Metal-organic frameworks (MOFs) are crystalline porous coordination polymers with attractive properties, with porosity being a key feature, reaching up to around 7800 m²•g -1 . This intrinsic characteristic makes MOFs highly suitable for gas storage and separation applications. The effectiveness of MOFs in these processes significantly depends on their structural properties. Various strategies have been devised to enhance the sorption properties for specific gases. For instance, Guo et al. demonstrated the use of MOFs with pores featuring exposed metal ions capable of distorting the electron cloud of methane, leading to polarization and enhanced gas adsorption. McDonald et al. explored the use of diamineappended metal-organic frameworks as CO2 adsorbents in gas separation, showcasing the insertion of CO2 molecules into metal-amine bonds, thereby enhancing the material's adsorption capabilities. Another intriguing approach to gas storage in MOFs is the strategy presented in this study, focusing on MOFs with narrow pore apertures smaller than the size of the gas guest. In this process, the gas guest is introduced into the pores under specific loading conditions and is not released immediately under ambient conditions. As a proof-of-concept investigation, we recently reported on xenon storage in a MOF known as MFU-4, demonstrating the feasibility of storing significant quantities of gas (larger than 40 wt%) within the voids, even when the material was exposed to air under ambient conditions. In follow-up studies we investigated the approach on an example of sulfur hexafluoride as a guest trapped in the pores of MOFs MFU-4 and ZIF-8. Herein, considering the practically boundless MOF design possibilities, we delve into an exploration of the gas storage properties of the MOF MFU-4 by tailoring its structural characteristics and incorporating diverse gas guests, namely krypton and xenon, and examine such systems comprehensively through a combination of experimental and theoretical methods. Our aim is to formulate the system properties required to achieve effective gas trapping. MFU-4 is an example of a benzobistriazolate-based MOF and belongs to the 'MFU-4-type' frameworks previously reported by us. MOFs of this family have been investigated for various applications, including H2/D2 separation, binding and activation of small molecules, catalysis, enzyme mimetics, or drug delivery. The 'MFU-4-type' frameworks comprise pentanuclear secondary building units with a general formula [M II 5X4(L -2 )3]. Within the pentanuclear coordination unit (Figure ), the central metal II ion adopts an octahedral geometry (M oct ), coordinated to six bis(triazolate) ligands (L -2 ). The remaining four peripheral metal II ions feature a tetrahedral coordination environment (M tetr ), and each of them is bound to three N-donor atoms from three different bis(triazolate) ligands and to one additional monodentate (anionic) ligand (X -). MFU-4 is constructed with benzobistriazole ligands [specifically 1H,5Hbenzo (1,2-d:4,5-d′)bistriazole] and Zn II cations (Figure ), featuring two types of voids of 3.9 and 11.94 Å. These small and large pores are connected by 2.53 Å narrow pore apertures (Table ). The MOF possesses a highly adaptable structure for customizing the size of its aperture. This versatility arises from the fact that the pore aperture is defined by four chlorido ligands (Figure ). Consequently, it can be modified by introducing other anionic ligands of varying sizes, such as different halides, as demonstrated in this work through the synthesis of a new MOF MFU-4-Br. Besides this new MOF, variants with hydroxide and fluorido side ligands (i.e., MFU-4-OH and MFU-4-F) are also known. However, unlike these two MOFs, which were prepared via postsynthetic ligand exchange, MFU-4-Br reported here is prepared via direct synthesis. 21.697(3) 10214(2) 2.53 3.96/2.53 = 1.57 ) 21.7110(10) 10236.9 10233.9 2.15 3.96/2.15 = 1.84 3.60/2.15 = 1.67