Solvation of Ag+ ions in some nitriles; A fourier transform Raman spectroscopic study

Silver nitrate solutions in four nitriles (acetonitrile, benzonitrile, ethylcyanoacetate and acrylonitrile), in a range of concentration between 37 and 3 molecules of solvent per mole of solute, have been studied using Fourier transform Raman spectroscopy. The new band in the nu(CN) region arising from the coordinated species Ag-+... (nitrile)(n) has been analysed in detail by means of deconvolution and band-fitting procedures. The wavenumber shift of the new band (about 19 cm(-1)) seems to be independent of the nitrile and in all the cases studied the molar scattering factors are strongly increased due to the effect of the cation. Weak solvation spheres around the silver ion are identified spectroscopically. An effect of the weak solvation is the lack of a definite and constant solvation number for the metal ion, and only numbers at infinite dilution can be obtained. These solvation numbers are two for benzonitrile and three for acrylonitrile, ethylcyanoacetate and acetonitrile. However, the solvation number obtained for acetonitrile in this work is important due to the effect of the Fermi resonance in the stretching bands used for calculations; because of this, the literature work for complexes in acetonitrile solution should be critically revised.