Synthesis,thermodynamic, photophysical and DFT studies of some trivalent metal chelates of a hexadentate tripodal hydroxyquinolinate-based ligand

The synthesis, complexation, evaluation of solution thermodynamics and photophysical properties of multidentate chelator 5-[[3-[(8-hydroxy-5-quinolyl)methoxy]-2-[(8-hydroxy-5-quinolyl)methoxy methyl]-2-methylpropoxy]methyl]quinolin-8-ol (TMOM5OX) with trivalent Fe, Al and Cr ions is described. The corresponding complexes were probed by elemental analysis, mass, infrared, absorption and emission spectroscopy, potentiometry, and theoretical (DFT) studies. The thermodynamically stable and soluble M³⁺ complexes show stability constants in the range log β₁₁₀ = 23–30 and pM in the range of 19–30. The ligand forms distorted octahedral complexes in a tripodal orchestration and firmly binds metal ion over wide pH range. Density functional theory with B3LYP functional and 6-311G* basis set was employed for optimization, vibrational modes, NBO analysis, excitation and emission properties of the protonated, neutral, deprotonated states of the ligand and its ferric complex. The photophysical properties of TMOM5OX obtained by TD-DFT calculations showed good agreement with the experimental data. The result of NBOs and frontier molecular orbital analysis of ground and excited states of the metal complexes of TMOM5OX were used to explain the nature of the metal center.