Below we describe our three approaches for obtaining SMILES for TMCs; fixing CSD SMILES, using xyz2mol with DFT-NBO input and xyz2mol with extended Hückel input. The latter requires only the xyz-coordinates, overall charge and RDKit, whereas the other two require either an initial SMILES from the CSD or a DFT calculation yielding the necessary NBO data. Since TMC SMILES are not currently incorporated in chemical research, there is no established consensus on how to represent e.g. bonds to transition metals. Here we choose a representation, where the electrons in the TM-ligand bond are located on the ligand, i.e. all TM-ligand bonds are represented by dative bonds (symbolized by an arrow in the SMILES). This has the advantage of making the ligand charges and metal oxidation states directly available. Contrary to organic chemistry relating to e.g. drug discovery, a chemical entity such as a carbene is a lot more common as a ligand in a TMC. Often another representation obeying the octet rule could also be drawn (Figure ). Here, we choose the carbene representation (non-zwitterionic). The carbene representation has the advantage of avoiding the ambiguity of assigning the positive charge on nitrogen for asymmetric ligands.