TY - JOUR
T1 - Ab initio molecular dynamics studies of ionic dissolution and precipitation of sodium chloride and silver chloride in water clusters, NaCl(H2O)n and AgCl(H2O)n, n = 6, 10, and 14
AU - Siu, Chi Kit
AU - Fox-Beyer, Brigitte S.
AU - Beyer, Martin K.
AU - Bondybey, Vladimir E.
PY - 2006/8/16
Y1 - 2006/8/16
N2 - An ab initio molecular dynamics method was used to compare the ionic dissolution of soluble sodium chloride (NaCl) in water clusters with the highly insoluble silver chloride (AgCl). The investigations focused on the solvation structures, dynamics, and energetics of the contact ion pair (CIP) and of the solvent-separated ion pair (SSIP) in NaCl(H2O)n and AgCl(H2O)n with cluster sizes of n = 6, 10 and 14. We found that the minimum cluster size required to stabilize the SSIP configuration in NaCl(H2O)n is temperature-dependent. For n = 6, both configurations are present as two distinct local minima on the free-energy profile at 100 K, whereas SSIP is unstable at 300 K. Both configurations, separated by a low barrier (< 10 kJ mol-1), are identifiable on the free energy profiles of NaCl(H2O)n for n = 10 and 14 at 300 K, with the Na+/Cl- pairs being internally solvated in the water cluster and the SSIP configuration being slightly higher in energy (< 5 kJ mol-1). In agreement with the low bulk solubility of AgCl, no SSIP minimum is observed on the free-energy profiles of finite AgCl(H2O)n clusters. The AgCl interaction is more covalent in nature, and is less affected by the water solvent. Unlike NaCl, AgCl is mainly solvated on the surface in finite water clusters, and ionic dissolution requires a significant reorganization of the solvent structure.
AB - An ab initio molecular dynamics method was used to compare the ionic dissolution of soluble sodium chloride (NaCl) in water clusters with the highly insoluble silver chloride (AgCl). The investigations focused on the solvation structures, dynamics, and energetics of the contact ion pair (CIP) and of the solvent-separated ion pair (SSIP) in NaCl(H2O)n and AgCl(H2O)n with cluster sizes of n = 6, 10 and 14. We found that the minimum cluster size required to stabilize the SSIP configuration in NaCl(H2O)n is temperature-dependent. For n = 6, both configurations are present as two distinct local minima on the free-energy profile at 100 K, whereas SSIP is unstable at 300 K. Both configurations, separated by a low barrier (< 10 kJ mol-1), are identifiable on the free energy profiles of NaCl(H2O)n for n = 10 and 14 at 300 K, with the Na+/Cl- pairs being internally solvated in the water cluster and the SSIP configuration being slightly higher in energy (< 5 kJ mol-1). In agreement with the low bulk solubility of AgCl, no SSIP minimum is observed on the free-energy profiles of finite AgCl(H2O)n clusters. The AgCl interaction is more covalent in nature, and is less affected by the water solvent. Unlike NaCl, AgCl is mainly solvated on the surface in finite water clusters, and ionic dissolution requires a significant reorganization of the solvent structure.
KW - Ab initio calculations
KW - Hydrogen bonds
KW - Ionic dissolution
KW - Molecular dynamics
KW - Water clusters
UR - http://www.scopus.com/inward/record.url?scp=33748369493&partnerID=8YFLogxK
U2 - 10.1002/chem.200501569
DO - 10.1002/chem.200501569
M3 - Article
AN - SCOPUS:33748369493
SN - 0947-6539
VL - 12
SP - 6382
EP - 6392
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
IS - 24
ER -