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Abstract: We present an ATR-FTIR study of three major perfluorinated ionomers that are used as proton exchange membranes in fuel cells (FCs) and that differ in their side chains: Nafion, Aquivion and 3M membrane. The choice of the following low-molecular-weight model compounds (MCs) that mimic the membrane side chains was essential for FTIR band assignment: perfluoro(3-methyl-2,4-dioxahexane)sulfonic acid for Nafion, perfluoro(2-ethoxyethane)sulfonic acid for Aquivion, and perfluoro(2-ethoxybutane)sulfonic acid for the 3M membrane. The major goal was to identify spectral bands that can be used for recognizing bonds involved in membrane fragmentation. A major focus was on the signals from the C–O–C bonds, which were assigned in some papers for Nafion and Aquivion membranes. Our ATR-FTIR results for 3M membranes did not conform to these assignments, and DFT calculations of the vibrational frequencies for the MCs were used to resolve this conundrum. The ATR-FTIR spectra of membranes and MCs and the DFT calculations led to an understanding of the fingerprint region of all membranes, and to a re-examination and re-assignment of results for Nafion and Aquivion membranes. The low intensity of the spectral bands for the ether link connected to the backbone (for all membranes) and also in the side chain (for Nafion) suggests that these bands cannot be used for the determination of the extent of degradation. [Copyright &y& Elsevier]

A combination of solid-state nuclear magnetic resonance (NMR) and first principles calculations was applied to obtain 17O, 25Mg, and 33S NMR parameters for two polymorphs of anhydrous magnesium sulfate. Working at the very high magnetic field of 21.14 T results in a dramatic improvement of resolution through a reduction of the effects of quadrupolar interactions and significant improvement in sensitivity. Experimental 25Mg and 33S spectra are dominated by quadrupolar interactions with quadrupolar parameters unique for each polymorph. In the case of 17O, there is a substantial contribution of the chemical shift anisotropy. The use of multiple-quantum magic-angle spinning (MQMAS) experiments allows the resolution of distinct oxygen species and assignment of signals in the experimental 17O spectrum. Chemical shielding constants and quadrupolar parameters for all three nuclei were calculated using plane wave pseudopotential density functional theory as implemented in the CASTEP computational package. The calculated NMR parameters are in very good agreement with the experimental results and help in signal assignment of the 17O spectrum. The results suggest applicability of such a combined computational and experimental solid-state NMR approach for the refinement of crystallographic data. [ABSTRACT FROM AUTHOR]

The crystal structure of 2-iodokojic acid, (2-jodo-3-hydroxy-6-hydroxymethyl)-4-H-pyran-4-one) (CHIO, Mr = 268.00) has been determined by single crystal X-ray diffraction analysis. The compound crystallizes in the orthorhombic crystal system with space group Pc2b and unit cell parameters: a = 4.0830(2), b = 15.3510(5), c = 23.517(1) Å and Z = 8. The final reliability index is 0.0288 for 2,584 observed reflections. The two molecules of iodokojic acid, slightly differing in their molecular structure, are localized in independent part of unit cell. The crystal packing is stabilized by O-H···O hydrogen bonds and I···O intermolecular interactions. The molecular structure of iodokojic acid determined experimentally little differs from that obtained by the applied theoretical (Hartree-Fock and four versions of DFT) methods, the differences should not be taken as a measure of the reliability of the theoretical methods. Graphical Abstract: The crystal structure of 2-iodokojic acid, (2-jodo-3-hydroxy-6-hydroxymethyl)-4-H-pyran-4-one) (CHIO, Mr = 268.00) has been determined by single crystal X-ray diffraction analysis. The two molecules of iodokojic acid, slightly differing in their molecular structure, are localized in independent part of unit cell. The crystal packing is stabilized by O-H···O hydrogen bonds and I···O intermolecular interactions. The molecular structure of iodokojic acid determined experimentally little differs from obtained by the applied theoretical (Hartree-Fock and four versions of DFT) methods, the differences should not be taken as a measure of the reliability of the theoretical methods.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Interaction of carbon monoxide with armchair single-walled carbon nanotubes (SWCNTs) of various diameters was investigated using the B3LYP density functional theory (DFT) level. For both the external and internal cases, the effect of molecular orientation on the adsorption process was studied. The adsorption energies, equilibrium distances, HOMO–LUMO energy gaps, partial charges, and natural atomic orbital occupancies of the interacting atoms were also studied. It was found that physisorption of molecular CO via the oxygen head was stronger than that via the carbon head, and that the most favorable adsorption angle between the molecular axis and x-axis of the tubes for all the armchair nanotubes was 135°. Furthermore, stability of the tube–molecule system for adsorption of a CO molecule on the outer wall of a nanotube decreases as the tube diameter increases, regardless of the adsorption angle. In contrast, CO penetration into a nanotube depends on the adsorption angle. The results show that molecular CO could be adsorbed on the inner walls of the armchair nanotubes provided that the molecular axis and the main axis of the nanotubes are parallel to each other. [Copyright &y& Elsevier]

We report studies based on a combination of ab initio electronic structure and Monte Carlo (MC) technique on the problem of cation partitioning among inequivalent octahedral sites, M1 and M2 in mixed olivines containing Mg and Fe ions. Our MC scheme uses interactions derived out of ab initio, density functional calculations carried out on measured crystal structure data. Our results show that there is no reversal of the preference of Fe for M1 over M2 as a function of temperature. Our findings do not agree with the experimental findings of Redfern et al. (Phys Chem Miner 27:630-637, ), but are in agreement with those of Heinemann et al. (Eur J Mineral 18:673-689, ) and Morozov et al. (Eur J Mineral 17:495-500, ). [ABSTRACT FROM AUTHOR]

The structure of 5-dimethylpyrazolo[1,5-a]pyrimidin-7(4H)-one 1 has been determined by X-ray crystallography. The compound 1 crystallizes in the space group P−1 with two molecules in the asymmetric unit solvated with one molecule of the acetic acid The unit cell parameters are a = 8.796(1) Å, b = 10.531(1) Å, c = 10.680(1) Å, α = 96.901(2)º, β = 98.135(2)º, γ = 107.248(2)º. In the crystal molecules A and B are linked into R(9) hydrogen bonded rings and these rings form chains parallel to [101] Overall, the supramolecular structure 1 consists of two hydrogen bonded and two π–π stacking dimers. An energetic interplay between these dimers has been studied using B3LYP DFT calculations. In addition π–π interactions are analyzed using the Bader’s atoms in molecules’ (AIM) theory. The structure of 5-dimethylpyrazolo[1,5-a]pyrimidin-7(4H)-one 1 has been determined by X-ray crystallography. The compound 1 crystallizes in the space group P−1 with two molecules in the asymmetric unit solvated with one molecule of the acetic acid The unit cell parameters are a = 8.796(1) Å, b = 10.531(1) Å, c = 10.680(1) Å, α = 96.901(2)º, β = 98.135(2)º, γ = 107.248(2)º. In the crystal molecules A and B are linked into R(9) hydrogen bonded rings and these rings form chains parallel to [ 101] Overall, the supramolecular structure 1 consists of two hydrogen bonded and two π–π stacking dimers. An energetic interplay between these dimers has been studied using B3LYP DFT calculations. In addition π–π interactions are analyzed using the Bader’s atoms in molecules’ (AIM) theory.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Acetylferrocene readily forms an adduct with BF3. The product is a neutral model for protonated acetylferrocene, a species that is a crucial intermediate in the formation of 1,3,5-trisferrocenyl-benzene and other conjugated heterometallic derivatives by cyclocondensation. The title compound’s structure was determined in the solid state by X-ray diffraction and its spectroscopic properties were examined in detail, particularly the electronic excitation spectrum, which confirms the previous identification of the in situ generated protonated ketone. [ABSTRACT FROM AUTHOR]

The UV–visible and near-IR spectra of the zinc phthalocyanine π-cation and π-anion radicals, [ZnPc(–1)]•+ and [ZnPc(–3)]•–, are investigated by time-dependent density functional theory (TDDFT) calculations using the pure, asymptotically correct, statistical average of (model) orbital potentials (SAOP) functional. The nature and intensity of the main spectral features are highlighted and interpreted on the basis of the ground-state electronic structure of the complexes. Similarities and differences with previous TDDFT/B3LYP results are discussed. TDDFT/SAOP results for the π-anion radical prove to be in excellent agreement with the solution spectra and generally in line with deconvolution analyses of solution absorption and magnetic circular dichroism (MCD) spectra. On the basis of these results a novel interpretation of the Q-band system is proposed. For the π-cation radical TDDFT/SAOP calculations provide a satisfactory description of the UV region of the spectrum. However, they do not reproduce accurately the energy and intensity of the Q band observed at 825 nm. The description of the Q-band region appears to be complicated by the presence of spurious non-Gouterman transitions. Furthermore, the calculations, either in the gas phase or in solution, do not account for the broad absorption near 500 nm that has been suggested to arise from a nondegenerate, z-polarized 2A2g excited state. Theory and experiment can be reconciled if the presence of an axial ligand such as CN– is explicitly considered in the calculations. TDDFT/SAOP results for the axially ligated [ZnPc(–1)(CN)]• species indicate that the 500 nm feature is related to the axial ligation induced symmetry lowering of the π-cation radical and this band is assigned to a z-polarized transition associated with the hole in the 2a1u. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Chemistry is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Chemistry is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Ab initio density functional theory (DFT) calculations of the interactions between selected semiconducting and metallic single-walled carbon nanotubes (SWCNTs) (as well between single and double graphene sheets) and single oxygen molecules are carried out in order to provide a rationale for the recent experimental observations of UV-light accelerated oxidation of carbon nanotubes and the accompanying changes in the thermoelectric power. The computational results obtained show that these experimental findings can be related to UV-light excitation of oxygen molecules from their ground spin-triplet state into a higher-energy spin-singlet state. Such excitation lowers the activation energy for molecular-oxygen chemisorption to a nanotube, increases the adsorption energy and promotes charge transfer from the nanotube to the oxygen molecule. Lattice defects such as 7-5-5-7 and Stone–Wales defects are found to play a critical role in enhancing oxygen molecule/nanotube bonding and in affecting the extent of charge transfer. Contrary to this, the effects of nanotube diameter and chirality and the number of walls appear to be less significant. [Copyright &y& Elsevier]

Ab initio density functional theory (DFT) calculations of the interactions between isolated infinitely-long semiconducting zig-zag (10, 0) or isolated infinitely-long metallic arm-chair (5, 5) single-walled carbon-nanotubes (SWCNTs) and single oxygen-molecules are carried out in order to determine the character of molecular-oxygen adsorption and its effect on electronic transport properties of these SWCNTs. A Green’s function method combined with a nearest-neighbor tight-binding Hamiltonian in a non-orthogonal basis is used to compute the electrical conductance of SWCNTs and its dependence on the presence of topological defects in SWCNTs and of molecular-oxygen adsorbates. The computational results obtained show that in both semiconducting and metallic SWCNTs, oxygen-molecules are physisorbed to the defect-free nanotube walls, but when such walls contain topological defects, oxygen-molecules become strongly chemisorbed. In semiconducting (10, 0) SWCNTs, physisorbed O2-molecules are found to significantly increase electrical conductance while the effect of 7-5-5-7 defects is practically annulled by chemisorbed O2-molecules. In metallic (5, 5) SWCNTs, both O2 adsorbates and 7-5-5-7 defects are found to have a relatively small effect on electrical conductance of these nanotubes. [Copyright &y& Elsevier]