THEORETICAL-STUDIES OF THE EFFECTS OF METAL-IONS ON THE HYDROGEN-BONDING OF POTASSIUM HYDROGEN DIACETATE

Studies on the proton-transfer potential energy curves for the potassi um hydrogen diacetate system with a short asymmetric hydrogen bond (O ... O, 2.476 Angstrom) were carried out by means of ab initio molecula r orbital theory and density functional theory. The ab initio theory a t the MP2/6-31G level predicts an asymmetric single-well potential en ergy function with an O-H distance of 0.998 Angstrom. The asymmetric p roperty of the hydrogen bond is ascribed to the asymmetric distributio n of a crystal field constructed by neighboring potassium ions. It is found that the static electric field generated by modeling point charg es cannot substitute the role of metal ions in the crystal environment . The computation results show that the hydrogen-bond proton in the fr ee dimer [H(CH3COO)(2)](-) would oscillate between the carboxyl and ca rboxylate groups, since a relatively flat potential well is found for the H bond. In addition, the performance of both the local approximati on DFT SVWN method and the DFT B3P86 method with nonlocal correction i s tested in this study, and the latter is found to be comparable with the ab initio calculation at the MP2/6-31G level.