Unipositive Ions Research Articles

Ions in a binary asymmetric dipolar mixture: Mole fraction dependent Born energy of solvation and partial solvent polarization structure

Mean spherical approximation (MSA) for electrolyte solution has been extended to investigate the role of partial solvent polarization densities around an ion in a completely asymmetric binary dipolar mixture. The differences in solvent diameters, dipole moments, and ionic size are incorporated systematically within the MSA framework in the present theory for the first time. In addition to the contributions due to difference in dipole moments, the solvent-solvent and ion-solvent size ratios are found to significantly affect the nonideality in binary dipolar mixtures. Subsequently, the theory is used to investigate the role of ion-solvent and solvent-solvent size ratios in determining the nonideality in Born free energy of solvation of a unipositive rigid ion in alcohol-water and dimethyl sulfoxide-acetonitrile mixtures, where the solvent components are represented only by their molecular diameters and dipole moments. Nonideality in Born free energy of solvation in such simplified mixtures is found to be stronger for smaller ions. The slope of the nonideality for smaller alkali metal ions in methanol-water mixture is found to be opposite to that for larger ion, such as quaternary tertiary butyl ammonium ion. For ethanol-water mixtures, the slopes are in the same direction for all the ions studied here. These results are in qualitative agreement with experiments, which is surprising as the present MSA approach does not include the hydrogen bonding and hydrophobic interactions present in the real mixtures. The calculated partial polarization densities around a unipositive ion also show the characteristic deviation from ideality and reveal the microscopic origin of the ion and solvent size dependent preferential solvation. Also, the excess free energy of mixing (in the absence of any ion) for these binary mixtures has been calculated and a good agreement between theory and experiment has been found.

An electrospray mass spectrometric investigation of gallium trihalide and indium trihalide solutions

Electrospray mass spectrometric data for acidic gallium trihalide solutions, GaX 3 (X = Cl or Br), reveal the unipositive ions [GaX 2] +, [GaX(OH)] + and [Ga(OH) 2] + often associated with molecules of H 2O or MeCN from the solvent phase. GaI 3 solutions yield mainly the solvated [Ga(OH) 2] + ion. Solutions of InX 3 produce the [InX 2] + cations in association with solvent molecules; the predominant hydrolysed cation is solvated [InO] +. Under negative ion conditions, solutions of GaX 3 + HX (X = Cl, Br or I) give rise to [GaX 4] − and [GaX 3(OH)] −, along with Ga 2 and Ga 3 species, particularly [(GaX 3) 2(OH)] −. Solutions of InX 3 + HX show [InX 4] − and [In 2X 7] −. ES-MS data are also reported for mixed halide solutions of gallium and for solutions of GaCl 3 containing the additional ligands F −, NO 3 − or NCS −, Complex cations [InI 2(18-crown-6)] + and [InI(OH)(18-crown-6)] + were detected by ES-MS on adding this crown ether to aqueous InI 3 solution.

Limiting Ionic Conductance of Symmetrical, Rigid Ions in Aqueous Solutions: Temperature Dependence and Solvent Isotope Effects

Limiting ionic conductance (Λ0) of rigid symmetrical unipositive ions in aqueous solution shows a strong temperature dependence. For example, Λ0 more than doubles when the temperature is increased from 283 to 318 K. A marked variation also occurs when the solvent is changed from ordinary water (H2O) to heavy water (D2O). In addition, Λ0 shows a nonmonotonic size dependence with a skewed maximum near Cs+. Although these important results have been known for a long time, no satisfactory theoretical explanation exists for these results. In this article we present a simple molecular theory which provides a nearly quantitative explanation in terms of microscopic structure and dynamics of the solvent. A notable feature of this theory is that it does not invoke any nonquantifiable models involving solvent-berg or clatherates. We find the strong temperature dependence of Λ0 to arise from a rather large number of microscopic factors, each providing a small but nontrivial contribution, but all acting surprisingly in the same direction. This work, we believe, provides, for the first time, a satisfactory explanation of both the anomalous size and temperature dependencies of Λ0 of unipositive ions in molecular terms. The marked change in Λ0 as the solvent is changed from H2O to D2O is found to arise partly from a change in the dielectric relaxation and partly from a change in the effective interaction of the ion with the solvent.

The thermorchemistry of the di-η 5-cyclopentadienyl derivatives of the first transition series and their unipositive ions

The heats of formation [△ H 0 f(MCp 2, c, 298)] have been determined for the di-η 5-cyclopentadienyl derivatives of magnesium, vanadium, chromium, manganese, iron, cobalt and nickel, by static-bomb calorimetry. They are (in kJ mol -1) (M =) Mg, 77.0 ± 3; V, 123 ± 4; Cr, 186 ± 3; Mn, 198 ± 2; Fe, 158 ± 4; Co, 205 ± 4; and Ni, 262 ± 3. the heats of formation [△ H 0 f(M(CO) x Cp, c, 298)] of tricarbonylcyclopentadienylmanganese and dicarbonylcyclopentadienylcobalt have also been determined as —478 ± 1 and —169 ± 10 kJ mol −1, respectively. By using the measured heats of formation of the metallocenes of the first transition series and other enthalpy values from the literature in Hess's law cycles, the feasibility of the process MCp 2 → MCp + 2 + e (obtained from the photoelectron ionisation energies) has been analysed and shown to be the result of the interplay of exchange energy and ligand-field stabilisation energy terms in these low-spin complexes. The feasibility order, V < Cr > Mn > Fe < Co > Ni is associated with the special stability associated with half-filled and filled shelss, which, because of the large ligand-field splitting, occur at d 3, d 6, d 8 and d 10. It is shown that bond energy additivity does not occur for the above cyclopentadienylmetal carbonyls.

Effect of ions on phospholipid layer structure as indicated by Raman Spectroscopy

Various anions and cations are found to induce changes in the layered structure of phosphatidylcholine-water systems as indicated by Raman Spectroscopy. From the ratio of Raman intensities, I 1064 I 1089 , it is inferred that dispositive ions decrease the proportion of gauche character in the hydrocarbon chains, with the relative influence being: Ba 2+ < Mg 2+ < Ca 2+ ≈ Cd 2+. Unipositive ions (Li +, K + and Na +) produce no observed changes in the Raman spectrum of the lecithin dispersion. The proportion of gauche character of the hydrocarbon chains is found to be nearly independent of the anion for: Br −, Cl −, acetate −, I −, ClO 4 −, CNS − and SO 4 2−. Dispersions prepared with a solution of KI + I 2 produced Raman spectra in which the 1089 cm −1 peak, which is characteristic of random lipid chains, was greatly intensified, presumably because of the presence of I 3 − which is known to penetrate the lipid lamellae. The observed trends are discussed.

Many-body effects in x-ray photoemission from magnesium

X-ray photoemission experiments were performed on samples of magnesium and aluminum prepared with clean surfaces in ultrahigh vacuum. Core-level binding energies were in excellent agreement with x-ray emission data. Asymmetries in core-level peaks were observed and are compared with theory. The Mg $\mathrm{KLL}$ Auger spectrum showed kinetic energies higher than the literature values. Many-body effects, in the form of extra-atomic relaxation, were present in core levels and Auger lines. Both $K{L}_{1}V$ and $K{L}_{2,3}V$ Auger peaks of Mg were observed. Many-body effects were also manifest as rich plasmon satellite structure accompanying every primary peak. The valence-band spectrum was compared with x-ray emission data and with the $K{L}_{2,3}V$ peak. The spectra were interpreted in terms of energy-level diagrams rather than one-electron "levels." It is argued that valence-band spectra obtained by different methods can be compared most directly among states with the same number of core holes. A hierarchical classification of hole states is suggested. The effect of the degree of localization of the hole state on the relaxation energies in metals is discussed and shown to be small. Finally it was observed that in several light metals the energies required to remove a valence-band electron or a unipositive ion core are about equal.

Valence electron studies with Gaussian-based model potentials and Gaussian basis functions. III Applications to two-valence-electron systems composed of combinations of Li, Na, H, or their unipositive ions

A previously developed simple valence-only electronic structure theory based on atomic core model potentials and using flexible Gaussian valence basis functions is applied to the two-valence electron systems Li2, Na2, NaLi, LiH, NaH, Li3+, Na3+, Li2Na+, LiNa2+, LiH2+, Li2H+, NaH2+, Na2H+, and H2, within the SCF MO model. Results for calculated equilibrium geometries and energy changes for certain chemical reactions are compared to the corresponding quantities from analogous all-electron ab initio calculations. The model potential results are quite similar to those from the ab initio ones and are generally satisfactory for such a simple theory. There is a tendency toward slightly long internuclear distances (average deviation of all unique independent distances is +0.06 bohr) and slightly high energy of complex relative to separate constituents (average deviation of dissociation reaction energies is −2.1 kcal/mole) in these calculations relative to the all-electron ones, the explanation of which will require future detailed analysis of both the model potential valence-electron and the ab initio all-electron calculations.

Polyelectrolyte acceleration of electron transfer reactions

The kinetics of electron-transfer reactions of some Co(III) complexes with Ru(NH 3) 6 2+ (outer sphere), Cr(H 2O) 6 2+ (inner sphere), and V(H 2O) 6 2+ (inner sphere) have been studied in the presence of varying concentrations of the sodium salt of poly(methacryloxyethylsulfonic acid), (PMES), using the stopped-flow technique. A large acceleration of reaction rates was observed with Ru(NH 3) 6 2+ and V(H 2O) 6 2+, with acceleration factors up to 20,000. The accelerated rates of electron transfer show a nonlinear dependence on polyelectrolyte concentrations: first, increasing with increasing polyelectrolyte concentration then reaching a maximum and subsequently decreasing. The magnitude of acceleration depends strongly on the charge of oxidants, being much larger for dipositive than for unipositive ions. Acceleration specificity is shown by the reduction of cis-Co(en) 2Cl 2 + by Ru(NH 3) 6 2+, in which case the acceleration factor is much higher in the presence of PMES than in the case of the corresponding trans isomer. The acceleration of the reaction of cis-Co(en) 2PyCl 2+ with Ru(NH 3) 6 2+ by the polyelectrolyte is practically equal to the acceleration of the reduction of this complex by V(H 2O) 6 2+, whereas the reduction of cis-Co(en) 2NH 2Cl 2+ by Ru(NH 3) 6 2+ is more strongly accelerated than the reduction by V(H 2O) 6 2+. Activation energies have been determined for some of the reactions and have been interpreted in terms of a multiple equilibrium reaction scheme. At a given concentration of reactants and polyelectrolyte, the acceleration factor increases with decreasing temperature and, further, the concentration of polyelectrolyte at which the maximum acceleration occurs decreases with decreasing temperature. The reaction rates of inner sphere reduction using Cr(H 2O) 6 2+ exhibit an entirely different behavior in the presence of PMES; no acceleration effect is observed. Two distinct reaction paths can be identified, with evidence for the formation and decay of one or more binuclear intermediates. The electron-transfer rate corresponding to the decay of the intermediates is much slower in the presence of PMES.

Ab Initio Predictions for Very Small Ions

Approximate ab initio calculations are made on all polyatomic unipositive ions with fewer than six electrons. Predictions are made regarding the stability of such ions. For those which are stable, estimates are made of binding energies, geometries, vibration frequencies, and center of charge. The wavefunctions are valence-bond configuration-interaction functions built form Gaussian orbitals. All possible valence-bond configurations within our chosen basis are used in order to eliminate a serious prejudice regarding geometry. BeH2+, LiHeH+, He3+, LiH3+, LiH2+, He2H+, HeH3+, H5+, HeH2+, H4+, and H3+ are found to be stable. (More accurate calculations on H4+ show that this ion is not stable relative to H3+ and H.) He2H2+, HeH4+, and H6+ are found to be unstable. Two stable isomers of BeH2+ are found: a stable triangular form and a metastable linear form. A semiclassical model is used to interpret and extrapolate our results.

Valence-states of boron, carbon, nitrogen and oxygen

Empirical values of the parameters in the Slater-Condon theory of atomic spectra are evaluated from experimental atomic energy levels for B, C, N and O, and for their unipositive ions. From extrapolations through isoelectronic series, parameter values for the uninegative ions are also obtained. The parameters are used to calculate energies of excitation from ground states to defined valence states. Ionization potentials and electron affinities of specified hybrid atomic orbitals are listed, and the relative electronegatives of the orbitals are evaluated. The effect of charge on the ionization potential of an electron from certain defined atomic orbitals is examined. By comparing the ionization potentials of OH 2, NH 3 and CH 3 with those calculated for O, N and C atoms of the same orbital geometry, we obtain maximum values for the degree of charge transfer to the central atoms in these molecules, and maximum values for the percentage ionic character of OH, NH and CH bonds: the correlation with electronegativity difference between bonded atoms is examined.

The anodic oxidation of zinc and cadmium in aqueous solution

In the absence of oxidizing agents in the electrolyte solution, only the bipositive ions are formed at zinc and cadmium anodes on electrolysis. In the presence of certain oxidizing agents (e.g. nitrate ion), however, both metals dissolve anodically with an initial mean valence number between one and two; in the presence of chlorate ion zinc dissolves with an initial mean valence number between one and two, whereas cadmium exhibits an initial mean valence number of two. In those solutions in which the initial mean valence number of the metal is less than two, its value decreases further with increasing temperature of electrolysis. No unipositive ion of zinc or cadmium could be isolated, and flow experiments indicated that if the unipositive ion is formed it has a very short lifetime with respect to further oxidation to the bipositive state. All of the experimental data can be explained, however, on the hypothesis that the primary anode reaction is the formation of the unipositive ion, which can then be oxidized to the bipositive state either electrolytically or by an oxidizing agent in the solution. The second oxidation can be thought of as competitive between the oxidizing agent and the electrode. This hypothesis is supported by the relation between the initial mean valence number and the quantity of reduced electrolyte in the anolyte solution.