Mixed-ligand complexes of lanthanides derived from an α-hydroxycarboxylic acid (benzilic acid) and 1,10-phenanthroline: Physicochemical properties and anticancer activity

Abstract

The reactions of [Ln(NO3)3·6H2O] (Ln = Pr and Sm), [SmCl3·6H2O] and [Nd(OAc)3·xH2O] with benzilic acid (H2ben) and 1,10-phenanthroline (phen) as an auxiliary ligand in basic media yielded isostructural, nine-coordinate complexes (monoclinic system, space group P21/n) of the type [Ln(Hben)3(phen)2(H2O)]·DMF·H2O (where Ln = Pr(III), Nd(III) and Sm(III)). In the structures, the monodeprotonated Hben− ligand connects the metal centres monodentately through the deprotonated carboxylate oxygen, and bidentately via the hydroxy oxygen and the carboxylate group oxygen. Additional stability of the crystal structures is provided by intra- and inter-molecular OH⋯O interactions, CH⋯O contacts, CH⋯π and parallel-displaced aromatic π⋯π interactions. The electronic absorption spectra of the complexes show π → π* transitions of the bidentate aromatic phen, as well as Laporte-forbidden 4f-4f transitions. Anticancer screen indicated that phen, and the Pr(III) and Nd(III) complexes, significantly reduced MCF-7 cell proliferation (p < 0.05). 1,10-Phenanthroline also exerted cytotoxic effects in HEC-1A cells (p < 0.05).