Comparison of structural, spectroscopic, theoretical and thermal properties of metal complexes (Zn(II), Mn(II), Cu(II), Ni(II) and Co(II)) of pyridazine-3-carboxylic acid and pyridazine-4-carboxylic acids

In our present work, we studied complexes of 3d-transition metals with pyridazine-3-carboxylic and pyridazine-4-carboxylic acids. The synthesis of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes with pyridazinecarboxylic acids was performed. The effect of selected 3d-transition metal ions on the electronic system of ligands and the thermal properties of the complexes by the use of TG-FTIR were studied. The products of dehydration and decomposition processes of studied compounds were determined from the TG (thermo-gravimetric) and DSC (differential scanning calorimetry) curves. The crystal structures of manganese(II) pyr-idazine-3-carboxylate acid and pyridazine-4-carboxylate were analysed by the use of single-crystal X-ray ana-lysis. The geometries, NBO atomic charges, energy of HOMO and LUMO orbitals were calculated in the B3LYP/6-311++G(d,p) level. The aromaticity of ligands and complexes were discussed on the basis of HOMA and Bird's indices. The influence of the type of metal ion coordination and the location of the carboxylate anion in the pyridazine ring on the aromaticity of complexes were discussed. The comparison of the effect of metal ions on the electronic charge distribution and aromaticity of pyridazynecarboxylic and pyridinecarboxylic acids (i.e. nicotinic and picolinic acids) was done.