Stimuli-responsive switchable molecules represent an important category of magnetic materials with significant potential for functional devices. However, engineering complexes with controlled switchability remains challenging due to their sensitivity to lattice interactions. Herein, we report a [Fe2Co2] square complex [FeTp(CN)3]2[Co{(F5-Ph)Py}2]2•2ClO4•4CH3OH•2H2O {1•4CH3OH•2H2O; (F5-Ph)Py = (Z)-N'-(perfluorophenyl) picolinimidamide and Tp = hydrotris(1-pyrazolyl)borate)}, tailored with hydrogen bonding (HB) donor and acceptor moieties for effective lattice interactions. The alteration in HB interactions in crystal phases obtained via single-crystal-to-single-crystal (SC-SC) transformation (i.e. 1•4CH3OH•2H2O  1•2H2O  1) led to a remarkable change in magnetic properties. 1•4CH3OH•2H2O and 1 possesses [FeIILS(-CN)CoIIILS] and [FeIIILS(-CN)CoIIHS] configurations, respectively. While, 1•2H2O demonstrates multi-responsive (thermo-, photo- and pressure) reversible two-step electron transfer coupled spin transition (ETCST) accompanied by thermal contraction and expansion. The complete diamagnetic [FeIILS(-CN)CoIIILS] configuration in 1•2H2O was obtained at an intermediate temperature accompanied by thermal contraction, an unusual behaviour observed for the first time in cyanide-bridged systems. Additionally, 1•2H2O displayed temperature-induced excited spin state trapping (TIESST) of ~70 % of paramagnetic [FeIIILS(-CN)CoIIHS] configuration at low temperatures. The isothermal relaxation of the thermally trapped paramagnetic state shows a much faster and complete conversion to a diamagnetic state at ~140 K, compared to the relaxation observed at other temperatures (100 K - 190 K), corroborating with the observed unique magnetic behaviour. Hence, this result provides valuable insight into the strategic design of complexes with enhanced and controlled switchability for potential applications such as actuators and sensors.

中文翻译：

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[Fe2Co2] 分立式普鲁士蓝类似物中热收缩的自旋态调制和动力学控制


刺激响应可切换分子是磁性材料中的一个重要类别，在功能器件方面具有巨大的潜力。然而，由于对晶格相互作用敏感，具有受控可切换性的工程复合物仍然具有挑战性。在此，我们报道了一种 [Fe2Co2] 方形络合物 [FeTp（CN）3]2[Co{（F5-Ph）Py}2]2•2ClO4•4CH3OH•2H2O {1•4CH3OH•2H2O;（F5-PH）Py = （Z）-N'-（全氟苯基）吡啶酰亚胺和 Tp = 氢化三（1-吡唑基）硼酸盐）}，由氢键 （HB） 供体和受体部分定制，以实现有效的晶格相互作用。通过单晶到单晶 （SC-SC） 转变 （即 1•4CH3OH•2H2O  1•2H2O  1） 获得的晶相中 HB 相互作用的改变导致磁性能的显着变化。1•4CH3OH•2H2O 和 1 分别具有 [FeIILS（-CN）CoIIILS] 和 [FeIIILS（-CN）CoIIHS] 构型。而 1•2H2O 表现出多响应（热、光和压力）可逆的两步电子转移耦合自旋跃迁 （ETCST），并伴有热收缩和膨胀。1•2H2O 中的完整抗磁性 [FeIILS（-CN）CoIIILS] 构型是在伴随着热收缩的中间温度下获得的，这是在氰化物桥系统中首次观察到的不寻常行为。此外，1•2H2O 在低温下表现出顺磁性 [FeIIILS（-CN）CoIIHS] 构型的温度诱导激发自旋态捕获 （TIESST） ~70%。与在其他温度 （100 K - 190 K） 下观察到的弛豫相比，热陷落顺磁状态的等温弛豫在 ~140 K 时显示出更快和完全地转换为抗磁状态，这与观察到的独特磁行为相吻合。 因此，这一结果为为执行器和传感器等潜在应用提供增强和受控开关能力的复合物的战略设计提供了有价值的见解。