H2O interaction with solid H3PW12O40: An IR study

The interactions of H2O with solid H3PW12O40 have been studied by TR spectr oscopy, and the results are compared with those obtained for H2O interactin g with other acidic or superacidic solid systems (acidic zeolites and the p erfluorosulfonic membrane H-Nafion). In fully dehydrated HPW a heterogeneou s family of hydroxyls is evidenced which, by interaction with water, leads to the formation of neutral 1:1 H-bond adducts. At higher water pressures, the formation of symmetric diaquahydrogen ions, and of clusters of protonat ed water is also observed. The H2O...H+...OH2 symmetrical adducts are chara cterized by a very broad absorption in the 1400-700 cm(-1) range, which, by comparison with theoretical studies on gas-phase dusters and with experime ntal results obtained on H5O2+ salts, is assigned to the vO...H+...O mode. On the contrary, the IR spectra of fully dehydrated HPW do not show any abs orption in this range.