The lowest-energy configuration for H-FAU_3H is qualitatively similar to the one obtained for H-FAU_2H_1_3. Although the H1•••Ofw hydrogen bond is shorter, the adsorption energy is slightly less negative. As the third proton of the 12MR lies at a distance of 3.25 Å from the H6 atom of 5-FU, repulsive electrostatic interactions between them are likely to be responsible for the somewhat reduced stability. For the more Al-rich models (Figure ), the lowest-energy configurations are generally very similar to those observed for the corresponding H-FAU_1H/2H models, with framework deprotonation occurring in the system with one proton per 12MR (H-FAU_16H) and solely hydrogen-bonded 5-FU in models with two protons per 12MR (H-FAU_32H_1_3/_1_4). Among the whole set of optimised configurations, there are two cases where 5-FU is hydrogen-bonded to framework protons pointing into different 12MRs