Proton control of the conformation of a macrobicyclic ligand

Crystal structure determinations for two salts show that the structures of metal-free cyclidene ligand salts are critically dependent on the degree of protonation, showing either a structure close to those found for corresponding metal complexes, or an entirely different conformation stabilised by N–H ⋯ Cl hydrogen bonds in an ‘ion quartet’, a cluster formed by the [LH5]5+ ion interacting with 3 Cl– ions.