Using a self-assembly process involving a [Mo^III(CN)₇]⁴⁻ unit, an Fe^II ion, and a 1,4-bis(4H-1,2,4-triazol-4-yl)benzene (btb) ligand, we have synthesized a novel coordination polymer, denoted as {K₂Fe^II(btb)[Mo^III(CN)₇]·5H₂O}_n (1). Single-crystal structure analysis revealed a three-dimensional (3D) Hofmann-type framework for compound 1. The [Mo^III(CN)₇]⁴⁻ unit engaged four cyanide groups to coordinate with Fe^II ions, creating an anionic two-dimensional (2D) cyano-bridged layer of {Fe^II[Mo^III(CN)₇]}_n. The btb ligands, in turn, coordinated axially with the Fe^II ions, bridging adjacent 2D layers and thus constructing a 3D framework. Magnetic studies have shown that compound 1 exhibits a hysteretic one-step spin-crossover behavior. Moreover, a ferrimagnetic ordering with a critical temperature of approximately 65 K was also observed, which may be ascribed to the compound's “core–shell” architecture: the main core is responsible for the SCO behavior, while the shell contributes to the ferrimagnetic characteristics. To the best of our knowledge, this is the first observation of spin-crossover behavior in compounds based on the [Mo^III(CN)₇]⁴⁻ unit.

中文翻译：

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由 [MoIII(CN)7]4− 单元构建的霍夫曼型金属有机框架中的滞后自旋交叉


使用包含 [Mo ^III (CN) ₇ ] ⁴⁻ 单元、Fe ^II 离子和1,4-双(4H-1,2,4-三唑-4-基)苯(btb)配体，我们合成了一种新型配位聚合物，记为{K ₂ Fe ^II (CN) ₇ ]·5H ₂ O} _n (1)。单晶结构分析揭示了化合物 1 的三维 (3D) 霍夫曼型骨架。 [Mo ^III (CN) ₇ ] ⁴⁻ 单元使四个氰化物基团与 Fe ^II 离子配位，形成阴离子二维 (2D) 氰基桥联层 {Fe ^II [Mo ^III ( CN) ₇ ]} _n 。 btb 配体反过来与 Fe ^II 离子轴向配位，桥接相邻的 2D 层，从而构建 3D 框架。磁性研究表明，化合物 1 表现出滞后的一步自旋交叉行为。此外，还观察到临界温度约为 65 K 的亚铁磁有序，这可能归因于该化合物的“核-壳”结构：主核负责 SCO 行为，而壳则有助于亚铁磁特性。据我们所知，这是基于 [Mo ^III (CN) ₇ ] ⁴⁻ 单元的化合物中自旋交叉行为的首次观察。