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.

Graphical abstractThe stepwise synthesis of mononuclear (4f) and heterodinuclear (3d–4f) Salen-like complexes has been investigated. In the first step, reaction of ligand H2L and Ln(NO3)3 · 6H2O gives 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)]. 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)]. Luminescent properties of the complexes have been discussed.Figure optionsDownload full-size imageDownload as PowerPoint slide