Synthesis, characterization and spectral properties of novel azo-azomethine-tetracarboxylic Schiff base ligand and its Co(II), Ni(II), Cu(II) and Pd(II) complexes

Abstract

Novel tetracarboxylic Schiff-base ligand, namely 5,5′-((1E,1′E)-(((1E,1′E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(4-hydroxy-3,1-phenylene))bis(diazene-2,1-diyl)) diisophthalic acid (L2) was prepared by the condensation reaction of ethane-1,2-diamine with 4-((3-formyl-4-hydoxyphenyl)diazenyl) isophthalic acid (L1) in anhydrous ethanol. A prepared organic compound is potential N,O-multidentate chelating ligand, which forms stable complexes with metal(II) ions in 1:1 up to 1:5 M ratio of the metal to ligand. Its reactions with corresponding nitrate salts have synthesized the complexes of L2 with Co(II) (1), Ni(II) (2), Cu(II) (3) and Pd(II) (4) ions. The prepared dye and its metal-containing complexes were investigated by the combination of elemental and ICP-MS analyses, infrared spectroscopy, thermal analysis, powder X-ray diffraction, 1H and 13C NMR and UV/VIS spectroscopy. UV/VIS titration measurements showed the stable formation of 1:1 Schiff-based complexes with four free carboxylic groups. Prepared metal-containing complexes are suitable linkers for metal–organic frameworks preparation with promising applications in gas storage and heterogeneous redox-catalysis.