Síntese e caracterização de complexos heterobimetálicos 3d-4f: estudo de propriedades luminescentes

Abstract

This work describes the synthesis and characterization of eight complexes involving the N,O-donor ligands, pyridine-3,5-dicarboxylate (3,5-pdc); pyridine-2,5dicarboxylate (2,5-pdc); pyridine-2,6-dicarboxylate (2,6-pdc) and isonicotinate (iso). All compounds were characterized by atomic absorption spectroscopy, infrared and Raman vibrational spectroscopies, CHN elemental analysis and thermal analysis (TG/DTA). The characterization techniques indicate that six of these are 3d-4f heterobimetallic complexes, in other words, present in their molecular formulae a dblock metal [Co (II) or Cu (II)] and a f-block metal [Eu (III) or Sm (III)]. The characterization techniques also suggest that complexes EuCo(3,5-pdc) and EuCu(3,5-pdc) are isostructural, as well as compounds SmCu(2,5-pdc), EuCo(2,5pdc) and EuCu(2,5-pdc). Two other complexes entitled Co(3,5-pdc) and Eu(iso) had their structures determined by single-crystal X-ray diffraction analysis. Complex Co(3,5-pdc) structure belongs to the monoclinic crystal system, space group P21/n, with molecular formula [Co(3,5-pdc)(H2O)5]dmso. Co(II) sites adopt a distorted octahedral geometry, with the coordination sphere composed of five aqua ligands and one nitrogen atom from 3,5-pdc ligand. In this case, the 3,5-pdc carboxylate groups are not involved in coordination. Eu(iso) compound, with molecular formula [Eu(iso)3(H2O)2]n crystallized in the monoclinic system, belonging to space group P21/c and appeared as a 1D coordination polymer. The Eu(III) ion is coordinated to eight oxygen atoms displaying distorted square antiprismatic geometry. The iso ligands adopt two coordination modes: bidentate chelate and bridging. The heterobimetallic compounds along with the complex Eu(iso), were studied by luminescence spectroscopy. The luminescence spectra indicate that the direct excitation wavelength of the π → π* transition of the ligands is more efficient than direct excitation into the metal, characterizing lanthanide sensitization. The CIE chromaticity diagram shows that the emissions have high purity, with X and Y coordinates near the edge.