Self-Assembly of Discrete Ru^II₈ Molecular Cages and Their in Vitro Anticancer Activity

Four new octanuclear Ru­(II) cages (<b>OC-1</b>–<b>OC-4</b>) were synthesized from dinuclear <i>p</i>-cymene ruthenium­(II) acceptors [Ru₂(μ–η⁴-C₂O₄)­(CH₃OH)₂(η⁶-<i>p</i>-cymene)₂]­(O₃SCF₃)₂ (<b>A</b>_<b>1</b>), [Ru₂(μ–η⁴-C₆H₂O₄)­(CH₃OH)₂(η⁶-<i>p</i>-cymene)₂]­(O₃SCF₃)₂ (<b>A</b>_<b>2</b>), [Ru₂(dhnq)­(H₂O)₂(η⁶-<i>p</i>-cymene)₂]­(O₃SCF₃)₂ (<b>A</b>_<b>3</b>), and [Ru₂(dhtq)­(H₂O)₂(η⁶-<i>p</i>-cymene)₂]­(O₃SCF₃)₂ (<b>A</b>_<b>4</b>) separately with a tetradentate pyridyl ligand (<b>L</b>_<b>1</b>) in methanol using coordination-driven self-assembly [<b>L</b>_<b>1</b>= <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetra­(pyridin-4-yl)­benzene-1,4-diamine]. The octanuclear cages are fully characterized by various spectroscopic techniques including single-crystal X-ray diffraction analysis of <b>OC-4</b>. The self-assembled cages show strong in vitro anticancer activity against human lung adenocarcinoma A549 and human cervical cancer HeLa cell lines as observed from the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Of all the octanuclear cages, <b>OC-3</b> exhibits remarkable anticancer activity against both cancer cell lines and is more active than that reported for cisplatin. The excellent anticancer activity of <b>OC-3</b> and <b>OC-4</b> highlights the importance of the synergistic effects of the spacer component of the dinuclear <i>p</i>-cymene Ru­(II) acceptor clips