N,N′-Ethylene-bis(3-methoxysalicylideneimine) mononuclear (4f) and heterodinuclear (3d–4f) metal complexes: Synthesis, crystal structure and luminescent properties

The stepwise synthesis of mononuclear (4f) and heterodinuclear (3d–4f) Salen-like complexes has been investigated through structural determination of the intermediate and final products occurring in the process. In the first step, reactions of ligand H2L and Ln(NO3)3 · 6H2O give rise to three mononuclear lanthanide complexes Ln(H2L)(NO3)3 [H2L = N,N′-ethylene-bis(3-methoxysalicylideneimine), Ln = Nd (1), Eu (2) and Tb (3)], in which N,N′-ethylene-bis(3-methoxysalicylideneimine) acts as tetradentate ligands with the O2O2 set of donor atoms capable of effective coordination. These species are fairly stable and have been isolated. Then, addition of Cu(Ac)2 · H2O to the mononuclear lanthanide complex yields expected heterodinuclear (3d–4f) complexes Cu(L)Ln(NO3)3 · H2O [Ln = Nd (4) and Eu (5)] where the Cu(II) ion is inserted to the inner N2O2 cavity. Luminescent analysis reveals that complex 3 exhibits characteristic metal-centered fluorescence of Tb(III) ion. However, the characteristic luminescence of both Sm(III) and Eu(III) ions is not observed both in solution and solid state of the complexes.