Abstract
Vibrational studies, using IR and Raman techniques, of potassium oxalate in H2O and D2O established the oxalate ion symmetry to be or D2. D2 symmetry would require the accidental degeneracy of two v(C-O) vibrations necessarily degenerate under D2d. Comparison of ammonium oxalate, ammonium chloride and potassium oxalate aqueous solutions established that the 1460 IR band was due to the NH+ ion, but the Raman scattering in this region was due to the oxalate ion. No explanation could be found for the 1455 Raman band. A choice between Cs or C1 symmetry of the acid oxalate ion in solution could not be made as out-of-plane vibrations were not observed. The symmetry of oxalic acid in H2O and D2O and some polar solvents was shown to be lowered at least to and possibly to MINDO/3 calculations supported non-planar configurations for the oxalate ion, acid oxalate ion and oxalic acid. The solvent (OH) Raman bands of aqueous solutions were shown to be suitable for intensity calibration of potassium oxalate and potassium hydrogen oxalate solutions. This calibration method and the scattering due to the v(C-C) of the hydrogen oxalate ion, enabled a spectroscopic estimation of the 1st dissociation of oxalic acid. Comparison of nine oxalate powders enabled assignment of all the oxalate ion fundamental vibrations. Raman spectra of calcium oxalate and calcium oxalate monohydrate are presented for the first time. The space group Pbam is suggested for the anhydrous potassium oxalate. The IR and Raman spectra of four acid oxalates are compared with respect to the strong, but subtly different, hydrogen bonding of these compounds. Single crystal Raman studies of potassium oxalate monohydrate, potassium hydrogen oxalate and sodium hydrogen oxalate monohydrate are presented for the first time. The potassium hydrogen oxalate and sodium hydrogen oxalate monohydrate results, spotlight the highly oriented effects associated with hydrogen bonding.