Heptacoordinated lanthanide(III) complexes based on 2,6-bis(1H-benzo[d]imidazol-2-yl)pyridine ligands (bbp, bmbp and bdmbp): Computational calculations, luminescent properties and cytotoxic evaluation.

Abstract

Two new series of heptacoordinated obtained of hydrated lanthanide(III) nitrates (Ln3+ = La, Nd, Sm, Eu, Gd, Tb and Dy) with 2,6-bis(1H-benzo[d]imidazol-2-yl)pyridine (bbp) and 2,6-bis(5,6-dimethyl-1H-benzo[d]imidazol-2-yl)pyridine (bdmbp) were synthesized and characterized by high-resolution mass spectrometry (HR-MS), elemental analysis (EA), melting point (MP), molar electrical conductivity (MEC), effective magnetic moment (EMM) and Fourier-transform infrared spectroscopy (FT-IR). The optical properties of complexes were evaluated by ultraviolet-visible (UV–Vis) absorption and emission spectroscopy in solution. Samarium(III), europium(III), and terbium(III) complexes exhibited luminescent properties and characteristic emission bands. IR and MEC studies indicated that only two of the three nitrate groups were coordinating with the lanthanide(III) ion in a bidentate manner and confirmed the presence of the third nitrate group outside the coordination sphere. EMM analyses indicated that the metal complexes present paramagnetism, except for those of lanthanum(III). The third series of these complexes with these same trivalent lanthanide ions derived from the ligand 2,6-bis(5-methyl-1H-benzo[d]imidazol-2-yl)pyridine (bmbp) were previously reported by our research group in this same research journal (10.1016/j.molstruc.2018.03.065). Therefore, the cytotoxic activity of the three series of complexes and their ligands against NIH-3T3, J774A.1 and HeLa cell lines was studied. Only the bdmbp-based complexes exhibited moderate cytotoxic activity versus the HeLa cell line compared to the other two cell lines, while the bbp- and bmbp-derived complexes exhibited weak cytotoxic activity against all three cell lines.