Those with energy gaps between possible spin states smaller than 5 kcal/mol were excluded, as they fall below the chemical accuracy of DFT for spin-state energetics of TM complexes. This filtering step also eliminates spin-crossover complexes, for which ground spin state changes with an external stimulus like temperature or pressure as a result of vibrational and electronic entropy contributions. Finally, complexes exhibiting an expectation value of Ŝ2 that deviates from the exact value of S(S + 1) by more than 0.1 for the singlet and doublet ground states, and more than 0.2 for the other ground state spins were also excluded. Overall, a total of 229 complexes were removed by the three consecutive filters. For further details on the in-depth analysis of the DFT results and excluded complexes, see section S2 in the SI.