Premium
Ca 2+ ‐Cl − Association in Water Revisited: the Role of Cation Hydration
Author(s) -
Salanne Mathieu,
Tazi Sami,
Vuilleumier Rodolphe,
Rotenberg Benjamin
Publication year - 2017
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201700286
Subject(s) - dissociation (chemistry) , chemistry , coordination number , molecule , potential of mean force , polarizability , coordination sphere , chemical physics , ionic bonding , ion , hydration energy , ab initio quantum chemistry methods , molecular dynamics , computational chemistry , atomic physics , crystallography , physics , organic chemistry
We investigate the dissociation of a Ca 2+ ‐Cl − pair in water using classical molecular dynamics simulations with a polarizable interaction potential, parameterized from ab initio calculations. By computing the potential of mean force as a function not only of the interionic distance but also of the coordination numbers by water molecules, we show that it is necessary to use a collective variable describing the cation hydration in order to capture the dissociation mechanism. In the contact ion pair, the Ca 2+ cation has a first coordination sphere containing 5 or 6 water molecules. The minimum free‐energy path for dissociation involves a two‐step process: First one or two additional water molecules enter the cation coordination shell, increasing the coordination number up to 7 with an almost fixed interionic distance. Then the dissociation of the ionic pair occurs at this fixed coordination number.