Synthesis and Structures of Ruthena-octahydrotetraborane Complexes

The reactivity of κ²-N,S-chelated ruthenium borate complexes, [Ru(PPh₃)(κ²-N,S-(NC₇H₄S₂)Ru{κ³-H,S,S′-H₂B (NC₇H₄S₂)₂}] ( 1 a ) and [Ru(PPh₃)(κ²-N,S-(NC₅H₄S){κ³-H,S,S′-H₂B(NC₅H₄S)₂}] ( 1 b ) with monoboranes have been explored. The prolonged room temperature reaction of [Ru(PPh₃){κ²-N,S-(NC₇H₄S₂)}{κ³-H,S,S′-H₂B(NC₇H₄S₂)₂}], 1 a with an excess of [BH₃ ⋅ THF] led to the formation of hydrogen-rich complex, arachno-[PPh₃(κ²-B₃H₈)Ru{κ³-H,S,S′-H₂B(NC₇H₄S₂)₂] ( 2 ). In a similar fashion, the isomeric ruthenatetraborane complexes of [Ru(PPh₃)(κ²-N,S-(B₃H₈){κ³-H,S,S′-H₂B(NC₅H₄S)₂}], 4 and 5 were isolated from the room temperature reaction of 1 b with [BH₃ ⋅ THF]. In complex 2 , the borate ligand, [H₂B(NC₅H₄S)₂] and the PPh₃ occupy the endo and exo sites of the butterfly-shaped RuB₃ core, respectively. In contrast, the borate unit [H₂B(NC₅H₄S)₂] in 4 sits on the exo position of the butterfly core, while the phosphine ligand occupies the endo site. Multinuclear spectroscopic analyses were done to characterize all new complexes and the structures were further confirmed by single-crystal X-ray diffraction analysis. Density functional theory (DFT) calculations were performed to probe into the bonding modes of these complexes.     

The structure of a new octahedral fluoride complex of niobium (Me4N)2[Nb6F6Br6(H2O)2Cl4]·6H2O

The substitution reaction of thiocyanide groups of the complex K₄[Nb₆F₆Br₆(NCS)₆] in aqueous hydrochloric acid has afforded a new fluoride cluster anion [Nb₆F₆ ⁱ Br₆ ⁱ Cl₄ ^a (H₂O)₂ ^a ]²⁻ isolated as the salt (Me₄N)₂[Nb₆F₆Br₆Cl₄(H₂O)₂]·6H₂O (space group R3m, a = 11.230(5) ?, c = 26.230(5) ?, V = 2865(2) ?³, Z = 3, R1 = 0.0362, R2w = 0.0886). The anion contains the cluster core Nb₆F₆Br₆ having ordered “inner” ligands. Difference in the atomic radii of “inner” ligands causes a significant distortion of the metal cluster along the three-fold axis. Original Russian Text Copyright ? 2008 by N. G. Naumov, S. Cordier, C. Perrin, and S. B. Artemkina __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 49, No. 6, pp. 1163–1166, November–December, 2008.     

Supramolecular Frameworks Based on Rhenium Clusters Using the Synthons Approach

The reaction of the K₄[{Re₆Sⁱ₈}(OH)^a₆]·8H₂O rhenium cluster salt with pyrazine (Pz) in aqueous solutions of alkaline or alkaline earth salts at 4 °C or at room temperature leads to apical ligand exchange and to the formation of five new compounds: [trans-{Re₆Sⁱ₈}(Pz)^a₂(OH)^a₂(H₂O)^a₂] (1), [cis-{Re₆Sⁱ₈}(Pz)^a₂(OH)^a₂(H₂O)^a₂] (2), (NO₃)[cis-{Re₆Sⁱ₈}(Pz)^a₂(OH)^a(H₂O)^a₃](Pz)·3H₂O (3), [Mg(H₂O)₆]_0.5[cis-{Re₆Sⁱ₈}(Pz)^a₂(OH)^a₃(H₂O)^a]·8.5H₂O (4), and K[cis-{Re₆Sⁱ₈}(Pz)^a₂(OH)^a₃(H₂O)^a]·8H₂O (5). Their crystal structures are built up from trans- or cis-[{Re₆Sⁱ₈}(Pz)^a₂(OH)^a_4−x(H₂O)^a_x]^x−2 cluster units. The cohesions of the 3D supramolecular frameworks are based on stacking and H bonding, as well as on H₃O₂₋bridges in the cases of (1), (2), (4), and (5) compounds, while (3) is built from stacking and H bonding only. This evidences that the nature of the synthons governing the cluster unit assembly is dependent on the hydration rate of the unit.     

Dislocation climb and low-temperature plasticity of an Al–Pd–Mn quasicrystal

Dislocations and phason faults have been studied by transmission electron microscopy in an Al-Pd-Mn sample deformed at 300°C under a high pressure. All dislocation movements have occurred by climb, in contrast with the usual interpretations of dislocation motion in quasicrystals. Several modes of dissociation and decomposition of dislocations have been observed, allowing for estimations of phason fault and antiphase-boundary energies. Work softening is tentatively explained in terms of a varying chemical stress.     

Liquid crystal properties resulting from synergetic effects between non-mesogenic organic molecules and a one nanometre sized octahedral transition metal cluster

This work presents the synthesis and studies of a red-NIR luminescent liquid crystal compound based on an octahedral metallic cluster core orthogonally bounded to six non-mesogenic organic ligands. It evidences synergetic effects between the organic and inorganic parts of the hybrid, resulting in the generation of liquid crystal properties on cooling from the isotropic melt.     

Large time behavior of differential equations with drifted periodic coefficients modeling carbon storage in soil

This paper is concerned with the linear ODE in the form y′(t) = λρ(t)y(t) + b(t), λ < 0 which represents a simplified storage model of the carbon in the soil. In the first part, we show that, for a periodic function ρ(t), a linear drift in the coefficient b(t) involves a linear drift for the solution of this ODE. In the second part, we extend the previous results to a classical heat non-homogeneous equation. The connection with an analytic semi-group associated to the ODE equation is considered in the third part. Numerical examples are given.     

Growth optimization and characterization of lattice-matched Al0.82In0.18N optical confinement layer for edge emitting nitride laser diodes

We present the growth optimization and the doping by the metal organic chemical vapor deposition of lattice-matched Al_0.82In_0.18N bottom optical confinement layers for edge emitting laser diodes. Due to the increasing size and density of V-shaped defects in Al_1?xIn_xN with increasing thickness, we have designed an Al_1?xIn_xN/GaN multilayer structure by optimizing the growth and thickness of the GaN interlayer. The Al_1?xIn_xN and GaN interlayers in the multilayer structure were both doped using the same SiH₄ flow, while the Si levels in both layers were found to be significantly different by SIMS. The optimized 8×(Al_0.82In_0.18N/GaN=54/6 nm) multilayer structures grown on free-standing GaN substrates were characterized by high resolution X-ray diffraction, atomic force microscopy and transmission electron microscopy, along with the in-situ measurements of stress evolution during growth. Finally, lasing was obtained from the UV (394 nm) to blue (436 nm) wavelengths, in electrically injected, edge-emitting, cleaved-facet laser diodes with 480 nm thick Si-doped Al_1?xIn_xN/GaN multilayers as bottom waveguide claddings.