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)] (1–4) have been accomplished via self-assembly of rudimentary dimanganese decacarbonyl, tetra(butylphenyl)-2,5-diamino-1,4-benzoquinonediimine (tbpdbd), and flexible ester-/ether-functionalized ditopic pyridyl-based ligands (L) (L = 4-pyridine carboxylic acid diethylene glycol diester (pcadgd), 4-pyridine carboxylic acid triethylene glycol diester (pcatrgd), 4-pyridine carboxylic acid tetraethylene glycol diester (pcatgd), and 1,4-phenylenebis(oxy)bis(ethane-2,1-diyl) diisonicotinate (pboedi)). Compounds 1–4 have been accomplished via an orthogonal bonding approach of an aminoiminoquinonato ligand (tbpdbd) and a flexible bis-pyridyl ligand to manganese carbonyl under facile one-pot reaction conditions. Metallacrown ethers 1–4 were characterized using elemental analyses, IR, UV–vis, NMR, and high-resolution ESI-mass spectrometry. The solid-state structure of the tbpdbd ligand was determined using single-crystal X-ray diffraction analysis. The molecular structure of 1 was elucidated by time-dependent density functional theory (TD-DFT) studies. The cation binding ability of 1–4 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 1–4 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 2.