Metal–organic frameworks (MOFs) provide versatile platforms to construct multi-responsive materials. Herein, by introducing the neutral tetradentate ligand and the linear dicyanoaurate(I) anion, we reported a rare cationic MOF [Fe^II(TPB){Au^I(CN)₂}]I·4H₂O·4DMF (TPB = 1,2,4,5-tetra(pyridin-4-yl)benzene) with hysteretic spin-crossover (SCO) behavior near room temperature. This hybrid framework with an open metal site (Au^I) exhibits redox-programmable capability toward dihalogen molecules. By means of post-synthetic modification, all the linear [Au^I(CN)₂]^– linkers can be oxidized to square planar [Au^III(CN)₂X₂]⁻ units, which results in the hysteretic SCO behaviors switching from one-step to two-step for Br₂ and three-step for I₂. More importantly, the stepwise SCO behaviors can go back to one-step via the reduction by l-ascorbic acid (AA). Periodic DFT calculations using various SCAN-type exchange-correlation functionals have been employed to rationalize the experimental data. Hence, these results demonstrate for the first time that switchable one-/two-/three-stepped SCO dynamics can be manipulated by chemical redox reactions, which opens a new perspective for multi-responsive molecular switches.

中文翻译：

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阳离子框架中的氧化还原可编程自旋交叉行为

金属有机框架 (MOF) 为构建多响应材料提供了通用平台。在此，通过引入中性四齿配体和线性二氰基金酸盐(I)阴离子，我们报道了一种罕见的阳离子MOF [Fe ^II (TPB){Au ^I (CN) ₂ }]I·4H ₂ O·4DMF (TPB = 1, 2,4,5-四（吡啶-4-基）苯）在室温附近具有滞后自旋交叉（SCO）行为。这种具有开放金属位点 (Au ^I ) 的混合框架对二卤素分子表现出氧化还原可编程能力。通过合成后修饰，所有线性 [Au ^I (CN) ₂ ] ^-接头可以被氧化成方形平面 [Au ^III (CN)₂ X ₂ ] ^{-单位，这导致 Br} ₂的滞后 SCO 行为从一步切换到两步，而 I ₂则从三步切换。更重要的是，逐步的 SCO 行为可以通过l-抗坏血酸 (AA) 的还原回到一步。已采用使用各种 SCAN 型交换相关泛函的周期性 DFT 计算来合理化实验数据。因此，这些结果首次证明了可切换的单步/两步/三步SCO动力学可以通过化学氧化还原反应来控制，这为多响应分子开关开辟了新的视角。