Synthesis of bis(m-phenylene)-32-crown-10-based discrete rhomboids driven by metal-coordination and complexation with paraquat

(Figure Presented) Two bis(m-phenylene)-32-crown-10 derivatives containing two pyridyl or carboxyl groups were made. They were used to prepare three bis(m-phenylene)-32-crown-10-based discrete rhomboids by coordination-driven self-assembly with high yields. The formation of these crown ether-based rhomboids was confirmed by NMR, UV-vis, CSI-TOF-MS, and elemental analysis. The complexation of these crown ether-based assemblies with paraquat (N,N′-dimethyl-4,4′-bipyridinium) was studied. The complexation of neutral bis(crown ether) rhomboid 1 with paraquat was found to be statistical with a 1:2 stoichiometry. The average apparent association constant K _av of the complexation of rhomboid 1 with paraquat was found to be about 8.8(±0.8) × 10³ M^-1 in acetone, about 17 times higher than the reported association constant value for the complexation of the corresponding simple bis(m-phenylene)-32-crown-10 with paraquat. This is possibly because the carboxylate groups provide additional noncovalent interactions between the host and guest. No obvious complexation was observed between the cationic rhomboids and paraquat when studied by NMR, UV-vis, and CSI-TOF-MS analysis. This could be attributed to the combination of the charge repulsion between cationic pyridinium rings and cationic platinum atoms and the weak π-π stacking and charge transfer interactions between the phenyl rings and the pyridinium rings caused by the electron-withdrawing effect of the cationic platinum atoms.