We next analyzed trends in common coordinating atoms and metals to gain insight into common metal-ligand environments represented in the curated dataset. The most common coordinating atom in the ligand dataset by far is nitrogen, representing over 52% of the total number of coordinating atoms across all ligands (Figure ). The 2p coordinating atoms carbon (19%) and oxygen (15%) are the next most common, while the 3p coordinating atoms phosphorus (7%), sulfur (6%), and silicon (0.4%) are less abundant (Figure ). We include silicon in our dataset despite its low occurrence because it is a known coordinating atom used in ligand design for TMCs and occurs far more frequently than any other coordinating atom element removed during filtering (SI Appendix, Figure ). Due to the imbalanced distribution of coordinating atom elements in the overall dataset, we anticipate that machine learning models will perform better on ligands containing the more abundant 2p coordinating atoms carbon, nitrogen, and oxygen rather than 3p coordinating atoms silicon, phosphorus, and sulfur. When analyzing the coordinating atom frequency for each specific denticity individually, we identify distinct trends from the global frequencies (SI Appendix, Figures ). For example, nitrogen is the most common coordinating atom overall, but carbon is the most common in the individual analysis of ligands with six coordinating atoms, which is indicative of the high presence of benzene coordinating motifs in six-coordinate ligands (SI Appendix, Figure ). We also assessed trends by ligand coordination number in the most frequent metal identities. While ruthenium is the most common metal overall and for one or six coordinating atoms, the sets of ligands with two, three, four, and five coordinating atoms each favor different metals (SI Appendix, Figures and). The abundance of one-coordinate ligands observed coordinated to ruthenium is in agreement with the known chemical relevance of Grubbs catalysts, which typically contain monodentate ligands. Six-coordinate ligands coordinated to ruthenium are similarly well-represented likely due to their use in ruthenium piano-stool complexes widely studied for their cytotoxic activity. Fivecoordinate ligands are most frequently observed coordinated to iron, consistent with the abundance of ferrocene structures in the CSD. While the cyclopentadienyl binding motifs characteristic of ferrocenes are an example of ligands with five coordinating atoms but different denticities and hapticities, many five-coordinate, pentadentate ligands consisting of bridged pyridine and pyrazole substructures are also observed. On the other hand, four-coordinate ligands being most frequently observed coordinated to nickel is in line with the known significance of bis(cyclooctadiene) nickel and related low-valent nickel species, which include four-coordinate octadiene and other haptic cycloalkene ligands. Two-and three-coordinate ligands are most often coordinated to copper, the second-most common transition metal center observed in the overall dataset, although their occurrence with ruthenium is still high. Despite these differences in metal preference among ligands with different numbers of coordinating atoms, nearly all metals are observed at least once in each category. The only exception to this is gold, which is not observed with five-or sixcoordinate ligands (SI Appendix, Figures ).