
%0 Journal Article
%A Sipos, Pal 
%A Bolden, Lee 
%A Hefter, Glenn 
%A May, Peter M. 
%T Raman Spectroscopic Study of Ion Pairing of Alkali Metal Ions with Carbonate and Sulfate in Aqueous Solutions
%J Australian Journal of Chemistry
%D 2001/04/05
%V 53
%N 10
%P 887-890
%K Contact ion pairs; sodium ion; potassium ion; caesium ion; carbonate; sulfate; Raman spectroscopy., Na+ &#60;K+ &#60; Cs+
%R https://doi.org/10.1071/CH00126
%U https://www.publish.csiro.au/paper/CH00126 
%X Raman spectra of carbonate and sulfate ions were recorded in aqueous solutions in the presence of large excesses of M&#8242;X (M&#8242;+ = Na+, K+ or Cs+; X&#8211; = OH&#8211; or Cl&#8211;) at 25&#176;C. The positions of the v1(A1&#8242;) symmetric stretching vibrations for both CO32&#8211; (at ~1060 cm&#8211;1) and SO42&#8211; (at ~980 cm&#8211;1) shift, by up to 10 cm&#8211;1, to lower frequencies and broaden (by up to 25%) with increasing concentrations of M&#8242;X. The shifts are slightly smaller for SO42&#8211; than for CO32&#8211; and also differ somewhat between M&#8242;OH and M&#8242;Cl solutions. The changes in the peak positions, which are indicative of contact ion pairing, show a clear dependence on the nature of the cation. However, the observed order, Na+ &#60; K+ &#60; Cs+, is directly opposite to the magnitudes of the (overall) ion-pairing constants. This anomaly is thought to be due to decreased hydration of Cs+ cf. Na+ in these highly concentrated, water-deficient solutions. Some implications of this for understanding ionic interactions in concentrated electrolyte solutions are suggested. 
