Chemical Manipulation of the Spin-Crossover Dynamics through Judicious Metal-Ion Dilution.

In 2019, our groups described a unique Fe complex, [Fe(L)(NCBH)] (L = -dimethyl--bis(2-pyridylmethyl)-1,2-ethanediamine) possessing a low-spin ground state that is not easily accessible due to the extremely slow dynamics of the high-spin to low-spin phase transition. Herein, we report the successful chemical manipulation of this spin-crossover (SCO) process through controlled metal-ion dilutions. The emergence or suppression of the thermally induced SCO behavior was observed depending on the radius of the metal ion used for the dilution (Ni or Zn). Reversible photo-switching has been confirmed in all mixed-metal complexes whether the low-spin state is thermally accessible. Remarkably, the dilution with Zn metal ions stabilizes HS Fe complexes with complete suppression of the thermally induced SCO process without destroying the reversible photoswitchability of the material.