The Solvation of Na- in the Sodide Solution, LiNa·10MeNH2

Alkalides, the alkali metals in their -1 oxidation state, represent some of the largest and most polarisable atomic species in condensed phases. This study determines the solvation environment around the sodide anion, Na-, in a system of co-solvated Li+. We present isotopically varied total neutron scattering experiments alongside empirical potential structure refinement and ab initio molecular dynamics simulations for the alkali-alkalide system, LiNa·10MeNH2. Both local coordination modes and the intermediate range liquid structure are determined which demonstrate that distinct structural correlations between cation and anion in the liquid phase extend beyond 8.6 A. Indeed, the local solvation around Na- is surprisingly well-defined with strong solvent orientational order. The ion paired Li(MeNH2)4+·Na- species appears to be the dominant alkali-alkalide environment in these liquids, whereby Li+ and Na- share a MeNH2 molecule through the amine group in their primary solvation spheres.