Comparison of the number of metal-containing and metal-free structures. The percentage of the structures containing a metal was found to be 32.3%, while the percentage lacking a metal was 67.7%. The dataset for this comparison was obtained from the Cambridge Structual Database by searching for all structures featuring the TFSI core framework (which has the molecular formula N(SO₂CF₃)^2-) as specified by connectivity only and agnostic of the individual atom-to-atom bond type.