Classification of metal-oxide bonded interactions based on local potential- and kinetic-energy densities

A classification of the hydrogen fluoride H-F-bonded interactions comprising a large number of molecules has been proposed by Espinosa et al. [J. Chem. Phys. 117, 5529 (2002)] based on the ratio /Vr(c)/ / Gr(c) where /Vr(c)/ is the magnitude of the local potential-energy density and Gr(c) is the local kinetic-energy density, each evaluated at a bond critical point r(c). A calculation of the ratio for the M-O bonded interactions comprising a relatively large number of oxide molecules and earth materials, together with the constraints imposed by the values of inverted Delta2rho r(c) and the local electronic energy density, Hr(c) = Gr(c) + Vr(c), in the H-F study, yielded practically the same classification for the oxides. This is true despite the different trends that hold between the bond critical point and local energy density properties with the bond lengths displayed by the H-F and M-O bonded interactions. On the basis of the ratio, Li-O, Na-O, and Mg-O bonded interactions classify as closed-shell ionic bonds, Be-O, Al-O, Si-O, B-O, and P-O interactions classify as bonds of intermediate character with the covalent character increasing from Be-O to P-O. N-O interactions classify as shared covalent bonds. C-O and S-O bonded interactions classify as both intermediate and covalent bonded interactions. The C-O double- and triple-bonded interactions classify as intermediate-bonded interactions, each with a substantial component of covalent character and the C-O single-bonded interaction classifies as a covalent bond whereas their local electronic energy density values indicate that they are each covalent bonded interactions. The ratios for the Be-O, Al-O, and Si-O bonded interactions indicate that they have a substantial component of ionic character despite their classification as bonds of intermediate character. The trend between the ratio and the character of the bonded interactions is consistent with trends expected from electronegativity considerations. The ratio increases as the net charges and the coordination numbers for the atoms for several Ni-sulfides decrease. On the contrary, the ratio for the Si-O bonded interactions for the orthosilicate, forsterite, Mg2SiO4, and the high-pressure silica polymorph, stishovite, decreases as the observed net atomic charges and the coordination numbers of Si and O increase in value. The ratio for the Ni-Ni bonded interactions for the Ni-sulfides and bulk Ni metal indicate that the interactions are intermediate in character with a substantial component of ionic character.     

Minimum Exposure Limits and Measured Relationships Between the Vitamin D,Erythema and International Commission on Non‐Ionizing Radiation Protection Solar Ultraviolet

The International Commission on Non‐Ionizing Radiation Protection (ICNIRP) has established guidelines for exposure to ultraviolet radiation in outdoor occupational settings. Spectrally weighted ICNIRP ultraviolet exposures received by the skin or eye in an 8 h period are limited to 30 J m^?2. In this study, the time required to reach the ICNIRP exposure limit was measured daily in 10 min intervals upon a horizontal plane at a subtropical Australian latitude over a full year and compared with the effective Vitamin D dose received to one‐quarter of the available skin surface area for all six Fitzpatrick skin types. The comparison of measured solar ultraviolet exposures for the full range of sky conditions in the 2009 measurement period, including a major September continental dust event, show a clear relationship between the weighted ICNIRP and the effective vitamin D dose. Our results show that the horizontal plane ICNIRP ultraviolet exposure may be used under these conditions to provide minimum guidelines for the healthy moderation of vitamin D, scalable to each of the six Fitzpatrick skin types.     

The Preparation of 4,5-Dihydro-5-Phenyl-5-(2-Phenylethenyl)Isoxazoles, 4,5-Dihydro-5-Methyl-5-(2-Phenylethenyl)Isoxazoles,or 4,5-Dihydro-5,5-DI-(2-Phenylethenyl)Isoxazoles from Dilithiated C(α),O-Oximes and Select α,β–-Unsaturated Ketones

C(α),O-oximes were dilithiated with lithium diisopropylamide and condensed with three α,β-unsaturated ketones: (2E)-1,3-diphenyl-2-propen-1-one, or (1E, 4E)-1,5-diphenyl-1,4-pentadien-3-one, or (3E)-4-phenyl-3-buten-2-one, followed by immediate acid cyclization to variously substituted 4,5-dihydroisoxazoles: 4,5-dihydro-5-phenyl-5-(2-phenylethenyl)isoxazoles, 4,5-dihydro-5-methyl-5-(2-phenylethenyl)isoxazoles, or 4,5-dihydro-5,5-di-(2-phenylethenyl)-isoxazoles.     

Kolbeckite,ScPO4·2H2O,isomorphous with metavariscite

This study presents the first structural report of kolbeckite, with the ideal formula ScPO₄·2H₂O (scandium phosphate dihydrate), based on single‐crystal X‐ray diffraction data. Kolbeckite belongs to the metavariscite mineral group, in which each PO₄ tetrahedron shares four vertices with four ScO₄(H₂O)₂ octahedra and vice versa, forming a three‐dimensional network of polyhedra.     

Inelastic neutron scattering study of hydrogen in d(8)-THFD(2)O ice clathrate

In situ neutron inelastic scattering experiments on hydrogen adsorbed into a fully deutrated tetrahydrofuran-water ice clathrate show that the adsorbed hydrogen has three rotational excitations (transitions between J=0 and 1 states) at approximately 14 meV in both energy gain and loss. These transitions could be unequivocally assigned since there was residual orthohydrogen at low temperatures (slow conversion to the ground state) resulting in an observable J=1-->0 transition at 5 K (kT=0.48 meV). A doublet in neutron energy loss at approximately 28.5 meV is interpreted as J=1-->2 transitions. In addition to the transitions between rotational states, there are a series of peaks that arise from transitions between center-of-mass translational quantum states of the confined hydrogen molecule. A band at approximately 9 meV can be unequivocally interpreted as a transition between translational states, while broad features at 20, 25, 35, and 50-60 meV are also interpreted to as transitions between translational quantum states. A detailed comparison is made with a recent five-dimensional quantum treatment of hydrogen in the smaller dodecahedral cage in the SII ice-clathrate structure. Although there is broad agreement regarding the features such as the splitting of the J=1 degeneracy, the magnitude of the external potential is overestimated. The numerous transitions between translational states predicted by this model are in poor agreement with the experimental data. Comparisons are also made with three simple exactly solved models, namely, a particle in a box, a particle in a sphere, and a particle on the surface of a sphere. Again, there are too many predicted features by the first two models, but there is reasonable agreement with the particle on a sphere model. This is consistent with published quantum chemistry results for hydrogen in the dodecahedral 5(12) cage, where the center of the cage is found to be energetically unfavorable, resulting in a shell-like confinement for the hydrogen molecule wave function. These results demonstrate that translational quantum effects are very significant and a classical treatment of the hydrogen molecule dynamics is inappropriate under such conditions.     

Methanesulfenyl fluoride, CH3SF, a missing link in the family of sulfenyl halides: formation and characterization through the matrix photochemistry of methyl thiofluoroformate, FC(O)SCH3

Matrix-isolation experiments have afforded the means of preparing the hitherto unknown sulfur(II) fluoride, methanesulfenyl fluoride, CH3SF. Broadband UV-visible irradiation of methyl thiofluoroformate, FC(O)SCH3, isolated in a solid Ar matrix results, first, in photoisomerization of the syn into the anti form of the molecule, and, subsequently, in the elimination of CO with the concomitant formation of CH3SF. Continued irradiation brings about tautomerization of this product with the detachment and migration of a hydrogen from the methyl group to give the molecular complex H2C==S...HF. The changes have been monitored and the photoproducts detected and identified by the IR spectra of the matrices, and the conclusions confirmed: 1) with reference to the corresponding behavior of the perdeuterated molecule FC(O)SCD3; 2) by analogy with the properties of related molecules, for example, ClC(O)SCH3, CH3SCl, and H2C==S...HCl, and; 3) by comparison with the vibrational properties simulated for the different molecules by ab initio and density functional theory methods.     

Preparation of substituted 1,2‐Dihydro‐3H‐pyrazol‐3‐ones from polylithiated 2′‐phenylphenylacetohydrazides and aromatic esters

Several 2′‐phenylphenylacetohydrazides were polylithiated with excess lithium diisopropylamide, and the resulting intermediates were condensed with several aromatic esters to afford C‐acylated intermediates that were not usually isolated, but acid cyclized directly to 1,4,5‐trisubstituted, 1,2‐dihydro‐3H‐pyrazol‐3‐ones.