Complexes of Group 2 dications with soft thioether- and selenoether-containing macrocycles

A new route to cationic complexes of Mg, Ca, Sr and Ba with 18-membered ring O4S2, O4Se2 and O2S4 donor macrocycles from metal acetonitrile complexes with weakly coordinating [BArF]? anions is described. The precursors used were [M(MeCN)x][BArF]2 (M = Mg, x = 6; M = Ca, x = 8) and [M?(acacH)(MeCN)5][BArF]2 (M? = Sr or Ba). Reaction of these with the heterocrowns, [18]aneO4S2 (1,4,10,13-tetraoxa-7,16-dithiacyclooctadecane), [18]aneO4Se2 (1,4,10,13-tetraoxa-7,16-diselenacyclooctadecane) or [18]aneO2S4 (1,10-dioxa-4,7,13,16-tetrathiacyclooctadecane) in anhydrous CH2Cl2 solution gave [M(heterocrown)(MeCN)2][BArF]2 for M = Mg, Ca or Sr, whilst the larger Ba forms [Ba(heterocrown)(acacH)(MeCN)][BArF]2. The complexes have been characterised by microanalysis, IR, 1H and 13C{1H} NMR spectroscopy. X-ray crystal structures are reported for [Ca([18]aneO2S4)(MeCN)2][BArF]2, [Ca([18]aneO4Se2)(MeCN)2][BArF]2, [Sr([18]aneO4S2)(MeCN)2][BArF]2, and [Sr([18]aneO4Se2)(MeCN)2][BArF]2 which contain 8-coordinate metal centres with trans-nitrile ligands and ?6-heterocrowns, and for the 9-coordinate [Ba([18]aneO4Se2)(acacH)(MeCN)][BArF]2. Adventitious hydrolysis of the magnesium complexes in solution results in six-coordinate complexes, [Mg(?3-[18]aneO4Se2)(OH2)2(MeCN)][BArF]2 and [Mg(?3-[18]aneO4S2)(OH2)2(MeCN)][BArF]2, whose structures were determined. X-ray crystal structures are also reported for [Mg(MeCN)6][BArF]2, [M(MeCN)8][BArF]2 (M = Ca, Sr) and [Ca(18-crown-6)(MeCN)2][BArF]

Thermal and Photochemical Reduction and Functionalization Chemistry of the Uranyl Dication, [U VI O2] 2+

The uranyl ion, [UVIO2]2+, possesses rigorously trans, strongly covalent, and chemically robust U-oxo groups. However, through the use of anaerobic reaction techniques, both one- and two-electron reductive functionalization of the uranyl oxo groups has been discovered and developed. Prior to 2010, this unusual reactivity centered around the reductive silylation of the uranyl ion which entailed conversion of the oxo ligands into siloxy ligands and reductive metalation of the uranyl oxo with Group 1 and f-block metals. This review surveys the large number of new examples of reductive functionalization of the uranyl ion that have been reported since 2010, including reductive borylation and alumination, metalation with d- or f-block metals, and new examples of reductive silylation. Other examples of oxo-group functionalization of [UVIO2]2+ that do not involve reduction, mainly with Group 1 cations, are also covered, along with new advances in the photochemistry of the uranyl(VI) ion that involve the transient formation of formally uranyl(V) [UVO2]+ ion

Electrokinetic generation of iron-rich barriers in soils:realising the potential for nuclear site management and decommissioning

Following earlier field-scale pilot work on nuclear site materials in the late 2000s, there has recently been renewed research and industry interest in the application of electrokinetic technologies for nuclear site management and remediation in the UK. One relatively novel application of electrokinetics is the use of sacrificial steel electrodes (coupled with an in situ generated pH-Eh gradient in the treated material) to precipitate sub-surface iron-rich barriers for groundwater and/or leachate containment, which could be used to grout or contain contaminated fluids in the sub-surface on working nuclear sites or sites undergoing decommissioning. Here, we report previously unpublished data from two work programmes exploring the higher Technology Readiness Level (TRL) application of this electrokinetic iron-barrier approach to materials typical of those found in the subsurface of the Sellafield nuclear licensed site, UK. The first programme, funded by the UK National Nuclear Laboratory (NNL), assessed the electrokinetic generation of iron-rich barriers at metre + scale in simulated Sellafield materials, while the second programme, funded under the current UK TRANSCEND consortium project, examined electrokinetic iron-barrier formation at smaller (&lt;1 m) scale, but in real site materials. Both programmes indicate that iron-rich barriers can be conveniently and electrokinetically grown in different geometries over reasonable timescales (months) in realistic site subsurface materials (sands), in electrolytes similar to natural waters found in the environment. Voltage requirements are low (&lt;1 V cm−1) with energy and consumables costs of no more than single-digit or tens of US dollars at the metre-plus scale. Further work is needed however to assess the longevity of the iron precipitates forming the subsurface barrier, and to explore barrier generation at the geometries and scales required for (site specific) field application.</p

Differential uranyl(v) oxo-group bonding between the uranium and metal cations from groups 1, 2, 4, and 12; a high energy resolution X-ray absorption, computational, and synthetic study

The uranyl(VI) ‘Pacman’ complex [(UO₂)(py)(H₂L)] A (L = polypyrrolic Schiff-base macrocycle) is reduced by Cp₂Ti(η²-Me₃SiC[triple bond, length as m-dash]CSiMe₃) and [Cp₂TiCl]₂ to oxo-titanated uranyl(V) complexes [(py)(Cp₂$Ti^{III}$OUO)(py)(H₂L)] 1 and [(ClCp₂$Ti^{IV}$OUO)(py)(H₂L)] 2. Combination of $Zr^{II}$ and $Zr^{IV}$ synthons with A yields the first $Zr^{IV}$–uranyl(V) complex, [(ClCp₂ZrOUO)(py)(H₂L)] 3. Similarly, combinations of $Ae^{0}$ and $Ae^{II}$ synthons (Ae = alkaline earth) afford the mono-oxo metalated uranyl(V) complexes [(py)₂(ClMgOUO)(py)(H₂L)] 4, [(py)₂(thf)₂(ICaOUO)(py) (H₂L)] 5; the zinc complexes [(py)₂(XZnOUO)(py)(H₂L)] (X = Cl 6, I 7) are formed in a similar manner. In contrast, the direct reactions of Rb or Cs metal with A generate the first mono-rubidiated and mono-caesiated uranyl(V) complexes; monomeric [(py)₃(RbOUO)(py)(H₂L)] 8 and hexameric [(MOUO)(py)(H₂L)]₆ (M = Rb 8b or Cs 9). In these uranyl(V) complexes, the pyrrole N–H atoms show strengthened hydrogen-bonding interactions with the endo-oxos, classified computationally as moderate-strength hydrogen bonds. Computational DFT MO (density functional theory molecular orbital) and EDA (energy decomposition analysis), uranium M₄ edge HR-XANES (High Energy Resolution X-ray Absorption Near Edge Structure) and 3d4f RIXS (Resonant Inelastic X-ray Scattering) have been used (the latter two for the first time for uranyl(V) in 7 (ZnI)) to compare the covalent character in the $U^{V}$–O and O–M bonds and show the 5f orbitals in uranyl(VI) complex A are unexpectedly more delocalised than in the uranyl(V) 7 (ZnI) complex. The $O_{exo}$–Zn bonds have a larger covalent contribution compared to the Mg–$O_{exo}$/Ca–$O_{exo}$ bonds, and more covalency is found in the U–$O_{exo}$ bond in 7 (ZnI), in agreement with the calculations

Electrokinetic Remediation and in-situ iron barrier generation

Electrokinetic remediation (EKR; simply put, moving things with electricity) uses low voltage DC current to control the migration (Figure 1) of contaminants in porous media and remove or degrade them. We have previously demonstrated that ex-situ EK techniques can treat plutonium-contaminated wastes at the AWE Aldermaston site1, and the technique is widely applied at scale for the destruction of substrates (soils, etc.) contaminated with organic pollution.Here, we present our work on using EKR to remediate a range of contaminated substrates, in controlled remediation of real Sellafield materials by growth of in-situ iron barriering