External Phosphate Binding Triggered Formation of Coordination Bridged Dimer of Macrocyclic Trinuclear Complex

Macrocyclic complexes with spatially-arranged coordination sites have the potential to create unique supramolecular systems that combine the precise switching of self-assembled structures with the coordinative recognition of specific molecules. We now report a macrocyclic trinuclear Zn complex that undergoes a unique dimerization by molecular binding from the outside. The multinuclear complex was synthesized from a trispap ligand, a designed macrocyclic trimer of an N,N,O-type tridentate chelating unit pap. This macrocyclic ligand is capable of fixing the metal centers and retaining their exchangeable coordination sites. The macrocyclic trimer reacts with zinc acetate to form the trinuclear complex, in which the coordination sites of the three zinc atoms are aligned perpendicular to the macrocyclic plane and capped with the acetates. Subsequently, phosphate anion, PO₄ ^3-, coordinates from one side of the macrocycle in a tripodal manner. This phosphate binding produced an electrically-neutral complex moiety with available coordination sites on the other side of the macrocycle which leads to the formation of the coordination-bridged dimer.