Here, we examine the metal coordination geometries, overall connectivities, and chemical composition for mononuclear transition metal complexes in the CSD, considering all 3d, 4d, or 5d transition metals and coordinating atoms. We curated a data set which we refer to as the mononuclear CSD data set, that comprises 242,829 mononuclear transition metal complexes (TMCs) from the Cambridge Structural Database 27 (CSD) version 5.41 (November 2019) combined with the March and May 2020 updates (Supporting Information Figure ). To assign the coordination geometry, we categorized the shape of the primary coordination sphere using the coordination number and all possible L 1 -M-L 2 angles. We reported a subset of this data with octahedral geometries (n = 85,575) in prior work , which we call the octahedral mononuclear CSD data set. We also identified a set of unique TMCs by computing their Weisfeiler-Lehman Zatom weighted connectivity graph hashes. The CSD primarily contains 3d TMCs with 2p coordinating atoms (Figure ). Overall, we find that Fe metal centers with N/C coordinating atoms are most heavily sampled across the full mononuclear CSD data set (Figure ). These observations shift only slightly when analyzing unique molecules, with Cu appearing in a high number of distinct complexes (Figure ). Later-group metals more frequently feature 3p metal-coordinating atoms, recapitulating expectations from hard-soft acid base theory (Supporting Information Figure ). There are numerous exceptions, however, that motivate further analysis across the full data set. Our data set is larger than both the tmQM 3 and cell2mol 2 data sets because we do not place constraints on the net charge or elemental identity of transition metal atoms, thus spanning the full set of mononuclear compounds in the CSD. We observe 10 distinct coordination geometries with varying coordination numbers (CN) across all mononuclear compounds: CN 4 (i.e., tetrahedral, square planar, seesaw), CN 5 (i.e., trigonal bipyramidal and square pyramidal), CN 6 (i.e., octahedral and trigonal prismatic), CN 7 (i.e., pentagonal bipyramidal), and ambiguous coordination number sandwich (hapticity, h, > 2) or edge (h = 2) compounds. Of these, CN 6 octahedral and CN 4 seesaw are the most and least common geometries, respectively (Supporting Information Figure and Table ). In accordance with molecular orbital theory, we find that metal identity influences the preferred coordination geometries. We find that 50% (29,540 out of 59,037) of mid-row 3d (i.e., Cr, Mn, Fe, and Co) TMCs are in octahedral geometries, whereas only 2% (1,066) are in square planar geometries and < 0.5% (244) are in seesaw geometries (Supporting Information Table ). This is in contrast to later 3d (i.e., Ni, Cu, Zn) TMCs that are comparably represented in our data set (i.e., mid-row: 59,037, late: 61,432) but sample geometries with lower coordination numbers. Only 28% (17,071 out of 61,432) of late TMCs are in octahedral geometries, with a comparable 28% (17,427 out of 61,432) in square planar geometries (Supporting Information Table ).