Dipole polarizabilities of noble gas endohedral fullerenes

First-principles calculations were performed on the polarizabilities of noble gas endohedral complexes, X@C₆₀ (X = He–Kr). The polarizability of X@C₆₀ increases from He–Kr, but is distinctly smaller than the sum of the X atoms and C₆₀, unlike many other non-bonded systems for which an additive rule holds. Compared to C₆₀, the increased polarizabilities in X@C₆₀ are mainly from the enhanced charge transfer contribution of the cage and the local polarization of the interior X atoms, though the interior atoms are found less polarized than the corresponding free ones.     

Induction of phr gene expression in E. coli strain KY706/pPL-1 by He-Ne laser (632.8 nm) irradiation

We have observed that He–Ne laser irradiation of E. coli strain KY706/pPL-1 leads to induction of photolyase gene, phr. The magnitude of induction was found to depend on the He–Ne laser fluence, fluence rate and post-irradiation incubation period in the nutrient medium. The optimum values for fluence and fluence rate were 7×10³ J/m² and 100 W/m², respectively, and the induction of phr gene was observed to saturate beyond an incubation period of 2 h. Experiments carried out with singlet oxygen quenchers and with D₂O suggest that the effect is mediated via singlet oxygen. Photoreactivation studies carried out after UVC exposure of both the He–Ne laser-exposed as well as unexposed cells showed a larger surviving fraction in the He–Ne laser pre-irradiated cells. This can be attributed to He–Ne laser irradiation-induced induction of phr expression. However, since even without photoreactivating light He–Ne laser pre-irradiated cells show higher survival against UVC radiation it appears that He–Ne laser irradiation induces both light-dependent as well as dark DNA repair processes.     

Isothermal vapour–liquid equilibria in the binary and ternary systems composed of 2-propanol, diisopropyl ether and 1-methoxy-2-propanol

Vapour pressures for 1-methoxy-2-propanol are reported as well as the vapour–liquid equilibrium data in the two binary 2-propanol + 1-methoxy-2-propanol, and diisopropyl ether + 1-methoxy-2-propanol systems, and in the ternary 2-propanol + diisopropyl ether + 1-methoxy-2-propanol system. The data were measured isothermally at 330.00 and 340.00 K covering the pressure range 5–98 kPa. The binary vapour–liquid equilibrium data were correlated using the Wilson, NRTL, and Redlich–Kister equations; resulting parameters were then used for calculation of phase behaviour in the ternary system and for subsequent comparison with experimental data.     

Chemical reactivity of two-photon excited trimethylsilylacetylene in aerosol particle formation with acrolein

Under irradiation with N₂ laser light, a gaseous mixture of trimethylsilylacetylene (ethynyltrimethylsilane) (TMeSiA) and acrolein (AC) produced sedimentary aerosol particles with a mean diameter of 1.0 μm. Nucleation process of the aerosol particles was studied by measuring monitor (He–Ne laser) light intensity scattered by the aerosol particles as formed under N₂ laser light irradiation. With increasing partial pressure of TMeSiA, the nucleation reaction of aerosol particles was accelerated due to additional generation of reactive species from TMeSiA molecules by a two-photon process. FT-IR spectra of the sedimentary particles showed that TMeSiA molecules were incorporated into polymerization reaction of AC by forming –Si–O–C– bond from R(CH₃)₂Si radicals. Two-photon processes of both AC and TMeSiA molecules under N₂ laser light irradiation were briefly discussed.     

Far infrared spectra, conformational equilibria, vibrational assignments, ab initio calculations and structural parameters for 2-bromoethanol

The far infrared spectrum from 370 to 50 cm⁻¹ of gaseous 2-bromoethanol, BrCH₂CH₂OH, was recorded at a resolution of 0.10 cm⁻¹. The fundamental O–H torsion of the more stable gauche (Gg′) conformer, where the capital G refers to internal rotation around the C–C bond and the lower case g to the internal rotation around the C–O bond, was observed as a series of Q-branch transitions beginning at 340 cm⁻¹. The corresponding O–H torsional modes were observed for two of the other high energy conformers, Tg (285 cm⁻¹) and Tt (234 cm⁻¹). The heavy atom asymmetric torsion (rotation around C–C bond) for the Gg′ conformer has been observed at 140 cm⁻¹. Variable temperature (−63 to −100°C) studies of the infrared spectra (4000–400 cm⁻¹) of the sample dissolved in liquid xenon have been recorded. From these data the enthalpy differences have been determined to be 411±40 cm⁻¹ (4.92±0.48 kJ/mol) for the Gg′/Tt and 315±40 cm⁻¹ (3.76±0.48 kJ/mol) for the Gg′/Tg, with the Gg′ conformer the most stable form. Additionally, the infrared spectrum of the gas, and Raman spectrum of the liquid phase are reported. The structural parameters, conformational stabilities, barriers to internal rotation and fundamental frequencies have been obtained from ab initio calculations utilizing different basis sets at the restricted Hartree–Fock or with full electron correlation by the perturbation method to second order. The theoretical results are compared to the experimental results when appropriate. Combining the ab initio calculations with the microwave rotational constants, r₀ adjusted parameters have been obtained for the three 2-haloethanols (F, Cl and Br) for the Gg′ conformers.     

Solid–liquid phase equilibrium in the systems of LiBr–H2O and LiCl–H2O

A set of empirical temperature-molar fraction expressions for solid–liquid equilibrium curves of LiBr–H₂O and LiCl–H₂O systems is presented. The expressions are based upon a body of experimental data that have been compiled and critically evaluated. The equations cover the full composition range for LiCl–H₂O system and compositions up to the salt mole fraction of x = 0.46 (i.e. mass fraction of w=0.805) for LiBr–H₂O, corresponding to transition from monohydrate to anhydrate. Temperatures and solution compositions at the eutectic point and at transition points between hydrates have been determined from intersections of the curves corresponding to the adjacent hydrate ranges of the phase diagram. Equations of a special structure were used, involving the coordinates of the transition points as parameters, which makes possible their direct non-linear optimization. To obtain more reliable results, a procedure was employed optimizing both the temperature–composition and composition–temperature equations simultaneously. The uncertainty in the obtained values of the transition point coordinates are estimated to be of the order of 1 K for temperature and 0.001 for the composition expressed in salt mole fraction. Gaps in the database are shown to give experimenters orientation for future research.     

A simultaneous TG–DTA study of the thermal decomposition of 2-hydroxybenzoic acid, 2-carboxyphenyl ester (salsalate)

Simultaneous thermogravimetry–differential thermal analysis (TG–DTA) and gas and liquid chromatography with mass spectrometry detection have been used to study the kinetics and decomposition of 2-hydroxybenzoic acid, 2-carboxyphenyl ester, commercially known as salsalate. Samples of salsalate were heated in the TG–DTA apparatus in an inert atmosphere (100 ml min⁻¹ nitrogen) in the temperature range 30–500 °C. The data indicated that the decomposition of salsalate is a two-stage process. The first decomposition stage (150–250 °C) had a best fit with second-order kinetics with E_a=191–198 kJ/mol. The second decomposition stage (300–400 °C) is described as a zero-order process with E_a=72–80 kJ/mol. The products of the decomposition were investigated in two ways:

(a)Salsalate was heated in a gas chromatograph at various isothermal temperatures in the range 150–280 °C, and the exit gas stream analyzed by mass spectrometry (GC–MS). This approach suggested that salsalate decomposes with the formation of salicylic acid, phenol, phenyl salicylate, and cyclic oligomers of salicylic acid di- and tri-salicylides.

(b)One gram samples of salsalate were heated in a vessel under nitrogen to 150 °C, and the residues were analyzed by liquid chromatography–mass spectrometry (LC–MS). The major compound detected was a linear tetrameric salicylate ester.

     

Vapor–liquid equilibria and excess molar volumes of diethylamine(1) + acetone(2) and diethylamine(1) + acetonitrile(2) binary systems

Isothermal vapor–liquid equilibrium (VLE) data for diethylamine(1)+acetone(2) and diethylamine(1)+acetonitrile(2) binary systems were obtained at 323.15 K by dynamic method. Excess molar volumes at 298.15 K for these systems were measured by a dilution dilatometer. VLE data have been checked for thermodynamic consistency and correlated by Wilson, NRTL and UNIQUAC equations. UNIFAC group interaction parameters for CH₂NH---CH₃CO and CH₂NH---CH₃CN pairs are also obtained from the experimental VLE data.     

Synthesis and characterization of P2O5–SiO2–X (X = phosphotungstic acid) glasses as electrolyte for low temperature H2/O2 fuel cell application

A new class of proton conducting glass membranes for hydrogen fuel cell applications are being developed using phosphotungstic acid. These glasses are being design to yield high proton conductivities could be potential substitutes for electrolytes in H₂/O₂ fuel cell. P₂O₅–SiO₂–PWA glasses have been non-crystalline phases confirmed by structural studies. The glass materials showed good mechanical and thermal stability, and also found a maximum proton conductivity of 9.1 × 10⁻² S/cm at 90 °C and 30% RH. The average pore size less than 5 nm was determined by Barrett–Joyner–Halenda (BJH) desorption method. The electrochemical activity was investigated by polarization curves and current–voltage profiles. A maximum power density value of 10.2 mW/cm² was obtained using 0.15 mg/cm² of Pt/C loaded on electrode and 5P₂O₅–87SiO₂–8PWA glasses at 30 °C and 30% humidity.     

Tautomeric properties, conformations and structure of N-(2-hydroxy-5-chlorophenyl) salicylaldimine

The crystal structure of N-(2-hydroxy-5-chlorophenyl) salicylaldimine (C₁₃H₁₀NO₂Cl) was determined by X-ray analysis. It crystallizes orthorhombic space group P2₁2₁2₁ with a=12.967(2) Å, b=14.438(3) Å, c=6.231(3) Å, V=1166.5(6) Å³, Z=4, D_c=1.41 g cm⁻³ and μ(MoK)=0.315 mm⁻¹. The title compound is thermochromic and the molecule is nearly planar. Both tautomeric forms (keto and enol forms in 68(3) and 32(3)%, respectively) are present in the solid state. The molecules contain strong intramolecular hydrogen bonds, N1–H1O1/O2 (2.515(1) and 2.581(2) Å) for the keto form and O1–H01N1 for the enol one. There is also strong intermolecular O2–HO1 hydrogen bonding (2.599(2) Å) between neighbouring molecules. Minimum energy conformations AM1 were calculated as a function of the three torsion angles, θ₁(N1–C7–C6–C5), θ₂(C8–N1–C7–C6) and θ₃(C9–C8–N1–C7), varied every 10°. Although the molecule is nearly planar, the AM1 optimized geometry of the title compound is not planar. The non-planar conformation of the title compound corresponding to the optimized X-ray structure is the most stable conformation in all calculations.     

Raman and infrared spectra, conformational stability, ab initio calculations and vibrational assignments for 2-chloroethyl silane

The infrared (3500–30 cm⁻¹) spectra of gaseous and solid and the Raman (3500–10 cm⁻¹) spectra of liquid with quantitative depolarization ratios and solid 2-chloroethyl silane, ClCH₂CH₂SiH₃, have been recorded. Similar data have been recorded for the Si–d₃ isotopomer. These data indicate that two conformers, trans and gauche, are present in the fluid states but only one conformer, trans, is present in the solid. The mid-infrared spectra of the sample dissolved in liquified xenon as a function of temperature (−55 to −100°C) has been recorded. The enthalpy difference between the conformers has been determined to be 181±12 cm⁻¹ (2.17±0.14 kJ/mol) with the trans rotamer the more stable form. From the isolated Si–H frequencies from the Si–d₂ isotopomer the r_o Si–H distances of 1.484 and 1.483 Å for the trans and 1.481 for the gauche conformers have been obtained. Ab initio calculations have been carried out with several different basis sets up to MP2/6-311+G** from which structural parameters and conformational stabilities have been determined. With all the basis sets the trans form is predicted to be the more stable conformer which is consistent with the experimental results. These results are compared to the corresponding quantities for the carbon analogue.     

Equilibrium bond lengths, force constants and vibrational frequencies of MnF2, FeF2, CoF2, NiF2, and ZnF2 from least-squares analysis of gas-phase electron diffraction data

The least-squares analysis of the electron diffraction data for MnF₂, FeF₂, CoF₂, NiF₂ and ZnF₂ was carried out in terms of a cubic potential function. The obtained equilibrium bond lengths (in Å) are r_e(Mn–F)=1.797(6), r_e(Fe–F)=1.755(6), r_e(Co–F)=1.738(6), r_e(Ni–F)=1.715(7), and r_e(Zn–F)=1.729(7). The determined force constants and the corresponding vibrational frequencies are listed. The bond length r_e(Cu–F)=1.700(14) Å for CuF₂ was estimated and the variations of bond lengths for the first-row transition metal difluorides were discussed in light of their electronic structure.     

Synthesis, structures and reactivity of triosmium clusters containing terminal pyrazines, bridging hydroxy and methoxycarbonyl ligands

Four triosmium carbonyl clusters bearing terminal pyrazines, bridging hydroxy and methoxycarbonyl ligands of general formula [Os₃(CO)₉(μ-OH)(μ-OMeCO)L] (1, L = pyrazine; 2, L = 2-methylpyrazine; 3, L = 2,3-dimethylpyrazine; 4, L = 2,3,5-trimethylpyrazine) were synthesized by the reactions of [Os₃(CO)₁₂] with the corresponding pyrazine derivatives and water in the presence of a methanolic solution of Me₃NO in moderate yields. Compounds [Os₃(CO)₉(μ-OH)(μ-OMeCO)L] react with a series of two electron donor ligands, L′ at ambient temperature to give [Os₃(CO)₉(μ-OH)(μ-OMeCO)L′] (5, L′ = PPh₃; 6, L′ = P(OMe)₃; 7, L′ = ^tBuNC; 8, L′ = C₅H₅N) in good yields by the displacement of the pyrazine ligands. This implies that the pyrazine ligands in 1–4 are relatively labile. Compounds 2, 3, 4, and 8 were characterized by single crystal X-ray diffraction analyses. All the four compounds possess two metal–metal bonds and a non-bonded separation of two osmium atoms defined by Os(1)Os(3), which are simultaneously bridged by OH and MeOCO ligands and a heterocyclic ligand is terminally coordinated to one of the two non-bonded osmium atoms.     

2D Cu(I) and 3D mixed-valence Cu(I)/Cu(II) coordination polymers: Synthesis and structural characterization of [CuCl(pyz-H)2]·2H2O and [Cu2Cl2(pyz)(H2O)]·H2O (pyz-H = pyrazinic acid)

Two new coordination polymers of copper(I) chloride and pyrazinic acid (pyz-H), namely [CuCl(pyz-H)₂]·2H₂O (1) and [Cu₂Cl₂(pyz)(H₂O)]·H₂O (2) have been prepared and characterized by spectroscopic, magnetic and crystallographic methods. The overall physical measurements suggest that 1 is diamagnetic and contains monodentate N-pyrazinic acid, whereas 2 is paramagnetic and contains tridentate N,N′,O- chelating bridging pyrazinato anion. In the structure of 1 as elucidated by X-ray single crystal analysis, the asymmetric units [CuCl(pyz)₂] are linked together forming a zigzag chain with tetrahedral copper(I) environment. The two lattice water molecules form hydrogen bonds with the uncoordinated N atom and carboxylate group O atom of pyz-H molecules. The Cu–N bond lengths are 2.009(6) Å and Cu–Cl distances are 2.337(2) Å. Complex 2 has a three-dimensional structure with the chains [Cu(I)Cu(II)(C₅H₃N₂O₂)Cl₂(H₂O)] interconnected by [Cu(I)Cl₂N] tetrahedral unit and [Cu(II)NO₂Cl₂] polyhedra. The Cu(I)–Cl and Cu(I)–N distances are 2.327(2)–2.581(2) Å and 1.988(6) Å, respectively, whereas the Cu(II)–Cl and Cu(II)–N bond lengths are 2.258(2), 2.581(2) Å, and 2.017(6) Å, respectively. Hydrogen bonds of the type O–HO are formed between lattice and coordinated water, and carboxylate oxygens of pyrazinato ligand giving rise to a three-dimensional network. The Cl⁻ anions act as bridging ligands in both complexes. The magnetic data of complex 2 have been measured from 2 to 300 K and discussed.     

Infrared and Raman spectra, conformational stability, ab initio calculations of structure, and vibrational assignment of 2-hexyne

The infrared spectra (3500–50 cm⁻¹) of the gas and solid and the Raman spectra (3500–50 cm⁻¹) of the liquid and solid have been recorded for 2-hexyne, CH₃–CC–CH₂CH₂CH₃. Variable temperature studies of the infrared spectrum (3500–400 cm⁻¹) of 2-hexyne dissolved in liquid krypton have also been recorded. Utilizing four anti/gauche conformer pairs, the anti(trans) conformer is found to be the lower energy form with an enthalpy difference of 74±8 cm⁻¹ (0.88±0.10 kJ/mol) determined from krypton solutions over the temperature range −105 to −150 °C. At room temperature it is estimated that there is 42% of the anti conformer present. Equilibrium geometries and energies of the two conformers have been determined by ab initio (HF and MP2) and hybrid DFT (B3LYP) methods using a number of basis sets. Only the HF and DFT methods predict the anti conformer as the more stable form as found experimentally. A vibrational assignment is proposed based on the force constants, relative intensities, depolarization ratios from the ab initio and DFT calculations and on rotational band contours obtained using the calculated equilibrium geometries. From calculated energies it is shown that the CH₃ group exhibits almost completely free rotation which is in agreement with the observation of sub-band structure for the degenerate methyl vibrations from which values of the Coriolis coupling constants, ζ, have been determined. The results are compared to similar properties of some corresponding molecules.     

Theoretical investigations on the SO2 + HO2 reaction and the SO2–HO2 radical complex

The mechanism of the SO₂ + HO₂ reaction was studied theoretically for the first time. Three product channels were revealed, namely, O₂ + HOSO, O₂ + HSO₂, and OH + SO₃. The O₂ + HOSO channel dominates the reaction under combustion conditions. A five-member-ring complex [SO₂–HO₂] exists at the entrance of the reaction. The structure and binding energy (D_e and D₀) of the SO₂–HO₂ complex have been calculated. In view of D₀ = 21.2 ± 2.0 kJ mol⁻¹, the SO₂–HO₂ complex should be stable at low temperature. The infrared spectra and frequency shifts were calculated for both SO₂–HO₂ and SO₂–DO₂, and compared with the available experimental data.     

1-Ethylthio-2-[2-thienyltelluro]ethane (L) a new (Te, S) ligand: Synthesis and complexation with Ag(I), Cu(I), Pd(II) and Pt(II) – Single crystal structures of [PdCl2(L)] and bis(thienyl) tellurium(IV) chloride

Lithium 2-thienyltellurolate, generated from 2-thienyl lithium, reacts at −78 °C in THF with chloroethyl ethyl sulfide to give a (Te, S) ligand 1-ethylthio-2-[2-thienyltelluro]ethane (L) as a red oil. The complexes [PdCl₂(L)] (1), [PtCl₂(L)] (2), [Ag(L)₂][ClO₄] (3) and [CuBr(L)]₂ (4) were synthesized. The complex [HgCl₂(L)] on crystallization decomposed giving Th₂TeCl₂ (5) [where Th = 2-thienyl], which was characterized by X-ray diffraction on its single crystals. The ligand L and complexes 1–4 exhibit proton and carbon-13 NMR spectra, which are characteristic. The coordination through Te in 1–4 is indicated by downfield coordination shifts in the position of the TeCH₂ signal of L. Complex 1 was characterized by X-ray diffraction on its single crystals. The geometry around Pd is square planar. The Pd–Te, Pd–S and Pd–Cl bond lengths are 2.5040(4), 2.273(1) and 2.322(1)/2.380(1) Å, respectively. There are intermolecular interactions between Te (coordinated to Pd) and Cl, and sulfur and Cl. The Te–Cl and S–Cl distances, 3.401 and 3.488 Å, respectively, are shorter than the sum of the van der Waal’s radii (3.81 and 3.55 Å, respectively). The Pd–Pd distance between the two molecules is 3.4156(6) Å, greater than the sum of van der Waal’s radii (3.26 Å). The structure of 5 is typical of that of a tellurium(IV) compound (saw-horse type). The two Te–Cl bond lengths are identical, 2.480(1) Å. The geometry around Te in 5 can be best described as pseudo tetrahedral (trigonal bipyramidal with a lone pair on one corner of the triangle).     

Modulation effects in A 2+1 electron spin echo pulse sequence

Conclusions Theoretical and experimental studies have been made on the ME trends in 2+1 sequences. The method has advantages over previous ones in having less dead time (not more than 50–100 nsec, as against not less than 300–400 nsec in the two-pulse case) and the absence of relaxation decay and combination frequencies.On the other hand, the method requires more exact information on the pulse lengths and amplitudes and exact shape data.We consider the method most promising for systems showing rapid fall in modulation amplitude, i.e., with nuclei close to the electron spin's.We are indebted to A. Yu. Pusep, S. A. Dikanov, and Yu. D. Tsvetkov for an extremely useful discussion.Institute of Chemical Kinetics and Combustion, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 29, No. 1, pp. 73–80, January–February, 1988.     

PVTx measurements for N2O + CH3F, N2O + CH2F2, and N2O + CHF3 binary systems

Isochoric PVTx measurements have been performed for the binary system of nitrous oxide + CH₃F (R41), +CH₂F₂ (R32), and +CHF₃ (R23) using a new experimental set-up. The experiments covered both the two-phase region and the superheated vapor region and were performed within the temperature range 214–358 K and within a pressure range from 270 to 5600 kPa. Data have been collected for not less than four compositions for each system. The vapor–liquid equilibrium data were derived correlating the experimental data by means of the Carnahan–Starling–De Santis equation of state. The studied systems show a positive deviation from the Raoult's law. The results obtained were compared with the Burnett PVTx data. The two methods showed a mutual consistency within an acceptable margin of error. No other experimental PVTx data were found in the literature for these binary systems.     

Vapor–liquid equilibria and excess volumes of the binary systems ethanol + ethyl lactate, isopropanol + isopropyl lactate and n-butanol + n-butyl lactate at 101.325 kPa

Isobaric vapor–liquid equilibrium data have been experimentally determined at 101.3 kPa for the binary systems ethanol + ethyl lactate, isopropanol + isopropyl lactate and n-butanol + n-butyl lactate. No azeotrope was found in any of the systems. All the experimental data reported were thermodynamically consistent according to the point-to-point method of Fredenslund. The activity coefficients were correlated with the NRTL and UNIQUAC liquid-phase equations and the corresponding binary interaction parameters are reported. The densities and derived excess volumes for the three mixtures are also reported at 298.15 K.