Potentiometric, spectrophotometric, theoretical studies and binding properties of a novel tripodal polycatechol-amine ligand with lanthanide(III) ions

Abstract

A new tripodal ligand cis, cis-1,3,5-tris[(2,3-dihydroxybenzylamino)aminomethyl] cyclohexane (TMACHCAT), bearing three catechol units attached to a tris-methylaminocyclohexane (TMACH) ring has been synthesized and characterized by elemental analyses, UV–VIS, IR and 1H NMR spectral data. The lowest energy molecular geometry of TMACHCAT was obtained through empirical followed by quantum mechanical treatment. Theoretical UV–VIS, IR and 1H NMR spectral data were calculated from the energy-minimized structure by applying semi-empirical ZINDO, PM3 and TNDO/2 method, respectively and compared with the experimental data. The complexation behaviour of the ligand with H +, La(III), Gd(III) and Lu(III) in an aqueous medium of 0.1 M KCl at 25 ± 1 °C was studied by potentiometric and spectrophotometric methods. Six protonation constants were determined for the ligand and used as input data to evaluate the formation constants of the metal complexes. The formation of complexes between the partially protonated ligand and lanthanide ions of the types MLH 3, MLH 2, MLH, ML 2H 6 have been observed. The solution structures of the metal complexes were proposed through experimental evidences along with the calculated minimum strain energy through molecular mechanics calculation using CAChe’s augmented MM3 force field.