Molecular dynamics simulations of Ca2+[sbnd]Cl− ion pair in polar mixtures of acetone and water: Solvation and dynamical studies

Abstract

The potentials of mean force (PMFs) have been used to assess the relative stabilities of contact ion pairs (CIPs), solvent assisted ion pairs (SAIPs) and solvent separated ion pairs (SSIPs) in acetone-water mixtures containing a calcium chloride ion pair. In the case of Cl−in (the second Cl− ion is placed within the solvation shell of Ca2+ ion), the CIPs are more stable than SAIPs for low mole fractions of acetone (xacetone) whereas the SAIPs are more stable than the CIPs for large values of xacetone. In the case of Cl−out (the second Cl− ion is placed outside the solvation shell of Ca2+ ion), the SAIPs are marginally more stable than CIPs in neat water and for low xacetone. However, CIPs become more stable than SAIPs with increase in xacetone. The Ca2+Cl− ion pair is preferentially solvated by water in all the mixtures.