Experimental and Theoretical Insights on Gas Trapping in MOFs: A Case Study with Noble Gases and MFU-4 Type MOFs

Isostructural metal-organic frameworks (MOFs), namely MFU-4 and MFU-4-Br, in which the pore apertures are defined by anionic side ligands (Cl− and Br−, respectively), were synthesized and loaded with noble gases. By selecting the type of side ligand, one can fine-tune the pore aperture size, allowing for precise regulation of the entry and release of gas guests. In this study, we conducted experiments to examine gas loading and release using krypton and xenon as model gases, and we complemented our findings with computational modeling. Remarkably, the loaded gas guests remained trapped inside the pores even after being exposed to air under ambient conditions for extended periods, in some cases for up to several weeks. Therefore, we focused on determining the energy barrier preventing gas release using both theoretical and experimental methods. The results were compared in relation to the types of hosts and guests, providing valuable insights into the gas trapping process in MOFs, as well as programmed gas release in air under ambient conditions. Furthermore, the crystal structure of MFU-4-Br was elucidated using the three-dimensional electron diffraction (3DED) technique, and the bulk purity of the sample was subsequently verified through Rietveld refinement. The data in this record are supplementary data to the manuscript with DOI 10.26434/chemrxiv-2024-vb8pj.

本研究合成并填充了具有相同结构的金属有机框架（MOFs），即MFU-4及其溴化物MFU-4-Br，其中孔径由阴离子侧配体（分别为Cl−和Br−）界定。通过选择侧配体的类型，可以精细调节孔径尺寸，从而实现对气体分子进出和释放的精确调控。在本研究中，我们以氪气和氙气为模型气体，进行了气体填充与释放的实验研究，并辅以计算模拟以补充验证。值得注意的是，即使在空气环境下长时间暴露，某些情况下长达数周，填充的气体分子仍被困于孔洞之中。因此，本研究重点在于利用理论与实验方法确定阻止气体释放的能量壁垒。结果与宿主和客体的类型相关联，为MOFs中的气体捕获过程以及大气环境下的程序化气体释放提供了宝贵的见解。此外，通过三维电子衍射（3DED）技术阐明了MFU-4-Br的晶体结构，并通过Rietveld精修法验证了样品的纯度。本记录中的数据是隶属于DOI 10.26434/chemrxiv-2024-vb8pj的手稿的补充数据。