ON THE AQUEOUS VIBRATIONAL-SPECTRA OF ALKALI-METAL OXALATES

Fourier transform infrared attenuated total reflectance and Fourier tr ansform Raman spectra of the series of aqueous alkali metal oxalates-l ithium oxalate (Li2C2O4), sodium oxalate (Na2C2O4), potassium oxalate (K2C2O4), rubidium oxalate (Rb2C2O4), and cesium oxalate (Cs2C2O4)-are presented for the first time. Fourier transform Raman spectra of the solid oxalates are also presented for the first time. The solid and aq ueous oxalate ions are assumed to possess D-2h and D-2d symmetry, resp ectively, and the assignment of fundamental vibrational modes is made accordingly. The effect of increasing alkali metal ion concentration o n the aqueous spectra of these oxalates is also reported. Spectral cha nges are explained in terms of the ability of the respective alkali me tal cations to interact with the oxalate anion in solution. It is prop osed that these differences arise because the alkali metal cations ass ociate with the aqueous oxalate anions to varying degrees, depending u pon the nature of the cation. The extent of the binding is found to de crease down the alkali metal series (Li > Na > K > Rb > Cs). Similar r esults obtained for the tetramethylammonium cation [(CH3)(4)N+] sugges t that it is a softer cation than cesium.