Metal complexes with two tri-aza, tri-oxa pendant-armed macrocyclic ligands: Synthesis, characterization, crystal structures and fluorescence studies

Metal complexes of two new tri-aza, tri-oxa macrocycles containing ethyl acetate (L1) or carboxymethyl (H2L2) pendant arms with hydrated nitrate or perchlorate salts of alkaline earth, post-transition and lanthanide metal ions have been synthesized and characterized by microanalysis FAB MS, conductivity measurements, IR, UV–Vis spectroscopy and fluorescence emission studies. The synthesis and characterization of the Pb(II) complexes with the armless macrocyclic precursors L (Schiff base macrocycle) and L′ (diaminic reduced macrocycle) are also reported. The crystal structures of complexes [PbL(ClO4)(H2O)](ClO4), [PbL′(ClO4)](ClO4) and ([Zn2L2(Cl)(H2O)](ClO4))∞ have been determined. In both lead(II) complexes, the metal ion is located inside the macrocyclic cavity and is coordinated by all N3O3 donor atoms in the complex with L′ but only by the nitrogen atoms present in the ligand in the complex with L. In both cases, the coordination sphere of the metal atom is completed with a perchlorate anion or a water molecule in the iminic complex of L. X-ray studies on the Zn(II) complex show the presence of a supramolecular structure that is consistent with a linear polymer formed alternately by an endomacrocyclic metal atom coordinated to a macrocyclic ligand and an exomacrocyclic metal ion in distorted octahedral and tetrahedral environments, respectively. UV–Vis and fluorescent emission studies were carried out on the ligands L1 and H2L2 and their metal complexes, but only the luminescence spectra of the Eu(III) and Tb(III) complexes with L1 in aqueous solution at ca. pH 7 show the characteristic visible emission of the metal. The value of the quantum yield determined for the Eu(III) complex is similar to that reported in the literature for other Eu(III) complexes.