Double-Walled Metal–Organic Framework with Regulable Pore Environments for Efficient Removal of Radioactive Cesium Cations

An anion double-walled metal–organic framework [Co2Li4(BTC)3(DMF)(H2O)·(CH3)2N]n (1) based on heterobimetallic Li+ and Co2+ ions was successfully constructed. Utilizing selective destruction and formation of Co–O/Co–N bonds in the metal chains, [Co2Li4(BTC)3(py)(H2O)·(CH3)2N]n (2) and [Co2Li4(BTC)3(pi)(H2O)·(CH3)2N]n (3) with the same skeleton but distinct pore structures can be surprisingly obtained. Additionally, compounds 2 and 3 can be transformed into [Co2Li4(BTC)3(H2O)2·(CH3)2N]n (4) by soaking them in an ethanol solution. This kind of single-crystal-to-single-crystal transformation successfully regulates the pore structure of MOFs and enriches the diversity of the pore wall on the premise of retaining the original framework. Most impressively, compound 1 shows high adsorption capacity for Cs+ cations and is a good candidate to selectively accommodate Cs+ among the common alkali metal ions, which is future identified by single-crystal X-ray diffraction and inductively coupled plasma mass spectrometry (ICP-MS) test. Meanwhile, compound 1 can selectively adsorb methylene blue (MB) and crystal violet (CV) molecules over Rhodamine B (RMB).