Fourier-transform Raman Spectroscopic Study of the Association Between Co(II) Ions and Acrylonitrile in Aqueous Solution

Abstract

The association between acrylo nitrile (propenenitrile) and cobalt ions in aqueous solution was investigated by Fourier-transform Raman spectroscopy. The new nu(C=N) band at 2268 cm(-1) attributable to cation-associated acrylonitrile, displaced by +32 cm(-1) From the wavenumber corresponding to the solvent (water/acrylonitrile mixture). was quantitatively studied in a range of concentrations of 2.452-4.001 M for cobalt [as cobalt(II) nitrate] and 2.241-2.584 M for acrylonitrile. The proposed equilibrium involves the interchange of one molecule of water and one molecule of acrylonitrile in the first solvation sphere of the cation, namely: [Co(H2O)(6)](2+) + ACN double left right arrow [Co(H2O)(5)ACN](2+) + H2O. The association constant calculated at infinite dilution was 0.315 +/- 0.024 l/mol at 25 degrees C, greater than that corresponding to the same equilibrium with nickel ions (0.221 +/- 0.0141/mol). This difference is explained by the higher hydration energy of the nickel ion.