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

Two stochastic methods in conjunction with ab initio optimizations and characterizations at high levels of theory were used to explore the potential energy surfaces (PES) 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 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})n]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.