Infrared studies of water in crystalline hydrates: NaClO4•H2O, LiClO4•3H2O, and Ba(ClO4)2•3H2O

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Abstract
Infrared spectra of undeuterated and partially deuterated NaclO4•H2O, LiClO4•3H2O, and Ba(ClO4)2•3H2O were examined. Crystallographic data point to a weak hydrogen bond between water molecules and the perchlorate ions in LiClO•3H2O. This is confirmed by the high HDO stretching frequencies for this compound. The nearly identical HDO stretching frequencies in LiClO4•3H2O, NaClO4•H2O, Ba(ClO4)2•3H2O, and in aqueous solutions of these salts show that similar weak hydrogen bonds occur in all three hydrates and in solution. The hydrogen bond energy is of the order of 2 kcal/mole. In all three compounds the water molecules are symmetric at room temperature. At −165° the water molecules become highly distorted in the sodium compound, slightly distorted in the barium compound, and remain undistorted in the lithium compound. Very narrow OD stretching bands are observed, showing that the hydrogen atom positions are ordered in all three hydrates.
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