Solvation of Na2 in the Sodide Solution, LiNȧ10MeNH2

Abstract

Alkalides, the alkali metals in their -1 oxidation state, represent some of the largest and most polarizable atomic species in condensed phases. This study determines the solvation environment around the sodide anion, Na2, 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, LiNȧ10MeNH2. 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 Na2 is surprisingly well defined with strong solvent orientational order, in contrast to the classical description of alkalide anions not interacting with their environment. The ion-paired Li(MeNH2)4+Na2 species appears to be the dominant alkali-alkalide environment in these liquids, whereby Li2 and Na2 share a MeNH2 molecule through the amine group in their primary solvation spheres.