title: Like-charge ion pairs of hydronium and hydroxide in aqueous solution?
abstract: The like-charge ion pairings of hydronium and hydroxide were investigated using both ab initio cluster calculations and QM/MM-MD aqueous simulations. While only a two-water-bridged H3O(+)(H2O)2H3O(+) is found in hydronium cluster calculations, three clusters of HO(-)(H2O)2HO(-), HO(-)(H2O)3HO(-) and HO(-)(H2O)4HO(-) are stable dihydroxide aggregates. In addition, an interesting yet very stable parallelogram structure of [O-H···H-O](2-) without any bridging water was also discovered using QM/MM-MD simulations. According to our analysis, its unique structure reduces the electrostatic repulsion and allows stable coordination with solvents at the same time. In conclusion, hydroxide can form stronger like-ion pairs than hydronium in aqueous solution mostly due to its versatile coordination ability with solvents.
authors.affiliation: Department of Chemistry and Green-Nano Materials Research Center, College of Natural Sciences, Kyungpook National University, Sangyeok, Bukgu, Daegu 702-701, South Korea. cchoi@knu.ac.kr.
authors.forename: Manik Kumer
authors.initials: MK
authors.lastname: Ghosh
authors.forename: Tae Hoon
authors.initials: TH
authors.lastname: Choi
authors.forename: Cheol Ho
authors.initials: CH
authors.lastname: Choi