Development of an Iron(II) Complex Exhibiting Thermal- and Photoinduced Double Proton-Transfer-Coupled Spin Transition in a Short Hydrogen Bond

Abstract

Multiple proton transfer (PT) controllable by external stimuli plays a crucial role in fundamental chemistry, biological activity, and material science. However, in crystalline systems, controlling multiple PT, which results in a distinct protonation state, remains challenging. In this study, we developed a novel tridentate ligand and iron(II) complex with a short hydrogen bond (HB) that exhibits a PT-coupled spin transition (PCST). Single-crystal X-ray and neutron diffraction measurements revealed that the positions of the two protons in the complex can be controlled by temperature and photoirradiation based on the thermal- and photoinduced PCST. The obtained results suggest that designing molecules that form short HBs is a promising approach for developing multiple PT systems in crystals.

Reversible structural change of [Co2Fe2] complexes between diamagnetic hydrogen-bonded 1D chains and paramagnetic complexes within a layered structure of amphiphilic anions

“…It should also be noted that a Fe spin crossover complex with a short HB has been reported to show a proton transfer-coupled spin transition. 14 Thus, combinations of [Co 2 Fe 2 ] complexes with amphiphilic anions may lead to a variety of assemblies whose structures and electronic properties change in response to external stimuli. Herein, we report a new hybrid of 1 2+ and an amphiphilic anion X − ( 1X 2 , Fig.…”