Aggregation-Induced Spin-Crossover Switching in a Spin-Labile Iron(II) Complex

In this study, an aggregate-responsive spin crossover (SCO) system was presented based on the spin-labile iron(II) complex Fe(HL)2(NCS)2<middle dot>2DMF (1) (HL = methyl 2-(2-pyridinyl)-1H-benzimidazole-6-carboxylate). Complex 1 exhibits the switchable SCO behavior between the solution and crystalline state through the solvent-driven aggregation control. The addition of the poor solvent dioxane to the methanol solution of the title complex not only generates nanoparticles with increasingly larger sizes in accompaniment with the absence of SCO but also changes the orientation of the isothiocyanate from cis in the methanol solution to the trans isomer in the aggregate or solid via an aggregation process.