A successful structural optimization was not achieved in each EB-cation combination and complex (Figure right). Accordingly, the "ideal" 1:1 EB:M z+ in complex as depicted in Figure was only stable with Na + , Mg 2+ and Ca 2+ , where the ions were coordinated by all six oxygen atoms of esters and amide, with the ion lifted slightly towards the amide groups. With Li + instead a highly distorted structure was obtained, where the small ion experiences a pseudo-tetrahedral coordination by two amide and two ester groups. However, with K + and Cs + , this structure was unstable and the cation was released out of the EB ring to afford a stable amide-ligated EB:M z+ out structure suggesting that 1:1 belted EB:M z+ in complexes of these two cations do not exist. The open-faced EB:M z+ out structure was stable with all tested ions. The EB2:M z+ sandwich complex, as shown in Figure and demonstrated or proposed previously, was obtained with K + , Cs + , Mg 2+ and Ca 2+ . Instead, with Na + and Li + distorted structure was formed. Na + was still coordinated by three amides of one EB ring, but the second ring "lifted off" and added only two additional amide coordinations creating a displaced EB-EB arrangement. With Li + the distortion was even more pronounced, where a trigonal coordination was achieved by two amides from one and the third from the other EB ring.