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.