An in silico design tool for Fe(II) spin crossover and light-induced excited spin state-trapped complexes.

The discovery of new coordination complexes that can support spin crossover (SCO) or light-induced excited spin state trapping (LIESST) could be radically improved by better computational tools. While methods such as density functional theory (DFT) are capable of high accuracy, they are too slow for molecular discovery, where millions of individual calculations may be required. In contrast, empirical ligand-field molecular mechanics (LFMM) captures the d-electron effects implicit in DFT and thus can be as accurate, but LFMM is up to 4 orders of magnitude faster. We demonstrate for simple Fe(II) am(m)ines how LFMM can be used to redesign "old" systems to generate novel, potential SCO and LIESST complexes.