Theoretical Studies of the Effects of Metal Ions on the Hydrogen Bonding of Potassium Hydrogen Diacetate

Abstract

Studies on the proton-transfer potential energy curves for the potassium hydrogen diacetate system with a short asymmetric hydrogen bond (O‚‚‚O, 2.476 Å) were carried out by means of ab initio molecular orbital theory and density functional theory. The ab initio theory at the MP2/6-31G* level predicts an asymmetric single-well potential energy function with an O-H distance of 0.998 Å. The asymmetric property of the hydrogen bond is ascribed to the asymmetric distribution of a crystal field constructed by neighboring potassium ions. It is found that the static electric field generated by modeling point charges cannot substitute the role of metal ions in the crystal environment. The computation results show that the hydrogen-bond proton in the free dimer [H(CH 3 COO) 2 ] -would oscillate between the carboxyl and carboxylate groups, since a relatively flat potential well is found for the H bond. In addition, the performance of both the local approximation DFT SVWN method and the DFT B3P86 method with nonlocal correction is tested in this study, and the latter is found to be comparable with the ab initio calculation at the MP2/6-31G* level.

QTAIM Study of Strong H-Bonds with the O−H···A Fragment (A = O, N) in Three-Dimensional Periodical Crystals

“…The strong intermolecular H-bond in 2,3,5,6-pyrazinetetracarboxylic acid dihydrate crystals is broken in the gas phase. Charged H-bonded dimers, e.g., (HCO 3 ) 2 2- in KHCO 3 , can indeed be associated with the gas-phase dimers under some limitations, ,, which however make problematic a direct comparison with their molecular crystal counterparts. Zwitterions (such as the molecular crystals of l -glutamic acid and l -tyrosine) are usually nonstable in the gas phase.…”