(A) Molecular structures of receptors 21 and 22.
(B) Single crystal X-ray structure of the complex [(CO3)2(H2O)2]4− ⊂ 214.
(C) Single crystal X-ray structure of the complex [(SO4)2]4− ⊂ 214.
(D) Single crystal X-ray structure of the complex [(SO4)2]4− ⊂ 224.
All anions encapsulated within the cavity are shown in space-filling form. Color code: C = gray, N = blue, Cl = green, S = yellow, and Br = brown. The counter cations and solvent molecules outside the cavities are omitted for clarity.