1 H NMR,spectroscopic and molecular modeling studies on paramagnetic lanthanide(III)-quercetin complexes

Nine coordinated [Ln(quercetin)₃]nH²O complexes were synthesized in non-aqueous solution (where, n = 0 for Pr, Sm, Gd, Tb, Dy and Ho; n = 3, for La and Nd). The complexes were characterized by elemental analysis, molar conductance, UV – vis spectra, IR spectra, thermal analysis and NMR spectra. The optimized structures of the complexes were obtained by molecular modeling. The complexes behave as non-electrolytes in DMSO. TGA study showed anhydrous nature of the complexes (except La and Nd). The ¹H NMR spectra of lanthanum, praseodymium, neodymium and samarium complexes have been studied in DMSO-d₆. The complexes do not dissociate in DMSO and retain their coordination number. The NMR spectra of paramagnetic and diamagnetic complexes of quercetin exhibit lower as well as higher field shifts that show change in geometry during the metal ligand coordination.