In this work, we address the synthesis of stable spin-crossover nanoparticles capable of undergoing a hysteretic spin transition at room temperature. For this purpose, we use the reverse-micelle protocol to prepare naked [Fe(NH₂trz)₃](NO₃)₂ and core@shell [Fe(NH₂trz)₃](NO₃)₂@SiO₂ nanoparticles. Through meticulous adjustment of synthetic parameters, we achieved nanoparticle sizes ranging from approximately 40 nm to 60 nm. Our findings highlight that [Fe(NH₂trz)₃](NO₃)₂ presents a modest thermal hysteresis of 7 K, which decreases by downsizing. Conversely, silica-coated nanoparticles with sizes of ca. 60 and 40 nm demonstrate a remarkable hysteretic response of approximately 30 K, switching their spin state around room temperature. Moreover, the presence of a SiO₂ shell substantially enhances the nanoparticles’ stability against oxidation. In this context, the larger 60 nm [Fe(NH₂trz)₃](NO₃)₂@SiO₂ hybrid remains stable in water for up to two hours, enabling the observation of an unreported water-induced spin transition after 30 min. Therefore, this work also introduces an intriguing avenue for inducing spin transitions through solvent exchange, underscoring the versatility and potential of these nanoparticles.

中文翻译：

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解锁纳米尺度的室温双稳态自旋跃迁：核@壳[Fe(NH2trz)3(NO3)2]@SiO2纳米粒子的合成

在这项工作中，我们解决了能够在室温下经历滞后自旋跃迁的稳定自旋交叉纳米粒子的合成。为此，我们使用反胶束方案制备裸[Fe(NH ₂ trz) ₃ ](NO ₃ ) ₂和核@壳[Fe(NH ₂ trz) ₃ ](NO ₃ ) ₂ @SiO ₂纳米粒子。通过对合成参数的精心调整，我们获得了约 40 nm 至 60 nm 的纳米颗粒尺寸。我们的研究结果强调，[Fe(NH ₂ trz) ₃ ](NO ₃ ) ₂呈现出 7 K 的适度热滞后，该热滞后会随着尺寸减小而降低。相反，二氧化硅涂覆的纳米颗粒的尺寸约为。 60 和 40 nm 表现出大约 30 K 的显着滞后响应，在室温附近切换其自旋状态。此外，SiO ₂壳的存在显着增强了纳米颗粒的抗氧化稳定性。在这种情况下，较大的 60 nm [Fe(NH ₂ trz) ₃ ](NO ₃ ) ₂ @SiO ₂杂化物在水中保持稳定长达两个小时，从而能够在 30 分钟后观察到未报告的水诱导自旋跃迁。因此，这项工作还引入了一种通过溶剂交换诱导自旋跃迁的有趣途径，强调了这些纳米颗粒的多功能性和潜力。