As a second example, the energetic ordering of those fluoride sites that are associated with 4MRs in IFR is investigated. Since the shortest F-F distance corresponds to the length of the c axis for symmetry reasons, it is essentially identical for all configurations, and the observed energy differences cannot be explained on this basis. An evaluation of distance between fluoride anions and N atoms of the closest BQol + cation, tabulated in Figure , shows that this distance is shortest for the lowest-energy site (F@Si6_1), indicating that attractive interactions between the positively polarized part of the OSDA and the fluoride anions play an important role in determining the energetically most favorable location. However, the large difference of 10.6 kJ mol -1 between the F@Si6_1 and F@Si6_2 sites, for which the F-N distance is (virtually) identical, cannot be rationalized on this basis. This observation can be explained with repulsive interactions between the fluoride anions and the O atoms of the BQol + OH group, both of which bear a significant negative charge (according to Hirshfeld partitioning, qHsf(F) = -0.49 e and qHsf(OBQol) = -0.75 e).