ABSTRACT Molecular cages with an adjustable cavity have great potential in selective separation, adsorption, drug releasing etc. But to construct resizable cages is highly challenging. Here, retractable cages with a continually change of cavity size are found for the first time. The as‐prepared 2 + 3 cages are highly compressed with only 2.83 Å height of cavity. However, the cage is prolonged to 12.88 Å by crystalizing from CHCl 3 /CH 3 OH and encapsulating six methanol molecules while it is transferred into half‐expanded state with 7.50 Å cavity if it is immersed in methanol and includes three methanol molecules. Interestingly, using CHCl 3 /CH 3 CN mixed solvent, compressed cages with both 2.83 and 5.29 Å cavity are obtained by rapid crystallization, whereas expanded cage with 12.12 Å height of cavity is got by slow crystallization. Furthermore, with acid treatment, the compressed cage is expanded to 12.29 Å height. Consequently, the cage's cavity could be continually and precisely adjusted between 12.88, 12.29, 12.12, 7.50, 5.29, and 2.83 Å. This cage change could be easily monitored by 1 H NMR, CPL, and visual color change etc. Due to adaptive adsorption, the scalable cage exhibits very high iodine uptake capacity of up to 6.02 g/g in iodine vapor and 3.70 g/g in water. Exceptionally, by reducing the rigid imine cage into the flexible amine cage, iodine uptake is enhanced by 37% in vapor and 91% in solution, giving an unprecedented example of organic adsorbents with high capacity from flexible cavity.
Hu et al. (Fri,) studied this question.