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Synthesis and Spectroscopic Characterisation of Cobalt (II) Complexes of 1-Phenyl-3-Methyl-4-Acyl Pyrazol-5-One Derivatives

O. C. Okpareke, J. N. Asegbeloyin, E. C. Okafor, O. T. Ujam and S. O. E. Okereke

The complexes of cobalt (II) with 4-acetyl (HPMAP), 4-benzoyl (HPMBP), 4-butyryl (HPMBUP), 4-capyroyl (HPMCP), 4-propionyl (HPMPRP) and 4-palmitoyl (HPMPP) derivatives of 1-phenyl-3- methyl pyrazol-5-ones has been synthesized. Characterisation was done by elemental analysis, UV, IR and conductivity measurements. The ligands behaved like bidentate enols, forming neutral chelates with cobalt (II) ions bonding through the keto oxygen or enolic hydrogen in the carbonyl group of the ligands ketoenol tautomer. The chelates were found to be neutral bis chelates having general molecular formular ML2.XH2O, Where M = Co, L is the 4-acyl pyrazolone anion, X is the No. of molecules of adducted water. The infrared spectra of the ligands and cobalt (II) complexes were measured between 4000 – 400 cm-1 and assignments proposed for the observed frequencies. The effect of 4-acyl substituents on the carbonyl stretching frequencies of the metal complexes were investigated and results showed that the stability of the C=O and CO-M bond depends on the nature of the alkyl substituent on the 4-acyl position.