The structure of the (2S,6S)-2,6-dimethyl-1,4,7,10,13,16-hexaoxacyclooctadecane complex with the potassium nitrate ion pair (C14H28KNO9) has been studied in chloroform solution and in the solid state by FTIR spectroscopy. The solid-state structure has also been determined by X-ray diffraction. The monoclinic crystals conform to space group P21 with a = 12.486 (5) Å, b = 8.515 (3) Å, c = 18.587 (9) Å, β = 91.97 (4)°, and Z = 4. The close correspondence of the solution and solid-state infrared spectra indicates that the structure is similar in both phases. The solution spectrum suggests that the ion pairs are externally complexed by the crown ether. which has a conformation with approximate D3d symmetry (ignoring the methyl substituents), similar to that observed for K+ complexes of unsubstituted 18-crown-6, and that the nitrate is coordinated to the K+ in a bidentate manner. © 1986, American Chemical Society. All rights reserved.