Fine-Tuning Apertures of Metal–Organic Cages: Encapsulation of Carbon Dioxide in Solution and Solid State

Abstract

Metal–organic cages are potential artificial models for mimicking biological functions due to their capability of selective encapsulation for certain guest molecules. In this work, we designed and synthesized a series of rhombic dodecahedral Ni-imidazolate cages (Ni14L24) with precisely controlled aperture for CO2 encapsulation. The aperture of the cages can be tuned by the strategies of ligand decoration and metal-ion hybridization. Similar to the breathing function of alveoli, CO2 passes through the dynamic aperture into the cages under a pressure of 2.0–3.0 bar in methanol solution, and slowly move out of the cages when the pressure goes down. In the solid state, CO2 is encapsulated and prisoned in the cages under a high pressure of 15.0–30.0 bar or supercritical conditions. By replacing the square-coordinated Ni2+ with Cu2+, the resulting Ni–Cu heteronuclear cage lost the capability of physically encapsulating CO2 even though the aperture’s size is only slightly changed.

Gas Storage in Porous Molecular Materials

“…Tuning the ligand used in the construction of PCCs to influence porosity can also be seen in the work published by Li et al. in 2019 [200] . Functionalization of the imidazolate‐based bridging ligand allowed for fine tuning of the pore window of the PCC.…”

Metal‐Organic Frameworks and Metal‐Organic Cages – A Perspective

“…When working with MOCs in the solid state it is important to consider whether they exhibit the same binding properties (and even have the same structure) as in solution. Recently an M 14 L 24 rhombic dodecahedral MOC was shown to encapsulate the important greenhouse gas CO 2 both in solution and in the solid state, [88] and other MOCs are known to encapsulate CO 2 [89] and H 2 [90] in the solid state. It is crucial to consider not only the internal cavities of MOCs in the solid state, but also the external cavities formed due to solid-state packing, as this may be where binding occurs.…”

Selective Separation of Polyaromatic Hydrocarbons by Phase Transfer of Coordination Cages

“…25,26 Porous organic cages have also been developed for the selective separation of xylene isomers, 27 noble gases, 28 and chiral molecules. 28 Our group has recently focused on the use of phase transfer 29−35 of coordination cages 36−48 and their molecular cargoes as a new strategy aiming to address practical separation problems. 49…”