Solution structures of alkali metal sym-(R)dibenzo-14-crown-4-oxyacetates

Abstract

Solution structures of alkali metal sym-(R)dibenzo-14-crown-4-oxyacetates with R = C₁₀H₂₁ (L1X) and R = H (L2X) have been probed by ¹H and ¹³C NMR spectroscopy. Analysis of the diastereotopic nonequivalence changes, Δδ_AB, especially for atoms remote from the sidearm attachment site, provides insight into the preferred orientation of the sidearm in solution. Cooperative metal ion complexation by the crown ether portion of the ligand and the sidearm is evident for all of the salts in CDCl₃. Solvent dependence of the structure is noted for the L2X salts. In DMSO-d₆ and D₂O, the degree of interaction between the cation and the crown ether moiety varies with the identity of the alkali metal cation. Three different metal ion coordination arrangements are deduced for L2Li in CDCl₃, DMSO-d₆, and D₂O. The Li⁺ is complexed by both the polyether unit and the carboxylate group of the sidearm in CDCl₃. In D₂O, the Li⁺ is coordinated to the polyether unit and through one or more water molecules to the carboxylate group of the sidearm. In DMSO-d₆, the Li⁺ does not associate with the crown ether unit.