Structural, dynamical, and transport properties of the hydrated halides: How do At- bulk properties compare with those of the other halides, from F- to I-?

摘要

The properties of halides from the lightest, fluoride (F-), to the heaviest, astatide (At-), have been studied in water using a polarizable force-field approach based on molecular dynamics (MD) simulations at the 10 ns scale. The selected force-field explicitly treats the cooperativity within the halide-water hydrogen bond networks. The force-field parameters have been adjusted to ab initio data on anion/water clusters computed at the relativistic Moller-Plesset second-order perturbation theory level of theory. The anion static polarizabilities of the two heaviest halides, I- and At-, were computed in the gas phase using large and diffuse atomic basis sets, and taking into account both electron correlation and spin-orbit coupling within a four-component framework. Our MD simulation results show the solvation properties of I- and At- in aqueous phase to be very close. For instance, their first hydration shells are structured and encompass 9.2 and 9.1 water molecules at about 3.70 +/- 0.05 angstrom, respectively. These values have to be compared to the F-, Cl-, and Brones, i.e., 6.3, 8.4, and 9.0 water molecules at 2.74, 3.38, and 3.55 angstrom, respectively. Moreover our computations predict the solvation free energy of At- in liquid water at ambient conditions to be 68 kcal mol(-1), a value also close the I- one, about 70 kcal mol(-1). In all, our simulation results for I- are in excellent agreement with the latest neutron-and X-ray diffraction studies. Those for the At- ion are predictive, as no theoretical or experimental data are available to date. (C) 2016 AIP Publishing LLC.