A new approach to the structure of concentrated aqueous electrolyte solutions using pulsed NMR methods

It is shown that selective measurements of the magnetic dipole—dipole interactions between specific pairs of nuclear spins in glasses of concentrated aqueous electrolytes can provide detailed structural information of relevance to the liquid. The validity of the approach is demonstrated by selective measurements of the inter- and intra-molecular (H₂O) proton—proton interactions in LiCl and LiBr solutions at 100 K. For LiCl,4H₂O, these measurements are consistent with a short range (≈0.8 nm) distorted sodium chloride structure with Cl^? and Li(H₂O)⁺₄ as basic units: each Cl^? ion is octahedrally coordinated to six OH bonds. For LiCl,RH₂O solutions in the composition range 4 <R < 10, the excess H₂O is packed interstitially at the interfaces between clusters of LiCl,4H₂O. This structure is consistent with various properties of the solution at room temperature. LiBr solutions have similar structures.