Ion solvation in water

Lubin, M.I., Bylaska, E.J., and Weare, J.H., Ab initio molecular dynamics simulations of aluminum ion solvation in water clusters, Chem. Phys. Lett., 322, 447, 2000. 

The gross coincidence of the solid and solution state distances is strong evidence that the value of d measures the distance between die nuclei of the cation ad the oxygen raflier than die center of the electron cloud ofdie whole ligand molecule. Actually, first RDF peaks for ion solvation in water and in nonaqueous oxygen donor solvents are very similar despite the different ligand sizes. Examples include methanol, formamide and dimethyl sulfoxide. ... 

Lifson S, Warshel A (1968) Consistent force field for calculations of conformations, vibrational Spectra and enthalpies of cycloalkane and n-alkane molectrles. J Chem Phys 49 5116-5129 Lubin MI, Bylaska EJ, Weare JH (2000) Ab initio molecttlar dynamics simulations of aluminum ion solvation in water clusters. Chem Phys Lett 322 447-453 Matsui M (1988) Molecular dynamics study of MgSiOs perovskite. Phys Chem Miner 16 234-238 Matsui M, Busing WR (1984) Computational modehng of the structrrre and elastic constants of the olivine and spinel forms of Mg2Si04. Phys Chem Miner 11 55-59 Matsrri M, Materrmoto T (1982) An interatomic potential-function model for Mg, Ca and CaMg olivines. 

Nucleation in a cloud chamber is an important experimental tool to understand nucleation processes. Such nucleation by ions can arise in atmospheric physics theoretical analysis has been made [62, 63] and there are interesting differences in the nucleating ability of positive and negative ions [64]. In water vapor, it appears that the full heat of solvation of an ion is approached after only 5-10 water molecules have associated with... 

Dang L X, J E Rice, J Caldwell and P A Kollman 1991. Ion Solvation in Polarisable Water Molecular Dynamics Simulations. Journal of the American Chemical Society 113 2481-2486. 

Calculations at the 6-3IG level indicate that in the gas phase, 2//-l,2,3-triazole is more stable than 1//-1,2,3-triazole by about 4.5 kcal moC. In solution, the IH isomer becomes the more stable species because the large difference in dipole moments favors the more polar tautomer. The triazolium ion (75) is predicted to be more stable than (76) by about 13.5 kcal mol <89Mi40i-0i>. 2//-1,2,3-Triazole represents more than 99.9% of the equilibrium mixture in the gas phase. However, the ab initio calculated proton affinity of 1//-benzotriazole is 10.2 kcal mol larger than that of 2//-benzotriazole, which is consistent with ICR measurements (1-methylbenzotriazole is 10 kcal mol more basic than 2-methylbenzotriazole). Measurements of enthalpies of solution, vaporization, sublimation and solvation in water, methanol and DMSO confirm the predominance of the IH tautomer in solution <89JA7348>. The energy difference between the tautomers of 1,2,3-triazole has also been estimated at the 6-31G (MP2)//3-21G level including zero-point effects. The... 

Quaternary ammonium or phosphonium salts. In the above-mentioned case of NaCN, the uncatalyzed reaction does not take place because the CN" ions cannot cross the interface between the two phases, except in very low concentration. The reason is that the Na ions are solvated by the water, and this solvation energy would not be present in the organic phase. The CN ions cannot cross without the Na ions because that would destroy the electrical neutrality of each phase. In contrast to Na+ ions, quaternary ammonium (R4N )4116 and phosphonium (R4P ) ions with sufficiently large R groups are poorly solvated in water and prefer organic solvents. If a small amount of such a salt is added, three equilibria are set up ... 

Models for solvation in water that allow for a structured solvent do indeed predict a multiexponential response. For instance, the dynamical mean spherical approximation (MSA) for water solvation predicts that solvation of an ion in water is well represented by two characteristic times [38]. Nonetheless, the specific relaxation times differ substantially from the observed behavior [33],... 

Metal ions dissolved in water have some unique characteristics that influence their properties as natural water constituents and heavy metal pollutants and in biological systems. The formulas of metal ions are usually represented by the symbol for the ion followed by its charge. For example, iron(II) ion (from a compound such as iron(II) sulfate, FeS04) dissolved in water is represented as Fe2+. Actually, in water solution each iron(II) ion is strongly solvated and bonded to water molecules, so that the formula is more correctly shown as Fe(H20)g+. Many metal ions have a tendency to lose hydrogen ions from the solvating water molecules, as shown by the following ... 

Fig. 2-9. Schematic multizone models for ion solvation in solvents (a) with low degree of order such as hydrocarbons, consisting of solvation shell A and disordered bulk solvent B [98] (b) in highly ordered solvents such as water, consisting of solvation shell A with immobilized solvent molecules, followed by a structure-broken region B, and the ordered bulk solvent C (Frank and Wen [16]).

Addition of excess iodide to the insoluble Hgl2 results in the formation of soluble mercury iodo complex [Hgl3] , with a trigonal planar structure. The ion is solvated in water and converts to a tetrahedral structure. Further, addition of H leads to tetrahedral [Hg ] ". Reaction of iodide salts with Hg can be used to produce mercury iodo complexes. Other halide and pseudohalides also form [HgXj] and [HgX4] . The tetrahalo anions see Anion) are usually tetrahedral, while the trihalo ions readily add solvent molecules to form distorted tetrahedral or Trigonal Bipyramidal structures. 

From (4-26), for a 1 1 electrolyte in water the Bjerrum critical distance is 3.6 X 10 cm. When it is realized that ions in water are normally highly solvated and that the sum of ionic crystal radii for typical anions and cations often approaches or exceeds 3.6 x 10 cm, it is reasonable to find that dissociation constants for ion pairs in water are large thus for sodium hydroxide the dissociation constant is about 5. On the other hand, for a 2 2 electrolyte in water the critical distance is 14.3 x 10 cm, and for a 1 1 electrolyte in ethanol, 11.5 x 10 cm. In these cases, even highly solvated ions can readily approach to the distance necessary to form an ion pair. For magnesium sulfate the dissociation constant in water is 6 x 10 , and for sodium sulfate, 0.2. 

E. Spohr, A computer simulation study of iodide ion solvation in the vicinity of a liquid water metal interface, Chem. Phys. Lett. 207 (1993) 214. 

If Arnett and McKelvey s assumption is correct, the cations in Table 22 have greater enthalpies of solvation in DMSO than in water, but chloride and bromide anions have greater enthalpies of solvation in water than in DMSO. Iodide ion is more solvated, enthalpy-wise, in DMSO than in water. These observations are in agreement with our qualitative ideas... 

Each ion dissolved in water and its surrounding solvation shell of water molecules constitute an entity held together by ion-dipole forces or by hydrogen bonds. These solvated ions can move as intact entities when an electric field is applied (Fig. 11.4). Because the resulting solution is a conductor of electricity, ionic species such as K2SO4 are called electrolytes. 

Solvation properties of Na+ and Cl- ions in bulk ice and bulk water were the focus of another study [37], where the solvation free energies obtained in liquid water at T = 230 K for Na+ and Cl- ions were —90.07 3.18 kcal/mol and —91.08 3.16 kcal/mol, respectively. In the case of ion solvation in bulk Ih ice at T 220 K, the free energies were less negative —82.68 1.14 kcal/mol for Na+ and —80.02 3.05 kcal/mol for Cl-, meaning a more favourable solvation of the ions in the bulk water phase. 

---