Polarized IR and Raman spectra of Na 5H 3(SeO 4) 4·2H 2O single crystals

Abstract

Polarized infrared (IR) and Raman spectra for the single crystal of Na 5H 3(SeO 4) 4·2H 2O were measured at room temperature. The stretching vibration of the strong (2.476(4) Å) centrosymmetric hydrogen bond gives rise to the strong and broad IR absorption extending between 2500 and 500 cm −1 with maxima at ca. 2300(vw), 1350 and 700 cm −1. Its out-of-plane bending vibration appears at ca. 1415 cm −1 and it is observed only in the polarized IR spectra. Two remaining hydrogen bonds (2.592(4) Å) give rise to an ABC-type feature. The A and B bands appear in IR and Raman spectra, whereas the C band is seen only in the IR spectra. Additionally, the powder IR spectra at low temperature were measured. Investigation by differential scanning calorimetry reveals a continuous phase transition at ca. 175 K. The polarized spectra clearly prove the centrosymmetric structure (space group P 1 ̄ ) at room temperature. The loss of the center of inversion below 175 K clearly follows from the powder IR spectra.