Transition metal chemical space remains challenging to traverse due to oxidation and spin state variability, a variety of metal-coordinating environments, and limited experimental data relative to organic chemistry. This chemical space holds the potential to discover new catalysts for known reactions , catalysts with new mechanisms , or functional materials with promising optical , sensing , or magnetic properties. Over the past two decades, this opportunity has motivated efforts to improve transition metal complex (TMC) design by mapping the space of known TMCs. Many of these efforts have been localized to specific metals or ligand classes to develop ligand knowledge bases (e.g. on phosphine or carbene 26 ligands) to understand how to design new TMCs with improved properties.