In Situ IR Spectrum of 12-Tungstophosphoric Acid Hexahydrate with Planar H5O2+

Abstract

The in situ IR spectra of H3PW12O40·nH2O (n = 0−6.2) in the range 4000−1100 cm-1 were measured, and that of H3PW12O40·6H2O (i.e., [H5O2+]3[PW12O403-]) with planar H5O2+ was investigated. The spectrum showed a broad continuum below 3700 cm-1, with peaks at 3420, 2720, 2030, and 1640 cm-1, and was deconvoluted into five bands at 3420, 2720, 2030, 1780, and 1640 cm-1. These bands, except for 2030 cm-1, were shifted by the deuteration and are assigned to the vibration modes of the planar structure. The vibration modes of the simplified model H5O2+·4OW(OH)4(OH2) were calculated by the quantum chemical method with the B3LYP/6-31+G* level: The 3420 cm-1 band is assigned to the overlap of the ν(OwHw) of the ν7 mode with the A component of Fermi resonance among ν8 (ν(OwHw)), ν3 (δ(OwHw2)), and ν11 (γ(OwHw2)) with the same species, of which the first mode is broadened by the anharmonic coupling of OwHw and OaHw vibrations. The bands at 2720 and 1780 cm-1 are probably assigned to separated BC components of the Fermi resonance. The 2030 cm-1 band is assigned to the overlap of overtone and combination vibrations of the skeletal vibration modes of νas(PO), νas(WO), and νas(WOcW) in the same way to that of Cs3PW12O40·0H2O: Cs3PW12O40·0H2O showed three bands at 2159, 2074, and 1988 cm-1, and the band positions were not changed by the deuteration and agreed with those of overtone and combination vibrations of skeletal vibration modes of νas(PO), νas(WO), and νas(WOcW). The 1640 cm-1 band is assigned to the HwOwHw bending vibration mode.