Polymorphism in PbBiOXO4 compounds (X=V, P, As): Part II—PbBiOPO4 and PbBiOAsO4 structures and characterization of related solid solutions

Reinvestigation of PbBiOXO₄ (X=V, P, As) thermal behaviour revealed a phase transition for V- and P-compounds, but no transition for the As-compound. As shown by single-crystal X-ray diffraction and high-resolution neutron powder diffraction, α-PbBiOVO₄ transforms to β-PbBiOVO₄ at 550 °C. The two PbBiOPO₄ varieties are isomorph to the vanadate forms, while PbBiOAsO₄ adopts the β-type structure whatever the temperature. PbBiP_1−xOAs_xO₄ and PbBiV_1−xOM_xO₄ (M=As, P, Cr, Mn) solid solutions display both triclinic and monoclinic domains, and the α→β transition temperature is a function of the substitution rate. The ionic conductivity of these compounds was investigated by impedance spectroscopy. The analysis of free space in the β-PbBiOVO₄ structure allows to propose a one-dimensional oxygen diffusion pathway along [010] when the temperature increases.     

Improved convergence order for augmented penalty algorithms

We refine the speed of convergence analysis for the quadratic augmented penalty algorithm. We improve the convergence order from 4/3 to 3/2 for the first order multiplier iteration. For the second order iteration, we generalize the analysis, and consider a primal–dual variant which asymptotically reduces to a Newton step for the optimality conditions.     

The magic effect of endocyclic but non-sterically hindering biisoquinoline chelates: From fast-moving molecular shuttles to [3]rotaxanes

The use of 8,8′-diaryl-substituted 3,3′-biisoquinolines allows the construction of new multi-component assemblies that are inaccessible with the 2,9-diaryl-substituted 1,10-phenanthroline ligands previously developed by the Sauvage group. This is due to the sterically non-hindering nature of the new chelates, which makes three-component entanglements around octahedral metal centres such as iron(II), cobalt(II) and ruthenium(II) readily possible. Among the newly synthesized molecular assemblies are [3]rotaxanes and [3]pseudorotaxanes in which two molecular strings pass through a single macrocycle, as well as molecular shuttles that exhibit greatly improved shuttling kinetics when compared to previously investigated molecular machines that are based on copper(I)/copper(II) redox chemistry.     

CuLn complexes with a single μ-oximato bridge

Two original dinuclear (LnYb, 3 and LnEr, 4) and one trinuclear Cu^IILn^IIICu^II (LnGd, 5) complexes derived from a polydentate non symmetrical Schiff base ligand H₂L have been prepared. The ligand possesses two functions (phenol and oxime) able to coordinate the Ln ions, but structural studies (X-ray diffraction and powder X-ray diffraction) show that the Cu^II and Ln^III ions are only bridged by the oximato (NO) pair. The missing phenoxo bridge is replaced by a surprising pseudo-bridge involving one oxygen atom of the nitrato anion linked to the Cu and Ln ions according to a η²: η¹: μ mode. Although this latter contact has no role from the magnetic point of view, it introduces a large deformation of the unique bridging network. The CuYb complex 3 and the trinuclear CuGdCu complex 5 present antiferromagnetic interactions, with a J_CuGd interaction equal to ?1.25 cm^?1 in 5. The genuine single bridge can be considered as responsible for the antiferromagnetic character of the interaction.     

Amorphous structure and electronic properties of the Ge1Sb2Te4 phase change material

Ge1Sb2Te4 is one of the most commonly used phase change materials, due to the large optical and electrical contrast between a metastable crystalline phase and the amorphous phase. We use ab initio molecular dynamics to generate an amorphous Ge1Sb2Te4 structure. By analysing the distance distributions, we show that the structure can be analysed in terms of 21% of tetrahedrally coordinated Ge atoms and 79% of 3-fold Ge atoms. These are involved in distorted octahedral shells with bond length correlations that are similar to the a-GeTe structure as a consequence of a Peierls-distortion. The electronic properties are shown to be in reasonable agreement with the experiment with an electronic gap of 0.45 eV with. The optical conductivity curve is also in agreement with the experiment, with a maximal conductivity at an energy of ～3 eV.     

Two minor phytoecdysteroids of the plant Silene viridiflora

Chemical investigations of Silene viridiflora (L.) yielded a new ecdysteroid, 20-hydroxyecdysone 20,22-monoacetonide-25-acetate (1), and a known ecdysteroid, 2-deoxypolypodine B-3-beta-D-glucoside (2). The elucidation of the chemical structures was established by 1D and 2D NMR experiments.     

Trumpet with near-perfect harmonicity: design and acoustic results

This paper presents a mathematical design methodology for determining the shape of a trumpet air column that has near-perfect harmonicity, whose components are discontinuity-free, and whose input impedance peak heights are balanced over the playing range. The simulation model employed assumes linear wave propagation and uses cylindrical element discretization with a plane wave approximation. Acoustic measurements are made using a test set-up with an estimated relative measurement error of ±3 cents. Comparisons of measured results are given for the presented design (Macaluso trumpet) and the same trumpet air column with the bell replaced by a commercially used generic trumpet bell of unknown shape (Generic trumpet). For acoustic resonance modes 2-13 (233-1515 Hz), the measured root-mean-square (rms) harmonicity deviation is 5 cents for the Macaluso trumpet, whereas it is 18 cents for the Generic trumpet. However, considering the estimated measurement uncertainty, each of those deviations is somewhat over-stated. For that same range of resonances, the rms deviation between measured and calculated resonance frequencies for the Macaluso trumpet is 3 cents, thus validating the presented simulation model and equations.     

On the role of the bridging dicyanamidobenzene ligand in a new binuclear ruthenium complex: [{Ru(tpy)(thd)}2(mu-dicyd)][PF6] with tpy = 2,2':6',2' '-terpyridine and thd = 2,2,6,6-tetramethyl-3,5-heptanedione

The dicyanamidobenzene-bridge diruthenium complex [{Ru(tpy)(thd)}(2)(mu-dicyd)][PF(6)] ([3][PF(6)]) (dicyd = 1,4-dicyanamidobenzene, tpy = 2,2':6',2' '-terpyridine, thd = 2,2,6,6-tetramethyl-3,5-heptanedione) and its mononuclear counterpart [Ru(tpy)(thd)(Ipcyd)] (2) [Ipcyd = 4-iodophenylcyanamide anion (Ipcyd(-))] were synthesized and fully characterized. Cyclic voltammetry of 3 showed the presence of four reversible one-electron redox couples. UV-vis-NIR spectroelectrochemistry and EPR spectroscopy of the electrogenerated paramagnetic intermediates were used to ascertain the oxidation-state distribution. The stable starting dinuclear complex 3(+) is found to be a ligand-centered anion radical as shown by EPR spectroscopy, magnetic susceptibility measurements, and DFT calculations. Oxidation of 3(+) to 3(2+) led to an EPR silent system due to substantial intramolecular antiferromagnetic interaction of the electron spins carried by the low spin ruthenium(III) atom and the bridging anion radical dicyanamido (dicyd(*)(-)), an observation which was supported by UV-vis-NIR, X-ray structure, and DFT calculations. Complex 3(3+) presented an EPR spectra consistent with a total effective spin S = (1)/(2) issued from an antiferromagnetic interaction of electron spins carried by two low spin ruthenium(III) atoms and the bridging anion radical dicyd(*)(-) in accordance with UV-vis-NIR. This study shows that the dicyanamidobenzene bridging ligand has indubitably a noninnocent behavior.