Synthese, caracterisation et etude des proprietes photoluminescentes des polymeres de coordination de co (ii), ni (ii), cu (ii), zn (ii) carboxylate avec la 2-aminopyridine

Abstract

This work concerns the synthesis, characterization and study of the photoluminescent properties of Co (II), Ni (II), Cu (II) and de Zn (II) coordination polymers. These polymers were synthesized by complexation reaction between the corresponding metal chlorides (CoCl2‧6H2O, NiCl2‧6H2O, CuCl2‧2H2O and ZnCl2) and mixed ligands consisting of 1H-pyrazole-4- carboxylic acid and 2-aminopyridine in a methanol/water mixture, following the ratio 1 :2 :2 (M : L₁ : L₂). The yield is between 45.26 and 61.09%. The synthesized compounds were characterized by physicochemical and spectroscopic methods including: quantitative analysis, solubility test, melting point measurement, infrared and UV-Visible spectroscopies in diffuse reflectance. The melting points of ligands L1 and L2 (282°C and 58°C) differ from those of the complexes (above 300°C). This difference in temperatures likely indicates the formation of the new compounds. Solubility test results show that the synthesized compounds are all insoluble in common solvants, further indicating their polymeric nature. Infrared spectroscopy data reveal the bidentate nature of ligand L1 (N- and O-donor sites) and monodentate nature of ligand L2 (N- donor site). UV-Visible spectroscopy allowed us to propose the Following geometries: octahedral for the cobalt (II) and nickel (II) polymers, square planar for the copper (II) polymers, and tetrahedral for the zinc (II) polymers. The photoluminescent properties of the synthesized coordination polymers were studied under excitation at 369 nm. All polymers exhibit fluorescent emission, but with varying intensities depending on the metal used. The fluorescence intensities measured for Ni (II), Cu (II), Zn (II), and Co (II) polymers are 108, 211, 2132, and 7092 a.u, respectively. The ascending order of luminescent intensity is therefore: Ni (II) < Cu (II) < Zn (II) < Co (II). These results indicate that the central metal has a direct influence on the emission efficiency of complexes, with the Co (II) polymer standing out as the most luminescent.