Structures of 18-crown-6/Cs+ complexes in aqueous solutions by wide angle X-ray scattering and density functional theory

•The oxygen atoms of 18-crown-6 and the hydrogen atoms of water molecule form strong hydrogen bonds in aqueous solution.•Cs+ is located directly above the 18-crown-6 ring plane, about 1.15 Å from the centroid of 18-crown-6.•The higher the concentration of CsCl, the lower the complexation percentage of 18-crown-6 to Cs+.•Cs+ complexing with 18-crown-6 mainly hydrates with four water molecules.