SMILES strings of mononuclear TMCs were extracted from the CSD as described by Frei and Orsi except that only d-block elements and all coordination numbers were * * * * Before fix After fix ID OPAKAT IXENEG : Example of moving a negative charge due to ligand atoms being equivalent for the isolated ligand but not for the whole complex (OPAKAT). IXENEG is an example of the NO 2 -group fix: we make sure all NO 2 -groups are described in the neutral form. considered. The initial screening process eliminated cases where the counter-ion also contained a metal, which eliminated some compounds that were included by Balcells and co-workers. We add these entries, making tmQMg a subset of the CSD dataset, and remove complexes containing group 1 or group 2 elements and complexes containing > 100 heavy atoms. This results in 230,550 SMILES. For 7,297 TMCs we are unable to retrieve a SMILES via the API and 7 entries have been deleted from the CSD after tmQMg was curated. Of the remaining 223,246 SMILES, RDKit can only successfully sanitize 123,147 SMILES strings and we therefore implemented a custom SMILES fixer process that all CSD SMILES strings were subjected to.