Reactions of [ReOX3(PPh3)2] Complexes (X = Cl,Br) with Phenylacetylene and the Structures of the Products

Oxorhenium(V) complexes [ReOX₃(PPh₃)₂] (X = Cl, Br) react with phenylacetylene under formation of complexes with ylide‐type ligands. Compounds of the compositions [ReOCl₃(PPh₃){C(Ph)C(H)(PPh₃)}] ( 1 ), [ReOBr₃(OPPh₃){C(Ph)C(H)(PPh₃)}] ( 2 ), and [ReOBr₃(OPPh₃){C(H)C(Ph)(PPh₃)}] ( 3 ) were isolated and characterized by X‐ray diffraction. They contain a ligand, which was formed by a nucleophilic attack of released PPh₃ at coordinated phenylacetylene. The structures of the products show that there is no preferable position for this attack. Cleavage of the Re–C bond in 3 and dimerization of the organic ligand resulted in the formation of the [{(PPh₃)(H)CC(Ph)}₂]²⁺ cation, which crystallized as its [(ReOBr₄)(OReO₃)]^2– salt.     

High-speed planar thermometry and velocimetry using thermographic phosphor particles

Simultaneous gas-phase temperature and velocity imaging using micrometer-size thermographic phosphor particles seeded into the flow is demonstrated at a 3 kHz repetition rate. The velocity field is measured using a standard particle image velocimetry approach, while the temperature is determined from the temperature sensitive phosphorescence emission of the particles following excitation at 355 nm. Since the particles are very small, they rapidly assume the temperature and velocity of the surrounding gas. A single shot temperature precision of better than 5 % was achieved at 500 K. Time-resolved measurements in the wake of a heated cylinder are presented, demonstrating the utility of these imaging diagnostics to observe transient, coupled heat and mass transfer phenomena.     

Stable nitridorhenium(V) complexes with an N-heterocyclic carbene

Nitridorhenium(V) complexes with the nucleophilic cyclocarbene 1,3,4-triphenyl-1,2,4-triazol-5-ylidene have been synthesised and are the first representatives of a new class of high-valent metallocarbenes.     

The redox thermodynamics of microperoxidase are dependent on the solvent medium

The redox thermodynamics of the heme undecapeptide, microperoxidase have been examined in aqueous buffer and in glycerol. The change in E(o)' on transition from water to glycerol is dominated by the change in deltaS(o)'.     

Synthesis and Structure of the Clusters [Hg2(μ—SePh)2(SePh)2(PPh3)2] and [Hg3Br3(μ—SePh)3] · 2 DMSO

The compounds [Hg₂(μ—SePh)₂(SePh)₂(PPh₃)₂] ( I ) and [Hg₃Br₃(μ—SePh)₃] · 2 DMSO ( II ) are formed by reactions of [Hg(SePh)₂] with PPh₃ in THF( I ) or with HgBr₂ in DMSO ( II ) at room temperature. X—ray crystallography reveals that the cluster I consists of a distorted square built by each two Hg and Se atoms. The Hg atoms have almost tetrahedral co‐ordination environments formed by selenium atoms of two (μ‐^—SePh) ligands and Se and P atoms of terminal ^—SePh and PPh₃ ligands. The compound II is a six‐membered ring with alternating Hg and Se atoms in the chair conformation. Two DMSO molecules occupy positions below and above the [Hg₃Se₃] ring with the oxygen atoms directed to the centre of the ring.     

Decay of vibrational coherence in ortho-para mixtures of solid hydrogen

Hydrogen crystals were pumped by stimulated Raman gain into coherent superpositions of the ground and 2 v = 1 vibrational exciton state and its amplitude monitored by coherent anti-Stokes scattering. The resulting non-exponential and temperature independent (1.6–4.2 K) decays, for o-H₂ concentrations between 0.22 and 2.7%, were attributed to compositional scattering.     

REFLECTANCE SPECTROSCOPY FOR THE CHARACTERIZATION OF PHOTOCHROMISM IN THE CRYSTALLINE STATE

Abstract— The Kubelka-Munk theory for diffuse reflectance has been applied to a quantitative study of photochromism in the crystalline state. For three systems investigated it was found possible to assign first order rate constants to the thermal relaxation process and estimate the pre-exponential factor A and the activation energy E_a in Arrhenius equation. For the fading of the red photocolored form, Λ_max=490 mμ, of benzaldehyde phenylhydrazone A = 1.4×10⁸ min^-1 and E_a= 15.7 kcal mole^-1. For the fading of the blue photocolored form, Λ_max=590 mμ, of 2–(2,4-dinitrobenzyl)pyridine A= 5×10¹⁴ min^-1 E_a =23.3 kcal mole^-1, Cinnamaldehyde semicarbazone showing 'reversed phototropy' has a photoactivated state, Λ_max=400 mμ, which in dark is transformed into a strongly absorbing yellow species, Λ_max= 430 mμ with A = 14 × 10¹⁰ min^-1 and E_a= 18.7 kcal mole-¹.