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Free energies of transfer of ZnCl2py2 and of related tetrahedral complexes from pyridine to other solvent media

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The standard Gibbs free energies of transfer from pyridine to pyridine+diluent mixtures are reported for the ZnCl2py2 complex at 25°C. Their variations with varying mixed solvent composition agree with those expected for regular solutions when the diluents are polar and basic while marked deviations are observed for non-polar, inert diluents. For protic diluents the free energies of transfer of ZnCl2py2 exhibit maxima, indicating specific interaction of the complex with both solvent components in these systems. The free energies of transfer of ZnCl2py2 to the pure diluents plotted vs. the solubility parameter of the latter reveal separate Hildebrand correlations for inert and for basic solvents, with the free energies of transfer of the complex to the protic solvents deviating from both. Weak specific interactions of ZnCl2py2 with the basic solvents and stronger interactions with the protic solvents are inferred and further examined in the light of the free energy of transfer data for the related tetrahedral complexes ZnBr2py2, ZnCl2(α-pic)2, CoCl2(α-pic)2, and ZnBr2(α-pic)2.1H-NMR spectrum of the pyridine ligands of ZnCl2py2 confirm their involvement in weak hydrogen-bond formation with the basic solvents, while the downfield shift observed for the solvent chloroform is consistent with hydrogen bond formation of the latter with the chloro-ligands.

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Libuś, W., Chachulska, K. & Stangret, J. Free energies of transfer of ZnCl2py2 and of related tetrahedral complexes from pyridine to other solvent media. J Solution Chem 12, 529–546 (1983). https://doi.org/10.1007/BF01150846

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Key words

  • Solubility
  • free energies of transfer
  • outer sphere interactions
  • transition metal complexes
  • pyridine
  • diluents
  • zinc chloride and bromide