Hydrogen bonding. Part 82. Thermodynamic and infrared study of dimethonium and pentamethonium halide dihydrates

2003 
Abstract We have carried out equilibrium dissociation vapor pressure measurements on dimethonium bromide dihydrate and pentamethonium chloride and bromide dihydrates. None of these salts forms a monohydrate. Surprisingly the thermodynamic parameters for the two pentamethonium hydrates are nearly identical, although the properties of these hydrates are quite different. This is explained by a larger negative differential lattice enthalpy for the chloride dihydrate dissociation, which lowers the observed enthalpy of H 2 O removal, and greater stabilization of saturated solution by chloride ion which makes the chloride dihydrate deliquescent while the bromide dihydrate is efflorescent. Infrared comparison suggests that tetramethonium chloride dihydrate and pentamethonium chloride and bromide dihydrates have the ladder type halide–water structure determined by X-ray analysis in tetramethonium bromide dihydrate.
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