Synthesis and structural characterization of some Schiff bases derived from 4-[{(aryl)imino}ethyl]-3-methyl-1-(4 ′-methylphenyl)-2-pyrazolin-5-one and spectroscopic studies of their Cu(II) complexes

A series of novel bidentate ligands have been synthesized by the condensation of 4-acetyl-2,4-dihydro-5-methyl-2-(4'-methylphenyl)-3H-pyrazol-3-one and various aromatic amines. All of these ligands have been characterized on the basis of elemental analysis, IR, H-1 and C-13{H-1} NMR data. The molecular geometries of five of these ligands have been determined by single crystal X-ray study. Crystallographic study reveals that these ligands exist in the amine-one tautomeric form in the solid state. NMR study also suggests the existence of the amine-one form in solution at room temperature. The reaction of these ligands with copper(II) resulted in the formation of mononuclear octahedral complexes of the general formulae [CuL2(H2O)(2)], with water molecules at the axial positions. These complexes were characterized on the basis of analytical and spectroscopic data. Thermal analyses of these complexes were also carried out. Magnetic moment measurements of these complexes at room temperature correspond to one unpaired electron. An ESR study of all these complexes in solution at room temperature, and also under frozen conditions at liquid nitrogen temperature, is consistent with the distorted octahedral geometry of the metal ion in these complexes. Semi-empirical quantum mechanical calculations (PM3) have been performed on the ligands to get charges over the coordinating atoms. A fairly good linear relation was found between the charges over the coordinating atoms of the ligands and the ligand field transition energies. (C) 2004 Elsevier Ltd. All rights reserved.