Triply phenoxo bridged Eu(iii) and Sm(iii) complexes with 2,6-diformyl-4-methylphenol-di(benzoylhydrazone): structure, spectra and biological study in human cell lines

Abstract

Two dinuclear lanthanide(III) complexes, [M₂(HL)₃] (M = Sm(III) (1), Eu(III) (2); H₃L, 2,6-diformyl-4-methylphenol-di(benzoylhydrazone)) were generated with good yield and characterised systematically. The single crystal X-ray structure determination of [Eu₂(HL)₃] (2) confirmed the tricapped trigonal prismatic geometry of the N₃O₆ coordination environment around europium. Indeed, Eu(1) and Eu(2) are bridged by phenolato-O belonging to the p-cresol ring, by deprotonated ‘enol’ groups from the benzoyl hydrazide part and by the imine-N centres. A temperature dependent magnetic study suggested that anti-ferromagnetic coupling occurs between the two Eu(III) ions and the magnetic moment was found to vary from 0.48 B.M. at 5 K to 3.03 B.M. at 300 K. Electron paramagnetic resonance spectroscopy confirmed that anti-ferromagnetic coupling occurs between the atoms of Eu(III) and Sm(III). Both the complexes show emission in the visible range. The ligand, H₃L and the complexes exhibit anti-mycobacterial activity against M. tuberculosis H37Rv (ATCC 27294) and M. tuberculosis H37Ra (ATCC 25177) strains. The molecular docking of H₃L with the enoyl acyl carrier protein reductase of M. tuberculosis H37R_v (PDB ID: 4U0K) was examined and the best docked pose of H₃L was shown to have one hydrogen bond with Thr196 (2.03 Å).