Room-Temperature Bistability in a Ni-Fe Chain: Electron Transfer Controlled by Temperature, Pressure, Light, and Humidity

Abstract

Bistable and stimuli-responsive molecule-based materials are promising candidates for the development of molecular switches and sensors for future technologies. The CN-bridged {NH₄ [Ni(cyclam)][Fe(CN)₆ ]⋅5 H₂ O}_n chain exists in two valence states: Ni^II -Fe^III (1^HT ) and Ni^III -Fe^II (1^LT ) and shows unique multiresponsivity under ambient conditions to various stimuli, including temperature, pressure, light, and humidity, which generate measurable response in the form of significant changes in magnetic susceptibility and color. The electron-transfer phase transition 1^LT ↔1^HT shows room-temperature thermal hysteresis, can be induced by irradiation, and shows high sensitivity to small applied pressure, which shifts it to higher temperatures. Additionally, it can be reversibly turned off by dehydration to the {NH₄ [Ni^II (cyclam)][Fe^III (CN)₆ ]}_n (1 d) phase, which features the Ni^II -Fe^III valence state over the whole temperature range, but responds to pressure by yielding Ni^III -Fe^II above 1.06 GPa.

Keywords: bistability; electron transfer; molecular switches; multiresponsivity; phase transitions.