Multicomponent Self-Assembly of Manganese(I)-Based NN∩NN Bis-Chelated Dinuclear Metallacrown Ethers: Synthesis, Characterization, Cation Binding, and Cytotoxicity Studies

Tricarbonyl manganese-(I)-core-based aminoiminoquinonato-bridged ester/ether functionality-containing dinuclear metallacrown ethers of general formula [{(CO)₃Mn-(μ-η⁴-tbpdbd)-Mn-(CO)₃}-(μ-L)] (<b>1</b>-<b>4</b>) have been accomplished via self-assembly of rudimentary dimanganese decacarbonyl, tetra-(butylphenyl)-2,5-diamino-1,4-benzoquinonediimine (<i>tbpdbd</i>), and flexible ester-/ether-functionalized ditopic pyridyl-based ligands (L) (L = 4-pyridine carboxylic acid diethylene glycol diester (<i>pcadgd</i>), 4-pyridine carboxylic acid triethylene glycol diester (<i>pcatrgd</i>), 4-pyridine carboxylic acid tetraethylene glycol diester (<i>pcatgd</i>), and 1,4-phenylenebis-(oxy)-bis-(ethane-2,1-diyl) diisonicotinate (<i>pboedi</i>)). Compounds <b>1</b>-<b>4</b> have been accomplished via an orthogonal bonding approach of an aminoiminoquinonato ligand (<i>tbpdbd</i>) and a flexible bis-pyridyl ligand to manganese carbonyl under facile one-pot reaction conditions. Metallacrown ethers <b>1</b>-<b>4</b> were characterized using elemental analyses, IR, UV-vis, NMR, and high-resolution ESI-mass spectrometry. The solid-state structure of the <i>tbpdbd</i> ligand was determined using single-crystal X-ray diffraction analysis. The molecular structure of <b>1</b> was elucidated by time-dependent density functional theory (TD-DFT) studies. The cation binding ability of <b>1</b>-<b>4</b> was investigated for three monocationic alkali metals and three dicationic alkaline-earth metals through electronic absorption spectroscopy, and the results demonstrated a strong binding interaction between receptor and cationic species. Furthermore, cytotoxicity studies of compounds <b>1</b>-<b>4</b> were also investigated against two cancer cell lines (breast cancer (MDA-MB-231) and lung cancer (A549)) and a normal cell line (HEK293). Moreover, the morphological observations established the induction of apoptosis caused by treatment of cancer cells using selected compound <b>2</b>.