Effects of thermal activation on the oxidation pathways of methanol at bulk Pt–Ru alloy electrodes

The competition between pathways that lead to adsorbed CO and CO₂ during the electrochemical oxidation of 1.0 M methanol in 0.1 M HClO₄ on two bulk Pt–Ru alloys (10 at.% Ru (X_Ru≈0.1) and 90 at.% Ru (X_Ru≈0.9)) was investigated for temperatures in the range of 25–80°C. On the high Ru content alloy studied (X_Ru≈0.9), the dissociative chemisorption of methanol was inhibited below 70°C; the faradaic current for methanol oxidation was low, and only small quantities of adsorbed CO and CO₂ were detected with infrared spectroscopy between 0.2–0.8 V (vs. RHE). At 80°C, strong infrared bands from CO₂ and adsorbed, atop coordinated CO were observed over the potential ranges of 0.4–0.8 V and 0.2–0.8 V, respectively. The infrared measurements are consistent with the observation that bulk, high Ru content alloy electrodes appear passivated toward methanol oxidation below 70°C. On the low Ru content alloy studied (X_Ru≈0.1), the methanol surface chemistry was similar to that of pure, polycrystalline Pt, but the electrode was more poison resistant than Pt. For both alloys, the persistence of strong adsorbed CO bands and rapid CO₂ production between 0.4–0.8 V suggests CO functions as a reactive species with high steady-state coverages at these potentials.     

Electrokinetic properties of mixed solutions of dodecyldimethylamine oxide and sodium dodecyl sulfate: specific adsorption effects of small ions

Electrophoretic light-scattering measurements and potentiometric titrations were carried out on aqueous mixtures of dodecyldimethylamine oxide and sodium dodecyl sulfate. The electrophoretic mobility and the surface charge density of the micelles were always negative, ranging from –2.5 to –3.1×10^–4 cm²V^–1s^–1, and –0.033 to –0.045 cm^–2, respectively, for all surfactant mixing ratios, indicating the specific adsorption of Cl^–, in addition to Na⁺, on micelles. The solution pH, as well as the aggregation number previously reported, displayed maxima at intermediate surfactant mole fractions, that is, the non-ideal behavior. The fractional adsorption of Na⁺ per surfactant molecule in the micelles increased gradually with mixing fraction up to 0.82 atX=[SDS]/([SDS]+[C₁₂DAO])=1, while that of Cl^– decreased from 0.25 atX=0 to zero atX>0.4.     

Synthesis and properties of 2,2′-dipyridyl and 4,4′-dipyridyl complexes with thulium salts

Summary New complexes of 2,2-dipyridyl and 4,4-dipyridyl with thulium salts TmX ₃ (whereX=Cl^–, Br^–, NO ₃ ^– , NCS^–, and ClO ₄ ^– ) have been prepared and their solubilities in water at 21 °C were determined. The IR spectra of these compounds are discussed. The conditions of thermal decomposition of the complexes were also studied.

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Synthese und Eigenschaften von 2,2-Dipyridyl- und 4,4-Dipyridylkomplexen mit Thuliumsalzen

Zusammenfassung Es wurden neue 2,2-Dipyridyl- und 4,4-Dipyridyl-Komplexen mit Thuliumsalzen TmX ₃ (X=Cl^–, Br^– No ₃ ^– , NCS^–, ClO ₄ ^– ) dargestellt und ihre Wasserlöslihkeit bei 21 °C bestimmt. Die IR-Spektren werden diskutiert. Das thermische Verhalten der erhaltenen Komplexe wurde untersucht.

     

A new continuous dilution vapor liquid equilibrium apparatus: The activity coefficients of benzene and water in cyclohexane at 50°C

A semi-automated apparatus to measure vapor pressure differences between a reference solvent and dilute solutions as a function of concentration at constant temperature is described. Application to the benzene-cyclohexane and benzene-cyclohexane-water systems at high cyclohexane concentrations and low water concentrations is reported. At 50°C in the two component mixture we find ln_B=ln(f _B/X _B f _B ⁰ )=0.408–0.89X_B for 10^–3 B <3×10^–2 and in the three component system, ln_W=6.79±0.04 for 10^–6 W <2×10^–5 and 10^–3 B <3×10^–2.Taken in part from a PhD. thesis, University of Tennessee, 1983.     

Electron transfer in the photochemical reactions of phenothiazine with halomethanes

Photochemical transformations of phenothiazine (PTA) in solutions of halomethanes CH_nX_4–n (X = Cl, Br; n = 0, 1, 2) and in n-hexane—CH_nX_4–n mixtures under the irradiation with = 337 and 365 nm were studied. The rate constants of quenching of PTA fluorescence with halomethanes (k _q) are 4·10⁵—1.3·10¹⁰ L mol^–1 s^–1. The process occurs due to electron transfer with the C—X bond cleavage in the radical anion fragment of the primary radical ion pair. This results in the formation of the stable radical cation salt (PTA^·+X^–). The plot of k _q vs. free energy of electron transfer corresponds to the Rehm—Weller empirical equation for a one-electron process and is satisfactorily described in terms of the theory of nonradiative electron transitions in the approximation of one quantum vibration.     

Li7PS6 and Li6PS5X (X: Cl,Br, I): Possible Three‐dimensional Diffusion Pathways for Lithium Ions and Temperature Dependence of the Ionic Conductivity by Impedance Measurements

Possible three‐dimensional diffusion pathways of lithium ions in crystalline lithium argyrodites are discussed based on earlier studies of local dynamics and site preferences. The specific Li‐ionic conductivities of the lithium argyrodites Li₇PS₆ and Li₆PS₅X (X: Cl, Br, I) and their temperature dependences are measured by impedance spectroscopy using different electron‐blocking and ion‐blocking electrode systems. Measurements were carried out between 160 K and 550 K depending on the respective sample. Bulk and grain boundary contributions and the influence of sample preparation are discussed. Typical values for the ionic conductivities at room temperature are in the range 10^–7 to 10^–5 S ·  cm^–1 and at 500 K between 10^–6 and 10^–3 S ·  cm^–1. Thermal activation energies are in the range 0.16 to 0.56 eV. The electronic conductivity at room temperature was measured by polarization measurements for the samples Li₆PS₅X (X: Cl, Br) and was shown to be in the order of magnitude of 10^–8 S ·  cm^–1. Chemical diffusion coefficients of lithium were calculated based on the polarization measurements. For Li₆PS₅Br a high value of 3.5 × 10^–6 cm² · s^–1 was found.     

Calorimetric determination of enthalpy changes for the proton ionization of N-tris(hydroxymethyl)methyl-4-aminobutanesulfonic acid (TABS), N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid (TAPS) and 3-[N-tris(hydroxymethyl)methylamino]-2-hyroxypropane sulfonic acid (TAPSO) in water–methanol mixtures

Enthalpies for the two proton ionizations of the biochemical buffers N-tris(hydroxymethyl)methyl-4-aminobutanesulfonic acid (TABS), N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid (TAPS) and 3-[N-tris(hydroxymethyl)methylamino]-2-hyroxypropane sulfonic acid (TAPSO) were obtained in water–methanol mixtures with methanol mole fraction (X_m) from 0 to 0.360. The ionization enthalpy for the first proton (ΔH₁) of all three buffers was small and exhibited slight changes upon methanol addition. The ionization enthalpy of the second proton (ΔH₂) of TABS increased from 39.6 to 49.8 kJ mol⁻¹ and for TAPS from 40.1 to 43.2 kJ mol⁻¹, with a minimum of 38.2 kJ mol⁻¹ at X_m = 0.059. For TAPSO the increase was from 33.1 to 35.6 kJ mol⁻¹ at X_m = 0.194, with measurements at higher X_m precluded by low solubility of TAPSO in methanol rich solvents. The solvent composition was selected so as to include the region of maximum structure enhancement of water by methanol. The results were interpreted in terms of solvent–solvent and solvent–solute interactions.     

Atomic interactions in the hydrides and alkyls of C,Si, Ge,and Sn

The spectra of these group IV (M=C, Si, Ge, and Sn) compounds show that induction from M increases in a sequence that qualitatively agrees with the Pauli-Gordy-Mulliken scale; the induction constant o* for (CH₃)₃M is –0.3, –0.72, –0.76, and –0.9 in the four cases. M also acts as an electron acceptor, the effect increasing from Si via Ge to Sn; this and the induction determine the electron-density distribution in adjacent bonds. These concepts explain the anomalous behavior of the optical parameters and chemical shifts in the methyl derivatives of M. The analogy with the magnetic parameters indicates that the Olred-Rakhov electronegativity scale (X _C=2.6; X _Sl=1.9; X _Ge=2.0; X _Sn=1.93) does not reflect the induction effects of M in pure form but provides a good measure of the sum of the electronic effects. The present results do not confirm the view that silicon transmits induction less readily than carbon.     

Good correlation between the calculated gas-phase first proton macroaffinities of some triazacycloalkanes ([X]aneN3, X = 9–12) with their protonation constants in solution

A theoretical study on first protonation step of a series of triazacycloalkanes with general formula {([X]aneN₃, X = 9–12)} (X = 9, L222; X = 10, L223; X = 11, L233; X = 12, L333) is reported. The geometry of all ligands and their monoprotonated forms were fully optimized at both the Hartree–Fock and DFT (B3LYP) levels of theory using 6-31+G* basis set. Then the first proton macroaffinities were calculated from the proton microaffinities according to defined equations. It is shown that there are good correlations between the calculated gas-phase first proton macroaffinities of these ligands with their protonation constants in solution.     

The low frequency IR and Raman spectra of some complexes of dithiooxamide with cadmium halides

summary The low frequency IR and Raman spectra of Cd(DH ₄)X ₂ (X=Cl, Br;DH=dithiooxamide) have been discussed. On the basis of the cadmium isotope and H-D shift as well as chlorine-bromine substitution a band assignment in the region 500–33 cm^–1 has been made. A polymeric structure of Cd(DH ₄)X ₂ involving both dithiooxamide and halogen bridges with D_4h symmetry of the cadmium environment is assumed.

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Die niederfrequenten IR- und Raman-Spektren einiger Komplexe von Dithiooxamid mit Cadmiumhalogeniden

Zusammenfassung Die IR- und Raman-Spektren von Cd(DH ₄)X ₂ (X=Cl, Br;DH=Dithiooxamid) werden im Bereich niedriger Frequenzen diskutiert. Basierend auf Cadmiumisotopen- und H-D-Verschiebungen mit zusätzlicher Cl-Br-Substitution werden die Banden im Bereich von 500–33 cm^–1 zugeordnet. Es wird eine polymere Struktur von Cd(DH ₄)X ₂ unter Anteilnahme sowohl von Dithioxamid- als auch Halogenbrücken mit einer D_4h-Symmetrie im Bereich des Cadmiumzentralions angenommen.

     

Structure of nm-sized InSb clusters formed by spontaneous alloying

The negative ion photoelectron spectrum of⁷Li ₂ ^– is reported at 488 nm (2.540 eV). Three electronic bands are observed in this spectrum and are assigned to the following photodetachment transitions:⁷Li₂,X ¹ _g ⁺ +e ^{– 7}Li ₂ ^– ,X ² _u ⁺ ;⁷Li₂,a ³ _u ⁺ +e ^{– 7}Li ₂ ^– ,X ² _u ⁺ ; and⁷Li₂,A ¹ _u ⁺ +e ^{– 7}Li ₂ ^– ,X ² _u ⁺ . The electron affinity of⁷Li₂ is determined to be 0.437±0.009 eV, leading to an anion dissociation energy,D ₀, of 0.865±0.022 eV for the ground state of⁷Li ₂ ^– . A Franck-Condon analysis of the⁷Li₂,X ¹ _g ⁺ +e ^{– 7}Li ₂ ^– ,X ² _u ⁺ band yields the following spectroscopic constants for the ground state of⁷Li ₂ ^– :B _e =0.502±0.005 cm^–1,r _e =3.094±0.015 Å, and _e =232±35 cm^–1.     

Metal ion complexes of 2-picolinamineN-oxide

Summary A series of cobalt(II), nickel(II) and copper(II) complexes of 2-picolinamineN-oxide, HA, has been prepared. Solids of formula [M(HA)₃](BF₄)₂ (M=cobalt(II) or nickel(II); [Cu(HA)₂]X₂ (X=BF ₄ ^– , NO ₃ ^– ); [Co(HA)₂X₂] (X=Cl^– or Br^–); [Ni(HA)₂Cl₂] and [Cu(HA)X₂] (X=Cl^– or Br^–] have been isolated and characterized by partial elemental analyses, molar conductivities, magnetic susceptibilities, DSC-TGA, and spectral methods. All complexes were found to be monomeric, and their spectral parameters are compared with those of the metal ion complexes ofN-alkyl-2-picolinamineN-oxides, 2-dialkylaminopyridineN-oxides and 2-picolinamine. The cobalt(II) and nickel(II) halide complexes spectrally show a mixture of octahedral and tetrahedral centres.     

Sulfito- und Thiosulfato-Komplexe des Kobalts(III) mitα-Benzildioxim Überα-Dioximinkomplexe der Übergangsmetalle, 52. Mitt.

Some new ligand exchange reactions of [Co(diph·H)₂Cl(H₂O)] and [Co(diph·H)₂(SO₃)(H₂O)]^– complexes with N₃ ^–, S₂O₃ ^2– and with aromatic and heterocyclic amines were carried out. A series of derivatives of the types [Co(diph·H)₂(SO₃)X] ^n– (X=N₃ ^–, S₂O₃ ^2– oramine) and [Co(diph·H)₂(S₂O₃)₂]^3– were described and characterized. Some structural problems are resolved and discussed on the basis of UV and IR spectral data.     

Complexes of dioxouranium(VI) with zwitter-ionic forms of Bi- and tetra-dentateSchiff bases

Potentially bi- and tetra-dentateSchiff bases derived from salicylaldehyde react with hydrated uranyl salts to give complexes: UO₂H₂ LX ₂, UO₂H₂ LX ₂ and UO₂(HL)₂ X ₂ [H₂ L=N,N-propane-1,3-diylbis(salicylideneimine), H₂ L=N,N-ethylenebis(salicylideneimine) and HL=N-phenylsalicylideneimine;X ^–=Cl^–, Br^–, I^–, NO₃ ^–, ClO₄ ^–, and NCS^–]. Because of marked spectral similrities with the structurally known Ca(H₂ L) (NO₃)₂, theSchiff bases are coordinated through the negatively charged phenolic oxygen atoms and not the nitrogen atoms of the azomethine groups which carry the protons transferred from phenolic groups on coordination. Halide, nitrate, perchlorate and thiocyanate groups are covalently bonded to the uranyl ion, resulting a 6-coordinated uranium ion in the halo and thiocyanato complexes and 8-coordinated in nitrato and perchlorato complexes.

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Komplexe von Dioxouranyl(VI) mit zwitterionischen Formen von zwei- und vierzähnigen Schiff-Basen

Zusammenfassung Von Salizylaldehyd abgeleitete zwei- und vierzähnigeSchiff-Basen reagieren mit hydratisierten Uranylsalzen zu Komplexen folgenden Typs: UO₂H₂ LX ₂, UO₂H₂ LX ₂ und UO₂(HL)₂ X ₂ [H₂ L=N,N-Propan-1,3-diylbis(salicylidenimin), H₂ L=N,N-Ethylen-bis(salicylidenimin) und HL=N-Phenylsalicylidenimin;X ^–=Cl^–, Br^–, I^–, NO₃ ^–, ClO₄ ^– und NCS^–]. Auf Grund eindeutiger spektraler Ähnlichkeiten mit dem bekannten Ca(H₂ L) (NO₃)₂ wird auf Koordination über die negativ geladenen phenolischen Sauerstoffatome (und nicht über die Azomethin-Stickstoffe) geschlossen. Die AnionenX ^– sind kovalent an das Uranyl-Ion gebunden; damit ergibt sich ein hexakoordiniertes Uranyl-Ion für die Halogen- und Thiocyanat-Komplexe und Oktakoordination für die Nitrat- und Perchlorat-Komplexe.

     

Contribution of Na counterions to H-AOT&Na-AOT-based W/O microemulsion formation using aqueous NaOH solutions as estimated by pyranine absorbance

The objective of this study is to estimate the contribution of Na⁺ as a counterion in the formation of H-AOT&Na-AOT-based W/O microemulsions using aqueous NaOH solution by pyranine absorbance measurements. A mixture of an aqueous NaOH solution containing pyranine/H-AOT&Na-AOT/isooctane was emulsified by changing the mixing ratio of Na-AOT (X_Na-AOT = 0–1) and the mole fraction of NaOH (X_NaOH = [NaOH]/the AOT⁻ concentration in the water pool = 0–1). The phase behavior of the emulsified mixture was evaluated from the absorbance of pyranine at the isosbestic point and by visual observations. W/O microelumsions are formed at the mid-range of X_Na-AOT, whereas the emulsified mixture separates into two phases at lower X_Na-AOT and higher X_Na-AOT. The two phase boundaries shift toward lower X_Na-AOT as with increasing X_NaOH. The phase behavior depends on the degree of screening of electrostatic repulsions between the polar headgroups of AOT⁻ by the Na⁺ counterion. Interestingly, nano-sized W/O microemulsions are formed without phase separation using a highly concentrated NaOH aqueous solution when the Na-AOT mixing ratio is appropriately adjusted. The phase behavior was plotted as X_NaOH versus X_Na-AOT, and the correlation equations for the two phase boundaries were obtained by fitting the points. The contribution of the Na⁺ counterion from NaOH to W/O microemulsion formation was estimated by the correlation equations. The absorbance of pyranine and the size of W/O microemulsions, as measured by DLS, were plotted as a function of X_Na⁺=(x[Na⁺   from   NaOH]+[Na⁺   from   Na-AOT])/[AOT⁻], in which x is the ratio contributed by NaOH. The absorbance and size correlates well with X_Na⁺, indicating that X_Na⁺ is a meaningful parameter for quantitatively estimating phase behavior and size variation.     

Solubility of Lithium Nitrate in Solutions of Lithium Halides

Solubility isotherms in LiNO₃ – LiX – H₂O (X = Cl, Br, I) systems at 298.15 K were measured for the first time with special regard to the retrograde solubility of lithium nitrate trihydrate. The compositions of solutions used as media in absorption refrigerators and heat pumps were compared with the results and subsequently discussed.     

Preparation,spectroscopic and structural analysis of uranium-arabinose complexes

The reaction betweenL-arabinose and hydrated uranyl salts has been investigated in aqueous solution and the solid complexes of the type UO₂(L-arabinose)X ₂ · 2 H₂O, whereX=Cl^–, Br^–, and NO ₃ ^– , have been isolated and characterized. Due to the marked similarities with those of the structurally known Ca(L-arabinose)X ₂ · 4 H₂O and Mg(L-arabinose)X ₂ · 4 H₂O (X=Cl^– or Br^–) compounds, the UO ₂ ²⁺ ion binds obviously to twoL-arabinose moieties, through O1, O5 of the first and O3, O4 of the second molecule resulting into a six-coordinated geometry around the uranium ion with no direct U-X (X=Cl^–, Br^– or NO ₃ ^– ) interaction. The intermolecular hydrogen bonding network of the freeL-arabinose is rearranged upon uranium interaction. The -anomer configuration is predominant in the freeL-arabinose, whereas the -anomer conformation is preferred in the uranium complexes.

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Darstellung, spektroskopische und Strukturanalyse von Uran-Arabinose Komplexen

Zusammenfassung Es wurde die Reaktion zwischenL-Arabinose und hydratisierten Uranylsalzen in wäßriger Lösung untersucht und kristalline Komplexe des Typs UO₂(L-Arabinose)X ₂ · 2 H₂O mitX=Cl^–, Br^– und NO ₃ ^– isoliert und charakterisiert. Wie aus markanten Ähnlichkeiten der Komplexe mit den bekannten Verbindungen Ca(L-Arabinose)X ₂ · 4 H₂O und Mg(L-Arabinose)X ₂ · 4 H₂O (X=Cl^– oder Br^–) abzuleiten ist, bindet das UO ₂ ²⁺ -Ion mit zweiL-Arabinose Einheiten, wobei sich durch die O1,O5-Koordination des ersten und die O3,O4-Koordination des zweiten Moleküls eine sechs-koordinierte Geometrie um das Uranylion [ohne direkte U-X (X=Cl^–, Br^– oder NO ₃ ^– ) Wechselwirkung] ausbildet. Die intermolekularen Wasserstoffbrücken zeigen nach der Wechselwirkung mit dem Uranylion eine Umgruppierung. In der freienL-Arabinose ist das -Anomere vorherrschend, in den Urankomplexen hingegen das -Anomere.

     

AC conductance of (Co0.45Fe0.45Zr0.10)X(Al2O3)1 − X nanocomposites

The influence of the composition on the AC carrier transport of the composite films containing ferromagnetic CoFeZr nanoparticles in amorphous aluminium oxide matrix has been investigated. The films 3–5 μm in thicknesses and with variable composition 30 at.% < X < 60 at.% were sputtered on a single substrate from the compound target in the chamber with argon–oxygen gas mixture. TEM and SEM measurements and Mössbauer spectroscopy data have shown that all the studied films of (Co_0.45Fe_0.45Zr_0.10)_X(Al₂O₃)_1 − X with 30 at.% < X < 65 at.% have revealed the structure with crystalline granular metallic alloy (with particles of a few nanometers in size) and amorphous alumina. AC conductance measurements were performed over the frequency range 10²–10⁶ Hz at temperatures from 80 to 330 K. DC conductance measurements have been carried out for this temperature region also. The presence of two critical regions for the metallic fraction (X₁ = 33–40% and X₂ = 50–55%), where diagram “electric property–composition” exhibited pronounced peculiarities, has been confirmed. A qualitative structural model of nanocomposite was offered to explain this behavior. In accordance with the model, the first critical region at X₁ is associated with a shift of percolation threshold due to the formation of oxide layer on metallic nanoparticles, owing to the presence of oxygen in gas ambient during the sputtering process. The second critical region of the composition at X₂ is ascribed to the formation of percolation net of magnetic metallic nanoparticles in the dielectric amorphous alumina matrix.     

Ab initio study of spin–orbit interaction in the ground electronic states of XH (X = C, Si, Ge and Sn) molecules

Electronic structure and spectroscopic properties for the ground electronic states of CH, SiH, GeH and SnH molecules were obtained using the multiconfigurational self-consistent field followed by spin–orbit multireference multistate perturbation theory. Spin–orbit splitting calculations for ground states of the four molecules were carried out with model core potential (MCP) and all-electron (AE) methods. MCP results are compared with corresponding AE values to estimate the accuracy of the saving cost MCP calculations. The potential energy curves, calculated for the Ω states CH(X₁²Π_1/2 and X₂²Π_3/2), SiH(X₁²Π_1/2 and X₂²Π_3/2), GeH(X₁²Π_1/2 and X₂²Π_3/2) and SnH(X₁²Π_1/2 and X₂²Π_3/2) using the MCP method, were fitted to analytical potential energy function using Murrell–Sorbie potential energy function. Based on the analytical potential energy function, force constants and spectroscopic constants for the Ω states were obtained.     

Extending bond orbital-connection matrix method to the QSPR study of alkylbenzenes: Some thermochemical properties

The properties of alkylbenzenes were estimated, using the contributions of the σ bonds, the conjugated π bond and the steric effect in alkylbenzene molecule. And a novel bond orbital-connection matrix, conjugated π bond orbital-connection matrix in aromatic molecules, was proposed. The eigenvalues of the conjugated π bond orbital-connection matrix can well express the contribution of the conjugated π bond to the properties of aromatic molecules. Using this eigenvalue together with the parameters proposed in our early works, the bond orbital-connection matrix method was extended successfully to the QSPR studies of alkylbenzenes and a general model was obtained to evaluate the thermochemical properties of alkylbenzenes, that is,

p_{(alkylbenzene)}=aN_C–C+b∑X_1CC+cN_C–H+d∑X_1CH+eS_Z/E+k∑X_1π,