The pore-to-pore minimum energy paths exhibit a slight minimum in the middle, i.e., close to the linkers. Optimizing the guest molecules at the window position of the previous NEB, i.e., close to linkers, converges instantaneously. The observed forces are very weak (below the convergence criterion of 0.02 eV/ Å) and energy differences are very small: all guest molecules exhibit energy differences between the window and center of the pore of less than 1.5 kJ/mol except for H2O where the energy difference is 2.5 kJ/mol. All molecules slightly favor the window position over the center of the pore. The energy difference between the centers of the large and small pores is also very small (the largest energy difference being 1.1 kJ/mol for CH3OH with a preference for the smaller cavity). The small energy differences between the center of the pore and the pore windows are within the accuracy of the methodology. Also, no significant forces are observed at either the pore window or center of the pore, suggesting a rather flat potential energy surface throughout the pore system. This fits well with the small size of the adsorbates compared to the large pore and window sizes. Using PoreBlazer 4.0 with default settings, we calculated the pore limiting diameter to be 9.4 Å (manually measured distances between hydroxy oxygens are approx. 9 Å). The diameters of the two pores, as determined by PoreBlazer, are 12.0 Å and 16.5 Å. As the pore windows are too large to significantly influence diffusion, we further investigated the adsorption energies of the guest molecules on a Zn-only node, to evaluate the potential role of non-catalytic nodes in the guest's mobility within the MOF. We calculated these adsorption energies by manually placing the guest molecules close to a Zn metal atom and performing a geometry optimization. Resulting adsorption energies are given in Table , together with adsorption energies on the active iron site. As observed for the methanol adsorption on the M site, the hydrogen-bonded conformation exhibits a significantly stronger interaction with the metal node than the conformation without a hydrogen bond, and the adsorption energy of methanol with a hydrogen bond is therefore comparable to that of water. The adsorption energy of methanol on the Zn site is furthermore significantly stronger (-52.7 kJ/mol) than on the M and MO sites (-35.2 and -34.4 kJ/mol), which could be useful to prevent overoxidation by binding product methanol molecules to a Zn site until removal from the pores. The strongest adsorption energy of methanol found on the linker is only -22.8 kJ/mol. An NEB calculation of the methanol movement from one Zn site across a linker to another Zn site results in an energy barrier of +39.6 kJ/mol (PBE, see Figure ). From this we conclude that the linker-methanol interactions are not strong enough along the entire linker to facilitate transport of methanol at the pore walls. The difference between the energy barrier along the linker and desorption to the center of the pore is less than 13.1 kJ/mol for methanol. Therefore, diffusion of methanol should be determined mainly by the interaction strength with the Zn sites, not by the pore size or linkers. All other guests show no significant preference for binding to Zn versus Fe sites (see Table ), and their diffusion is therefore expected to be influenced mainly by the relatively small host-guest interactions (which are dispersion dominated). These insights suggest one major route to achieve a higher selectivity towards methanol in a non-continuous setup of this catalytic system: exploiting the stronger zinc-methanol interactions to immobilize methanol at abundant non-reactive sites.