Synthesis and Electronic Structure Determination of Uranium(VI) Ligand Radical Complexes

   Pentagonal bipyramidal uranyl complexes of salen ligands, N,N’-bis(3-tert-butyl-(5R)-salicylidene)-1,2-phenylenediamine, in which R = tBu (1a), OMe (1b), and NMe2 (1c), were prepared and the electronic structure of the one-electron oxidized species [1a-c]+ were investigated in solution. The solid-state structures of 1a and 1b were solved by X-ray crystallography, and in the case of 1b an asymmetric UO22+ unit was found due to an intermolecular hydrogen bonding interaction. Electrochemical investigation of 1a-c by cyclic voltammetry showed that each complex exhibited at least one quasi-reversible redox process assigned to the oxidation of the phenolate moieties to phenoxyl radicals. The trend in redox potentials matches the electron-donating ability of the para-phenolate substituents. The electron paramagnetic resonance spectra of cations [1a-c]+ exhibited gav values of 1.997, 1.999, and 1.995, respectively, reflecting the ligand radical character of the oxidized forms, and in addition, spin-orbit coupling to the uranium centre. Chemical oxidation as monitored by ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy afforded the one-electron oxidized species. Weak low energy intra-ligand charge transfer (CT) transitions were observed for [1a-c]+ indicating localization of the ligand radical to form a phenolate / phenoxyl radical species. Further analysis using density functional theory (DFT) calculations predicted a localized phenoxyl radical for [1a-c]+ with a small but significant contribution of the phenylenediamine unit to the spin density. Time-dependent DFT (TD-DFT) calculations provided further insight into the nature of the low energy transitions, predicting both phenolate to phenoxyl intervalence charge transfer (IVCT) and phenylenediamine to phenoxyl CT character. Overall, [1a-c]+ are determined to be relatively localized ligand radical complexes, in which localization is enhanced as the electron donating ability of the para-phenolate substituents is increased (NMe2 > OMe > tBu)

Different standards: engineers’ expectations and listener adoption of digital and FM radio broadcasting

As digital radio broadcasting enters its third decade of operation, few would argue that it has met all expectations expressed at the time of its launch in the mid-1990s. Observers are now more circumspect, with views divided on the pace of transition to an all-digital future. In exploring this mismatch between expectation and actuality, this article considers the introduction of FM radio from the 1950s. It too was expected to replace its forebear (AM) but, like digital radio, its adoption by listeners was slower than anticipated. An examination of published literature, in particular engineering and technical documents, reveals a number of similarities in the development of digital radio and FM. Assumptions about listeners’ needs and preferences appear to have been based on little actual audience research and, with continual reference in the literature to the supposed deficiencies of the predecessor technology, suggest an emphasis in decision making on the technical qualities of radio broadcasting over an appreciation of actual audience preferences

Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM

Control of Oxo-Group Functionalization and Reduction of the Uranyl Ion

yesUranyl complexes of a large, compartmental N8-macrocycle adopt a rigid, “Pacman” geometry that stabilizes the UV oxidation state and promotes chemistry at a single uranyl oxo-group. We present here new and straightforward routes to singly reduced and oxo-silylated uranyl Pacman complexes and propose mechanisms that account for the product formation, and the byproduct distributions that are formed using alternative reagents. Uranyl(VI) Pacman complexes in which one oxo-group is functionalized by a single metal cation are activated toward single-electron reduction. As such, the addition of a second equivalent of a Lewis acidic metal complex such as MgN″2 (N″ = N(SiMe3)2) forms a uranyl(V) complex in which both oxo-groups are Mg functionalized as a result of Mg−N bond homolysis. In contrast, reactions with the less Lewis acidic complex [Zn(N″)Cl] favor the formation of weaker U−O−Zn dative interactions, leading to reductive silylation of the uranyl oxo-group in preference to metalation. Spectroscopic, crystallographic, and computational analysis of these reactions and of oxo-metalated products isolated by other routes have allowed us to propose mechanisms that account for pathways to metalation or silylation of the exo-oxogroup

Use of Artificial Nest Boxes to Facilitate Egg Collection for an Eastern Hellbender Head-Starting Program

Population declines have been taking place throughout the entire geographic range of the eastern hellbender (Cryptobranchus alleganiensis) in North America. The declines and local extinctions have led to multiple head-starting programs to augment or restore hellbender populations. Once widespread throughout the Susquehanna River basin, the eastern hellbender is now restricted to several tributaries of the West Branch watershed. In order to establish a head-starting program for the Susquehanna River basin, we are collecting fertilized eggs to be transported to zoological facilities that are prepared to raise larval and juvenile hellbenders until they are of a size where they are unlikely to be subject to predation (3-5 years of age). To facilitate the collection of fertilized eggs, we installed 17 artificial nest boxes in the late summer of 2014. The boxes are distributed across three stream reaches occupied by hellbenders and within a single tributary of the West Branch watershed. The boxes are made of concrete and weigh 27 kg. By mid-September, no adult hellbenders had taken up residence in, nor had nested within, the concrete boxes. We now believe that the nest boxes should have been installed several months in advance of the nesting season so that adult hellbenders would have had more opportunities to find the boxes and take up residence. We plan to leave the boxes in place until the next nesting season, but will modify the boxes to darken the chamber, making it more suitable for permanent residency and egg deposition. In lieu of collecting eggs from the artificial nest chambers, we are currently searching for natural nests from which we hope to collect eggs to be transported to the head-start facility

Habitat Preferences, and Population Structure and Stability, in an Eastern Hellbender Population in the West Branch of the Susquehanna River

We collected habitat and population data over two field seasons (2012 and 2014) for an eastern hellbender (Cryptobranchus alleganiensis) population in a tributary of the West Branch of the Susquehanna River. Analyses of population data show that the population has been stable across the sample years, with no significant change in linear density. Analyses of habitat use show that hellbenders take up residency in or near the thalweg, where the majority of cover rocks are located. Peripheral cover rocks are only rarely used by hellbenders. We found a positive relationship between the size (total body length) of hellbenders and the size (length) of the cover rock. Population size/age structure and sex ratios were similar between the two sample years. During the second field season (2014), we observed American eels (Anguilla rostrata) beneath cover rocks, but in no case did we find eels and hellbenders beneath the same cover rock. We observed no eels in the study area in 2012. Recent eel introductions in the watershed likely explain the sudden appearance of eels in the study reach. The precipitous co-occurrence of eels and hellbenders raises the concern that eels may compete with hellbenders for rock cover and for a limited food resource that consists mainly of Allegheny crayfish (Orconectes obscurus). Significant competition for food and cover, and eel predation on hellbender eggs, larvae and juveniles, could potentially initiate a decline in an otherwise stable hellbender population

Reductive silylation of a uranyl dibenzoylmethanate complex: an example of controlled uranyl oxo ligand cleavage

Reaction of UO2(dbm)2(THF) (dbm = OC(Ph)CHC(Ph)O) with 1 equiv. of R3SiH (R = Ph, Et), in the presence of B(C6F5)3, results in the formation of U(OB{C6F5}3)(OSiR3)(dbm)2(THF) (R = Ph, 1; Et, 2), which were isolated as red-orange crystalline solids in good yields. Interestingly, the addition of 1 equiv. of H(dbm) to 2 results in protonation of the –OSiEt3 ligand and formation of U(OB{C6F5}3)(dbm)3 (4) in 33% yield, along with formation of HOSiEt3. Furthermore, addition of HOSiEt3 and 1 equiv. of THF to 4, results in the formation 2, revealing that this process is reversible. The two-step conversion of UO2(dbm)2(THF) to 4 represents a rare example of controlled uranyl oxo ligand cleavage at ambient temperature and pressure. Comparison of diffraction and density functional theory data for 4 suggests the presence of the inverse trans influence, with a very shallow potential energy well for distortion along the trans U–O bond

CCDC 994968: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures