Structural study of the Li(0.5)Na(0.5)MnFe2(PO4)3 and Li(0.75)Na(0.25)MnFe2(PO4)3 alluaudite phases and their electrochemical properties as positive electrodes in lithium batteries

The alluaudite lithiated phases Li(0.5)Na(0.5)MnFe(2)(PO(4))(3) and Li(0.75)Na(0.25)MnFe(2)(PO(4))(3) were prepared via a sol-gel synthesis, leading to powders with spongy characteristics. The Rietveld refinement of the X-ray and neutron diffraction data coupled with ab initio calculations allowed us for the first time to accurately localize the lithium ions in the alluaudite structure. Actually, the lithium ions are localized in the A(1) and A(1)' sites of the tunnel. M?ssbauer measurements showed the presence of some Fe(2+) that decreased with increasing Li content. Neutron diffraction revealed the presence of a partial Mn/Fe exchange between the two transition metal sites that shows clearly that the oxidation state of the element is fixed by the type of occupied site. The electrochemical properties of the two phases were studied as positive electrodes in lithium batteries in the 4.5-1.5 V potential window, but they exhibit smaller electrochemical reversible capacity compared with the non-lithiated NaMnFe(2)(PO(4))(3). The possibility of Na(+)/Li(+) ion deintercalation from (Na,Li)MnFe(2)(PO(4))(3) was also investigated by DFT+U calculations.     

On the Stability and Accuracy of Least Squares Approximations

We consider the problem of reconstructing an unknown function f on a domain X from samples of f at n randomly chosen points with respect to a given measure ρ _X . Given a sequence of linear spaces (V _m ) _m>0 with dim(V _m )=m≤n, we study the least squares approximations from the spaces V _m . It is well known that such approximations can be inaccurate when m is too close to n, even when the samples are noiseless. Our main result provides a criterion on m that describes the needed amount of regularization to ensure that the least squares method is stable and that its accuracy, measured in L ²(X,ρ _X ), is comparable to the best approximation error of f by elements from V _m . We illustrate this criterion for various approximation schemes, such as trigonometric polynomials, with ρ _X being the uniform measure, and algebraic polynomials, with ρ _X being either the uniform or Chebyshev measure. For such examples we also prove similar stability results using deterministic samples that are equispaced with respect to these measures.     

Access to "Friedel-Crafts-restricted" tert-alkyl aromatics by activation/methylation of tertiary benzylic alcohols

Herein we describe a two-step protocol to prepare m-tert-alkylbenzenes. The appropriate tertiary benzylic alcohols are activated with SOCl(2) or concentrated HCl and then treated with trimethylaluminum, affording the desired products in 68-97% yields (22 examples). This reaction sequence is successful in the presence of a variety of functional groups, including acid-sensitive and Lewis-basic groups. In addition to t-Bu groups, 1,1-dimethylpropyl and 1-ethyl-1-methylpropyl groups can also be installed using this method.     

Spectre de photoélectrons et calcul des facteurs de franck-condon pour H2O,D2O,HDO

The first band of the photoelectron spectrum of HDO has been recorded. In agreement with the selection rules of the group theory, the fundamental terms of the three symmetric vibrations of HDO (C_s symmetry) have been observed. Taking the geometry of the ion as parameters, the Franck-Condon factors for the ionization of H₂O, D₂O and HDO have been calculated. The geometry of the H₂O⁺, D₂O⁺, HDO⁺ ions (ground state) have been determined accurately by comparison of the calculated results with the corresponding photoelectron spectra. This geometry is approximately the same for the three ions: r_OH  1,00 Å and < HOH  110°.     

La deprotection electrochimique des amines : (II) - Problèmes posés par la coupure cathodique des p.toluéne sulfonamides

The deprotection of amines may be conducted via the cathodic cleavage of the corresponding sulfonamides. However, the selectivity of the reaction depends on parameters such as the tendency of the sulfonamide in the absence of proton donors to be decomposed into imine at the cathodic interface. The problem is discussed as a function of the molecular structure of the starting sulfonamide. Results on simple sulfonomides are applied successfully in the deprotection of polysulfonamides and may allow the synthesis of new polyazaligonds.     

Complexing ability of the versatile,redox-active, 3-[3-(diphenylphosphino)propylthio]-3',4,4'-trimethyl-tetrathiafulvalene ligand

The synthesis of a ligand containing as an electroactive core a tetrathiafulvalene moiety, 3-[3-(diphenylphosphino)propylthio]-3',4,4'-trimethyl-tetrathiafulvalene, is reported. Its versatile ability to act as a bidentate or a monodentate ligand, as demonstrated by the metal carbonyl complexes obtained, is described. The novel cis-Mo(CO)(4)(P-TTF)(2) 4 and cis-W(CO)(4)(P,S-TTF) 6 complexes have been characterized by X-ray diffraction analyses and cyclic voltammetry measurements. Within complex 4, no significant influence of the two electroactive ligands on the molybdenum center was detected, whereas, in complex 6, a weak influence of the TTF redox-active core can be observed on the redox behavior of the metal center.     

Effective computational modeling of constitutional isomerism and aggregation states of explicit solvates of lithiated phenylacetonitrile

We present the first calculations which accurately account for the position of metalation and aggregation state of lithiated nitriles. Solvation is found to be a key determinant of structure. Five known solvates of lithiated phenylacetonitrile were examined computationally to determine the minimum level of theory required to reproduce the observed X-ray and multinuclear NMR structures. In all cases Hartree-Fock 3-21G energies of explicit solvates calculated at PM3 geometries correctly predict the observed N-lithiated constitutional isomer. Selected density functional theory (B3LYP/6-31+G*//PM3) energy calculations reproduce this trend. We also show that 3-21G//PM3 calculations which do not include explicit solvent molecules, or which include water as a model for diethyl ether, may lead to incorrect predictions of the preferred constitutional isomer. 3-21G//PM3 energies also adequately account for observed aggregation states of the TMEDA, diethyl ether, and THF solvates. Finally, calculations of THF-solvated monomers up to the B3LYP/6-31+G*//B3LYP/6-31+G level indicate a significant (6.8 kcal/mol) preference for N-lithiation.     

French laboratory proficiency testing program for food microbiology

The proficiency testing program in food microbiology (Réseau d'Analyses et d'Echanges en Microbiologie des Aliments; RAEMA), created in 1988, currently includes 440 participating laboratories. The program establishes proficiency in detection of Salmonella and Listeria monocytogenes, as well as quantitation of aerobic microorganisms, Enterobacteriaceae, coliforms, Escherichia coli, Clostridium perfringens, coagulase-positive Staphylococcus, and Listeria monocytogenes. Twice a year, 5 test samples are sent to participants to assess their precision and trueness for enumeration and detection of microorganisms. Results show an increasing involvement of food microbiology laboratories in quality assurance programs and use of standard and validated analytical methods. However, the percentage of laboratories obtaining questionable and unsatisfactory microbiological results remains relatively constant.