Formation of Heteropolynuclear Lanthanide Complexes Using Macrocyclic Phosphonated Cyclam-Based Ligands.

Ligands and , respectively based on a cyclam and a cross-bridged cyclam scaffold functionalized at N1 and N8 by 6-phosphonic-2-methylene pyridyl groups, are described. While complexation of lanthanide (Ln) cations with was not possible, a family of complexes has been prepared with , of the general formulae [LnH]Cl (Ln = Lu, Tb, Yb) or [LnH] (Ln = Eu). The solution, structural, potentiometric, and photophysical data for these novel ligands and their complexes have been investigated, including a solid-state study by X-ray diffraction (, , and [EuH]), H NMR complexation investigations (Lu), as well as UV-vis absorption and luminescence spectroscopy in water and DO (pH ≈ 7). forms 1:1 metal-ligand stoichiometric octadentate complexes in solution. Importantly, the pyridyl phosphonate functions are capable of simultaneous chelation to the metal center and of interaction with a second metal center. H NMR (Lu) and spectrophotometric titrations of the isolated [Tb] complex by EuCl salts demonstrated the formation of high-order (hetero)polymetallic species in aqueous solution (HO, pH = 7). Global analysis of the luminescence titration experiment points to the formation of 4:1, 3:1, and 3:2 [Tb]/Eu heteropolynuclear assemblies, exhibiting a strong preference to forming [Tb]Eu at increased europium concentrations, with energy transfer occurring between the kinetically inert terbium complex and added europium cations.