Considering the different guest sizes (kinetic diameter of Xe: 3.96 Å, kinetic diameter of Kr: 3.60 Å), one could expect the impact of this parameter on the gas release kinetics to be significant. And indeed, the smaller the guest, the faster the guest release was observed (Fig. ). For the systems with krypton as a guest, i.e. Kr/MFU-4 and Kr/MFU-4-Br, the gas was released within few hours and few days, respectively, if the samples were exposed to air under ambient conditions (Fig. and S16, and Table and). However, in the case of the other two samples, i.e. Xe/MFU-4 and Xe/MFU-4-Br, the release was much more gradual and even after several weeks, a significant amount of the gas remained in the pores (Fig. and S14, and Table and). For instance, after 42 days approximately 27% of the originally loaded xenon remained in the pores of MFU-4, and 68% in the case of MFU-4-Br.