Anticancer Activity of Self-Assembled Molecular Rectangles via Arene–Ruthenium Acceptors and a New Unsymmetrical Amide Ligand

Two new and large molecular rectangles 4 and 5 were synthesized from two different arene–ruthenium [Ru2(μ-η4-C2O4)­(MeOH)2(η6-p-PriC6H4Me)2]­[O3SCF3]2 (2) and [Ru2(p-cymene)2(donq)­(OH2)2]­[O3SCF3]2 (donq = 5,8-dioxydo-1,4-naphthaquinonato) (3) acceptors and a new unsymmetrical N-(4-(pyridin-4-ylethynyl)­phenyl) isonicotinamide (1) donor ligand. X-ray crystallography of 4 confirmed a molecular rectangle. The 1H NMR spectra of both rectangles 4 and 5 showed a mixture of two structural, head-to-tail (HTT) and head-to-head (HTH), type isomers in a 1:1 ratio. The cytotoxicities of both rectangles have been established against Colo320 (colorectal cancer), A549 (lung cancer), MCF-7 (breast cancer), and H1299 (lung cancer) human cancer cell lines. The cytotoxicity of rectangle 5 was found to be considerably stronger against all cancer cell lines than that of the reference drug cisplatin.