Preferential Solvation of Ions in Mixed Solvents. 5. The Alkali Metal, Silver, and Thallium(I) Cations in Aqueous Organic Solvents According to the Inverse Kirkwood-Buff Integral (IKBI) Approach

The inverse Kirkwood-Buff integral (IKBI) approach is applied, as far as the relevant data exist in the literature, to the preferential solvation of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, and Tl⁺ in aqueous mixtures of methanol, ethanol, 1,2-ethanediol (EG), acetonitrile, formamide, N,N,-dimethylformamide (DMF), N,N,N′,N′,N″,N″-hexamethyl phosphoric triamide (HMPT), and dimethyl sulfoxide (DMSO). In aqueous EG and formamide the preferential solvation is very small. Water is the preferred solvent in the solvation shells in aqueous methanol, ethanol and acetonitrile (except for Ag⁺ in the latter solvent) but the co-solvent is preferred in aqueous mixtures of DMF, HMPT, and DMSO over most or all of the composition range. For the latter three mixtures the larger donicity of the co-solvents causes their preference, whereas where water is preferred over other protic solvents, it is the small size of the water molecules that appears to be the cause.     

The structuredness of solvents. 2. Data for ambient conditions

In view of the inadequacy of Trouton's constant for the expression of the structuredness of solvents at ambient temperatures, alternative measures have been sought. Calculations of the entropy deficit _vapS⁰/R of solvents at ambient conditions relative to their vapors and compared to presumably unstructured alkanes with the same number and arrangement of skeletal atoms have been made. Data for nonpolar, dipolar aprotic, non-hydroxylic protic and hydroxylic solvents are presented, with _vapS⁰/R>2 representing structured solvents. Empirically, the heat capacity density of solvents at ambient temperatures, [C _p (l)-C _p (g)]/V], is another meaningful measure of the structuredness of solvents, compatible with the former one. Values>0.6 J-K^–1-cm^–3 signify a structured solvent.     

The solubility and solvation of salts in mixed nonaqueous solvents. 1. Potassium halides in mixed aprotic solvents

The solubilities of potassium fluoride, chloride, and bromide in acetonitrile, N,N-dimethylformamide, and dimethylsulfoxide and in binary mixtures of these solvents were determined at 25°C. The standard molar Gibbs free energies of solution, _solnG°, in the neat solvents were related to the polarizabilities and basicities of the anions and the dipole moments and acidities of the solvents. The values of _solnG° in the mixtures were fitted by expressions from the quasi-lattice quasi-chemical theory. The mean number of each kind of solvent in the nearest environment of the ions was obtained from these results.     

Solvation Numbers of Divalent Metal Salts and Ions in Some Non-aqueous Solvents

The few data available so far for the solvation numbers of divalent metal salts in non-aqueous solvents at infinite dilution are augmented by values in methanol, acetonitrile, N,N-dimethylformamide, and dimethylsulfoxide for alkaline earth and first row transition metal salts at 298.15 K. These were obtained from the isothermal compressibilities and the molar electrostriction volumes, as appropriate, with good agreement where comparable. Solvation numbers were evaluated for the individual ions, where possible. The intrinsic volume of the triflate anion was evaluated for this purpose.     

Current-induced anisotropy and reordering of the electron liquid-crystal phases in a two-dimensional electron system

The correlated phases in a two-dimensional electron system with a high index partially filled Landau level are studied in transport under nonequilibrium conditions by imposing a dc-current drive. At filling 1/4 and 3/4 of these Landau levels, where the charge density wave picture predicts an isotropic bubble phase, the dc drive induces anisotropic transport behavior consistent with stripe order. The easy axis of the emerging anisotropic phase is perpendicular to the drive. At half filling the anisotropic stripe phase is stabilized by the dc drive provided drive and easy-axis directions coincide.     

On Water Structure in Concentrated Salt Solutions

In concentrated salt solutions the average distances between the ions, d ^av=1.1844⋅(∑ν _i c _i )^−1/3 nm, are commensurate with the sizes of the solvated ions, so that no ‘bulk solvent’ remains. This is illustrated with two saturated aqueous solutions, where 16.67 mol⋅dm⁻³ CsF at 75 °C has d ^av(Cs–F)=0.368 nm and 14.54 mol⋅dm⁻³ LiI at 80 °C has d ^av(Li–I)=0.385 nm. The minimal distance required for the bare ions (sum of their radii) are 0.303 nm for CsF and 0.289 nm for LiI. Hence no water molecule, diameter 0.276 nm, can be fitted between the ions to form linear or slightly bent hydrogen bonds. Some recent work ignoring such constraints, even in 3–6 mol⋅dm⁻³ solutions, is criticized on this account.     

Effect of exchange interaction on spin dephasing in a double quantum dot

We measure singlet-triplet dephasing in a two-electron double quantum dot in the presence of an exchange interaction which can be electrically tuned from much smaller to much larger than the hyperfine energy. Saturation of dephasing and damped oscillations of the spin correlator as a function of time are observed when the two interaction strengths are comparable. Both features of the data are compared with predictions from a quasistatic model of the hyperfine field.     

Are Ionic Stokes Radii of Any Use?

The derivation of ionic Stokes radii, r _iSt, from ion mobilities (conductivities ?? _i ^?? ) and their relation to the actual ionic radii, of the bare or the hydrated ions, is followed through the years. It is concluded that such quantities as r _iSt do not convey any useful information beyond what is already available in the ?? _i ^?? , and in particular that the r _iSt should not be used for the estimation of solvation numbers. The concept of a Stokes radius of ions that are smaller than or commensurate with molecules of the solvent should be scrapped altogether.