Synthesis of monosubstituted dipicolinic acid hydrazide derivative and structural characterization of novel Co(III) and Cr(III) complexes

A novel monosubstituted dipicolinic acid hydrazide derivative (H2L = 6-{; ; ; ; [2- (phenylcarbonyl)hydrazino]carbonyl}; ; ; ; pyridine-2- carboxylic acid) was prepared by the multi-step synthesis route starting from methoxy- substituted pyridine-2, 6-dicarboxylic acid. Reaction of the prepared compound with Co and Cr salts in the presence of 1, 6-diaminohexane resulted in formation of discrete complex compounds (CoL and CrL). The synthesized compounds were identified by chemical analyses and characterized by IR spectroscopy, thermal analysis and the ligand additionally by NMR spectroscopy. The crystal and molecular structure of the prepared complexes were determined by the single-crystal X-ray diffraction and electrochemical properties by cyclic voltammetry. The molecular structure of the complex compounds is found to be isostructural with rather small differences in the crystal packing arrangement. In both complexes the coordination geometry is octahedral and each metal ion is coordinated by two mutually orthogonal ligand molecules that act as N, N, O-tridentate ligand. In the crystal structure, the molecules are linked via multiple O–H⋯O, N–H⋯O and N–H⋯Cl hydrogen bond interactions thus forming a supramolecular zig- zag motif that is additionally stabilized by a series of hydrogen bond interactions that involve water molecule, diaminohexane cation, uncoordinated oxygen atom of carboxylic group and oxygen atom of carbonyl group. Electrochemical analysis of complex compounds indicated irreversible oxidation of Cr3+ in CrL and reduction of Co3+ to Co2+ in CoL, which agrees with the proposed oxidation state of the metal in complexes.