Structure of Ion Pair Receptor Combined with Li⁺Cl^– in Concentrated Acetonitrile Solutions Studied by Neutron Diffraction with ⁶Li/⁷Li Isotopic Substitution Method

Neutron diffraction measurements with the ⁶Li/⁷Li isotopic substitution method have been carried out to obtain direct structural information on the ion pair receptor, C₁₆H₃₄O₄N₄, combined with Li⁺Cl^- ion pair in concentrated acetonitrile solutions. The difference interference term, Δ_Li(<i>Q</i>), was derived from the difference between the total interference term observed for ⁶Li- and ⁷Li-enriched sample solutions. Structural parameters concerning the Li⁺Cl^--receptor complex were determined by the least-squares fitting analysis of the observed Δ_Li(<i>Q</i>). It has been found that the Li⁺ forms bonds with two ether-oxygen atoms of the receptor molecule with the distances of <i>r</i>(Li⁺···O) = 1.88(4) and 1.9(1) Å and simultaneously one Cl^- and one N atom of a CD₃CN molecule in concentrated 12 and 7 mol % LiCl-receptor solutions in CD₃CN, respectively.