Reversible Photo- and Thermo-Induced Spin-State Switching in a Heterometallic {<i>5d-3d</i>} W₂Fe₂ Molecular Square Complex

Abstract

Following the complex-as-a-ligand strategy, self-assembly of [W(CN)₈]^3- and iron(II) with bidentate nitrogen donor ligand bik (bik = bis(1-methyl-1<i>H</i>-imidazol-2-yl)ketone) ligand affords a cyanide-bridged [W₂Fe₂] molecular square complex [HNBu₃]₂{[W(CN)₈]₂[Fe(bik)₂]₂}·6H₂O·CH₃OH (<b>1</b>). The complex was characterized by single-crystal X-ray diffraction analyses, (photo)magnetic studies, optical reflectivity, electrochemical studies, and spectroscopic studies. Structural analyses revealed that in the [W₂Fe₂] square motif tungsten(V) and iron(II) centers reside in an alternate corner of the square and are bridged by the cyanide ligands. Complex <b>1</b> exhibits thermo-induced spin crossover (SCO) between {W^V (<i>S</i> = 1/2) - Fe^II_LS (<i>S</i> = 0)} and {W^V (<i>S</i> = 1/2) - Fe^II_HS (<i>S</i> = 2)} pairs near room temperature and photoinduced spin-state switching with <i>T</i>_LIESST = 70 K under light irradiation at low temperature. To the best of our knowledge, <b>1</b> represents the first complex containing iron(II) and [W^V(CN)₈]^3- units exhibiting both SCO and photomagnetic effect.