Solute-solvent interactions in water-tert-butyl alcohol mixtures. X. Partial molal volumes of alkali and halide lons

Ultrasonic vibration potentials for five alkali metal chlorides and five bromides in water-tert-butanol (t-BuOH) mixtures (t-BuOH mole percent X=2.5; 5.0; 7.5; 10.0 and 13.1%) have been measured as a function of concentration. From these data it has been possible to obtain for the first time the partial molal volumes of the individual ions in solvent mixtures. The partial molal volumes of Cl^– and Br^– ions go through a shallow minimum while those for alkali ions first incease or level off and then decrease as X is increased. A rapid decrease in the partial molal volumes occurs for H⁺ and Li⁺ in a narrow range of composition and these two ions appear to be essentially solvated by t-BuOH at X=13%. The modified Hepler's plots yield a single straight line for anions and cations up to X=5.0%, whereas two distinct lines are found at X7.5%. This change of behavior appears to be related to the maximum structuring effect of water upon addition of t-BuOH, which occurs in the same range.     

Partial molal volumes of ions in organic solvents. IV. Ethylene glycol

Apparent molal volumes have been measured for several electrolytes in ethylene glycol (EG) and the standard state partial molal volumes, V₂°, evaluated. Ultrasonic vibration potentials (uvp) have also been measured for most of the alkali metal halides in EG, and these employed to evaluate ionic partial molal volumes, V° (ion). The results show unambiguously that the uvp is essentially independent of solvent viscosity. The V₂° data have also been divided into ionic components by four other techniques including, the method of Mukerjee, the use of Ph₄AsBPh₄, the correspondence method and an extrapolation of V₂° for a series of tetraalkylammonium bromides as a funtion of cation molecular weight. With the exception of the latter technique, all methods used give 30±2 cm³-mol^–1 for V° (ion), although the uvp leads to the largest value for V° (ion). The divisions have been analyzed also with the aid of Hepler's equation, and the results suggest that the uvp method gives a more accurate division and that the EG dipole is more hindered than the dipole in ethanol.     

Electrostriction around colloid molecules and interfacial action of inhalation anesthetic: Volume function

Poly( -lysine) exists as a polyelectrolyte in an aqueous solution with charged -NH₃⁺ of the side-chain terminals at pH values below 10.5, while it loses the charges above this pH. Due to the electrostatic repulsion, the conformation of the charged form is random coil while that of the uncharged form is helix. The densities of each form were measured by an oscillation densimeter at several poly( -lysine · HBr) concentrations and the apparent molal volumes were estimated. By extrapolating the apparent molal volumes to infinite dilution, the partial molal volumes of each form at infinite dilution were obtained. When expressed by the partial molal volume per residue at infinite dilution, the values were 125.3 cm³ residue⁻¹ for the uncharged form and 112.8 cm³ residue⁻¹ for the charged form at 298.15°K. From the temperature dependence of the partial molal volume, the partial molal expansibilities were found to be 0.070 cm³ residue⁻¹ deg⁻¹ for the uncharged form and 0.106 cm³ residue⁻¹ deg⁻¹ for the charged form. The smaller partial molal expansibility of the uncharged form compared to the charged form is in agreement with the general pattern that hydrophobic macromolecules show smaller expansibility than hydrophilic macromolecules. An inhalation anesthetic, methoxyflurane, did not alter the volume of the uncharged form and expanded only the charged form. At the anesthetic concentration of 1.7 × 10⁻³ m, the partial molal volume of the charged poly( -lysine · HBr) was expanded by 0.27%. The partial molal volume of methoxyflurane in aqueous solution was 108.5 cm³ mole⁻¹ at 278.15°K while that of the pure liquid state was 113.1 cm³ mole⁻¹. The decrease of the partial molal volume of methoxyflurane in aqueous solution is attributable to the structuring of water molecules around the anesthetic. The partial molal volume of the anesthetic in the 1.0 × 10⁻⁴ m charged poly( -lysine · HBr) solution was 110.9 cm³ mole⁻¹. This increase of the partial molal volume of methoxyflurane in the peptide solution indicates that the anesthetic-water contact is partially destroyed by the binding.     

Partial molar volumes of 18-crown-6 ether in organic solvents at 25°C

The partial molar volumes at infinite dilution of 18-crown-6 ether (CE) in a variety of polar and polarizable solvents with molar volumes ranging from 18 to 170 cm³-mol^–1, were measured at concentrations ranging from 0.02 to 0.1 mol-L^–1 at 25°C. The partial molar volumes of the solute at infinite dilution showed remarkable dependancy on the molar volume of the solvent. The partial molar volumes at infinite dilution for the CE increases as the solvent molar volume increases.     

Does the ion–molecule reaction between HCCH and HCN lead to CH2CH–CN? A computational and experimental study of the reverse process

The title ion–molecule reaction has been proposed to play an important role in interstellar chemistry if it yields acrylonitrile ions CH₂CH–CN⁺. This question was probed by examining the formation of HCCH⁺ and HCN from low-energy ions CH₂CH–CN⁺ and related isomers, using tandem mass spectrometry based experiments (D and ¹³C labelling) in conjunction with model chemistry calculations (CBS-QB3/APNO). We conclude that the title reaction is a barrierless multistep rearrangement that may not effectively compete with the straightforward formation of stable distonic ions HCCH–NCH⁺ from HCCH⁺(ion)–HCN(dipole) encounter complexes.     

Comparative studies of static dipole polarizabilities of ionic crystals on the basis of different self-consistent potentials

The static dipole polarizabilities, ^D , have been studied for the ions O^2–, F^–, Na⁺, Mg²⁺, Cl^–, K⁺ and Ca²⁺ in the crystals NaF, KF, NaCl, KC1, MgO and CaO. The starting zero-order wave functions have been generated using various exchange- and exchange-correlation potentials in order to study the effect of these potentials on ^D . The direct contribution to the dipole polarizability, _o ^D , has been determined by the uncoupled Hartree-Fock method. Self-consistency effects have been included by the geometric approximation. The crystal potential is incorporated using the Watson sphere model. Good agreement between theoretical and experimental results are found for those self-consistent potentials which exclude self-interaction.     

Ultrasonic vibration potentials,apparent molal volumes,and apparent molal heat capacities of 1:1 electrolytes in acetonitrile

The ultrasonic vibration potentials and apparent molal volumes for many inorganic and organic electrolytes were measured in acetonitrile at 25°C and combined to obtain ionic contributions to the standard partial molal volumes V°(ion). Monatomic cations and anions of the same size essentially have the same V°(ion). Their size dependence can be interpreted through Hepler's equation. The apparent molal heat capacities were also measured in acetonitrile and used to derive standard values. Various methods of estimating C _p ⁰ (ion) were investigated and an ionic scale is proposed. It is concluded that C _p ⁰ (ion) of large organic ions are very close to the intrinsic heat capacities of the ions, and the solvation contribution to monatomic ions is positive for both cations and anions.     

Singly excited bound states in continuum: a time-dependent perturbation approach

Summary Time-dependent coupled Hartree-Fock (TDCHF) scheme has been applied to study the behaviour of bound excited states embedded in the continuum for the negative ions Li^–, F^–, Na^– and Cl^–. The excited states have been obtained from the position of the poles of the dynamic polarizability values which are evaluated for all the ions within and beyond the normal dispersion region. Transition energies and dipole allowed oscillator strengths have been obtained for several transitions which lie in the continuum. Although the excited state functions are extremely diffuse, they show proper asymptotic behaviour and furnish correct number of nodes. Oscillator strengths are found to follow a different trend than observed in normal bound state calculations.     

Peculiarities of interaction of H+, Me3C+, and Me3Si+ ions with multifunctional molecules in the gas phase

Peculiarities of interaction of H⁺, Me₃C⁺, and Me₃Si⁺ ions with functional groups of molecules in the gas phase have been studied. Proton tends to form chelates with virtually all of the functional groups studied, whereas Me₃Si⁺ ions exhibit no capacity for chelation. Using isomeric xylenes as examples it was shown that Me₃Si⁺ ions (unlike Me₃C⁺ ions) experience virtually no steric hindrance when they react with nucleophilic centers. Effects of functional groups present in molecules of nitriles on the generation of [M+Me₃C]⁺ adducts in the gas phase and the Ritter reaction in solution were estimated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1767–1773, September, 1995.This work was carried out with financial support from the International Science Foundation (Grant MA7 000) and the Russian Foundation for Basic Research (Project No. 93-03-18033).     

Apparent molal volumes of aqueous solutions of bis-tetraalkylammonium salts at 25°C: Methylene-group contribution to the limiting molal volume

Densities of aqueous solutions of a series of polymethonium chloride and bromide salts (CH₃)₃–N–(CH₂)_n–N–(CH₃)₃X₂ have been measured at 25°C. Apparent molal volumes have been calculated, and methylene-group contributions to the limiting apparent molal volumes °_v have been estimated. Constant values of the methylene-group contribution of 16.5 and 17.0 cm³-mole^–1 were obtained for the bromide and chloride salts, respectively. These values are consistent with methylene-group contributions reported for other series of organic electrolytes.     

Äthylensulfit als Lösungsmittel, 1. Mitt.: Halogenokomplexe von Kobalt (II)

Zusammenfassung Die Bildung von Chloro-, Bromo- und Jodokomplexen von Co²⁺ wurde in Äthylensulfit (ES) auf spektrophotometrischem, potentiometrischem und konduktometrischem Wege untersucht. Folgende Komplexformen dürften gebildet werden: [CoCl(ES)₅]⁺, CoCl₂(ES)₂, [CoCl₃ ES]^–, [CoCl₄]^2–, [CoBr(ES)₅]⁺, CoBr₂(ES)₂, [CoBr₄]^2– und [CoJ₄]^2–. Die Ergebnisse werden hinsichtlich der des Lösungsmittels und des sterischen Baues des Lösungsmittelmoleküles mit denen in anderen Lösungsmitteln verglichen und diskutiert.

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Reactions involving the formation of complex species of Co²⁺ with chloride, bromide and iodide ions have been investigated by spectrophotometric, potentiometric and conductometric methods using ethylene sulphite (ES) as solvent. The following complexes appear to be formed: [CoCl(ES)₅]⁺, CoCl₂(ES)₂, [CoCl₃ ES]^–, [CoCl₄]^2–, [CoBr(ES)₅]⁺, CoBr₂(ES)₂, [CoBr₄]^2– and [CoI₄]^2–. The influence of the donor number of the solvent and steric contributions by the solvent molecules are discussed.

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Mit 8 Abbildungen     

Volumes and heat capacities of benzene derivatives in water at 25°C: Group additivity of the standard partial molal quantities

Differences in densities and heat capacities per unit volume were measured in water with a flow densimeter and a flow microcalorimeter for a series of substituted benzene compounds in water at 25°C. Apparent molal volumes and heat capacities were calculated from the data, and, by extrapolation to infinite dilution, the standard partial molal quantities were dervied. An additivity scheme is proposed to obtain the group contribution to these systems. The standard partial molal volumes and heat capacities of rather complex aromatic molecules in water can be predicted inside about 1 cm³ mol^?1 and 10 J K^?1 mol^?1. The values of the volumes and heat capacities of groups adjacent to an aromatic ring are not the same as those on an aliphatic molecule but a simple relation exists between both sets.     

Products of Ag+, Cu+ and Cu2+ Ion Implantation in the Surface of Polycrystalline Cadmium Sulfide as Photocatalysts for the Oxidation–Reduction Reaction of Methylene Blue with Formaldehyde

Semiconductor–semiconductor and molecule (molecular ion)–semiconductor products are formed upon the implantation of Ag⁺, Cu⁺, and Cu²⁺ ions in the CdS surface. Possible mechanisms were examined for their photocatalytic action in the reduction of methylene blue.     

Volumetric properties of dilute aqueous solutions of cobalt-amine-type salts. Part I. Densities at 25°C

The densities of dilute aqueous solutions of [CoL₃]X₃ [L=1,2-diaminoethane(en), 1,2-diaminopropane(pn), 1,3-diaminopropane(tn) X=Cl^–, Br^– and (ClO₄)^–] have been measured at 25°C from 0 to 5×10^–2m. The apparent molar volumes were calculated and extrapolated to infinite dilution. Ion-solvent interactions were detected from the change of the ionic partial molar volumes with concentration. These interactions depend both on the properties of the ion (polarization charge density at the surface, hydrophobic groups, etc.) and the characteristics and structure of the solvent.     

Volumetric properties of dilute aqueous solutions of cobalt amine type salts. Part 2. Densities at 15 and 5°C

Apparent molar volumes have been determined by density measurements of aqueous solutions for a series of salts [Co(L)₃]X₃, where X=Cl^– and Br^– and L¹=1,2-diaminoethane (en), L²=1,2-diaminopropane (pn) and L³=1,3-diaminopropane (tn) at 15°C and 5°C. Apparent molar volumes at infinite dilution for the complex cations at 0°C are estimated. The resulting values are related to the structure of solvent water molecules around the ions.     

Partial molal heat capacity of aqueous ferrous chloride from measurements of integral heats of dilution

Heats of dilution of concentrated aqueous solutions (4.43 moles-kg^–1) of FeCl₂ were measured at 15, 25, and 35°C. The heat capacities of these concentrated solutions were also measured at the same temperatures. From these data the partial molal heat capacity, C _p2 ⁰ (FeCl₂, aq, 298.15°K)=–2.56±30 J–°K^–1–mole^–1, was calculated. The partial molal heat capacity of Fe²⁺(aq), –2±30 J-°K^–1-mole^–1, was correlated with the correspondence principle equations of Criss and Cobble.     

Molar volumes of LiI in H2O and D2O solutions; Structural hydration interactions

According to a recent study of the H₂O and D₂O molar volume isotope effect (MVIE) of the alkali metal chloride solutions, neither the standard nor the excess MVIE of the LiCl corresponds to the usual hydrophilic hydration characteristics of the inorganic ions above room temperatures. This phenomenon can not be rationalized by electrostriction, with the collapse of the “loose” tetrahedral (“ice-like”) water structure due to the electrostatic (ion + dipole) interaction.It seemed possible that this unique hydration behaviour of the Li⁺ would be stronger and could reveal further structural information with a less hydrophilic anion than the chloride. Therefore we have determined the MVIE of the LiI as a function of temperature and concentration. The densities of normal and heavy water solutions of LiI have been measured with six-figure precision at T = (288.15, 298.15, and 308.15) K from (0.03 to 4) molal, m, using a vibrating-tube densitometer. The solvent isotope effect on the apparent molar volume, as well as on the solute and solvent partial molar volumes, was evaluated.As expected, with the rationalization of the MVIE of LiI instead of the geometric structural differences of the isotopic solvents, the energetic contributions have to be considered at all the temperatures investigated. At infinite dilution, a high degree of compensation between the reversed influences of the Li⁺ and I^? on the activities of the isotopic solvents determines the MVIE. By increasing concentration, the highly asymmetric energetic interactions of the Li⁺ and the I^? with the solvent apparently result in a “mutual salting-out” effect. At a concentration ≈0.7m, a uniquely abrupt structural rearrangement results in a “solvent-separated ion-pair” solution structure.     

Volumetric properties of tetraphenylporphine,their metallo-complexes and some substituted tetraphenylporphines in benzene solution

Densities, apparent molar volumes and partial molar volumes of benzene solutions of tetraphenylporphine, H₂TPP, tetraphenylporphine metallo-complexes, MTPP (where M=Ni,Cu,Zn,Pd,Ag, and Cd), and some substituted tetraphenylporphines H₂T(i-R)PP (where i=2–4 and R=–Cl,–CH₃,–OCH₃) H₂T(i-F)PP (where i-2,3), H₂T(3-Br)PP, and H₂T(3-I)PP were determined at 25°C. It was found that the partial molar volumes of the studied compounds correlate linearly with the first ionization potential of the corresponding metal atom. The calculated values of the surface and volume accessible to the solvent, and the solvent-excluded volume for different conformations of H₂TPP, were compared with experimental data. The volume per molecule for different crystalline forms of H₂TPP and MTPP were compared with the partial molar volumes of the corresponding compounds in benzene solutions. The correlation between the partial molar volumes of H₂T(3-R)PP and their Van der Waals volumes are presented for R=–H, –F,–CH₃,–Cl,–Br,–OCH₃, and –I. The experimental data are rationalized in terms of differences in the conformational states of the molecules.     

Group additivity for partial molal heat capacities and volumes of alkanes in methanol at 25°C

A flow heat capacity calorimeter and a flow vibrating tube densimeter have been used to measure the apparent molal heat capacities and volumes of 14 linear and branched alkanes in methanol at 25°C. These quantities have been extrapolated to infinite dilution to obtain the standard partial molal heat capacities and volumes. The C _p2 ^o and V ₂ ^o data can be expressed by equations having the general form: Y=A_Y+ N_k Y_k+(steric factors), where A_Y is solute independent and the Y_k terms are the individual group contributions. A rationale for use of the above equation is presented.     

Ion-induced CO adsorption on polycrystalline nickel. Secondary ion mass spectrometry study

In the process of ion-induced CO adsorption (Ar⁺, 4 keV, 4 A/cm²) on polycrystalline Ni at room temperature and P=(1–40)×10^–6 Pa the emission of Ni⁺, NiCO⁺, CO⁺, NiO⁺ and C⁺ ions is observed. The emission of the last three ions is due to the ion-stimulated dissociation of weakly bound CO state and NiO formation. The weakly bound state is formed owing to surface defects produced by ion bombardment. The cross sections of the ion-induced desorption are 1.8 and 0.8×10^–14 cm², respectively, for weakly bound and strongly bound states.