La(III), Ce(III), Pr(III) and Eu(III) complexes with fenamic acid based ligands: preparation, spectral and thermal analysis and evaluation of their cytotoxicity in MDA-MB-231 breast cancer cells

Six lanthanide complexes with substituted fenamic acid ligands {[La(L¹)₃].2H₂O (C1), [La(L²)₃].2H₂O (C2), [Ce(L¹)₃] (C3), [Ce(L²)₃].2H₂O (C4), [Pr(L¹)₃].3H₂O (C5) and [Eu(L²)₃] (C6); HL¹ = 2-(4-chlorophenylamino)benzoic acid and HL²= 2-(4-methoxyphenylamino)benzoic acid} were isolated and characterized by elemental CHN microanalyses, DMF solution electrical conductivities and spectral (FTIR and UV–Visible) data. These analyses assigned the monoanionic character of the ligands and their bidentate chelation mode through the carboxylate group oxygen atoms. In addition, the complexes dissolve in dichloromethane, dimethylformamide and dimethyl sulfoxide, and are nonelectrolytes. Thermo-analytical techniques (TG/DTA) analyzed the complexes in the air and revealed that all water contained in them is lattice-based (uncoordinated), while complexes C3 and C6 are anhydrous. Moreover, all complexes, during heating up to 700 °C, decomposed to the respective oxides (Ln₂O₃). The complexes were tested for potential activity against human MDA-MB-231 breast cancer cells and the results uncovered low cytotoxic effect with high IC₅₀ doses, comparing to paclitaxel, on these cells.