The remaining structures have been included in the ESI. It was evident that the larger ionic radius of the Cl -ion was not a good size match for the central tetralactam cavity. In all cases, the remaining host:guest Cl -complexes (2a•Cl -, 3a•Cl -, 4b•Cl -) formed hydrogen bonding interactions above and below the plane of the cavity or resulted in the macrocyclic scaffold buckling to adjust the hydrogen bond donors into a more energetically favourable conformation (Figure , a, S60, and S63). In comparison, the other F -complex, 3a•F -, confirms that the atomic radius of the F -anion is a perfect size match for the tetralactam cavities (Figure ). Both F -complexes contain F -bound directly within the binding cavity. Similarly to the Cl - complexes, the host macrocycles of the F -complexes also buckled to reorient the hydrogen bond donors for guest binding interactions. While most of the Cl -complexes obtained for the series show 1:1 guest binding, the solid-state structures of 1b•2Cl -and 2a•2Cl -also revealed the ability of 1:2 host:guest complex formation (Figure and). In both instances, one anion was bound above the cavity by two amide protons and the other below the cavity by the other two amide protons. Notably, the same crystal that yielded the 2a•2Cl -complex also produced the 1:1 complex (2a•Cl -), which exhibited all four direction amide protons forming hydrogen bonding interactions with the one Cl -anion above the central cavity (Figure and).