Thermal and Spectroscopic Investigations of Complexes of the Selected Transition Metal Ions with a β-L-Aspartyl Amide Derivative

Abstract

The aim of the presented research was to synthesize and characterize via elemental analysis, HRMS, thermogravimetric analysis, FTIR and EPR a novel series of transition metal complexes of Cu(II), Co(II), Ni(II) and Mn(II) with β-L-aspartyl-cyclohexyl amide as ligand. The HRMS recorded spectra confirm the obtaining of new compounds. The changes in the FTIR spectra of the metal complexes, compared to the ligand, support the complexation process. The thermal stability of the ligand and its metal complexes was discussed in the 20-800⁰C temperature range, in air atmosphere. In all of the studied complexes, the aspartyl amide acts as a bidentate ligand, its coordination involving the carboxylate oxygen and the nitrogen atom belonging to the free amino group of the amino acid. Metal complexes are formed in the 1:2 (Metal:Ligand) ratio as found by the elemental analysis. Except the free ligand, all the metal complexes are hydrating with water molecules, and the thermal stability of these suggested whether the water molecules are inside or outside the coordination sphere. The shape of EPR spectrum for copper complex at room temperature suggests the presence of CuN₂O₂ monomeric species with a rhombic distortion around the metallic ion. The results indicate that their stability range obeys the Irving-Williams series.