Following our report of the first near-linear lanthanide (Ln) complex, [Sm(N)] (1), herein we present the synthesis of [Ln(N)] [N = {N(SiPr)}; Ln = Eu (2), Tm (3), Yb (4)], thus achieving approximate uniaxial geometries for a series of "traditional" Ln ions. Experimental evidence, together with calculations performed on a model of 4, indicates that dispersion forces are important for stabilization of the near-linear geometries of 1-4. The isolation of 3 under a dinitrogen atmosphere is noteworthy, given that "[Tm(N″)(μ-N″)]" (N″ = {N(SiMe)}) has not previously been structurally authenticated and reacts rapidly with N(g) to give [{Tm(N″)}(μ-η:η-N)]. Complexes 1-4 have been characterized as appropriate by single-crystal X-ray diffraction, magnetic measurements, electrochemistry, multinuclear NMR, electron paramagnetic resonance (EPR), and electronic spectroscopy, along with computational methods for 3 and 4. The remarkable geometries of monomeric 1-4 lead to interesting physical properties, which complement and contrast with comparatively well understood dimeric [Ln(N″)(μ-N″)] complexes. EPR spectroscopy of 3 shows that the near-linear geometry stabilizes m states with oblate spheroid electron density distributions, validating our previous suggestions. Cyclic voltammetry experiments carried out on 1-4 did not yield Ln reduction potentials, so a reactivity study of 1 was performed with selected substrates in order to benchmark the Sm → Sm couple. The separate reactions of 1 with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), azobenzene, and benzophenone gave crystals of [Sm(N)(TEMPO)] (5), [Sm(N)(NPh)] (6), and [Sm(N){μ-OPhC(CH)CPhO-κO,O'}] (7), respectively. The isolation of 5-7 shows that the Sm center in 1 is still accessible despite having two bulky N moieties and that the N-donor atoms are able to deviate further from linearity or ligand scrambling occurs in order to accommodate another ligand in the Sm coordination spheres of the products.

As the dominant radionuclide by mass in many radioactive wastes, the control of uranium mobility in contaminated environments is of high concern. U speciation can be governed by microbial interactions, whereby metal-reducing bacteria are able to reduce soluble U­(VI) to insoluble U­(IV), providing a method for removal of U from contaminated groundwater. Although microbial U­(VI) reduction is widely reported, the mechanism(s) for the transformation of U­(VI) to relatively insoluble U­(IV) phases are poorly understood. By combining a suite of analyses, including luminescence, U M4-edge high-energy resolved fluorescence detection–X-ray absorption near-edge structure (XANES), and U L3-edge XANES/extended X-ray absorption fine structure, we show that the microbial reduction of U­(VI) by the model Fe­(III)-reducing bacterium, Shewanella oneidensis MR1, proceeds via a single electron transfer to form a pentavalent U­(V) intermediate which disproportionates to form U­(VI) and U­(IV). Furthermore, we have identified significant U­(V) present in post reduction solid phases, implying that U­(V) may be stabilized for up to 120.5 h.

The introduction of (N2)3–• radicals into multinuclear lanthanide molecular magnets raised hysteresis temperatures by stimulating strong exchange coupling between spin centers. Radical ligands with larger donor atoms could promote more efficient magnetic coupling between lanthanides to provide superior magnetic properties. Here, we show that heavy chalcogens (S, Se, Te) are primed to fulfill these criteria. The moderately reducing Sm­(II) complex, [Sm­(N††)2], where N†† is the bulky bis­(triisopropylsilyl)­amide ligand, can be oxidized (i) by diphenyldichalcogenides E2Ph2 (E = S, Se, Te) to form the mononuclear series [Sm­(N††)2(EPh)] (E = S, 1-S; Se, 1-Se, Te, 1-Te); (ii) S8 or Se8 to give dinuclear [{Sm­(N††)2}2(μ-η2:η2-E2)] (E = S, 2-S2 ; Se, 2-Se2 ); or (iii) with TePEt3 to yield [{Sm­(N††)2}­(μ-Te)] (3). These complexes have been characterized by single crystal X-ray diffraction, multinuclear NMR, FTIR, and electronic spectroscopy; the steric bulk of N†† dictates the formation of mononuclear complexes with chalcogenate ligands and dinuclear species with the chalcogenides. The Lα1 fluorescence-detected X-ray absorption spectra at the Sm L3-edge yielded resolved pre-edge and white-line peaks for 1-S and 2-E 2 , which served to calibrate our computational protocol in the successful reproduction of the spectral features. This method was employed to elucidate the ground state electronic structures for proposed oxidized and reduced variants of 2-E 2 . Reactivity is ligand-based, forming species with bridging superchalcogenide (E2)−• and subchalcogenide (E2)3–• radical ligands. The extraordinarily large exchange couplings provided by these dichalcogenide radicals reveal their suitability as potential successors to the benchmark (N2)3–• complexes in molecular magnets.

A non-axenic culture of Pseudanabaena catenata, a close relative of the bloom-forming cyanobacterium found in the high pH First Generation Magnox Storage Pond at the Sellafield Nuclear Facility, was supplemented with 1 mM of SrCl 2 , to determine its effect on the fate of Sr. The addition of 1 mM Sr to the P. catenata culture resulted in ∼16% reduction in the overall growth of the culture (OD 600nm) and a 21% reduction in the concentration of chlorophyll-a (Chl-a) compared to those without Sr. The fate of Sr was assessed using a multi-technique approach. Inductively coupled plasma atomic emission spectroscopy showed that virtually all of the Sr was removed from solution, while extracellular biomineral precipitates were analyzed using transmission electron microscopy analysis, and were shown to contain Sr, Ca, and S using energy-dispersive X-ray spectroscopy analysis. In addition, intracellular P-containing electron-dense features, likely to be polyphosphate bodies, were associated with the P. catenata cells and contained Sr. Bulk analysis of the cultures by X-ray diffraction showed the presence of Ca-containing strontianite whilst Extended X-ray Absorption Fine Structure analysis showed the presence of strontium phosphate minerals. The presence of Sr associated with intracellular polyphosphate was unexpected, and contrasts with other model photosynthetic systems in the literature that have highlighted carbonate biominerals as the dominant sink for Sr. Understanding the fate of Sr with microorganisms associated with the Spent Nuclear Fuel Ponds (SNFPs) is crucial to understanding the fate of radioactive 90 Sr in such extreme environments, and could also suggest a potential remediation strategy for treatment of 90 Sr contaminated waters from Spent Nuclear Fuel Ponds SNFPs and in contaminated aquatic systems.

No abstract