The influence of various loading conditions, such as pressure, temperature and time, on the xenon loading into MFU-4 was studied previously in detail. Herein we compared the optimized loading conditions to the conditions needed to load krypton into MFU-4, and krypton and xenon into MFU-4-Br. The amount of the loaded gas was quantified by TGA (Fig. -S10 and Table -S11). The loading results clearly indicate that the size of the guest and the pore aperture has an impact on the optimal loading conditions (Table ). Generally, it can be concluded that the higher the ratio of guest size to pore aperture size, the higher loading temperature is needed to load comparably high amounts of the gas guest. For instance, the highest amount of xenon loaded into MFU-4 was achieved at 30 bar at 100 °C, while for the loading of xenon into MFU-4-Br, a loading temperature of 200 °C was needed. Moreover, thermogravimetric analysis also revealed that the larger the guest in comparison to the pore aperture size, the higher temperature of the maximal gas release was (Fig. ). ); the measurement was carried out under a nitrogen atmosphere with a heating rate of 10 K•min -1 ; the weight derivation as a function of temperature is depicted as dotted lines with temperature of maximum gas release indicated. These findings indicate that the activation energy barrier of the guest release from the pores depends on the guest-pore aperture size ratio. For instance, it can be expected that the activation energy barrier of gas release from MFU-4 is lower in comparison to the activation energy of the same gas guest loaded into the pores of MFU-4-Br. This has been further confirmed by experimental and computational studies and is discussed in detail later in this article.