Lanthanide complexes with N-(2,6-dimethylphenyl)oxamate: Synthesis, characterisation and cytotoxicity

Abstract

The complexation reactions of Ce(III), Nd(III), Gd(III) and Er(III) ions with the chelating/ bridging monoanionic ligand N-(2,6-dimethylphenyl)oxamate (Hpma−) in basic media were performed in view of the potential applications of oxamate derivatives as cytotoxic agents. The coordination compounds were characterised by different physico-chemical techniques: elemental analysis, conductivity measurements, IR, 1H NMR and UV–Vis-NIR spectroscopy, and X-ray crystallography. The anionic Hpma− ligand was obtained through conversion of the proligand ethyl (2,6-dimethylphenylcarbamoyl)formate (Hdmp). The reactions afforded lanthanide(III)–oxamate coordination polymers of the formulae: {[Ln(Hpma)3(MeOH)(H2O)]∙2MeOH}n (Ln = Ce (1) and Nd (2)), {[Gd2(Hpma)6(MeOH)4]∙6MeOH}n (3), {[Er2(Hpma)6(MeOH)(H2O)3]∙2MeOH}n (4) and [Ln2Na2(Hpma)8(EtOH)(H2O)6]n (Ln = Nd (5) and Gd (6)). The polymeric complexes feature Ln-Hpma moieties bridged by μ2-η1:η1:η1 Hpma− ligands, giving one-dimensional zig-zag chains of the LnOCOLn type. Atomic charge analysis and the MEP map of the Hpma− moiety using the DFT/B3LYP method were consistent with the chelating and bridging modes of the anionic ligand through all the oxygen atoms. An evaluation of the cytotoxic activities of the metal salts, the proligand and the novel lanthanide complexes on MCF-7, HEC-1A and THP-1 cells revealed that only the rare-earth metal salts [Ce(NO3)3·6H2O] and [Nd(NO3)3·6H2O] showed moderate cytotoxicity against MCF-7 and HEC-1A cells, respectively.