Spectroscopic and theoretical studies on axial coordination of bis(pyrrol-2-ylmethyleneamine)phenyl complexes

Metal (M=Zn(II), Ni(II), Cu(II)) complexes with tetradentate Schiff base ligand, bis(pyrrol-2-ylmethyleneamine)phenyl, has been synthesized and characterized by elemental analyses, (1)H NMR, mass spectra and UV-vis spectra. The standard association constants (K(theta)) and the thermodynamic parameters (Delta(r)H(m)(theta),Delta(r)S(m)(theta),Delta(r)G(m)(theta)) for axial coordination of imidazole derivatives with these Shiff base complexes were measured with UV-vis spectrophotometric titration. The decrease of enthalpy is found to be the drive of the axial coordination. Our Schiff base complexes can incorporate two axial ligands, except 2-Et-4-MeIm with two big substituents of great steric bulk according to stoichiometry of 1:1. ZnL displays high selectively binding to imidazole due to the steric bulk effect. Supporting density functional theory (DFT) calculations have been undertaken on B3LYP/6-31G(d) level.