In addition to coordination number, the size and flexibility of the coordinating ring also is expected to play a role in determining ion preference. We define the coordinating ring as the smallest continuous closed ring of atoms in the complex that contains at least three ioncoordinating atoms, where the 'ring size' is the number of atoms in this coordinating ring. The coordinating ring therefore represents the narrowest confinement region of an ion channel, e.g., in a nanoporous material. While the complexes CEGFIG, CEJFAA, and SONJAG (i.e., the extreme cases of the Li-native distribution in Fig. ) in the natively Li + -coordinating set all have a coordination number of 5 in comparison to an average in the set of 5.7, only CEGFIG has a preference for larger Na + and K + ions over the smaller Li + . Its unique characteristic is its larger ring size of 18 compared to 12 for CEJFAA and SONJAG, where the average in the set is 13.2. This trend is also generally seen across the three datasets, where larger ring sizes favor exchange to larger ions given a fixed coordination number (Supporting Information Figure ). This suggests that larger ring sizes are more conducive to flexible adjustment of the complex to incorporate larger-sized ions.