Preferential solvation of Co2+ and Ni2+ ions in mixed solvents: n.m.r. methods

A method for the study of preferential solvation in the outer coordination spheres from paramagnetic broadening of solvent proton n.m.r. signals was proposed by Frankel, Stengle, and Langford. It is now extended to determinations of the relative concentrations of water and dioxane, dimethylformamide, or dimethylsulfoxide in the inner coordination spheres of Co2+ and Ni2+ ions in the binary solvent mixtures. The assumptions of the analysis are cross-checked by a new method based on the contact shifts experienced by protons on solvent molecules in the coordination spheres of paramagnetic ions. The second method depends upon assumptions independent of the first. Three cases are presented as tests of these n.m.r. approaches. It is clear that highly precise solvation sphere populations will be difficult to obtain but that useful and significant information can be obtained in situations to which alternative methods are almost totally inapplicable.The results indicate that dimethylsulfoxide and dimethylformamide are good competitors for coordination sites but that dioxane is excluded by water.

Download Full-text

Solvation in pure and mixed solvents: Some recent developments

Pure and Applied Chemistry ◽

10.1351/pac200779061135 ◽

2007 ◽

Vol 79 (6) ◽

pp. 1135-1151 ◽

Cited By ~ 49

Author(s):

Omar A. El Seoud

Keyword(s):

Hydrogen Bonding ◽

Hydrophobic Interactions ◽

Preferential Solvation ◽

Mixed Solvents ◽

Effect Of Temperature ◽

Binary Solvent ◽

Solvent Mixtures ◽

Dispersion Interactions ◽

Binary Solvent Mixtures ◽

Recent Developments

The effect of solvents on the spectra, absorption, or emission of substances is called solvatochromism; it is due to solute/solvent nonspecific and specific interactions, including dipole/dipole, dipole-induced/dipole, dispersion interactions, and hydrogen bonding. Thermo-solvatochromism refers to the effect of temperature on solvatochromism. The molecular structure of certain substances, polarity probes, make them particularly sensitive to these interactions; their solutions in different solvents have distinct and vivid colors. The study of both phenomena sheds light on the relative importance of the solvation mechanisms. This account focuses on recent developments in solvation in pure and binary solvent mixtures. The former has been quantitatively analyzed in terms of a multiparameter equation, modified to include the lipophilicity of the solvent. Solvation in binary solvent mixtures is complex because of the phenomenon of "preferential solvation" of the probe by one component of the mixture. A recently introduced solvent exchange model allows calculation of the composition of the probe solvation shell, relative to that of bulk medium. This model is based on the presence of the organic solvent (S), water (W), and a 1:1 hydrogen-bonded species (S-W). Solvation by the latter is more efficient than by its precursor solvents, due to probe/solvent hydrogen-bonding and hydrophobic interactions. Dimethylsulfoxide (DMSO) is an exception, because the strong DMSO/W interactions probably deactivate the latter species toward solvation. The relevance of the results obtained to kinetics of reactions is briefly discussed by addressing temperature-induced desolvation of the species involved (reactants and activated complexes) and the complex dependence of kinetic data (observed rate constants and activation parameters) in binary solvent mixtures on medium composition.

Download Full-text

Solubility modelling, solution thermodynamics and preferential solvation of hymecromone in binary solvent mixtures of N,N-dimethylformamide + methanol, ethanol or n-propanol

RSC Advances ◽

10.1039/c7ra07587a ◽

2017 ◽

Vol 7 (73) ◽

pp. 46378-46387 ◽

Cited By ~ 2

Author(s):

Xinbao Li ◽

Jiao Chen ◽

Gaoquan Chen ◽

Hongkun Zhao

Keyword(s):

Preferential Solvation ◽

Mixed Solvents ◽

Solution Thermodynamics ◽

Binary Solvent ◽

Solvent Mixtures ◽

Binary Solvent Mixtures

Solubilities of hymecromone in neat solvents of N,N-dimethylformamide (DMF), methanol, ethanol and n-propanol, and their binary mixed solvents of DMF + methanol, DMF + ethanol and DMF + n-propanol were determined.

Download Full-text