Infrared spectra of Cs3CoCl5

The infrared spectra, transmittance, and polarized reflectance of Cs₃CoCl₅ are reported. The group theoretical analysis was executed and a vibrational assignment proposed on the basis of D_4h symmetry. Factor group and site effects are discussed.     

Carbon-13 NMR spectroscopy of heterocyclic compounds—III : A 20 MHz study of chemical shifts and carbon-proton coupling constants for the methyl coumarins

Complete assignments of chemical shifts and extensive assignments of carbon-proton coupling constants are presented for the 3-, 4-, 6-, 7- and 8-methylcoumarins, together with similar parameters for 5,8- and 6,8-dimethylcoumarin. Shifts in 6,8-dimethylcoumarin can be predicted with high precision from the substituent effects observed in the 6- and 8-methyl derivatives, and shifts are predicted for the 5-methyl derivative, which was not studied.     

The chemical shift tensor for the hydroxyl proton: Ca(OH)2

The proton chemical shift tensor of the hydroxyl proton in calcium hydroxide has been measured using multiple pulse NMR techniques. The tensor is axially symmetric with susceptibility corrected components σ_tT = ?9.3 ± 1 ppm and

ppm relative to TMS. 792 79     

The formation and stability of hydrated and anhydrous uranyl phosphates

The stabilities of the hydrated uranyl phosphates (UO₂)₃(PO₄)₂ · 4 H₂O, UO₂HPO₄ · 4 H₂O, and UO₂(H₂PO₄) · 3 H₂O have been reinvestigated. The compounds identified by thermal analysis have been prepared isothermally and characterized by their strongest X-ray reflections. During dehydration, oxygen was not evolved and the crystalline compounds (UO₂)₃(PO₄)₂, (UO₂)₂P₂O₇, UO₂(PO₃)₂, and probably (UO₂)₃P₄O)₁₃ were found.

At still higher temperatures, the uranyl phosphates are reduced. The decomposition products lose phosphorus oxide above 1300–1400°C. The present results are summarized in a tentative pseudo-binary phase diagram UO_x(x = 3 to 2)—UO₂(PO₃)₂.     

Photochemical and thermal transformations of 7-silabicyclo[2.2.1]Heptadiene and 7-silabicyclo[2.2.1]heptene systems

2,3-Dicarbomethoxy-7,7-dimethyl-7-silabicyclo[2.2.1]hepta-2,5-diene (III) on photolysis gave dimethyl tetraphenylphthalate whereas the photolysis of 7,7-dimethyl-7-silabicyclo[2.2.1]hep-5-ene-2,3-dicarboxylic anhydride (XIa) resulted in the formation of 1,1-dimethyl-2,3,4,5-tetraphenyl-1-silacyclopentadiene (XIIIa). The thermolysis of XIa also gave rise to XIIIa. Similarly, the photolysis as well as thermolysis of 1,4,5,6,7,7-hexaphenyl-7-silabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride (XIb) led to hexaphenylsilacyclopentadiene (XIIIb). Attempts to detect radical intermediates in these thermal and photochemical transformations by carrying out the reaction in the presence of hydroquinone, hydrazobenzene, 3,6-diphenyl-1,2-dihydro-1,2,4,5-tetrazine, cumene and tolan were unsuccessful. An attempted preparation of 7-silabicyclo[2.2.1]hepta2,5-dienes by the reaction of silacyclopentadienes such as 1-methyl-1-vinyl2,3,4,5-tetraphenyl-1-silacyclopentadiene (XV) and 1-methyl-1,2,3,4,5-pentaphenyl-1-silacyclopentadiene (XVI) with dimethyl acetylenedicarboxylate resulted in the isolation of dimethyl tetraphenylphthalate indicating that the corresponding 7-silabicyclo[2.2.1]hepta-2,5-dienes are thermally unstable.     

Dissociation and solubility variation versus pO2- of scheelite CaWO4 in molten NaCl−KCl (At 1000 K)

The conditional solubility of scheelite CaWO₄ in molten NaCl?KCl (1:1) has been studied either in oxobasic or oxoacidic media. In the former case it is increased by formation of sparingly soluble CaO according to:Ca²⁺ + O²CaO(s), pK_s^CaO = 10800/T ? 5.8 (molality scale) In the later case, WO₄^2- behaves as an oxobase according to the following equilibria:WO₄^2?WO₃ (s) + O^2? pK₀ = 10.0 at 1000 K3 WO₄^2?W3O₁₀^2? pK₃ = 12.7 at 1000KThe latter equilibrium favours an increase in the W^VI solubility when pO^2- is increased, for instance by injection of HCl. The whole set of results has been summarized by a conditional solubility diagram of scheelite versus pO^2-.     

Influence of the exchange‐correlation functional in all‐electron calculations of the vibrational frequencies of corundum (α‐Al2O3)

The equilibrium structural parameters, high‐ and low‐frequency dielectric tensors, Born effective charges, and Γ‐point vibrational frequencies of bulk Al₂O₃ corundum are calculated by using the periodic, ab initio program CRYSTAL, which adopts an all‐electron Gaussian‐type basis set. The effect of basis set and the performance of three different functionals, i.e., LDA, PW91, and B3LYP, are discussed. The mean absolute deviation from the measured frequencies is as small as 7 cm^?1 for both the LDA and B3LYP functionals, indicating that these functionals perform extremely well in this case. The mean absolute deviation increases to 18 cm^?1 when the PW91 functional is used. All three functionals reproduce the equilibrium geometry of corundum to a high level of accuracy, with LDA and B3LYP outperforming PW91 slightly. The comparison of the current all‐electron calculations with previous plane‐wave, pseudo‐potential calculations shows an overall similar performance. The results of isotopic substitution for both Al and O are also presented. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Infrared spectroscopic properties of water molecules dissolved in some oxygen bases

The infrared spectra in the OH-stretching and HOH-bending regions of H₂O, and in the OH-stretching region of HDO dissolved in a number of ketones and ethers have been recorded. The number of component bands and their wavenumbers, halfwidths and intensities, as well as the total OH-stretching intensity in each solvent, have been interpreted in terms of a model for the types of hydrogen bonded solvent:water complexes formed in these systems.The effect of temperature on the spectra of H₂O in some of the ketones has been rationalized on the basis of the equilibrium existing between the different hydrogen bonded species present in solution.     

Conformational analysis of some (E)-α-phenyl-β-(2-thienyl)- and -(2-furyl_acrylic acids

NMR spectral data of some (E)-α-phenyl-β-(2-thienyl) acrylic acids indicate that these compounds exist in the preferred s-trans conformation. In the case of (E)-α-phenyl-β-(2-furyl)acrylic acids and their methyl esters the presence of only s-cis rotamer has been established.     

Thermal and photo-degradation of unstabilized ABS

Thermal- and photo-stabilities of unstabilized acrylonitrile-butadiene-styrene terpolymer, ABS, have been investigated by i.r. spectroscopy. Degradation of ABS samples is initiated by attack on the polybutadiene (PB) component; oxidation products containing hydroxyl and carbonyl groups are produced. The effect of prior thermal processing is to introduce into the polymer hydroperoxides arising from oxidative destruction of PB-unsaturation; these hydroperoxides act as catalysts during subsequent u.v. irradiation. The insolubility of degraded samples of ABS is associated with the formation of cross-linked structures and occurs mainly in the PB segment. It is concluded that the degradation characteristics of ABS are essentially those of the polybutadiene component.