Polyaza metacyclophanes as ditopic anion receptors.

Five macrocyclic polyaza metacyclophanes L1-L5 prepared by dipode coupling of the tosylated precursors have been studied. The basicity of the ligands has been measured potentiometrically and their ability to complex halides and perchlorate has been studied in the solid state by X-ray crystallography. The results reveal that the ligands generally act as ditopic halide receptors with even the largest, L5, being too small to envelop the anion. The ligand's basicity behaviour parallels that observed for related para-analogues. Despite the ready crystallisation of fluoride, HF2-, chloride, bromide, iodide and triiodide salts in the solid state, there appears to be little affinity for halides in aqueous solution in the pH range accessible via potentiometry. The results do give a detailed insight into the role of the aryl ring in restricting the conformational flexibility of the ligands and, hence, the ability to chelate perching anions.