Until now, the synthesis of new multi-step spin-crossover (SCO) materials is still a great challenge although they have attracted significant attention due to their potential applications in high-order data storage and multi-switches. Here, based on the four-step SCO complex [Fe(dpoda){Ag(CN)₂}₂]·1.5naph (1·1.5naph, dpoda = 2,5-di-(pyridyl)-1,3,4-oxadiazole, naph = naphthalene), the strategy of incorporating a substituent on an aromatic guest is applied. Since the replacement of H with an F atom can be regarded as isosteric substitution, the introduction of the 2-fluoronaphthalene (Fnaph) guest does not give rise to large structural changes and the four-step SCO behavior is maintained in 1·1.5Fnaph; however, fine-tuning of the framework is indeed achieved by the fluoro substituent. The spin transition temperatures of 1·1.5Fnaph shift to the low-temperature region, which should be due to the contributions of the size effect and the decrease in the Fe–NC angle. Meanwhile, the thermal hysteresis loop disappears, which results from the competitive contributions of the π⋯π and F⋯Ag interactions. Therefore, the F substituent on the guest can effectively modify the four-step SCO behavior, which provides a simple solution to synthesize more multi-step SCO materials.

中文翻译：

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取代基客体对四步自旋交联行为的影响

到目前为止，尽管新的多步自旋交叉（SCO）材料的合成由于其在高阶数据存储和多开关中的潜在应用而引起了广泛的关注，但它们仍然是一个巨大的挑战。在此，基于四步SCO络合物[Fe（dpoda）{Ag（CN）₂ } ₂ ]·1.5naph（1·1.5naph，dpoda = 2,5-di-（pyridyl）-1,3,4 -恶二唑，萘＝萘），采用在芳族客体上引入取代基的策略。由于用F原子取代H可以视为等位取代，因此引入2-氟萘（Fnaph）客体不会引起大的结构变化，并且四步SCO行为保持在1·1.5Fnaph; 然而，通过氟取代基确实可以实现骨架的微调。1·1.5Fnaph的自旋转变温度移至低温区，这应该归因于尺寸效应的贡献和Fe–N C角的减小。同时，热磁滞回线消失了，这是由π⋯π和F⋯Ag相互作用的竞争作用造成的。因此，客体上的F取代基可以有效地改变四步SCO的行为，这为合成更多的多步SCO材料提供了一种简单的解决方案。