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)]center dot 2H(2)O (Ln = La (1), Ce (2) and Nd (3)), [Er (Hpma)(2)(phen)(OAc)(H2O)]center dot EtOH center dot H2O (4), [Yb(Hpma)(3)(phen)]center dot 2EtOH (5) and [Ln(Hpma)(3)(phen)(H2O)]center dot 4H(2)O (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 center dot center dot center dot O and N-H center dot center dot center dot O), C-H center dot center dot center dot O contacts, C-H center dot center dot center dot pi, N-H center dot center dot center dot pi and offset pi-pi 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 pi -> pi * transitions of phen and the Laporte-forbiddenf-f transitions of the Nd(III), Er(III) and Gd(III) ions from the I-4(9/2), I-4(15/2) and S-8(7/2) ground states, respectively, to the various excited Jlevels. Cytotoxicity studies revealed antiproliferative activity in MCF-7 cells (p < 0.05) after treatment with phen and coordination compounds 1-7. Statistically significant cytotoxic effects were also exerted by Nd(NO3)(3)center dot 6H(2)O, phen, 3, 6 and 7 in HEC-1A cells (p < 0.05). No cytotoxic effects were observed in THP1 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. (C) 2020 Elsevier Ltd. All rights reserved.