The inimitable electronic structures of the lanthanide (Ln) ions are key to advanced materials and technologies involving these elements. The trivalent ions are ubiquitous and are used much more widely than the divalent and tetravalent analogues, which possess vastly different optical and magnetic properties. Hence, alteration of the valence electron count by external stimuli can lead to dramatic changes in materials properties. Compounds exhibiting a temperature-induced complete Ln(III) ⇄ Ln(II) switch, referred to as a valence tautomeric (VT) transition, are rare. Here we present an abrupt and hysteretic VT transition in a lanthanide-based coordination polymer, SmI₂(pyrazine)₃, driven by the interconversion of Sm(II)–pyrazine(0) and Sm(III)–pyrazine(·−) redox pairs. Alloying SmI₂(pyrazine)₃ with Yb(II) yields isomorphous Sm_1–xYb_xI₂(pyrazine)₃ solid solutions with VT transition critical temperatures ranging widely from 200 K to ∼50 K at ambient pressure. These findings demonstrate a simple strategy to realize thermally switchable magnetic materials with chemically tunable transition temperatures.

镧系元素 (Ln) 离子独特的电子结构是涉及这些元素的先进材料和技术的关键。三价离子无处不在，并且比二价和四价类似物应用更广泛，后者具有截然不同的光学和磁性特性。因此，外部刺激引起的价电子数的改变会导致材料性能的巨大变化。表现出温度诱导的完全 Ln(III)  ⇄  Ln(II) 转换（称为价互变异构 (VT) 转变）的化合物很少见。在这里，我们在镧系配位聚合物 SmI ₂ (pyrazine) ₃中提出了由 Sm(II)–pyrazine(0) 和 Sm(III)–pyrazine(·−) 氧化还原相互转化驱动的突然且滞后的 VT 转变。对。将 SmI ₂ (吡嗪) ₃与 Yb(II) 合金化可生成同晶 Sm _{1– x} Yb _x I ₂ (吡嗪) ₃固溶体，在环境压力下，VT 转变临界温度范围广泛为 200 K 至∼ 50 K。这些发现展示了一种实现具有化学可调转变温度的热可切换磁性材料的简单策略。