Comparison of 2 with receptors 6 and 7 that have similar geometry but possess either -H (6,  = 1.5 D, ESP(Ha) = 117 kJ mol -1 ) or -Br (7,  = 4.3 D, ESP(Ha) = 163 kJ mol -1 ) substituents in the upper rim points to the crucial role of the electron withdrawing nitro substituent. For 6, Cl -binding affinity is three orders of magnitude lower, while for 7 it is 20 times lower than for 2. Multivalency and convergence are also crucial, as illustrated by binding affinities of 4 and 5. Almost no binding was observed for the acyclic monomer 5. Macrocycle 4, which adopts a boat conformation, also binds anions but considerably in a weak manner, and uses OH groups from the upper rim rather than CHas from the lower rim. This is in agreement with the DFT calculations, which show much lower ESP values for I and no accumulation of the ESP at Has of 4 (Fig. ).