In the presence of H2P2O7 2-, all three macrocycles were able to adopt conformations in which all four Hbond donors are interacting with the guest (Figure ), however with different NH to O bond lengths: the NH to O distances fall within the range of 1.47-1.80 Å with averages of 1.64 Å and 1.70 Å for macrocycles 2 and 3 respectively, whereas the average H-bond length of macrocycle 1 is 1.88 Å. Macrocycles 2 and 3 can furthermore adapt their conformation to have all four NH groups interacting with a smaller Cl -anion (Figure and 2i, NH to Cl distances of 2.19-2.35 Å), while the more rigid macrocycle 1 is unable to utilize all four NH groups to interact with the Cl -anion, which is thus located at one of the two dipicolinic bisamide sites (Figure , NH to Cl distances of 1.99 and 2.03 Å).