Room temperature bistability in an Ni‐Fe chain: electron transfer controlled by temperature, pressure, light and humidity

Bistable and stimuli-responsive molecule-based materials are promising candidates for the development of molecular switches and sensors for future technologies. The CN-bridged {NH 4 [Ni(cyclam)][Fe(CN) 6 ]∙5H 2 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 in 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 {NH 4 [Ni II (cyclam)][Fe III (CN) 6 ]} n ( 1d ) phase, which shows the Ni II -Fe III valence state in the whole temperature range, but responds to pressure giving  Ni III -Fe II above 1.06 GPa.