The larger ionic radii of I -(2.20 Å), Br -(1.96 Å), and Cl -(1.81 Å) prevents the anions from binding directly within the cavity, unlike F -(1.33 Å). The two hydrophobic oxo-anions NO3 -(1.79 Å) and ClO4 -(2.50 Å) had the lowest transport rate due to the poor geometrical fit hindering their binding to the rigid binding cavity. However, further analysing the average halide selectivity sequence of I -> Br -> Cl -showed that along with a favourable geometry, transport selectivity increased as halide hydration enthalpies decreased, anion hydrophobicity increased, and ionic radii increased. Despite I -binding to NH-based anion receptors generally observed to be weak in organic solvents, many NH-based anion transporters including the tetralactam series shows the highest selectivity for it over the other halides due to the lower free energy of solvation (ΔGhyd = -280 kJ mol -1 ) and higher hydrophobicity, enabling more efficient membrane partitioning. Likewise, Br -is more hydrophobic and has a weaker hydration energy (ΔGhyd = -318 kJ mol -1 ) than Cl -(ΔGhyd = -344 kJ mol -1 ), accounting for the observed Br -> Cl - transport selectivity. Also aiding in the observed halide > oxo-anion selectivity are the enhanced binding interactions and greater stability afforded by the macrocyclic effect after the formation of the host:guest complexes.