In this work, the aim is to characterize how an Fe-based metal-organic framework (MOF) behaves when gases, like carbon dioxide, are inserted through their channels and to characterize the nature and strength of those interactions. Despite the computational nature of the project, it is based on the experimental results obtained in 2016 by Minguez-Espallargas and coworkers (J. Am. Chem. Soc. 2013, 135, 15986-15989). Those MOFs were found to selectively allocate/adsorb CO2 , having as a drawback that apparently each cavity allocates only one CO2 molecule. Despite truncating the MOF to its unitary cell, the whole cavity of the MOF can be described in detail by precise ab initio calculations. Another computational goal is to unravel why experimentally CO2 was preferred with respect to N-2, and for the sake of consistency, a list of common gases will be further studied, such as H-2, O-2, H2O, CH4, C2H6 , N2O, or NO.