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

The reactions of [Ln(NO3)(3)center dot 6H(2)O] (Ln = Pr and Sm), [SmCl3 center dot 6H(2)O] and [Nd(OAc)(3)center dot xH(2)O] with benzilic acid (H2ben) and 1,10-phenanthroline (phen) as an auxiliary ligand in basic media yielded isostructural, ninecoordinate complexes (monoclinic system, space group P21/n) of the type [Ln(Hben)(3)(phen)(2)(H2O)]center dot DMF center dot 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 O-H center dot center dot center dot O interactions, C-H center dot center dot center dot O contacts, CAH center dot center dot center dot pi and parallel-displaced aromatic pi center dot center dot center dot pi interactions. The electronic absorption spectra of the complexes show pi -> pi* 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). (C) 2020 Elsevier Ltd. All rights reserved.