Synthesis and characterization of cobalt (II), nickel (II) and copper (II) complexes of Cyclohexylamine-N-methyl Mannich base ligands

Abstract

Three Mannich base ligands, Cyclohexylamine-N-methylurea (CHMU), Cyclohexylamine-Nmethylacetamide (CHMAA) and Cyclohexylamine-N-methylacetone (CHMA) and their cobalt(II), nickel(II) and copper(II) complexes were synthesized and chelating properties investigated with the view to determine the coordination modes and the stoichiometric ratio of the metal complexes. The Mannich ligands, CHMU, CHMAA and CHMA were prepared by the reaction of cyclohexylamine, formaldehyde and urea; cyclohexylamine, formaldehyde and acetone; cyclohexylamine, formaldehyde and acetamide respectively at 25°C . They were characterized using infra-red (IR) spectroscopy. Their cobalt(II), nickel(II) and copper(II) complexes were equally prepared and characterized by infrared and UV-Visible spectroscopy. The solubilities of the ligands and their complexes in common solvents were also investigated. All the metal(II) complexes are stable in air and decomposed without melting at temperature >300°C . The infra-red spectra of the ligands show absorption bands in the region 3450-3300cm^-1 due to (ʋN-H) stretching vibration and 1644-1636cm^-1 due to(amide ʋC=O) stretching frequency in addition to other characteristic bands. These bands experienced significant shift downwards to 3434cm^-1 and 1634cm^-1 respectively on coordination with the metal ions. The coordination was further confirmed by the appearance of new bands at about (455-534) cm^-1 and (600-645)cm^-1  which are characteristics of M-N and M-O stretching bands. The coordinating atoms however vary with the metal ion as well as the ligand. With CHMAA, copper(II)ion coordinates through the two nitrogen atoms to form four –membered rings while nickel(II) ion coordinates through the oxygen atom and one of the nitrogen atoms to form six – membered rings. Cobalt(II) ion coordinates through both oxygen and the nitrogen atoms to form four –membered rings. With CHMA, copper(II)ion coordinates through the two nitrogen atoms, nickel(II) ion and cobalt(II) ion coordinate through the oxygen atom and one of the nitrogen atoms to form six – membered rings. The results from the percentage composition of the metals in the complexes of metal-CHMU confirm the preparatory procedure of metal to ligand ratio of 1: 2 (M: L).Thus, the prepared complexes have the general formulae [ML₂]. 

Keywords: Mannich base ligands, synthesis, characterization, metal complexes