DFT and 1 H NMR molecular spectroscopic studies on biologically anti-oxidant active paramagnetic lanthanide(III)-chrysin complexes

Abstract

The interaction of trivalent lanthanide chlorides and chrysin in methanol results in formation of the complexes [Ln(chrysin)₃], where Ln = La, Pr, Nd, Sm, Gd, Tb and Ho. The complexes have been characterized by elemental analyses, molar conductance, IR, UV–Vis, TGA/DTA and NMR spectroscopic studies. They behave as non-electrolytes in DMF solution. The TGA data indicated that the complexes were anhydrous. The electronic spectra of the complexes were recorded in methanol DMF and DMSO solutions. ¹H NMR spectra of lanthanum, praseodymium, neodymium, samarium and gadolinium complexes have been studied in DMSO-d₆. ¹H NMR spectra of paramagnetic and diamagnetic complexes exhibit down-field as well as up-field shifts of chrysin resonances that shows a change in geometry during the ligand coordination to the metal ion. A theoretical study of the chrysin molecule was conducted through DFT, ab initio, and AM1 methods and this determined the coordination environment of the metal ions.