A molecular entity comprising a monocyclic ligand assembly that contains three or more binding sites held together by covalent bonds and capable of binding a guest in a central (or nearly central) position. The adducts formed are sometimes known as 'coronates'. The best known members of this group are macrocyclic polyethers, such as '18-crown-6', containing several repeating units $\ce{–CR2–CR2O–}$ (where $\ce{R}$ is most commonly $\ce{H}$), and known as crown ethers.