Binding and selectivity aspects of an expanded azamacrocycle for anions.

An expanded azamacrocycle L, containing four secondary and two tertiary amines was synthesized, and its binding ability towards chloride, bromide, iodide, sulfate, nitrate and perchlorate were determined by (1)H NMR titrations in D(2)O at pH 1.7. The results suggest that the ligand is capable of forming a complex with each of the anions examined, showing the selectivity for sulfate in water. X-ray diffraction analysis of the perchlorate complex of L suggests that the ligand is tetraprotonated and is involved in interacting anions from both sides forming a ditopic complex with strong NH···O bonds. In the packing diagram, the macrocycles and external perchlorates are alternatively linked though hydrogen bonding to form a 1D chain.