For the complexes in the curated data set, we first examine metal-ligand bond lengths in the experimental low-T and high-T X-ray crystal structures to confirm that they capture a change typical of a spin transition (i.e., LS to HS increase of ca. 0.1-0.2 Å). For this analysis, we focus on scaled bond lengths evaluated relative to the sum of covalent radii of each ligand connecting atom and iron, as done in prior work 122 , to account for the expected differences of Fe-S bond lengths compared to Fe-N and Fe-O bond lengths due to the larger size of S. A spin transition is evident in the crystal structures, with high-T structures typically exhibiting longer scaled bond lengths by ca. 0.07 in comparison to low-T structures, i.e., we observe an increase in bond lengths of ca. 0.16 Å (Figure and Supporting Information Table ). There are some differences within each spin state by ligand denticity, with shorter scaled bond lengths (ca. by 0.02) for SCO complexes with ligands of higher denticities, and longer metal-ligand bond lengths (ca. 1.02) are observed for some hexakis monodentate complexes (Figure and Supporting Information Table ). Outliers are also observed predominantly for bis tridentate cases such as a complex (refcode: QACKAJ 149 ) that has relatively similar average metal-ligand bond lengths (ca. 2.13 Å and 2.16 Å) in low-T and high-T structures (Figure and Supporting Information Table ). The bond length filter employed during data set curation does not screen out complexes with relatively comparable bond lengths since the cut off we use for bond length difference is only > 0.02 Å. Nevertheless, low-T and high-T structures are assigned LS and HS states, respectively through magnetic susceptibility experiments and Mössbauer spectroscopy 149 , and thus the rigidity of the tridentate ligands in this example likely prevents significant bond length changes with spin state. We next analyzed the change in scaled metal-ligand bond lengths with change in spin state observed in the DFT-optimized geometries of these SCOs (Figure ). The B3LYP scaled metal- ). The B3LYP-optimized HS scaled bond lengths are typically longer than their experimental high-T counterparts, and the LS scaled bond lengths are also longer than the low-T experimental bond lengths for most (87) structures, although there are exceptions (Figure and Supporting Information Table ). For the 8 SCOs where B3LYPpredicted LS scaled bond lengths are shorter than the low-T experimental values, they correspond to cases where low-T experimental bond lengths were longer than typically expected values (i.e., significantly above 0.95 relative bond lengths 122 , Figure and Supporting Information Table ).