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

Two new and large molecular rectangles <b>4</b> and <b>5</b> were synthesized from two different arene–ruthenium [Ru₂(μ-η⁴-C₂O₄)­(MeOH)₂(η⁶-<i>p</i>-Pr<i>ⁱ</i>C₆H₄Me)₂]­[O₃SCF₃]₂ (<b>2</b>) and [Ru₂(<i>p</i>-cymene)₂(donq)­(OH₂)₂]­[O₃SCF₃]₂ (donq = 5,8-dioxydo-1,4-naphthaquinonato) (<b>3</b>) acceptors and a new unsymmetrical <i>N</i>-(4-(pyridin-4-ylethynyl)­phenyl) isonicotinamide (<b>1</b>) donor ligand. X-ray crystallography of <b>4</b> confirmed a molecular rectangle. The ¹H NMR spectra of both rectangles <b>4</b> and <b>5</b> showed a mixture of two structural, <i>head-to-tail</i> (HTT) and <i>head-to-head</i> (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 <b>5</b> was found to be considerably stronger against all cancer cell lines than that of the reference drug cisplatin