Hydrogen bonding Part 46. Thermodynamic and IR study of stability and structure of tetraethylammonium fluoride·2.75H2O, tetraethylammonium fluoride·2.00H2O, tetramethylammonium fluoride·3.00H2O, and tetraethylammonium fluoride·5.00H2O

Add time:08/28/2019    Source:sciencedirect.com

An equilibrium vapor pressure study of the dissociation of tetraethylammonium fluoride·2.75H2O to the dihydrate demonstrates that hydrogen bonds between H2O and F−, and between H2O and H2O are broken in this process. This conclusion is based on comparison of the observed enthalpy of dissociation with values calculated for various patterns of hydrogen bond breaking. For these calculations a value of approximately 14 kcal mol−1 for HOH⋯F− hydrogen bonds in the hydrates was estimated by comparison of crystalline state and gas phase water—halide hydrogen bond strengths. Coupled with the IR spectrum, this information leads to a proposed formulation for the water—fluoride ion structure of the dihydrate in which C2h planar (H2O·F−)2 clusters are linked by H2O molecules which bridge between H2O in one cluster and F− in an adjacent cluster. Material with the composition of tetramethylammonium trihydrate is an extraordinarily hard, crystalline substance; dissociation vapor pressure measurements suggest that only HOH⋯OH2 hydrogen bonds are broken as this material dehydrates to the dihydrate. Stoichiometric liquid tetraethylammonium pentahydrate can be nucleated to a crystalline solid for which diffraction studies should be possible.

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