Existence of oriented ion-hydroxide clusters in concentrated aqueous NaCl solution at pH 13

We probe the local electronic structure at solvated Na⁺ ions in 1 M aqueous NaCl solutions as a function of pH. A dramatic change in the Na ⁺ white line intensity in X-ray absorption is observed for high pH values, reflecting a changing local electronic structure at the Na⁺ ions when OH^- is present. Given the relative abundance of sodium and hydroxide ions, we conclude that one OH^- affects at least 2.4 ± 0.6 Na⁺ ions in an electronically noticeable way at pH 13. From the experimental data we infer that spatially extended clusters or networks incorporating Na⁺ and OH^- can exist in the electrolyte solution. The experimental data are complemented by molecular dynamics simulations, which indicate the presence of structured clusters incorporating Na⁺, OH^-, and solvent molecules.