VI) centred visible LMCT emission directly observable in the presence of uranyl(VI).

Room temperature detection of neptunyl(VI) LMCT emission in a coordination compound and in the presence of uranyl(VI) is reported for the first time. Differences in the excitation profiles of the complexes enable spectral editing so either exclusively neptunyl(VI) or uranyl(VI) emission is observed or a sum of the two.

The influence of radioactive decay on actinide magnetic susceptibility measurements obtained using the Evans method.

In order to explain the higher magnetic susceptibility of some aquo actinide ions than predicted by Hund's rules, the molar magnetic susceptibilities of two americium isotopes ((241)Am and (243)Am) were measured using the Evans method. The results obtained show a growing change in the magnetic susceptibility with α and also a β(-) activity increase in solution. β(-) particle effects appear to be stronger than radicals formed by α particles on the experimental values.

Evidence for covalence in a N-donor complex of americium(III).

The molecular origin of the selectivity of N-donor ligands, such as alkylated bis-triazinyl pyridines (BTPs), for actinide complexation in the presence of lanthanides is still largely unclear. NMR investigations of an Am(nPrBTP)3(3+) complex with a (15)N labelled ligand showed that it exhibits large differences in (15)N chemical shift for coordinating N-atoms in comparison to both lanthanide(III) complexes and the free ligand. The temperature dependence of NMR chemical shifts observed for this complex indicates a weak paramagnetism.

Noncovalently and covalently cross-linked polyurethane gels as alignment media and the suppression of residual polymer signals using diffusion-filtered spectroscopy.

With polyurethane (PU), a novel alignment medium for organic solvents is introduced and characterized, which is very robust and easy to produce on a large scale. Linear PU already constitutes an elastomer gel with several solvents based on its ability to form hydrogen bonds. Covalent cross-linking of the polymer with accelerated electrons provides an alignment medium with different properties.

Region of elongation factor 1A1 involved in substrate recognition by Legionella pneumophila glucosyltransferase Lgt1: identification of Lgt1 as a retaining glucosyltransferase.

Lgt1 is one of the glucosyltransferases produced by the Gram-negative bacterium Legionella pneumophila. This enzyme modifies eukaryotic elongation factor 1A (eEF1A) at serine 53, which leads to inhibition of protein synthesis and death of target cells. Here we studied the region of eEF1A, which is essential for substrate recognition by Lgt1.

Electron transfer chemistry between DNA and DNA-binding tripeptides.

A DNA system consisting of pyrene-modified oligonucleotides and nitrobenzoate (Nb)-modified DNA-binding tripeptides has been applied to study electron-transfer processes through the DNA-peptide interface. 5-(Pyren-1-yl)-2'-deoxyuridine (Py-dU) has been used as the photoinducible charge generator. Upon excitation at 350 nm, a pyrene-like excited state (Py-dU) is formed which undergoes an electron transfer yielding the charge-separated state which is the contact ion pair Py(*)(+)-dU(*)(-).