Mixed complexes of nickel(II) with amino acids and dicarboxylic acids

Abstract

A series of novel mixed-ligand coordination compounds of Nickel(II) containing various dicarboxylic acids (oxalic, malonic, succinic, phthalic) and amino acids (glycine, alanine, phenylalanine, histidine) were successfully synthesized and systematically evaluated. Due to the optimization of the reaction parameters, stable chelate architectures were isolated with high yields ranging from 65% to 78%. The stoichiometric framework of the resulting complexes was verified via elemental analysis, precisely matching the general formula [Ni(L1 )(L2 )(H2O)x], where L1 and L2 represent the amino acid and dicarboxylic acid segments, respectively. The variance between the theoretically calculated and experimentally observed values remained strictly below 0.4%, demonstrating the exceptional purity of the final products and validating the efficiency of the synthetic pathway. FT-IR spectroscopic investigations revealed a distinct shift of the carboxyl stretching frequencies toward lower wavenumbers, indicating the active coordination of donor oxygen atoms. Furthermore, the emergence of specific ν(Ni–O) and ν(Ni–N) absorption bands within the 400–600 cm-1 spectral region unequivocally substantiates the direct coordination of both amine and carboxyl functions to the central metal ion.