Lanthanide(III) complexes with N-(2,6-dimethylphenyl)oxamate and 1,10-phenanthroline: Synthesis, characterisation and cytotoxicity against MCF-7, HEC-1A and THP-1 cell lines

Seven novel mixed-ligand complexes, [Ln(Hpma)2(phen)2(OAc)]·2H2O (Ln = La (1), Ce (2) and Nd (3)), [Er(Hpma)2(phen)(OAc)(H2O)]·EtOH·H2O (4), [Yb(Hpma)3(phen)]·2EtOH (5) and [Ln(Hpma)3(phen)(H2O)]·4H2O (Ln = Nd (6) and Gd (7)) (Hpma = N-(2,6-dimethylphenyl)oxamate; phen = 1,10-phenanthroline) were prepared in the presence of NaOH. Complexes 1–3 are isostructural and each metal ion is ten-coordinate, adopting a distorted sphenocorona geometry, with continuous shape measures of 2.702, 2.677 and 2.592, respectively. In contrast, the nona-coordinate complexes 4, 6 and 7 displayed spherical capped square antiprism molecular geometry, while the Yb(III) complex is bonded to three bidentate Hpma– ligands and one phen, forming a square antiprism structure (coordination number = 8). Besides the strong Ln(III)-ligand bonds as the main driving force for coordination, the relatively weak hydrogen bonds (O H∙∙∙O and N H∙∙∙O), C H∙∙∙O contacts, C H∙∙∙π, N H∙∙∙π and offset π-π interactions between the aromatic rings, play a key role in crystal packing. The UV–Vis-NIR absorption spectra of the metal complexes are associated with the π → π* transitions of phen and the Laporte-forbidden f-f transitions of the Nd(III), Er(III) and Gd(III) ions from the 4I9/2, 4I15/2 and 8S7/2 ground states, respectively, to the various excited J-levels. Cytotoxicity studies revealed antiproliferative activity in MCF-7 cells (p 0.05) for all the compounds, except for the positive control curcumin; indicating that the target compounds do not exert adverse effects on the immune system monocytes.