Concerted and stepwise proton-coupled electron transfers in aquo/hydroxo complex couples in water: oxidative electrochemistry of [Os(II)(bpy)(2)(py)(OH(2))](2+)

Successive oxidation of transition metal(II) aqua complexes (M(II)OH(2) to M(III)OH) is a domain in which proton-coupled electron transfer reactions are extremely common. The mechanism of these PCET reactions-concerted or stepwise-is an important issue in the understanding and design of natural or artificial systems catalyzing the formation of dioxygen by four-electron oxidation of water. Concerted proton-coupled electron transfer from an aqua metal(II) to a hydroxo metal(III) complex requires the close proximity of a proton-accepting group with a pK value between those of the aqua complexes. Otherwise, stepwise electron-proton or proton-electron pathways involving high-energy intermediates are followed. Concerted proton-electron pathways involving water as proton-acceptor or proton-donor group are inefficient. Cyclic voltammetry of the title complex in buffered aqueous solution and re-examination of previous results for the same complex attached to an electrode surface are used to establish these conclusions, which provide a starting point on the route to higher degrees of oxidation, such as those involved in the catalysis of water oxidation.     

Exploring the rotational isomerism in non-classical Wells-Dawson anions {W18X}: a combined theoretical and mass spectrometry study

We present a combined theoretical and mass spectrometry study of the rotational isomerism of the non-classical Wells-Dawson anions. The structure is larger than the Keggin anion and six geometric isomers are predicted (α, β, γ, α*, β*, γ*) on the basis of structural arguments. This work explores the geometrical differences between the isomers and evaluates the stability of these unusual clusters based upon the inclusion of the different heteroatoms. We connect the theoretical results with experimental studies by exploring the fragmentation of the parent clusters by electrospray-ionisation mass spectrometry (ESI-MS). Both approaches show a general stability trend that can be postulated as follows: γ* > β* > α* > α ? β > γ where the isomers γ*, β* and α are the only anions of this type known to have been synthesised.     

The numerical integration of relative equilibrium solutions. The nonlinear Schrodinger equation

We analyse different error propagation mechanisms for conservativeand nonconservative time-integrators of nonlinear Schrödingerequations. We use a geometric approach based on interpretingwaves as relative equilibria.     

Connecting theory with experiment to understand the initial nucleation steps of heteropolyoxometalate clusters

A complimentary combination of Density Functional Theory (DFT) methodology and Electrospray Ionization-Mass Spectrometry (ESI-MS) has been utilized to increase our limited understanding of the first nucleation steps in the formation of the [XM(12)O(40)](n-) Keggin polyoxometalates (POMs) (where addenda metal atom M = W or Mo, and the heteroatom X = P or As). We postulate that the first key steps of nucleation into discrete, high nuclearity heteropolyanions proceed via the formation of isodinuclear species (e.g. [M(2)O(7)](2-)), which undergo successive steps of protonation and water condensation to form a heterotrinuclear fragment, which acts as a template for the constituent parts required for subsequent aggregation and formation of the plenary Keggin heteropolyanion. The stability of calculated structures of the numerous postulated intermediates has been analysed and discussed in detail, and these results complemented using experimental mass spectrometry, using an assembly (reaction solution analysis) and disassembly (fragmentation of single crystals) approach. Overall, no significant differences between the Keggin POMs were found when changing the addenda metal atom (W or Mo) or the heteroatom (P or As); although small differences among the lowest-energy structures were detected.     

Small Cage Uranofullerenes: 27 Years after Their First Observation

The tetravalently stabilized fullerene cage of C₂₈ is historically the most elusive small fullerene cage observed by employing the laser vaporization synthesis methodology. Its first observation reported by Smalley et al. in 1992 suggests that C₂₈ is potentially the smallest and most stable fullerene ever observed. By using the Krätschmer?Huffman arc discharge synthesis method, we have recently succeeded in synthesizing a series of uranium‐endohedral fullerenes which differ from those reported by Smalley and co‐workers. Intrigued by this interesting mismatch, we tuned our experimental conditions to favor the formation and detection of these missing species. Experiments done using solvents of varying polarity allowed the observation of several empty and uranofullerenes. Extractions with pyridine and o‐DCB allowed for observation of small U@C_2n (2n=28, 60, 66, 68, 70) by high resolution Fourier‐Transform Ion Cyclotron Resonance Mass Spectrometry (FT‐ICR MS). This is the first time that U@C₂₈ is observed in soot produced by the Krätschmer‐Huffman arc‐discharge methodology. Carbon cage selection and spin density distribution on the endohedral metallofullerenes (EMFs) U@C₆₀, U@C₇₀, and U@C₇₂ were studied by means of density functional theory (DFT) calculations. A plausible pathway for the formation of U@D_3h‐C₇₄ from U@D_5h‐C₇₀ through two C₂ insertions and one Stone‐Wales rearrangement is proposed.