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A theoretical investigation on the structures of (NH 3 )·(H 2 SO 4 )·(H 2 O) 0‐14 clusters
Author(s) -
Xu ZhenZhen,
Fan HongJun
Publication year - 2019
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.25850
Subject(s) - protonation , chemistry , crystallography , ion , ternary operation , cluster (spacecraft) , proton , gibbs free energy , thermodynamics , physics , organic chemistry , quantum mechanics , computer science , programming language
Ternary clusters (NH 3 )·(H 2 SO 4 )·(H 2 O) n have been widely studied. However, the structures and binding energies of relatively larger cluster ( n > 6) remain unclear, which hinders the study of other interesting properties. Ternary clusters of (NH 3 )·(H 2 SO 4 )·(H 2 O) n , n = 0‐14, were investigated using MD simulations and quantum chemical calculations. For n = 1, a proton was transferred from H 2 SO 4 to NH 3 . For n = 10, both protons of H 2 SO 4 were transferred to NH 3 and H 2 O, respectively. The NH 4 + and HSO 4 − formed a contact ion‐pair [NH 4 + ‐HSO 4 − ] for n = 1‐6 and a solvent separated ion‐pair [NH 4 + ‐H 2 O‐HSO 4 − ] for n = 7‐9. Therefore, we observed two obvious transitions from neutral to single protonation (from H 2 SO 4 to NH 3 ) to double protonation (from H 2 SO 4 to NH 3 and H 2 O) with increasing n. In general, the structures with single protonation and solvated ion‐pair were higher in entropy than those with double protonation and contact ion‐pair of single protonation and were thus preferred at higher temperature. As a result, the inversion between single and double protonated clusters was postponed until n = 12 according to the average binding Gibbs free energy at the normal condition. These results can serve as a good start point for studies of the other properties of these clusters and as a model for the solvation of the [H 2 SO 4 ‐NH 3 ] complex in bulk water.