The Effect of 4-Acyl Substituents on the Infrared Stretching Frequencies of Some 1-Phenyl -3- Methyl -4- Acylpyrazol -5-Ones and their Magnesium (Ii), Cobalt(Ii), Copper (Ii) and Zinc (Ii) Chelates

The divalent metal chelates of Mg,Co,Cu and Zn with 4-acetyl (hpmap), 4-benzoyl(hpmbp),4-butyryl(hpmbup),4-capyroyl(hpmcp),4-propiony (hpmprp) and 4-palmitoyl(hpmpp) derivatives of 1-phenyl -3-methyl pyrazol-5-one have been synthesized and characterized by UV ,IR, and conductivity measurements. It is shown that the ligands behaved like bidentate enols, all forming neutral chelates with the metal ions , bonding through oxygen of the enolic hydroxyl group and /or the oxygen atom of the carbonyl group of the ligands keto-enol tautomer. The i.r spectra of the ligands and their chelates have been measured between 4000cm-1 and 400cm-1and assignments proposed for observed frequencies. The effect of 4-acyl substituents on the carbonyl stretching frequencies of the complexes was also investigated and the results showed that there was an increase in the carbonyl stretching frequency bands as the length of the alkyl substituent increased for magnesium (II), cobalt(II) and copper (II) chelates and the reverse trend was observed for zinc (II) chelates.The infrared carbonyl and metal oxygen stretching frequencies of the transition metal chelates were also compared with the Irving and Williams stability order for transition metal complexes(Cu > Ni >Co >Mn >Zn) and it was observed that the magnitude of the M-O stretching frequencies followed closely the Irving Williams stability order while the C=O stretching frequencies did not. This +has been attributed to electronic and steric effects.