Synthesis, spectral, redox and antimicrobial activities of Schiff base complexes derived from 1-phenyl-2,3-dimethyl-4-aminopyrazol-5-one and acetoacetanilide

Novel terdentate neutral complexes of Cu-II, Ni-II, Co-II, Mn-II, Zn-II, Cd-II, Hg-II, VOII, ZrOII and UO2II have been prepared using a Schiff base derived from 1-phenyl-2,3-dimethyl-4-aminopyrazol-5-one (4-aminoantipyrine) and acetoacetanilide. The structural features of the chelates have been confirmed by microanalytical data, i.r., u.v.-vis., H-1-n.m.r., e.s.r. and mass spectral techniques. Electronic absorption and i.r. spectra of the complexes indicate an octahedral geometry around the central metal ion, except for the VOII and ZrOII complexes which show square pyramidal geometry. The monomeric and neutral nature of the complexes are confirmed from their magnetic susceptibility and low conductance values. The cyclic voltammogram of the copper complex in MeCN at 300 K shows a quasi-reversible peak for the couple Cu-II/Cu-III at Ep(c) = 0.47 and Ep(a) = 0.61 V versus Ag/AgCl and two irreversible peaks for Cu-II --> Cu-I and Cu-I --> Cu-0 reduction at Ep(c) = -0.63 and - 0.89 V respectively. The e.s.r. spectra of copper and vanadyl complexes in DMSO solution at 300 K and 77 K were recorded and their salient features are reported. The molecular orbital coefficients (alpha (2), beta (2)) were calculated for complexes. The antimicrobial activity of the ligand and its complexes have been extensively studied on microorganisms such as Staphylococcus aureus, Klebsiela pneumoniae, Bacillus subtillis, Escherichia coli, Citrobacter ferundii and Salmonella typhi. Most of the complexes have higher activities than that of the free ligand.