engleski

Hydrogen bonding of hydronium and hydroxide ions the solid state: a contribution to the theory of the proton transfer

Geometry, coordination and hydrogen bonding of hydronium and hydroxide ions were studied using data extracted from the Cambridge Structural Database. The average Ohyd-H...A and D-H...Ohyd distances and bond angles match those obtained by spectroscopical measurements and theoretically calculated ones. The hydronium ion is exclusively a triple proton donor and does not accept hydrogen bonds, whereas the hydroxide ion is a poor donor. However, it can accept three or four hydrogen bonds. The coordination of these ions in solid state is similar to that in aqueous solutions. An existence of triple solvated H3O+(H2O)3 (also called the Eigen-ion) and the proton-sharing dimer H5O2+ (Zundel-ion), and their role in the proton transfer have been known for a long time. Inspection of the Cambridge Structural Database reveals quite a number of structures with these complex ions, even a controversial solvated Zundel-ion, H5O2+(H2O)4. The analysis of these structures shows typical coordination of oxygen in H3O+ and OH- given in the figure presented ; structures observed are supported by spectroscopic evidences and theoretical calculations. Our analysis of structures containing the OH- species is in disagreement to the previously accepted mechanism on proton transfer reactions. However, the most recent paper by R. Ludwig [Angew. Chem., Int. Ed., 42 (2003) 258-260] explains the mechanism of proton transfer that perfectly matches the structural data extracted from the Cambridge Structural Database.

hydronium; hydroxide; hydrogen bond; proton transfer; CSD

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