A Comprehensive Picture of the Structures, Energies, and Bonding in [SO₄(H₂O)]^2-, n = 1-6

Two stochastic methods in conjunction with ab initio computations were used to explore the potential energy surfaces for the microsolvation of SO₄^2- with up to six explicit water molecules. At least three water molecules are needed to stabilize the Coulomb repulsion that prevents the existence of isolated SO₄^2-. The formal charge in SO₄^2- is strong enough to induce water dissociation and subsequent microsolvation of the resulting HSO₄^-, OH^- ionic pair. Hydrogen bonds characterized as having complex contributions from covalency and from ionicity are at play stabilizing [SO₄(H₂O)]^2- clusters. Ionicity and covalency act concomitantly rather than opposedly to strengthen both intermolecular interactions and the resulting O-H bond in HSO₄^- after proton abstraction.