The metal complexes of heterocyclic β-diketones and their derivatives—V. The synthesis, structure and i.r. spectral studies of metal(II) complexes of 1-phenyl-3-methyl-4-acetyl-pyrazolone-5 (HPMAP)

Abstract

The divalent metal complexes of Be, Mn, Co, Ni, Cu, Zn, Pb, Hg and Ba with 1-phenyl-3-methyl-4-acetyl-pyrazolone-5 (HPMAP), have been synthesized for the first time. It is shown that even though the ligand, HPMAP, has four potential coordination sites, it behaves like a bidentate enol forming neutral metal chelates through the carbonyl and enolic hydroxyl groups. The complexes were characterized by means of elemental analyses, conductivity measurements, i.r. proton NMR spectroscopy. Proton magnetic resonance spectral data for some of the chelates have been recorded and discussed. The i.r. spectra of HPMAP and its chelates have been measured between 4000 and 200 cm −1 and assignments are proposed for the observed frequencies. Replacement of a methyl group in the acetylacetonate by the pyrazolone moiety fused to the chelate ring has been found to strengthen the C … O and MO bonds and weaken the C … C bond of the chelate ring. The magnitudes of MO stretching frequencies for the transition metals follow very closely the Irving-Williams stability order Cu > Ni > Zn > Co > Mn.