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

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

Overview of erosion–deposition diagnostic tools for the ITER-Like Wall in the JET tokamak

This paper presents scientific and technical issues related to the development of erosion–deposition diagnostic tools for JET operated with the ITER-Like Wall: beryllium and tungsten marker tiles and several types of wall probes installed in the main chamber and in the divertor. Markers tiles are the standard limiter and divertor components additionally coated first with a thin sandwich of Ni–Be and Mo–W for, beryllium and tungsten markers, respectively. Both types of markers are embedded in regular arrays of limiter and divertor tiles. Coated W–Be probes are also inserted in the Be-covered Inconel cladding tiles on the central column. Other types of erosion–deposition diagnostic tools are: rotating collectors, deposition traps, louver clips, quartz microbalance and mirrors for the First Mirror Test at JET for ITER. The specific role of these tools is discussed in detail

Oxo Ligand Substitution in a Cationic Uranyl Complex: Synergistic Interaction of an Electrophile and a Reductant

Reaction of [U^VIO₂(dppmo)₂(OTf)]­[OTf] (dppmo = Ph₂P­(O)­CH₂P­(O)­Ph₂) with 4 equiv of Ph₃SiOTf and 2 equiv of Cp₂Co generates the U­(IV) complex U^IV(OTf)₄­(dppmo)₂ (<b>1</b>), as a yellow-green crystalline solid in 83% yield, along with Ph₃SiOSiPh₃ and [Cp₂Co]­[OTf]. This reaction proceeds via a U­(IV) silyloxide intermediate, [U^IV(OSiPh₃)­(dppmo)₂­(OTf)₂]­[OTf] (<b>2</b>), which we have isolated and structurally characterized. Similarly, reaction of [U^VIO₂­(TPPO)₄]­[OTf]₂ (TPPO = Ph₃PO) with 6 equiv of Me₃SiOTf and 2 equiv of Cp₂Co generates the U­(IV) complex, [Cp₂Co]­[U^IV(OTf)₅­(TPPO)₂] (<b>3</b>), as a yellow-green crystalline solid in 76% yield, concomitant with formation of Me₃SiOSiMe₃, [Ph₃POSiMe₃]­[OTf], and [Cp₂Co]­[OTf]. Complexes <b>1</b> and <b>3</b> have been fully characterized, including analysis by X-ray crystallography. The conversion of [U^VIO₂(dppmo)₂­(OTf)]­[OTf] and [U^VIO₂(TPPO)₄]­[OTf]₂ to complexes <b>1</b> and <b>3</b>, respectively, represents rare examples of well-defined uranyl oxo ligand substitution