Catalysis by Ir(III), Rh(III) and Pd(II) metal ions in the oxidation of organic compounds with H2O2

Catalytic activities of three transition metals, as iridium (III) chloride, rhodium (III) chloride and palladium (II) chloride, were compared in the oxidation of six aromatic aldehydes (benzaldehyde, p‐chloro benzaldehyde, p‐nitro benzaldehyde, m‐nitro benzaldehyde, p‐methoxy benzaldehyde and cinnamaldehyde), two hydrocarbons (viz. (anthracene and phenanthrene)) and one aromatic and one cyclic alcohol (cyclohexanol and benzyl alcohol) by 50% H₂O₂. The presence of traces (substrate: catalyst ratio equal to 1:62500 to 1:1961) of the chlorides of iridium(III), rhodium(III) and palladium(II) catalyze these oxidations, resulting in good to excellent yields. It was observed that in most of the cases palladium(II) chloride is the most efficient catalyst. Conditions for the highest and most economical yields were obtained. Deviation from the optimum conditions decreases the yields. Oxidation in aromatic aldehydes is selective at the aldehydeic group only and other groups remain unaffected. This new, simple and economical method, which is environmentally safe, also requires less time. Reactive species of catalysts, existing in the reaction mixture are also discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Average local electrostatic potential and the core-valency separation in atoms

The average local electrostatic potential function, V(r)/ ρ(r), is calculated for 87 atoms, Li-Ac, in the ground state using the nonrelativistic average-over-configuration numerical Hartree-Fock density. It is found empirically that in a given atom the shell boundaries are expressed as the successively increasing maxima in V(r)/ ρ(r) and the outermost maximum presents good approximate estimates of the core-valence separation in atoms. The likeness in behavior of V(r)/ ρ(r) at each shell boundary with the maximum hardness principle is discussed. The single-exponent-fit parameters for the electron density in the valency region are provided for all atoms. © 1995 John Wiley & Sons, Inc.     

Aminonaphthalic anhydrides as red-emitting materials: electroluminescence, crystal structure, and photophysical properties

The red and orange emitters (ANA-1-3) consisting of a 4-amino-1,8-naphthalic anhydride group were synthesized. The lowest absorption band of these ANA molecules centered at approximately 450 nm is assigned to be a charge-transfer transition with emission at 514-536 nm in nonpolar solvents such as n-hexane and at approximately 590-640 nm in polar solvents such as THF and CH(2)Cl(2) and in the solid states. Emission lifetimes are measured with time-correlated single photon counting. Shorter lifetimes are observed for the ANA molecules when dissolved in polar solvents compared with those in nonpolar solvents. Strong dipole-dipole interaction of ANA molecules with solvents is indicated. At high concentrations the measured emission lifetimes, generally shortened from self-quenching, are found to remain about the same order of magnitude in ANAs. This implies that the exciton states of aggregates are formed and they exhibit a relatively long lifetime. Crystallographic data of 4-(phenyl antracen-9-yl) (ANA-2) and 4-(phenyl-2-naphthyl) amino-1,8-naphthalic anhydrides (ANA-3) show that the molecules exist as dimeric structures with antiparallel head-to-tail stacking of naphthalic anhydride planes in addition to other pi-pi stacking. The strong dipole-dipole interactions and the pi-pi stacking account for the observed red-shifted emissions of ANAs in the powders. For films prepared from vacuum sublimation, a structure similar to that in the crystal but with less crystalline order is expected based on the emission wavelength. Several electroluminescent devices based on these ANAs are reported here; they emit orange-red light at 602-628 nm with high brightness and steady external quantum efficiency.     

The use of McMurry coupling for the synthesis of indolophanes and cis-stilbenophanes

Treatment of 2 equiv of indole-3-aldehyde with o, m, p-xylyl, 2,5-dimethoxy-p-xylyl dibromides and 4,4′-bis(bromomethyl)-1,1′-biphenyl gave the bisalkylated products, which underwent McMurry coupling with low valent titanium to give indolophanes. Various cis-stilbenophanes with m-terphenyl building blocks were also synthesized by application of the McMurry coupling technique.     

Kinetic and mechanistic studies on the formation of bis(dicarboxylato)carbonatochromate(III) complexes

The reaction of the Cr(xx)₂(H₂O)₂ ⁻ (xx = oxalate, malonate and methylmalonate) complexes with dissolved CO₂ was studied by stopped-flow spectrophotometry in the 7 < pH < 9 range and between 20 to 30°C at an ionic strength of 0.5 mol dm⁻³ (NaCl). Under the experimental conditions the aqua complex ion consists of a pH-dependent mixture of Cr(xx)₂(H₂O)₂ ⁻, Cr(xx)₂(OH) (H₂O)²⁻ and Cr(xx)₂(OH)₂ ³⁻. The monohydroxo and dihydroxo species undergo CO₂ uptake and subsequent intramolecular carbonate ligand chelation independently, at rates which are readily distinguishable and are governed by the uptake rate constants k ₁ and k ₂ and chelation rate constants k ₃ and k ₄, respectively. Only the k ₁ values for oxalato, malonato and methylmalonato complexes could be calculated; k ₁ = 1084 and 1333 and 1650 mol⁻¹ dm³ s⁻¹, respectively. The results obtained were compared with those obtained from other systems that have either cobalt(III), iridium(III) or rhodium(III) as central atoms. This revised version was published online in June 2006 with corrections to the Cover Date.     

HPTLC Method for Quantification of Apigenin in the Dried Root Powder of Gmelina arborea Linn.

JPC – Journal of Planar Chromatography – Modern TLC - A sensitive high-performance thin-layer chromatographic method has been established for quantification of apigenin in dried root...     

Spectrophotometric determination of vanadium with n-benzoyl-o-tolylhydroxylamine

N-Benzoyl-o-tolylhydroxylamine is shown to provide a virtually specific reagent for the spectrophotometric determination of vanadium. The reddish-violet complex formed with the reagent in 4–8 N hydrochloric acid after extraction with chloroform shows absorption maxima at 510 mm, and obeyes Beer's law from 0.5 to 10 μg with an optimum range of 2–10 μg; the percent relative error is 2.7. The sensitivity is 0.0108 μg V/cm². The complex contains the metal and the reagent in a ratio of 1:2 and the dissociation constant is of the order of 10^-9.     

Preparation of thin stable erbium target sandwiched between carbon layers

Targets of isotopically enriched ¹⁷⁰Er (erbium) were prepared on 45 μg/cm² carbon backing using the method of vacuum evaporation. Another layer of carbon with thickness 23 μg/cm² was deposited on it as a protective cap with the help of an electron gun. Carbon backing, Er and the capping carbon layer were deposited using resistive heating and electron gun deposition without disturbing the vacuum. The thickness of ¹⁷⁰Er was measured by X-ray fluorescence analysis as well as with Rutherford backscattering spectrometry and it was found to be 150 μg/cm². Successful preparation of sandwiched targets was very sensitive to substrate temperature, deposition rate, duration of in situ annealing, cooling rate etc.     

Understanding guest and pressure‐induced porosity through structural transition in flexible interpenetrated MOF by Raman spectroscopy

Interpenetrating metal organic frameworks are interesting functional materials exhibiting exceptional framework properties. Uptake or exclusion of guest molecules can induce sliding in the framework making it porous or non‐porous. To understand this dynamic nature and how framework interaction changes during sliding, metal organic framework (MOF) 508 {Zn(BDC)( 4,4′‐Bipy)_0.5 · DMF(H₂O)_0.5} was selected for study. We have investigated structural transformation in MOF‐508 under variable conditions of temperature, pressure and gas loading using Raman spectroscopy and substantiated it with IR studies and density functional theory (DFT) calculations. Conformational changes in the organic linkers leading to the sliding of the framework result in changes in Raman spectra. These changes in the organic linkers are measured as a function of high pressure and low temperature, suggesting that the dynamism in MOF‐508 framework is driven by ligand conformation change and inter‐linker interactions. The presence of Raman signatures of adsorbed CO₂ and its librational mode at 149 cm⁻¹ suggests cooperative adsorption of CO₂ in the MOF‐508 framework, which is also confirmed from DFT calculations that give a binding energy of 34 kJ/mol. Copyright © 2015 John Wiley & Sons, Ltd.     

Lyotropic self-assembly of high-aspect-ratio semiconductor nanowires of single-crystal ZnO

Lyotropic nanowire dispersions are attractive precursors for semiconductor device fabrication because they permit the alignment control of active nanomaterials. The reliable production of nanowire-based mesophases, however, is very challenging in practice. We show that appropriately functionalized high-aspect-ratio nanowires of single-crystal ZnO spontaneously form nematic phases in organic and aqueous media. These systems show isotropic, biphasic, and nematic phases on increasing concentration, in reasonable agreement with Onsager's theory for rigid rods interacting via excluded volume. Suspensions were readily processed to produce films with large-area monodomains of aligned nanowires. Imprints of the director field in quiescently dried films display a propensity for bend deformation in the organic mesophase versus splay deformation in the aqueous case, suggesting that system elasticity may be tuned via surface functionalization. These results provide critical insight for the utilization of semiconductor nanowires as novel mesogens and further enable the use of solution-based routes for fabricating optoelectronic devices.