Molar extinction coefficients of solutions of some organic compounds

Molar extinction coefficients of aqueous solutions of some organic compounds, viz. formamide (CH₃NO),N-methylformamide (C₂H₅NO),NN-dimethylformamide (C₃H₇NO),NN-dimethylacetamide (C₄H₉NO), 1,4-dioxane (C₄H₈O₂₄), succinimide (C₄H₅NO₂) and solutions of acetamide (C₂H₅NO) and benzoic acid (C₇H₆O₂) in 1,4-dioxane (C₄H₈O₂) have been determined by narrow beam γ-ray transmission method at 81, 356, 511, 662, 1173 and 1332 keV. The experimental values of mass attenuation coefficients of these compounds have been used to calculate effective atomic numbers and electron densities. The additivity rule earlier used for aqueous solution has been extended to non-aqueous (1,4-dioxane) solutions.     

Measurement of attenuation cross-sections of some fatty acids in the energy range 122–1330 keV

The mass attenuation coefficients (μ_m) have been measured for undecylic acid (C₁₁H₂₂O₂), lauric acid (C₁₂H₂₄O₂), tridecylic acid (C₁₃H₂₆O₂), myristic acid (C₁₄H₂₈O₂), pentadecylic acid (C₁₅H₃₀O₂) and palmitic acid (C₁₆H₃₂O₂) using ⁵⁷Co, ¹³³Ba, ¹³⁷Cs, ⁶⁰Co and ²²Na emitted γ radiation with energies 122, 356, 511, 662, 1170, 1275 and 1330 keV, respectively. The accurate values of the effective atomic number (Z_eff), atomic cross-section (σ_t,), electronic cross-section (σ_e) and the effective electron density (N_eff) have great significance in radiation protection and dosimetry. These quantities were obtained by utilizing experimentally measured values of mass attenuation coefficients (μ_m). A NaI(Tl) scintillation detector with 8.2% (at 662 keV) resolution was used for detecting of attenuated γ-photons. The variation in Z_eff and N_eff of fatty acids with energy is discussed. The experimental and theoretical results are in good agreement within 2% deviation.     

Oxidation of di-n-propyl ether: Characterization of low-temperature products

The oxidation of di-n-propyl-ether (DPE) was performed in a jet-stirred reactor at 1 and 10 atm, at residence times of 1 and 0.7 s, respectively, and initial fuel concentrations of 5000 and 1000 ppm at 1 and 10 atm, respectively. Atmospheric pressure experiments were used for characterization of cool flame products. The 10 atm experiment provided KHPs profile vs. temperature and mole fraction profiles of stable species which were obtained through sonic probe sampling, gas chromatography, Fourier transform infrared spectrometry analyses. High resolution mass spectrometry analyses (HRMS) with syringe direct injection or ultra-high-pressure liquid chromatography coupling was used to characterize hydroperoxides (C₃H₈O₂, C₆H₁₄O₃), diols (C₆H₁₄O₃), ketohydroperoxides (C₆H₁₂O₄), carboxylic acids, and highly oxygenated molecules (C₆H₁₂O₆, C₆H₁₂O₈) resulting from up to four O₂ additions on fuel's radicals. Heated electrospray and atmospheric pressure chemical ionizations (HESI and APCI) were used in positive and negative mode. Whereas the CH₂ groups neighboring the ether function are the most favorable sites for H-atom abstraction reactions, speciation indicated that other sites can react by metathesis forming a large pool of intermediates. Our kinetic reaction mechanism represents the experimental data for most of the stable species but need to be expended for simulating the formation of newly detected species.     

Calculated Vibrational Frequencies of PMo12O40 3- and its Fragments

Calculated vibrational frequencies are reported for the PMo₁₂O₄₀ ^3– ion according to a 53-atomic tetrahedral model (T_d). The results are compared with calculated frequencies for fragments of this structure, viz. PO₄ (T_d), Mo₃O₁₃ (C_3v), Mo₃O₇ (C_3v, Mo₂O₁₁ (C_s) and Mo₂O₁₀ (C_s).

A complete vibrational analysis of the PMo₁₂O₄₀ ^3– ion has been performed. The adopted model of T_d symmetry is an idealization of x-ray structure data. 1 The normal modes of vibration according to this model are distributed as:     

Isotopic effects on non-linearity, molecular radius and intermolecular free length

Computation of non-linearity parameter (B/A), molecular radius (r _m) and intermolecular free length (L _f) for H₂O, C₆H₆, C₆H₁₂, CH₃OH, C₂H₅OH and their deuterium-substituted compounds have been carried out at four different temperatures, viz., 293.15, 303.15, 313.15 and 323.15 K. The aim of the investigation is an attempt to study the isotopic effects on the non-linearity parameter and the physicochemical properties of the liquids, which in turn has been used to study their effect on the intermolecular interactions produced thereof.     

Ni-Al layered double hydroxides modified with citrate, malate, and tartrate: Preparation by coprecipitation and uptake of Cu from aqueous solution

We report on aqueous Cu²⁺ uptake by Ni-Al layered double hydroxides (Ni-Al LDHs) modified with citrate (C₆H₅O₇³⁻), malate (C₄H₄O₅²⁻), and tartrate (C₄H₄O₆²⁻) anions via coprecipitation. Dropwise addition of a mixed aqueous solution of Ni(NO₃)₂ and Al(NO₃)₃ to the respective organic acid solutions at a constant pH of 7.0-9.0 afforded LDHs with intercalated C₆H₅O₇³⁻ and Ni(C₆H₅O₇⁾⁻, C₄H₄O₅²⁻, and C₄H₄O₆²⁻ in their interlayers. The anions were also likely adsorbed on the LDH surface. Citrate·Ni-Al LDH could rapidly take up Cu²⁺ at a constant pH of 5.0, mainly via chelation by the intercalated and adsorbed anions, rather than coprecipitation with dissolved Al³⁺ to form Cu-Al LDH. By contrast, malate and tartrate were not active as chelating agents, probably because they formed bridges between brucite-like layers by direct coordination of the two −COO⁻ groups with Al³⁺ in those layers.     

二硫酸-二元胺锰和二羟基-二元胺锰纳米片磁性的第一性原理研究

We perform first-principles simulations on a type of two-dimensional metal-organic nanosheet derived from the recently reported manganese bis-dithiolene Mn₃C₁₂S₁₂ [Nanoscale 5, 10404 (2013)] and manganese bis-diamine Mn₃C₁₂N₁₂H₁₂ [ChemPhysChem 16, 614 (2015)] mono-layers. By coordinating chalcogen (S or O) atoms and -NH- group to Mn atoms with trans- or cis-structures and preserving space inversion symmetry, four configurations of this type of nanosheet are obtained: trans-manganese dithiolene-diamine Mn₃(C₆S₃N₃H₃)₂, cis- manganese dithiolene-diamine Mn₃(C₆S₆)(C₆N₆H₆), trans-manganese dihydroxyl-diamine Mn₃(C₆O₃N₃H₃)₂, and cis-manganese dihydroxyl-diamine Mn₃(C₆O₆)(C₆N₆H₆). The ge- ometric con guration, electronic structure and magnetic properties of these metal-organic nanosheets are systematically explored by density functional theory calculations. The cal- culated results show that Mn₃(C₆S₃N₃H₃)₂, Mn₃(C₆O₃N₃H₃)₂ and Mn₃(C₆O₆)(C₆N₆H₆) monolayers exhibit half-metallicity and display strong ferromagnetism with Curie transition temperatures near and even beyond room temperature, and Mn₃(C₆S₆)(C₆N₆H₆) monolayer is a semiconductor with small energy gap and spin frustration ground state. The mechanisms for the above properties, especially in uences of diflerent groups (atoms) substitution and coordination style on the magnetism of the nanosheet, are also discussed. The predicted two-dimensional metal-organic nanosheets have great promise for the future spintronics ap-plications.     

Photoelectron spectra and electronic structure of boron acetylacetonates with organic substituents

Based on experimental data and theoretical results obtained by photoelectron spectroscopy and density functional theory, the electronic structure of the valence levels of boron diethyl acetylacetonate (C₂H₅)₂BAA, boron diphenyl acetylacetonate (C₆H₅)₂BAA, and 1,2-phenylene dioxyboron acetylacetonate C₆H₄O₂BAA is examined. For the compounds studied, in contrast to F₂BAA, a significant mixing of the π₃ MO of the chelate ring with the orbitals localized on the boron atom, as well as on the (C₂H₅)₂, and (C₆H₅)₂ fragments, is revealed. The C₆H₄O₂BAA complex is demonstrated to have MOs mainly localized on the oxygen atoms of the C₆H₄O₂ fragment. It is shown that the calculated results closely reproduce the experimental sequences of energy levels and the energy intervals between the ionized states of the complex.     

2D molecular square grid of Cobalt(II) with tridentate phenylglycinate and mandelate: structure and magnetism

The hydrothermal synthesis, single crystal X-ray structures and magnetic properties of two layered cobalt-carboxylate complexes, _∞²[Co^II(O₂C^∗CH(OH)C₆H₅)₂] (1) and _∞²[Co^II(O₂C^∗CH(NH₂)C₆H₅)₂] (2), where O₂CCH(OH)C₆H₅ is mandalate and O₂CCH(NH₂)C₆H₅ is phenylglycinate, are described. Pale pink crystals of 1 and 2 were obtained by the reaction of cobalt nitrate and the enantiomer-pure acids at 120 °C. In each case, the structure consists of stacks of quasi square-grid polymeric sheets consisting of carboxylato- bridges, M-O-C-O-M, and the presence of both d- and l-enantiomers of the ligands segregated on each face of the layer. The ligands exhibit both chelating and bridging functions with the carboxylate group adopting an anti-anti mode. The magnetic properties are characteristic of weakly interacting paramagnets where the moments are elevated by an important orbital contribution via spin-orbit coupling.     

Photophysical Properties of New Terbium (III) Organophosphonates

This paper reports on the synthesis, characterization and photophysical properties of the Tb³⁺ organophosphonates, TbH(O₃PR)₂, methylphosphonate (R=CH₃), ethylphosphonate (R=C₂H₅), propylphosphonate (R=C₃H₇), and phenylphosphonate (R=C₆H₅). The layered Tb³⁺ organophosphonates were characterized by X-ray diffraction, IR spectroscopy, TG and elemental analysis. The interlayer distances of the Tb³⁺ organophosphonates evaluated by the X-ray diffractogram were 9.50 Å for TbH(O₃PCH₃)₂, 12.18 Å for TbH(O₃PC₂H₅)₂, 14.84 Å for TbH(O₃PC₃H₇)₂ and 15.20 Å for TbH(O₃PC₆H₅)₂. The Tb³⁺ luminescence data revealed highly green emissive materials when they were excited at 368 nm, where the characteristic ⁵D₄ → ⁷F _J (J=6, 5, 4 and 3) transitions of Tb³⁺ were observed at 488, 543, 585 and 619 nm, respectively. The lifetime of the Tb^{3+ 5}D₄ → ⁷F₅ transition (λ_exc=368 nm and λ_em=543 nm) for the Tb³⁺ organophosphonates was evaluated from the decay curves, which values were of 2.88, 2.22, 2.14 and 2.59 ms, respectively for TbH(O₃PCH₃)₂, TbH(O₃PC₂H₅)₂, TbH(O₃PC₃H₇)₂ and TbH(O₃PC₆H₅)₂. TG analysis revealed that these materials are thermally highly stable, with no water molecule in their composition, which makes them potential luminophores.     

Solvatochromic properties of long alkyl chain π* indicators: comparison of N,N‐dialkyl‐4‐nitroanilines and alkyl 4‐nitrophenyl ethers

Hydrophobic forms of the N,N‐dialkyl‐4‐nitroaniline (DNAP) (p‐O₂NC₆H₄NR₂) ( 1a–f ) and alkyl‐4‐nitrophenyl ether (p‐O₂NC₆H₄OR) ( 2a–c ) solvatochromic π* indicators have been characterized and compared with respect to: (a) solvatochromic bandshape, (b) sensitivity expressed as ?s , ( / d π * ), and (c) trends in ? s with increasing length of alkyl chain(s) on the probe molecule. ? Octyl 4‐nitrophenyl ether (p‐O₂NC₆H₄OC₈H₁₇) ( 2b ) and ? decyl 4‐nitrophenyl ether (p‐O₂N C₆H₄ OC₁₀H₂₁) ( 2c ) were synthesized and their solvatochromic UV/Vis absorption bands were found to maintain a Gausso‐Lorentzian bandshape for the indicators in non‐polar and alkyl substituted aromatic solvents, for example, hexane(s) and mesitylene. Corresponding absorption bands for 1a–f display increasing deviation from a Gausso‐Lorentzian shape in the same solvents as the alkyl chains on the indicator are increased in length all the way to C₁₀ and C₁₂, for example, N,N‐didecyl‐4‐nitroaniline (p‐O₂NC₆H₄N (C₁₀H₂₁)₂) and N,N‐didodecyl‐4‐nitroaniline (p‐O₂NC₆H₄N (C₁₂H₂₅)₂) ( 1d–f ). A plot of ? s versus C_n follows a 1st order decay for the DNAP indicators but is linear for the alkyl 4‐nitrophenyl ethers. A discussion of how the long alkyl chains on the two types of indicators affect the orientation and overlap of n and π * orbitals, and resulting solvatochromic bands is presented. For DNAP, overextending the alkyl chains to obtain greater hydrophobic character may cause the alkane component to dominate solute‐solvation processes at the expense of the probe's fundamental solvatochromic character. Copyright © 2007 John Wiley & Sons, Ltd.     

Low-temperature absorption and fluorescence spectra of phthalocyanine in n-alcanes and in polyethylene (Shpolskii's effect)

Absorption and fluorescence spectra of free base phthalocyanine were studied in matrices of n-alcanes (C₈H₁₈, C₁₂H₂₆, C₁₆H₃₄) and polyethylene at 77 K and 4·2 K. The spectra show quasi-line structure whose multiplicity increases with increasing number of carbon atoms of the solvent and decreasing temperature. In the low-temperature spectra of phthalocyanine in polyethylene films only band spectra have been observed.I wish to thank Prof. DrSc K.Vacek, Head of The Department of Chemical Physics, Charles University for stimulating discussions.     

Hidden chemistry in phenoxyl radical (C6H5O•) coupling reaction mechanism revealed

A novel hidden reaction of the phenoxyl radical (C₆H₅O^?) with a specific daughter is found to significantly alter its hitherto accepted coupling reactions' scheme. Transient characterizations and mechanistic evaluations in highly acidic to strongly alkaline aqueous medium reveal this concurrent reaction competing favorably in nanosecond–microsecond time‐scale with the five distinct C₆H₅O^? + C₆H₅O^? reactions, which produce various phenolic end‐products as reported earlier (M. Ye and R. H. Schuler, J. Phys. Chem. 1989, 93, 1898). Presently, only the symmetric 4,4′‐dioxo transient precursor, O?C₆H₅? H₅C₆?O that leads to the stable 4,4′‐biphenol product, gets partially oxidized by a fraction of remaining C₆H₅O^?. The resulting secondary transient ^?C₁₂H₉O₂ radical is generated at diffusion‐controlled rate, k > 5.0 × 10⁹ M^?1 s^?1, and follows an independent chemistry. Consequently, when the previously reported five coupled end product distribution ratios were appropriately updated, the respective fractional values revealed a closer match for the symmetric 2,2′‐ and 4,4′‐biphenols with their suggested coupling reaction branching probabilities based on the atomic spin‐density distributions in the C₆H₅O^? radical (P. Neta, R. W. Fessenden, J. Phys. Chem., 1974, 78, 523). Results also suggest that in the remaining fraction, differential solvation in aqueous medium of various orientation‐related encounter complexes (C₆H₅O…C₆H₅O) formed during coupling favors rearrangement only toward 2,4′‐biphenolic product, at the cost of 2‐ and 4‐phenoxyphenolic species. Copyright © 2009 John Wiley & Sons, Ltd.     

Temperature and pressure effects on formation and decomposition of phenylvinylperoxy radicals in the C6H5C2H2 + O2 reaction

The effects of temperature and pressure on the formation and decomposition of C₆H₅C₂H₂O₂ in the C₆H₅C₂H₂ + O₂ reaction have been investigated at temperatures from 298 to 378 K by directly monitoring the C₆H₅C₂H₂O₂ radical in the visible region by cavity ringdown spectrometry (CRDS). The rate constant for the C₆H₅C₂H₂ + O₂ association and that for fragmentation of C₆H₅C₂H₂O₂ were found to be k₁ (C₆H₅C₂H₂ + O₂ → C₆H₅C₂H₂O₂) = (3.20 ± 1.19) × 10¹¹ exp(+760/T) cm³ mol⁻¹ s⁻¹ and k₂ (C₆H₅C₂H₂ O₂ → C₆H₅CHO + HCO) = (1.68 ± 0.13) × 10⁴ s⁻¹, respectively. Additional kinetic measurements by pulsed laser photolysis/mass spectrometry show that C₆H₅CHO was produced in the C₆H₅C₂H₂ + O₂ reaction as predicted and the formation of C₆H₅CHO from the decomposition of C₆H₅C₂H₂O₂ is temperature-independent, consistent with the CRDS experimental data.     

Structural conformations and electronic interactions of the natural product,oroxylin: a vibrational spectroscopic study

The oroxylin, 5,7‐dihydroxy 6‐methoxy flavone is a potent natural product extracted from ‘Vitex peduncularis’. Density functional theory (DFT) at B3LYP/6‐311G(d,p) level has been used to compute energies of different conformers of oroxylin to find out their stability, the optimized geometry of the most stable conformer and its vibrational spectrum. The conformer ORLN‐1 with torsion angles 0, 180, 180 and 0 degrees, respectively, for H₁₃ O₁₂ C₆ C₅, H₁₄ O₁₀ C₄ C₅, H₁₃ O₁₂ C₆ C₅ and H₁₄ O₁₀ C₄ C₅ is found to be most stable. The optimized geometry reveals that the dihedral angle φ between phenyl ring B and the chrome part of the molecule in − 19.21° is due to the repulsive force due to steric interaction between the ortho‐hydrogen atom H₂₉ of the B ring and H₁₈ of the ring C (H₂₉·H₁₈ = 2.198 Å). A vibrational analysis based on the near‐infrared Fourier transform(NIR‐FT) Raman, Fourier transform‐infrared (FT‐IR) and the computed spectrum reveals that the methoxy group is influenced by the oxygen lone pair‐aryl p_z orbital by back donation. Hence the stretching and bending vibrational modes of the methoxy group possess the lowest wavenumber from the normal values of methyl group. The carbonyl stretching vibrations have been lowered due to conjugation and hydrogen bonding in the molecules. The intramolecular H‐bonding and nonbonded intramolecular interactions shift the band position of O₁₀ H₁₄ and O₁₂ H₁₃ stretching modes, which is justified by DFT results. Copyright © 2008 John Wiley & Sons, Ltd.     

Studies on partially oxidised one-dimensional bis(oxalato)platinate salts containing divalent cations

The preparation and electrical conduction properties of the isostructural one-dimensional conductors Ni_0.84[Pt(C₂O₄)₂]·6H₂O(Ni-OP) and Mn_0.81[Pt(C₂O₄)₂]·6H₂O(Mn-OP) are described. Ni-OP exhibits a similar tem dependence of conductivity to the isostructural compounds Co_0.83[Pt(C₂O₄)₂]·6H₂O(Co-OP) and Zn_0.81[Pt(C₂O₄)₂]·6H₂O whereas the behaviour of Mn-OP is rather like that of K₂[Pt(CN)₄]Br_0.3·3H₂O. These differences are discussed in terms of the variation from compound to compound of the critical temperature for the formation of the “non-Peierls” superstructure (T_c) and the temperature at which the CDW/PD on adjacent conducting chains undergo three-dimensional ordering (T_3D). The variation of thermopower with temperature for Co-OP and Mg_0.82[Pt(C₂O₄)₂]·6H₂O is reported and related to the conduction properties and phase changes which have been observed for these compounds. For the isostructural series M_0.8[Pt(C₂O₄)₂]·6H₂O (M = Mg, Mn, Co, Ni or Zn) the variation of (T_3D) from compound to compound is related to differences in the polarizing power of the cations.     

Spectra of europium-doped yttrium oxide and yttrium vanadate phosphors

The spectral distributions of the visible absorption and fluorescence emission under electron beam excitation of Eu³⁺-doped (Y₂O₃) and (YVO₄) powders have been detected and analyzed. (Y₂O₃: Eu³⁺) has a cubicC crystal structure with a unit cell dimension a=10·61 Å. Its observed transitions from⁷ F ₀ to many upper states have been recognized; the observed number of Stark components is in agreement with that based on theC ₂ site symmetry of the Eu³⁺ ion in Y₂O₃. Eu³⁺-doped yttrium vanadate has a typical zircon tetragonal crystal structure with unit cell dimensions ofc=6·29 Å anda=7·11 Å. The observed transitions in (Eu³⁺: YVO₄) have been identified and assigned in accordance with theD _2d site symmetry of the Eu³⁺ ion in this lattice.The authors would like to express their deep gratitude to Professor G. F. J.Garlick, University of Hull, England, for offering experimental facilities in his Physics Department.     

The structure and extinction of nonpremixed methane/nitrous oxide and ethane/nitrous oxide flames

Knowledge of combustion of hydrocarbon fuels with nitrogen-containing oxidizers is a first step in understanding key aspects of combustion of hypergolic and gun propellants. Here an experimental and kinetic-modeling study is carried out to elucidate aspects of nonpremixed combustion of methane (CH₄) and nitrous oxide (N₂O), and ethane (C₂H₆) and N₂O. Experiments are conducted, at a pressure of 1 atm, on flames stabilized between two opposing streams. One stream is a mixture of oxygen (O₂), nitrogen (N₂), and N₂O, and the other a mixture of CH₄ and N₂ or C₂H₆ and N₂. Critical conditions for extinction are measured. Kinetic-modeling studies are performed with the San Diego Mechanism. Experimental data and results of kinetic-modeling show that N₂O inhibits the flame by promoting extinction. Analysis of the flame structure shows that H radicals are produced in the overall chain-branching step 3H₂ + O₂ ? 2H₂O + 2H, in which molecular hydrogen is consumed. Hydrogen is also consumed in the overall step N₂O + H₂ ? N₂ + H₂O where stable products are formed. Inhibition of the flames by N₂O is attributed to competition between these two overall steps.