Structure,insertion electrochemistry,and magnetic properties of a new type of substitutional solid solutions of copper,nickel, and iron hexacyanoferrates/hexacyanocobaltates

Substitutional solid solutions of metal hexacyanometalates in which low-spin iron(III) and cobalt(III) ions populate the carbon-coordinated sites were synthesized and studied by powder diffraction including Rietveld refinement, cyclic voltammetry of immobilized microparticles, diffuse reflection vis-spectrometry, and magnetization techniques. The continuous solid solution series of potassium copper(II), potassium nickel(II), and iron(III) [(hexacyanoferrate(III))(1-x)(hexacyanocobaltate(III))(x)] show that the substitution of low-spin iron(III) by cobalt(III) in the hexacyanometalate units more strongly affects the formal potentials of the nitrogen-coordinated copper(II) and high-spin iron(III) ions than those of the remaining low-spin iron(III) ions. In the case of copper(II) and iron(III) [(hexacyanoferrate(III))(1-x)(hexacyanocobaltate(III))(x)] the peak currents decrease much more than can be explained by stoichiometry, indicating that the charge propagation is slowed by the substitution of low-spin iron(III) by cobalt(III). The Rietveld refinement of all compounds confirmed the structure initially proposed by Keggin for Prussian blue and contradicts the structure described later by Ludi. The dependencies of lattice parameters on composition exhibit in all series of solid solutions studied similar, although small, deviations from ideality, which correlate with the electrochemical behavior. Finally, a series of solid solutions of the composition KNi(0.5)(II)Cu(0.5)(II)[Fe(III)(CN)(6)](1-x)[Co(III)(CN)(6)](x), where both the nitrogen- and carbon-coordinated metal ions are mixed populated and were synthesized and characterized. These are the first examples of solid solutions of metal hexacyanometalates with four different metal ions, where both the nitrogen- and the carbon-coordinated sites possess a mixed population.     

Über Thio-, Selenido- und Telluridogermanate (III): Zur Kenntnis von K6Ge2S6, K6Ge2Se6 und Na6Ge2Te6

On Thio-, Selenido-, and Telluridogermanates (III): K₆Ge₂S₆, K₆Ge₂Se₆, and Na₆Ge₂Te₆ The new compounds K₆Ge₂S₆ and K₆Ge₂Se₆ crystallize in the monoclinic system, space group C2/m (No 12); lattice constants see “Inhaltsübersicht”. The compounds are isotypic and form the K₆Si₂Te₆ structure. Na₆Ge₂Te₆ crystallizes in the K₆Sn₂Te₆ structure, monoclinic, space group P2₁/c (No 14); lattice constants see “Inhaltsübersicht”.     

Synthesis of 1-Fluoro-2-amino-1,3-cyclohexadienes and 1-Fluorobicyclo[2.2.2]octan-2-ones

Conjugated β-fluoro-enamines 4 undergo cycloaddtion to methyl acrylate regio- and stereospecifically, affording the 1-fluorobicyclo[2.2.2]octan-2-one 6a after hydrolysis.     

Influence of substituents on regioselectivity of vinyllithium formation with acrylic acid Derivatives

β-Alkoxy, β-dialkylamino, and β-N-alkylacylamino substituents determine the regioselectivity of the vinylic deprotonation of acrylic ester and nitrile derivatives: either α- or β-vinyllithium species may be generated. The corresponding acrylamides or systems with additional α-alkyl or α-methylmercapto substituents are lithiated at β-position.     

Electron attachment to gas-phase uracil

We present results about dissociative electron attachment (DEA) to gas-phase uracil (U) for incident electron energies between 0 and 14 eV using a crossed electron/molecule beam apparatus. The most abundant negative ion formed via DEA is (U-H)-, where the resonance with the highest intensity appears at 1.01 eV. The anion yield of (U-H)- shows a number of peaks, which can be explained in part as being due to the formation of different (U-H)- isomers. Our results are compared with high level ab initio calculations using the G2MP2 method. There was no measurable amount of a parent ion U-. We also report the occurrence of 12 other fragments produced by dissociative electron attachment to uracil but with lower cross sections than (U-H)-. In addition we observed a parasitic contaminating process for conditions where uracil was introduced simultaneously with calibrant gases SF6 and CCl4 that leads to a sharp peak in the (U-H)- cross section close to 0 eV. For (U-H)- and all other fragments we determined rough measures for the absolute partial cross section yielding in the case of (U-H)- a peak value of sigma (at 1.01 eV)=3 x 10(-20) m2.     

An efficient synthesis of the phytoestrogen 8-prenylnaringenin from xanthohumol by a novel demethylation process

8-Prenylnaringenin, a flavonoid, is the strongest known phytoestrogen (plant derived estrogen mimic) used in phytomedicinal applications. Starting from xanthohumol a byproduct of hops-extraction, 8-prenylnaringenin can be synthesized via isoxanthohumol. Of various demethylation procedures tested, the best yield (92%) is obtained by treatment with scandium trifluoromethanesulfonate and potassium iodide without any need of protection. The demethylation with AlBr₃/collidine and of the TIPS protected isoxanthohumol provides good results too.     

Mycosporine-glutamicol-glucoside: a natural UV-absorbing secondary metabolite of rock-inhabiting microcolonial fungi

Microcolonial ascomycetes are known to inhabit bare rock surfaces in cold and hot deserts and thus are habitually exposed to high levels of solar radiation. Several of these stress-tolerant fungal isolates, cultivated in the laboratory under daylight illumination, were studied for the presence of effective UV-radiation protection substances. Liquid chromatography/mass spectrometry (LC/MS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) analyses allowed for efficient separation and structure clarification of two mycosporines. It was demonstrated that both mycosporine-glutamicol-glucoside and mycosporine-glutaminol-glucoside are natural and constitutive secondary metabolites of microcolonial fungi. The function and relation of these substances in the fungal cell are discussed.     

Fingerprints of damped quantum rotation observed in solid-state proton NMR spectra.

(1)H NMR spectra of the methyl group in an oriented crystal sample of methylmalonic acid with all three non-methyl protons replaced by deuterons are interpreted in terms of the damped quantum rotation (DQR) theory of NMR line shapes. The DQR approach offers a perfect theoretical reproduction of the observed spectra while the conventional Alexander-Binsch line-shape model shows evident defects in the present case. The temperature trends of the quantities characterizing the coherent and incoherent dynamics of the methyl group in the DQR approach (the effective tunnelling frequency and two coherence-damping rates) derived from the spectra are fairly reproduced using a model reported previously. The present findings provide further evidence of limitations to the validity of the common belief that molecular rate processes in condensed phases are necessarily classical.