An investigation of the electron density of a Jahn–Teller‐distorted CrII cation: the crystal structure and charge density of hexakis(acetonitrile‐κN)chromium(II) bis(tetraphenylborate) acetonitrile disolvate

In the crystal structure of the title homoleptic Cr^II complex, [Cr(CH₃CN)₆](C₂₄H₂₀B)₂·CH₃CN, the [Cr(CH₃CN)₆]²⁺ cation is a high‐spin d⁴ complex with strong static, rather than dynamic, Jahn–Teller distortion. The electron density of the cation was determined by single‐crystal X‐ray refinements using aspherical structure factors from wavefunction calculations. The detailed picture of the electronic density allowed us to assess the extent and directionality of the Jahn–Teller distortion of the Cr^II cation away from idealized octahedral symmetry. The topological analysis of the aspherical d‐electron density about the Cr^II cation showed that there are significant valence charge concentrations along the axial Cr—N axes. Likewise, there were significant valence charge depletions about the Cr^II cation along the equatorial Cr—N bonds. These charge concentrations are in accordance with a Jahn–Teller‐distorted six‐coordinate complex.     

Light-induced hetero-Diels-Alder cycloaddition: a facile and selective photoclick reaction

2-Napthoquinone-3-methides (oNQMs) generated by efficient photodehydration (Φ=0.2) of 3-(hydroxymethyl)-2-naphthol undergo facile hetero-Diels-Alder addition (k(D-A)～ 4×10(4) M(-1) s(-1)) to electron-rich polarized olefins in an aqueous solution. The resulting photostable benzo[g]chromans are produced in high to quantitative yield. The unreacted oNQM is rapidly hydrated (k(H2O) ～145 s(-1)) to regenerate the starting diol. This competition between hydration and cycloaddition makes oNQMs highly selective, since only vinyl ethers and enamines are reactive enough to form the Diels-Alder adduct in an aqueous solution; no cycloaddition was observed with other types of alkenes. To achieve photolabeling or photoligation of two substrates, one is derivatized with a vinyl ether moiety, while 3-(hydroxymethyl)-2-naphthol is attached to the other via an appropriate linker. The light-induced Diels-Alder "click" strategy permits the formation of either a permanent or hydrolytically labile linkage. Rapid kinetics of this photoclick reaction (k=4×10(4) M(-1) s(-1)) is useful for time-resolved applications. The short lifetime (τ ～7 ms in H(2)O) of the active form of the photoclick reagent prevents its migration from the site of irradiation, thus, allowing for spatial control of the ligation or labeling.     

Microwave-assisted solvothermal synthesis and characterization of metastable LiFe(1-x)(VO)(x)PO4 cathodes

Vanadyl ion substituted LiFePO(4) cathodes of the form LiFe(1-x)(VO)(x)PO(4) for 0 ≤ x ≤ 0.25 have been synthesized by a rapid microwave-solvothermal process at <300 °C within 10 min. Clear evidence of vanadyl ion substitution is demonstrated, despite a large size difference between Fe(2+) and (VO)(2+), by characterizing the products structurally, spectroscopically, and electrochemically. The vanadyl ion substitution is accompanied by the formation of iron vacancies in the lattice and Fe(3)O(4) impurity phase, which increases with increasing (VO)(2+) substitution for Fe(2+) and could be removed with a magnetic stir bar. The formation of iron vacancies, along with the oxidation of some Fe(2+) to Fe(3+) to maintain charge neutrality, results in a decrease in the unit cell volume with increasing x despite the substitution of larger (VO)(2+) for Fe(2+). Charge-discharge data of the vanadyl ion substituted samples suggest suppression of the two-phase plateau behavior that is characteristic of LiFePO(4). Electrochemical data collected without any carbon coating reveal that the capacity and rate capability decreases, but the capacity retention improves with (VO)(2+) substitution.     

Novel crosslinked membranes based on sulfonated poly(ether ether ketone) for direct methanol fuel cells

Novel covalently crosslinked membranes based on sulfonated poly(ether ether ketone) and carboxylated polysulfone exhibit much lower methanol crossover and better performance in direct methanol fuel cells at 65 °C in 1 and 2 M methanol solutions compared to Nafion 115 membranes.     

Surface-segregated, high-voltage spinel LiMn1.5Ni0.42Ga0.08O4 cathodes with superior high-temperature cyclability for lithium-ion batteries

The substitution of a small amount of Ga in the high-voltage spinel cathode LiMn_1.5Ni_0.42Ga_0.08O₄ leads to superior cyclability at room temperature and 55 °C along with higher rate capability with conventional electrolytes compared to that found with the LiMn_1.5Ni_0.5O₄ cathode. The superior performance is attributed to the segregation of the inert Ga³⁺ ions to the surface during the synthesis process, providing a robust, more stable interface with the electrolyte at the high operating voltage (~ 4.7 V), along with the stabilization of the spinel structure with a disordering of the cations in the octahedral sites.     

A novel access to highly functionalised β-lactams by regio- and stereoselective 1,3-dipolar cycloaddition reaction

A highly regio- and stereoselective synthesis of novel spiro pyrrolidines/pyrrolizidines containing β-lactam and oxazolone moieties under two different conditions is achieved using [3+2] cycloaddition methodology in moderate to good yield.     

Donor properties of the nitrone function in copper(II) complexes of some 2-hydroxy-1-naphthylnitrones

Summary Copper(II) complexes of the type CuL₂, 2H₂O and CuL₂. Py where L=-(2-hydroxy-1-naphthyl)-N-R-nitrone (R= methyl, phenyl and variously substituted phenyls) have been isolated and characterised. They have normal magnetic moments. Their ligand field spectra indicate an octahedral geometry for the dihydrates and a five-coordinate environment for the pyridine adducts. Increased (C=N) and considerably decreased (N-O) frequencies in these complexes reveal the presence of - and -interactions of the ligand with copper through nitrone oxygen. The effect of pyridine adduct formation is to increase the Cu-O -interaction.     

Pd-Ti and Pd-Co-Au electrocatalysts as a replacement for platinum for oxygen reduction in proton exchange membrane fuel cells

Fuel cells are appealing for a variety of energy needs, but the high materials and manufacturing costs have hampered their commercialization. The limited availability and the high cost of the currently used platinum catalysts, for example, pose a serious problem in their practical application. We report here non-platinum electrocatalyst systems, such as Pd-Co-Au and Pd-Ti, that are proposed from simple thermodynamic guidelines and selected by a rapid screening technique, which show electrochemical performance in proton exchange membrane fuel cells (PEMFC) similar to that found with commercial platinum catalysts. This finding opens up a new avenue to develop potentially less expensive electrocatalysts.     

NMR spectrum of benzo[b]furan in a nematic phase

The proton NMR spectrum of benzo[b]furan has been investigated in the nematic phase of a liquid crystal. Dipolar couplings obtained from the spectral analysis have been used to derive the interproton distance ratios. The phenyl ring geometry differs from that in benzo[b]thiophene. The deviations have been explained in terms of bond polarization effects.