Redetermination of iron dialuminide,FeAl2

The crystal structure of iron dialuminide [Corby & Black (1973). Acta Cryst. B 29 , 2669–2677] has been redetermined on a single crystal synthesized from the elements by arc melting. The compound crystallizes in the triclinic space group P with 19 atoms per unit cell, one Fe site being on an inversion centre. The crystal structure can be described as an inclusion‐plus‐deformation derivative of the orthorhombic YPd₂Si structure type.     

Oxygen nonstoichiometry of tetragonal La2-xSr(x)CuO4-δ (x = 0.15-1.2) and in situ XPS studies at elevated temperatures

The peculiarities of oxygen nonstoichiometry (δ) in tetragonal La(2-x)Sr(x)CuO(4-δ) solid solution with x(Sr) = 0.15-1.2 were studied by XRD, NPD, in situ high-temperature XPS, and chemical analysis. Temperature dependences of oxygen nonstoichiometry, δ = δ(T), were obtained for different Sr contents at 1 bar of O(2). Two types of charge compensation during replacement of lanthanum by strontium are discussed: an increase of the average copper oxidation state and a formation of oxygen vacancies. The average copper oxidation state V(Cu) exhibits a maximum of 2.32 at x(Sr) = 0.6, while δ increases with x(Sr). Oxygen vacancies are unambiguously located on the 4c site ({CuO(2)} plane) for compositions with different strontium contents, which electronic state is described by the O 2p core electron peak at about 531 eV. Thermal stability of the solid solution in a vacuum is associated with the extraction of practically the entire oxygen from CuO(2) layers and the formation of Cu(+) at least in the near-surface region. The higher average copper oxidation state after synthesis in the Sr-rich phases in comparison with the Sr-poor compositions prevents oxygen removal and the formation of Cu(+) and, therefore, stabilizes the structure during heating in a vacuum.     

Electrochemical properties of Cr doped V2O5 between 3.8 V and 2.0 V

Cr_0.1V₂O_5.15 was prepared by an oxalic acid assisted sol–gel method. X-ray diffraction showed that Cr doping induced a slight expansion (ΔV/V ≈ 2.3%) in the crystal lattice of V₂O₅. The electrochemical properties of Cr_0.1V₂O_5.15 in the potential range of 3.8–2.0 V were studied by cyclic voltammetry, galvanostatic charge–discharge cycling and potentiostatic intermittent titration technique. Cyclic voltammetry showed that the irreversible phase transition of V₂O₅ during the first cycle was effectively prevented by Cr doping. This caused the good charge–discharge cycling performance of the doped material. The discharge capacities were recorded to be 200, 170 and 120 mAhg^− 1 after fifty cycles at the C/10, C/2 and 1C rates, respectively. However, ex-situ X-ray diffraction showed that the crystal structure of the material was destroyed after long-term cycling. The lithium diffusion coefficient of Cr_0.1V₂O_5.15 varied between 10^− 11 and 10^− 12 cm² s^− 1, which was larger than that of crystalline V₂O₅, and was close to those of metal doped V₂O₅ in previous reports. The improvement in lithium diffusion kinetics was regarded as an important reason for the good electrochemical performance of Cr_0.1V₂O_5.15.     

Bistable bacterial growth rate in response to antibiotics with low membrane permeability

We demonstrate that growth rate bistability for bacterial cells growing exponentially at a fixed external antibiotic concentration can emerge when the cell wall permeability for the drug is low and the growth rate sensitivity to the intracellular drug concentration is high. Under such conditions, an initially high growth rate can remain high, due to dilution of the intracellular drug concentration by rapid cell volume increase, while an initially low growth rate can remain low, due to slow cell volume increase and insignificant drug dilution. Our findings have implications for the testing of novel antibiotics on growing bacterial strains.     

ChemInform Abstract: Li4Ge2B as a New Derivative of the Mo2B5 and Li5Sn2 Structure Types.

Single crystals of Li₄Ge₂B are obtained by solid state reaction of stoichiometric mixtures of the elements (sealed Ta crucible, 1473 K, 15 min; rapid cooling to 25 °C).     

Li12Cu12.60Al14.37: a new ternary derivative of the binary Laves phases

New ternary dodecalithium dodecacopper tetradecaaluminium, Li₁₂Cu_12.60Al_14.37 (trigonal, Rm, hR39), crystallizes as a new structure type and belongs to the structural family that derives from binary Laves phases. The Li atoms are enclosed in 15‐ and 16‐vertex and the Al3 atom in 14‐vertex pseudo‐Frank–Kasper polyhedra. The polyhedra around the statistical mixtures of (Cu,Al)1 and (Al,Cu)2 are distorted icosahedra. The electronic structure was calculated by the TB–LMTO–ASA (tight‐binding linear muffin‐tin orbital atomic spheres approximation) method. The electron localization function, which indicates bond formation, is mostly located at the Al atoms. Thus, Al—Al bonding is much stronger than Li—Al or Cu—Al bonding. This indicates that, besides metallic bonding which is dominant in this compound, weak covalent Al—Al interactions also exist.     

Synthesis and structure determination of copper perrhenate, CuReO4

Copper(I) perrhenate, CuReO₄, has been synthesized as a single-phase sample in sealed silica tubes at 500-800 °C, and its structure was determined for the first time by single-crystal X-ray diffraction. CuReO₄ forms a new structure type derived from the diamond-structure and crystallizes in space group I4₁cd with lattice parameters a=13.6965(5) Å and c=7.7729(5) Å, Z=16 (rotation method data acquisition using ω and ? scans, R₁=0.0191, wR₂=0.0403). Cu and Re atoms are tetrahedrally coordinated by O atoms, these tetrahedra are corner-shared, forming spirally twisted rings of 4-6-8-10-MeO₄ like Si_xO_y-rings in some silicon dioxide modifications or aluminosilicates. According to low-temperature powder X-ray diffraction and differential thermal analysis, CuReO₄ shows no phase transition down to 80 K and up to its melting point, 703 K.