Functionalized spin-crossover metal-organic frameworks (SCO-MOFs) are promising candidates for multi-responsive molecular switches which have garnered great attentions in advanced material science for their hi-tech applications toward sensors, memory storage and electronic devices. Post-synthetic modification (PSM) is a judicious expanding toolkit to modify targeted functionalities in SCO-MOFs but rarely reported up to now. Reversible PSM in SCO materials remains a great challenge, which may be expected to widen its application scenarios and allow multitasking operations within one reprogrammable platform. Herein, we present the manipulations of switchable SCO behaviors via the coupling of spin transition and reversible redox states. The reverse Hofmann-type SCO-MOFs [Fe(TPB){M(CN)n}] (M = AuI, n = 2; M = PtII, n = 4; TPB = 1,2,4,5-tetra(pyridin-4-yl)benzene) display redox-programmable capability toward dihalogen molecules (X2) thanks to the redox-active cyanometallate modules and guest-accessible channels in lattices. Chemo-redox PSM onto the open metal sites via oxidative intercalations of X2 or reductive elimination by ascorbic acid/sodium thiosulfate results in the switchable SCO behaviors between hysteretic single-step and stepwise spin transition. Periodic DFT calculations using various SCAN-type exchange-correlation functionals have been employed to rationalize the SCO dynamics. These findings open a new perspective for designing multi-responsive molecular switches.

Redox-programmable spin-crossover behaviors in reverse Hofmann-type frameworks

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