Advances on the Determination of the Astatine Pourbaix Diagram: Predomination of AtO(OH)2− over At− in Basic Conditions

It is generally assumed that astatide (At^?) is the predominant astatine species in basic aqueous media. This assumption is questioned in non‐complexing and non‐reductive aqueous solutions by means of high‐pressure anion‐exchange chromatography. Contrary to what is usually believed, astatide is found to be a minor species at pH=11. A different species, which also bears a single negative charge, becomes predominant when the pH is increased beyond 7. Using competition experiments, an equilibrium constant value of 10^?6.9 has been determined for the formation of this species from AtO(OH) with the exchange of one proton. The identification of this species, AtO(OH)₂^?, is achieved through relativistic quantum mechanical calculations, which rule out the significant formation of the AtO₂^? species, while leading to a hydrolysis constant of AtO(OH) in excellent agreement with experiment when the AtO(OH)₂^? species is considered. Beyond the completion of the Pourbaix diagram of astatine, this new information is of interest for the development of ²¹¹At radiolabeling protocols.     

Aerosol‐Assisted Synthesis of Porous TiNxOy@C Nanocomposites

Porous TiN_xO_y‐based particles were synthesized by an aerosol spray process. At first, the starting sol solution containing the metal precursor and the nitrogen source is sprayed to form an aerosol that is subsequently pyrolysed at different temperatures. The obtained dried particles are an amorphous coordination “polymer” rich in carbon and nitrogen. These “glassy” particles are finally thermally treated at 800 °C, promoting the crystallization of the particles and the release of a major part of the carbon. As the particles keep their original shape, carbon loss and density increase during the crystallization step and lead to the development of an accessible pore structure. The process was analyzed and extended to the synthesis of other metal nitrides, such as VN and W₂N, thereby showing its general validity for the production of functional nanocrystalline nitride ceramics with high porosity still occupying a relatively small volume, and otherwise not easily accessible.     

On the use of x-ray-excited optical luminescence (XEOL) for the analysis of multisite rare-earth systems

The realization of a XEOL (X-ray-excited optical luminescence) spectrometer is reported. The aim of the present paper is to show that a comparison between UV-excited emission spectra and XEOL spectra can be helpful in the assignment of some weak transitions for multiple site rare-earth compounds. The case of c-Y₂O₃ doped with Eu³⁺ cations is considered in some detail, as in the XEOL spectrum three lines to be assigned to transitions occurring at the centrosymmetrical Eu³⁺ (C_3i) site are strongly enhanced. Additional site-selective UV-excited emission spectra are also reported supporting the present discussion.     

The hydrocyanation of free and polymer-bound benzoquinone

The polymer-bound quinone2 has been prepared and used in column form with organic solvents for the convenient preparation of other quinones. In contrast to the solution reaction hydrocyanation of this quinone by the Thiele-Meisenheimer reaction did not yield a useful proportion of polymer-bound dicyanohydroquinone but instead gave a mixture of products including much monocyanohydroquinone. Helferich and Bodenbender's 2,3-dicyanocyclohexan-1, 4-dione is in fact wholly the di-enol and is a likely intermediate in the hydrocyanation of benzoquinone, being oxidised by the latter to 2,3-dicyanocyclohex-2-ene-1, 4-dione which tautomerises to the observed product, 2,3-dicyanohydroquinone. A lower accessibility to polymer-bound reactants as compared with those in solution is implied by these results.     

α'β-Elimination and wittig rearrangement of the carbanion from benzyl cyclooctyl ether

Beside the Wittig rearrangement and the migration of the cyclooctyl radical to the para position, the title carbanion gives rise to an elimination in a syn process.     

The mass spectra of some naphthoquinones. Lapachol,isolapachol and related compounds

Several alkylhydroxynaphthoquinones and chemically related cyclic compounds were subjected to mass spectrometric investigation. Fragmentation pathways were elucidated by use of metastable ions, relative intensities of normal ions and accurate mass measurement. In these series, differences in the spectra of 1,2- and 1,4-naphthoquinones are slight. Evidence for ring expansion in ions from furans is suggested.     

The non-existence of gaseous cyclopentadienyl cations: An overdue correction to the literature using collision-induced decompositions and charge stripping of negative ions

The C₅H₅⁺ fragment ion bound in many EI spectra is determined not to be cyclopentadienyl cation by CID-MIKE spectrometry.     

Comparison between the point-charge electrostatic model and the angular overlap model: The general case

The aim of this paper is to explore in detail the mathematical connection between the point-charge electrostatic model and the angular overlap model. More precisely, for any configuration nl^x in any symmetry, the matrix elements, and therefore the energy levels, as given by the angular overlap model restricted to the antibonding effects λ (for any of the possible λ's), are deduced from an effective potential constructed according to the point-charge electrostatic model. This allows us to give a mathematical proof of the equivalence between the point-charge electrostatic model and the angular overlap model taking into account all the antibonding effects λ. Finally, the sum rules for the angular overlap model are examined in the light of the formulae connecting the two models considered. Numerical tables for obtaining the results as given by the angular overlap model restricted to any of the antibonding effects from those as given by the point-charge electrostatic model are listed for the configurations nl^x with l = p, d, f and g.