Are all short O-H...O contacts hydrogen bonds? A quantitative look at the nature of O-H...O intermolecular hydrogen bonds

摘要

The hydrogen-bonded nature of short O-H~-...O contacts has been investigated by comparing the components of the intermolecular interaction energy in the O-H...O contacts present in the H_2O...H_2O, H_2O...(OH~-) and (OH~-)...(OH~-) model dimers, and then in the more chemically significant H_2C_2O_4...H_2C_2O_4, H_2C_2O_4...(HC_2O_4~_) and (HC_2O_4~-)...(HC_2O_4~-) dimers, oriented as in the crystal of KHC_2O_4. The energy components were computed by means of intermolecular perturbation theory (IMPT). The inter-anion contacts are found to be repulsive due to the dominant repulsive character of the electrostatic term the strongest terms in all dimers analyzed in this work. The same term is attractive in the neutral O-H...O and even stronger in the charge assisted O-H...O~- contacts, whose hydrogen-bonded character is well known.