Synthesis, IR, Magnetic, Solid Reflectance, and Thermal Characterization of Transition Metal Chelates with 2‐(5‐Acetylamino‐2‐hydroxyphenylazo)‐benzoic Acid

Abstract

The azo ligand 2‐(5‐acetylamino‐2‐hydroxyphenylazo)benzoic acid (H₂L) is derived from the diazotization of 4‐acetamidophenol with anthranilic acid. Metal(II) and (III) chelates were prepared and characterized by elemental and thermal analyses, conductance, IR, mass, magnetic, and diffuse reflectance spectra. The complexes were found to have the formulae [Cr(HL)₂]Cl · H₂O; [Cd(HL)₂] · 2H₂O; [M(HL)(H₂O) _z ]X · nH₂O for M = Co(II) (X = Cl, z = 1, n = 2), M = Ni(II) (X = Cl, z = 1, n = 2.5); M = Cu(II) (X = AcO, z = 2, n = 2), and M = Zn(II) (X = AcO, z = 1, n = 2); and [Fe(HL)Cl₂(H₂O)] · 2H₂O. The molar conductance data reveal that the Cd(II) and Fe(III) chelates are non‐electrolytes, while the Cr(III), Co(II), Ni(II), Cu(II), and Zn(II) chelates are 1:1 electrolytes. IR spectra show that the ligand is coordinated to the metal ions in a terdentate manner with ONO donor sites of the phenolic OH, azo–N, and carboxylic OH. Magnetic and solid reflectance spectra were used to infer the coordinating capacity of the ligand and the geometrical structure of these complexes. The mass spectra give the possible molecular ion fragments resulting from the fragmentation of the chelates. The thermal behavior of these chelates shows that water molecules (coordinated and uncoordinated) and anions are removed in two successive steps followed immediately by decomposition of the ligand molecule in the subsequent steps. The relative thermal stability of the anhydrous chelates is evaluated. The final decomposition products are found to be the corresponding metal oxides. The thermodynamic activation parameters, such as, E*, ΔH*, ΔS*, and ΔG* are calculated from the TG curves and discussed.

Keywords:

• 2‐(5‐Acetylamino‐2‐hydroxyphenylazo)benzoic acid complexes
• IR
• Conductance
• Solid reflectance
• Mass spectra
• Thermal analyses