Although octahedral geometries (n = 85,575) significantly outnumber both square planar (n = 49,643) and square pyramidal (n = 12,782) geometries, they have comparable numbers of unique tetradentate ligands (Supporting Information Table ). We find that 10% (957 out of 9,855) of these tetradentate ligands appear in two coordination geometries and 176 appear in all three (Supporting Information Figure ). For example, a dianionic N 4 ligand that appears with Fe in an octahedral geometry with two cyanopyridine ligands (refcode: CESBEH) also appears with Fe in a square pyramidal geometry with a methanol ligand (refcode: KARFUF) and without any axial ligands, in a square planar geometry (refcode: KARFOZ), indicating that the additional ligands are removable (Supporting Information Figure ). Nevertheless, complexes with intrinsically labile ligands may simply have not been crystallized without these ligands, suggesting the identified complex counts in multiple coordination geometries represent a lower bound on such complexes. It is not generally known which coordination geometry a given metal and ligand combination will favor. We might expect larger metals to prefer ligands with lower connectivity if it allows for more flexibility around the metal. To identify these relationships, we defined "closed" and "open" tetradentate ligands as those with or without a closed ring containing all four metal-coordinating atoms, respectively. The relative frequency of closed and open structures is roughly comparable among octahedral, square pyramidal, and square planar coordination geometries, indicating that overall tetradentate ligand connectivity alone does not dictate coordination geometry (Figure and Supporting Information Figure ). Because many metalcoordinating atoms appear within rings (i.e., are cyclic), we investigated the frequencies of ring substructures. Octahedral TMCs less frequently contain cyclic coordinating atoms relative to square planar or square pyramidal TMCs, indicating that metal-local atom connectivity influences crystallized geometry more than the global tetradentate connectivity (Figure and Supporting Information Figure ). Pyrrole and pyridine substructures are frequently observed in tetradentate ligands, whereas the 3p equivalents of these substructures (i.e., phospholes or phosphorines) appear infrequently (Supporting Information Figure ). Additionally, we find that 3p coordinating atoms more frequently appear in non-cyclic environments relative to 2p coordinating atoms (2p: 43% cyclic, 3p: 4% cyclic). In line with hard-soft acid-base theory, we find that ligands with any 3p coordinating atoms tend to coordinate heavier (e.g., 4d or 5d) metals, which are also less frequently sampled overall (Supporting Information Figure ). Thus, re-metalating existing 3p-coordinating tetradentate ligands with new 4d or 5d transition metals is a promising strategy for chemical space exploration. Finally, given that we have identified tetradentate ligands paired with one or more monodentate ligands as candidates for catalytic applications, we searched for TMCs that have not yet been used for catalysis but are good candidates for such purposes. Using our previous approach for text mining manuscripts , we curated a corpus for octahedral and square planar TMCs that contain tetradentate ligands. Using a lexicon selected by trial and error to perform keyword matching, we identified when the publications corresponding to the deposited structures did not draw conclusions on catalytic activity (Supporting Information Table and a list of DOIs are provided in the Zenodo repository). We examined keywords in the main text as well as in article titles. Surprisingly, only a minority (28%) of octahedral compounds containing planar tetradentate ligands with downloadable manuscripts had been studied for catalysis, and the fraction was even lower for other coordination geometries (square planar: 22%, Supporting Information Table ).