Syntheses, characterization and crystal structures of mixed-ligand Cu(II), Ni(II) and Mn(II) complexes of N-(1-phenyl-3-methyl-4-propenylidene-5-pyrazolone)-salicylidene hydrazide containing ethanol or pyridine as a co-ligand

Five new mixed-ligand complexes [CuL(EtOH)] (1), [NiL(EtOH)3] (2), [Mn2L2(μ2-EtOH)2(EtOH)2] (3), [CuL(Py)] · MeOH (4) and [NiL(Py)3] (5) (L2− = N-(1-phenyl-3-methyl-4-propenylidene-5-pyrazolone)-salicylidene hydrazide anion, Py = pyridine) have been synthesized and characterized by elemental analyses, IR spectra, thermal analyses and single crystal X-ray diffraction. The crystallographic structural analyses of these complexes reveal that the ligand (H2L) itself undergoes isomerization from the keto form to the enol form in the reaction, then loses two protons and acts as a double negatively charged tridentate chelating agent coordinated to the metal ion in the solution. The final results show that when a co-ligand was present in the synthetic reaction, other coordination sites around the metal ions Cu2+ and Ni2+ were completed either by the ethanol or pyridine molecules under the common solvent reaction or solvothermal syntheses conditions, respectively. In the case of the Mn2+ ion, it was still coordinated with the solvent molecules regardless of whether it was synthesized under the common solvent reaction or solvothermal syntheses with pyridine. The reason for this difference might be attributed to the fact that the coordination modes and bonding effect of the co-ligand with the metal ions are different, the final complexes tend to form the most stable compound.

Graphical abstractFive mixed-ligand complexes of Cu(II), Ni(II) and Mn(II) have been synthesized and characterized. The results show that the ligand undergoes isomerization in the reaction and acts as a double negatively charged tridentate chelating agent coordinated to the metal ion, other coordination sites of metal ions were completed either by the ethanol or pyridine molecules.Figure optionsDownload full-size imageDownload as PowerPoint slide