Metal-organic cages containing two types of binding sites: trapping hydrocarbon gas in solution

The design and synthesis of artificial molecular containers for the encapsulation of hydrocarbon gases to study their host-guest chemistry are highly important for potential application in gas storage, separation, and understanding of their biological functions. In this work, we report the subcomponent self-assembly of four cubic Zn8L12Br4 (HL = N-(4-R)-1-(5-methyl-1H-imidazole-4-yl)methanimine) cages with good solubility in chloroform, which are capable of binding hydrocarbon gases including methane, ethane, and ethene in solution at ambient temperature. Two types of gas binding sites (one is in the cavity, and the other is at the window) are discovered in these cages, which are documented by nuclear magnetic resonance (NMR) spectra and density functional theory (DFT) calculations. Their performance of encapsulation of hydrocarbon gases can be tuned by carefully adjusting substituent groups. These metal-organic cages containing two types of binding sites provide new artificial models to mimic the structures and functions of biological systems in binding and transforming hydrocarbon gases.