Abstract:

 A thermodynamic study is reported for the coordination reaction of three new metal imidazolate complexes of unsymmetrical tetradentate schiff bases and four substituted imidazoles with zinc meta-substituted tetraphenylporphyrins (ZnT(m-X)PP, X=NO2, Cl, OCH3, H, CH3) in dichloromethane solvent by spectrophotometric technique. The isosbestic behavior is exhibited in the region between 450 nm and 700 nm. The equilibrium constants K at 25 ℃ were determined by the method of Rose-Drago. It was found that the stoichiometric number is unity for all 35 coordination reaction systems studied. A Hammett linear relationship exists between the ratio or equilibrium constant and the Hammett constant of substitutents on the phenyl ring of porphyrin.

Key words: Zinc meta-substituted tetraphenylporphyrin, Metal schiff base, UV-Vis spectra, Axial coordination reaction, Equilibrium constant, Hammett linear relationship