We curate a dataset from the Cambridge Structural Database (CSD) composed of molecular complexes that are natively coordinated to K + , Na + , and Li + ions (Supporting Information Text S1). The three selected ion species represent some of the most difficult cases of separation due to their similar size, charge, and chemical characteristics. The ionic radii of the three alkali ions range from 0.68 Å for Li + , to 0.97 Å for Na + , to 1.33 Å for K + , 25 but these ions exhibit a range of water coordination numbers, making their hydrated radii difficult to distinguish. The curated molecular complexes range from 20 to 275 atoms and provide a computationally efficient proxy for representing ion channels in larger, periodic materials. From a full set of 8,190 K + , 8,342 Na + , and 10,792 Li + complexes from the CSD, we apply a screening procedure to identify complexes that are suitable for binding energy calculations using density functional theory (DFT) and are representative of ion channels (Figure , Supporting Information Text S1). From this larger set of complexes in the CSD, we next sought to identify "confined" complexes, which we defined as complexes where there exists a contiguous ring of atoms that contains three or more of the ion-coordinating atoms. From this curated set, we examined trends in the coordinating atom environment for each complex and its natively bound ion that we may be able to leverage for selectivity. We obtain geometric features such as the relative ion-coordinating atom distance and coordination number as well as electronic features such as coordinating atom charges and the average electrostatic potential at the coordinating atoms (ESP, Figure ). The relative ion-coordinating atom distance d rel is a normalized distance accounting for ion size and can be defined as: 𝑑 !"# (ion -𝑋) = 𝑑(ion -𝑋)