Preparation and Properties of Nb-Coated Barium Titanate Composite Particles by Surface Modification with Nb Alkoxide in Hydrophobic Solvent

Chemical processing for the preparation of Nb-coated barium titanate composite particles was investigated using surface modification technology, hydrolyzing Nb ethoxide on the surface of barium titanate particles dispersed in hydrophobic solvent.It was confirmed from the measurements of specific surface area and zeta potential as well as SEM, TEM and EDX observations of the resulting composite particles that the original barium titanate particles were coated uniformly with hydrolysis product of Nb ethoxide.Barium titanates coated with 1 wt% of Nb as oxide were well sintered at 1200–1300°C. The dielectric constants of the sintered barium titanates showed flattened temperature dependence, but it depended upon the average particle size of original barium titanate. The sintered bodies of Nb-coated barium titanate powders with average particle size of 0.2 m gave dielectric constants of 2000–3000 and those of barium titanate with average particle size of 0.5 m showed dielectric constants of 3000–4000 at room temperature.The microstructure of the sintered barium titanate coated with Nb oxide consisted of grains of about 1 m, smaller than those of sintered original barium titanate.     

Kinetics of solvolysis and of formation of tetrachloroplatinate(II) in alcohol: Water mixtures

Summary Rate constants are reported for the reaction of [PtCl₄]^2– with hydrochloric-perchloric acid mixtures, in aqueous methanol and aqueous t-butanol at 308.2 K. The observed first-order rate constants are, from their dependence on chloride concentration, divisible into forward and reverse rate constants for the equilibrium: [PtCl₁₄]^2–+H₂O[PtCl₃(OH₂)]^–+Cl^–. The solvent dependence of aquation rates for [PtCl₄]^2– is compared with those for other chlorotransition metal complexes, and discussed in terms of the Grunwald-Winstein method of mechanism diagnosis in organic systems. The solvent dependence of rates of [PtCl₄]^2– formation is compared with the rates of formation of other metal complexes; differences between this platinum reaction and, for example, nickel(II) formation, are rationalised in terms of the reactant charge product difference and consequent solvent permittivity effects on rate trends.     

Complex Formation of Crown Ethers with Cations in the Water–Organic Solvent Mixtures. Part VII. Thermodynamic of Interactions of Na+ Ion with 15-Crown-5 Ether in the Mixture of Water with N,N-Dimethylacetamide at 298.15 K

The thermodynamic functions of the complex formation of 15-crown-5 ether with sodium cation in mixtures of water with N,N-dimethylacetamide at 298.15K are calculated. The equilibrium constants of complex formation of 15-crown-5 ether with sodium cation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by a calorimetric method at 298.15K. The complexes are enthalpy-stabilized but entropy-destabilized in this mixed solvent. A quantitative dependence of the excess molar enthalpy and entropy of complex formation on the structural and energetic properties of interactions between water and organic solvent molecules in the mixtures of water with N,N-dimethylacetamide, N,N-dimethylformamide and dimethylsulfoxide has been found. The linear entropy–enthalpy relationship for complex formation is also presented. The solvation enthalpy of the complex in the water–N,N-dimethylacetamide mixtures is discussed.     

Equilibrium NH acidities of acridan,phenanthridone, 9-acridone,and substituted 9-acridones

The equilibrium NH acidities of acridan, phenanthridone, 9-acridone, and 2-substituted 9-acridones (substituents: Me₂N, MeO, F, Br, I, and NO₂) were measured by transmetallation in dimethyl sulfoxide (DMSO). The role of conjugation and the aromatic character of the heterocyclic ring in stabilization of the anions is discussed. The energies of deprotonation of phenanthridone and 9-acridone were estimated by the CNDO/2 (complete neglect of differential overlap) method; it is shown that the difference between them is in agreement with the experimental results. The dependence pK = 16.2 – 3.37_I – 1.84_R (s 0.23, r 0.989) was obtained for the 2-substituted 9-acridones.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1241–1244, September, 1982.We thank É. S. Shcherbakova for her assistance in the correlation analysis of the data on the acidities of the substituted 9-acridones.     

The pH-dependence of preferential solvation as studied by intermolecular homo- and heteronuclear NOE measurements of adenosine in water–trifluoroethanol mixtures

A study of the state of solvation of the adenine ring in adenosine and adenosine 5-monophosphate disodium salt in water and in a (7.5:2.5) water–TFE mixture has been carried out by measurement of homo- and heteronuclear intermolecular NOE enhancements between water or TFE and the aromatic protons of these compounds. The results give evidence of site specificity in solute–solvent interaction for both solvent systems and preferential solvation of the solute by TFE in the water–TFE mixture. Significant pH dependence of these interactions has been discovered.     

Effect of complexation on electrical conductivity in system consisting of an anion-radical salt and a crown ether

Various experimental methods have been used in a study of the effect of complexation on the electrical conductivity in systems consisting of an anion-radical salt of an alkali metal, a crown ether (CE), and a polar solvent. The electrical conductivity of solutions of M⁺TCQDM (TCQDM = tetracyanoquinodimethane) in the presence of the CE is determined by the ratio () of the radius of the CE cavity to that of the metal ion. The equilibrium constants of the processes taking place in these systems have been determined. It has been established that the electrical conductivity of the systems is determined by the following: a) electrostatic interaction (with = 0–0.8 and > 2); b) formation of complexes {M⁺...CE (with }- 1); c) formation of ternary associates {A...M⁺...CE (with }- 1.4). In the last case, the symmetry of the environment of the M⁺ ion is increased and the potential barrier to the transition of ions between the equilibrium positions is lowered, which is responsible for the observed increase in mobility of the ions in solution.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 2, pp. 188–196, March–April, 1986.     

Neutral molecule/crown ether interactions 5. Comparison of the C−H acidic interactions of nitromethane and acetonitrile with 18-crown-6 and dibenzo-18-crown-6. Crystal structures of dibenzo-18-crown-6·2 CH3NO2 and dibenzo-18-crown-6·2 CH3CN

Complete structural characterization of dibenzo-18-crown-6·2 CH₃NO₂ and dibenzo-18-crown-6·2 CH₃CN have been carried out, including location and refinement of the methyl hydrogen atoms. Dibenzo-18-crown-6·2 CH₃NO₂ is monoclinic,P2₁/c, with (at –150°C)a=9.573(2),b=14.636(2),c=33.471(7) Å, =93.77(2)°, andD _calc=1.37 g cm^–3 forZ=8. Interactions between the solvent methyl groups and the crown ethers and other solvent nitro groups associate the 1 : 2 complexes into polymeric chains alongb. The acetonitrile adduct exists as discreet 1 : 2 complexes in the solid state with C–H...O interactions exlusively to the ether. This complex is triclinic,P 1, with (at –150°C)a=9.458(6),b=9.570(5),c=14.404(5) Å, =73.18(4), =79.85(5), =66.82(6)°, andD _calc=1.28 g cm^–3 forZ=2. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82070 (22 pages).For part 4, see reference [1].     

An ab initio study of the structures and enthalpies of the hydrogen-bonded complexes of the acids H2O,H2S,HCN, and HCl with the anions OH−, SH−, CN−, and Cl−

Ab initio calculations at second-order Møller-Plesset perturbation theory with the 6-31 + G(d,p) basis set have been performed to determine the equilibrium structures and energies of a series of negative-ion hydrogen-bonded complexes with H₂O, H₂S, HCN, and HCl as proton donors and OH^–, SH^–, CN^–, and Cl^– as proton acceptors. The computed stabilization enthalpies of these complexes are in agreement to within the experimental error of 1 kcal mol^–1 with the gas-phase hydrogen bond enthalpies, except for HOHOH^–, in which case the difference is 1.8 kcal mol^–1. The structures of these complexes exhibit linear hydrogen bonds and directed lone pairs of electrons except for complexes with H₂O as the proton donor, in which cases the hydrogen bonds deviate slightly from linearity. All of the complexes have equilibrium structures in which the hydrogen-bonded proton is nonsymmetrically bound, although the symmetric structures of HOHOH^– and ClHCl^– are only slightly less bound than the equilibrium structures. MP2/6-31 + G(d,p) hydrogen bond energies calculated at optimized MP2/B-31 + G(d,p) and at optimized HF/6-31G(d) geometries are similar. Using HF/6-31G(d) frequencies to evaluate zero-point and thermal vibrational energies does not introduce significant error into the computed hydrogen bond enthalpies of these complexes provided that the hydrogen-bonded proton is definitely nonsymmetrically bound at both Hartree-Fock and MP2.     

Conductance behavior of 1∶1 electrolytes in N,N-dimethylmethanesulfonamide

The conductances of eleven 1:1 salts have been measured at 50°C in N,N-dimethylmethanesulfonamide (DMMSA) for electrolyte concentrations of 1.2–55.0×10^–4 mol-dm^–3. The conductance data were analyzed using the equation of Lee and Wheaton. Calculations for different values of the distance parameter R indicate that all salts studied are only slightly associated in DMMSA. Association was somewhat greater for the trimethylphenylammonium halides than for the tetraalkylammonium salts. Ionic limiting molar conductances were estimated using the tris (isopentyl) butylammonium tetraphenylborate approximation. The markedly smaller value for _o (Na⁺) compared to the values for _o (Br^–) and _o (I^–) indicates that the sodium ion is probably more extensively solvated than the halide ion. In general, it appears that DMMSA (dielectric constant=80.31 at 50°C) is similar in its solvent properties to dipolar aprotic heterocyclic solvents such as 2-cyanopyridine and 3-methyl-2-oxazolidone which have similar dielectric constants.     

Thermodynamic parameters for the reaction of 1,8-diazabicyclo [5.4.0] undec-7-ene with 4-nitrophenylnitromethane in several aprotic solvents

Equilibrium constants K for reaction of the C-acid, 4-nitro/phenylnitromethane with 1,8-diazabicyclo [5.4.0] undec-7-ene have been determined in aprotic solvents over a range of temperature. Corresponding measurements have been made for the deuterated acid 4-NPNM-d₂. Thermodynamic parameters K, H^o and S^o, for proton and for deuteron transfers are not very differet in a given solvent, but show a considerable solvent dependence. There is an increase in magnitude of K with increase in solvent dielectric constant, a finding which is consistent with formation of an ion-pair. The range of extent of exothermicity of the reaction is quite small, –40 to-65 kJ-mol^–1, and the values of S^o (large, negative) indicate, in general, increasing solvent restriction by the product with increasing solvent polarity. A modest bathochromic solvatochromism of the product is observed as the dielectric constant increases.     

Solvent effects on the kinetics of solvolysis of trans-dichlorobis (N-methylethylenediamine)cobalt(III) ion in water–propan-2-ol and water–acetonitrile mixtures

First order solvolysis rates of the trans-dichlorobis (N-methylethylenediamine) cobalt(III) ion have been measured over a wide range of solvent compositions and temperatures in water–propan-2-ol and water–acetonitrile mixtures. The rate of solvolysis is faster in the former mixtures rather than the latter. Plots of log(rate constant) versus the reciprocal of the dielectric constant of the co-solvent, and also versus the Grunwald–Winstein Y-values are non-linear for both co-solvents; this non-linearity is derived from a large differential effect of solvent structure between the initial and transition states. However, extrema in the variation of enthalpy H and entropy S of activation correlate well with the extrema in physical properties of the mixtures which are related to changes in solvent structure. Linear plots of H versus S were obtained and the isokinetic temperature indicates that the reaction is entropy controlled. The application of a free-energy cycle shows that changes in solvent structure affect the pentacoordinated cobalt(III) ion in the transition state more than the hexacoordinated cobalt(III) ion in the initial state. In addition, the stabilizing influence of changes in solvent structure is greater in propan-2-ol–water mixtures than in acetonitrile–water mixtures, and the difference becomes greater as the mole fraction, x2 of the organic co-solvent increases.     

Molecular Structure of PrBr3 and HoBr3 According to Simultaneous Electron Diffraction and Mass Spectrometry Experiment

The saturated vapors of praseodymium and holmium tribromides were investigated for the first time by electron diffraction with mass spectral monitoring at 1100(10) and 991(10) K. It is established that the molecules have a pyramidal effective configuration with bond angles Br–Pr–Br = 114.7(10)° and Br–Ho–Br = 115.3(11)°. Given the low deformation vibration frequencies of lanthanide tribromide molecules, the insignificant pyramidality of the r_g configuration may correspond to the planar equilibrium geometry of D_3h symmetry for the molecules. The internuclear distances r_g(Pr–Br) = 2.696(6) and r_g(Ho–Br) = 2.594(5) point to the lanthanide compression effect. The vibration frequencies of PrBr₃ and HoBr₃ molecules were estimated from electron diffraction data.     

Kinetics and mechanism of osmium(VIII) mediated cerium(IV) oxidation of dimethylsulfoxide in aqueous sulfuric acid

Under the experimental conditions [DMSO]T [CeIV]T [Os]T the kinetics of oxidation of dimethylsulfoxide (DMSO) to dimethylsulfone (DMSO2) have been followed at different temperatures (40–55°C) in 1.0 mol dm–3 sulfuric acid media. The rate of disappearance of [CeIV] shows a first-order dependence on both [Os]T and [DMSO]T and zeroth-order kinetics with respect to [CeIV]. The suggested mechanism involves oxidation of DMSO by OsVIII in a rate-determining step through an outer-sphere mechanism, followed by rapid regeneration of OsVIII by CeIV from OsVI. The rate law conforms to: –d[CeIV]/dt=k0=k[Os]T[DMSO]T. The values of k and the activation parameters are: 102k=(4.9 ± 0.10) mol–1 dm3 s–1 at 40°C, [H2SO4] =1.0 mol dm–3;H=58±3kJmol–1, S= –88 ±5JK–1mol–1.     

Indoles

Dinordeoxy-10-methylhomoeseroline and a number of its derivatives, substituted in the benzene ring and at the indole nitrogen atom, were obtained by condensation in neutral, aqueous alcoholic solutions of arylhydrazines with -haloketones with an -methine group. The compounds of the homoeseroline series exist in neutral solutions in the form of a mixture of ring and chain tautomers, and the position of the tautomeric equilibrium depends on the solvent. The dependence of the ring-chain tautomeric equilibrium on the pH of the medium was determined, and the region of the existence of an equilibrium mixture in acidic solutions was found.See [1] for Communication XII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1489–1494, November, 1970.     

Effects of Solvent, Structure, and Temperature on the Ionization Equilibrium Constants of Phenols and Pyridinium Ions in Mixtures of Water and 1,4-Dioxane

An extensive collection of data has been used to study the effects of solvent, structure, and temperature on the ionization equilibrium constants of some substituted phenols and pyridinium ions in water–1,4-dioxane mixtures (0–70% weight fraction in dioxane) and temperatures ranging from 10 to 50°C. The effects of structure and solvent are explained using Hammett's equation and the Marshall–Quist model at all temperatures. An equation allowing an analysis of the three effects together on the pK values has been developed. The pK data under all experimental conditions fit this equation well, with standard errors of less than 0.3 pH units. Hammett's reaction constant for the ionization of phenols and pyridinium ions has been obtained for all the experimental conditions. The pK and Hammett's reaction constants for the different ionizations in water–1,4-dioxane mixtures correlate well with Kamlet and Taft's solvatochromic parameters ^* and , which measure the dipolarity/polarizability and hydrogen-bonding capacity of the solvent, respectively. These correlations explain more thoroughly the different contributions and origin of the effects of the solvent on the pK.     

IR-Spectroscopic investigation of the hydration of tetrabutylammonium bromide in methylene chloride

The concentration dependence of the H₂O spectra in solutions of tetrabutylammonium bromide Bu₄NBr in methylene chloride was investigated by IR-spectroscopy. At low salt and H₂O concentrations the equilibrium: Br _f ^– +HOH_fBr^–HOH dominates where f indicates free or not hydrogen-bonded Br^– and H₂O. With increasing salt content, Br^–H–O–HBr^– complexes are present in addition. At high salt and H₂O content, including the saturated aqueous Bu₄NBr solution, H-bonded cyclic dimers seem to be important.Presented at the sixth Italian meeting on Calorimetry and Thermal Analysis (AICAT) held in Naples. December 4–7, 1984.     

Comparison of Ab Initio MP2/6-311+G(d,p) Predicted Carbon–Hydrogen Bond Distances with Experimentally Determined r 0 (C–H) Distances

Fifty different carbon–hydrogen distances have been predicted from ab initio MP2/6-311+G(d,p) calculations, which range from a short value of 1.0611 Å for HCNO to a long value of 1.1044 Å for H₂CO. The values include those predicted for a series of methyl (CH₃) moieties where the two different C–H distances vary by as much as 0.005 Å. These predicted values are compared to r ₀(C–H) distances obtained from the isolated carbon–hydrogen stretching frequencies, as well as to r ₀ or r _s parameters obtained from microwave data. Except for the very short C–H bonds, the ab initio values from the MP2/6–311+G(d,p) calculations can be used for the carbon–hydrogen distances with error limits of ± 0.003 Å. By utilizing the spectral data from CD₃CClO, it is shown that combination bands in the C–H stretching region could cause problems in the identification of the isolated C–H stretching frequency from the CD₂HCClO isotopomer. The value of the ab initio predicted C–H distances for checking unusually long or short r _s (C–H) or r ₀ values is demonstrated.     

Ellipsometrical measurements on porous copper films

Summary Porous films are prepared by depositing copper onto glass substrates at 77 K. The structure of the films is characterized ellipsometrically (=632.8 nm) and by means of resistivity measurements. The measured dielectric function of the porous films is=–6.5 –4.6i, a value which deviates strongly from the corresponding value of bulk copper ( _m=–18 –1.6i). A quantitative evaluation on the basis of the EMA theory yields a void concentration of about 20%. In addition, the interaction of the films with oxygen is investigated. The gas tends to penetrate into the near-surface portion of the voids.

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Ellipsometrische Messungen an porösen Kupferschichten

     

Tetranuclear copper complexes with new β-diketone and β-iminoketone-containing ligands

Novel tetranuclear copper complexes, Cu4(OH)2(ClO4)3 (HA)·H2O (1) and Cu4(ClO4)5(H3B)·3H2O (2), were synthesized by reacting 1,5-bis(1-phenyl-3-methyl-5-pyrazolone-4)-1 ,5-pentanedione with 1,3-propanediamine and 2-hydroxyl-1,3-propanediamine in the presence of a template reagent copper ion. New [2+2] type open cyclic multidentate ligands are also obtained from the reaction (H4A and H6B stand for new compounds from 1,3-propanediamine and 2-hydroxyl-1,3-propanediamine, respectively). They each contain five C = O, three C = N and one NH2 groups. The complexes were characterized by elemental analyses, conductivity, FT-i.r. (micro-i.r., deconvolution technique), FAB-MS, e.s.r., electronic spectra and extended X-ray absorption fine structure (EXAFS). Copper ions in (1) are basically four coordinate with tetragonal geometry. The average coordination bond distances of Cu–N and Cu–O are 1.91 Å and 2.05 Å. In (2), copper ions are primarily five coordinate with square-based pyramidal geometry. The average coordination bond distances of Cu–N and Cu–O are 1.93Å and 2.08Å. Four copper atoms in molecules may be arranged tetragonally. Both the ligand field and the coordination bonds in complex (1) are stronger than those in (2). Investigations on variable temperature susceptibilities show that some antiferromagnetic exchange interaction exist in the complexes. The plots of –1 versus T obey the Curie-Weiss law only at low temperature. Preliminary results of a bioassay indicate that the two complexes have some antitumour activity in vitro.     

Kinetics and mechanism of the interaction of azide with [(H2O)(tap)2RuORu(tap)2-(H2O)]2+ ion at physiological pH

The title reaction has been studied spectrophotometrically in aqueous medium as a function of [substrate complex], [ligand], pH and temperature at constant ionic strength. At the physiological pH (7.4) the interaction with azide shows two distinct consecutive steps, i.e., it shows a non-linear dependence on the concentration of N₃ ^–; both processes are [ligand]-dependent. The rate constant for the processes are: k ₁10^–3 s^–1 and k ₂10^–5 s^–1. The activation parameters calculated from Eyring plots are: H ₁ = 14.8 ± 1 kJ mol^–1, S ₁ = –240 ± 3 J K^–1 mol^–1, H ₂ = 44.0 ± 1.5 kJ mol^–1 and S ₂ = –190 ± 4 J K^–1 mol^–1. Based on the kinetic and activation parameters an associative interchange mechanism is proposed for the interaction process. From the temperature dependence of the outersphere association equilibrium constant, the thermodynamic parameters calculated are: H ₁ ⁰ = 4.4 ± 0.9 kJ mol^–1, S ₁ ⁰ = 64 ± 3 J K^–1 mol^–1 and H ₂ ⁰ = 14.2 ± 2.9 kJ mol^–1, S ₂ ⁰ = 90 ± 9 J K^–1 mol^–1, which gives a negative G ⁰ value at all temperatures studied, supporting the spontaneous formation of an outersphere association complex.