Tuning the spin-crossover properties of Fe II4L6 cages via the interplay of coordination motif and linker modifications

Abstract

Despite the increasing number of spin-crossover Fe^II-based cages, the interplay between ligand modifications (e.g. coordination motif substituents and linker) is not well-understood in these multinuclear systems, limiting rational design. Here, we report a family of Fe^II₄L₆ spin-crossover cages based on 2,2′-pyridylbenzimidazoles where subtle ligand modifications lowered the spin crossover temperature in CD₃CN by up to 186 K. Comparing pairs of cages, CH₃ substituents on either the coordination motif or phenylene linker lowered the spin-crossover temperature by 48 K, 91 K or 186 K, attributed to electronic effects, steric effects and a combination of both, respectively. The understanding of the interplay between ligand modifications gained from this study could be harnessed on the path towards the improved rational design of spin-crossover cages.