Lanthanide(III) complexes with pyridine head macrocyclic ligands

The ability of lanthanide(III) ions to form stable complexes with three different macrocyclic ligands, L-1, L-2 and L-3, has been investigated. The Schiff base macrocycle L-1 and its corresponding reduced ligand L-2 are derived from 2,6-bis(2-formylphenoxymethyl)pyridine and diethylentriamine; the reduced ligand L-3 is derived from 2,6-diformylpyridine and N,N-bis(3-aminopropyl)methylamine. Lanthanide nitrate complexes of L-1 and L-2 have been prepared by direct reaction between each ligand and the appropriate hydrated lanthanide nitrate; attempts to obtain the corresponding perchlorate complexes have been unsuccessful. All nitrate complexes of L-1 give the expected [1:1, Ln: L-1] stoichiometry; however, complexes obtained with L-2 show a [2:1, Ln: L-2] stoichiometry. Finally, complexation reactions with L-3 have been carried out in order to investigate the coordination capability of this small and flexible ligand towards the Ln(III) ions.