Książek Maria, Weselski Marek, Dreczko Agnieszka, Maliuzhenko Vladyslav, Kaźmierczak Marcin, Tołoczko Aleksandra, Kusz Joachim, Bronisz Robert
Institute of Physics, University of Silesia, 75 Pułku Piechoty 1, 41-500 Chorzów, Poland.
Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland.
Dalton Trans. 2020 Jul 21;49(28):9811-9819. doi: 10.1039/d0dt01696a.
1,4-Di(1-ethyl-1,2,3-triazol-5-yl)butane (bbtre) was prepared by lithiation of 1-ethyl-1,2,3-triazole, followed by alkylation with 1,4-dibromobutane. The ligand bbtre forms a three-dimensional network with Fe(ii), Fe(bbtre)32·2CH3CN, that exhibits thermally induced spin crossover (SCO). A change of temperature or change of spin state results in various types of structural transformation, leading to different structures that are stable in strictly defined temperature ranges. As a result, there are three spin crossover transitions arranged via two different paths. Thus, cooling below 280 K involves a HT(HS) → LT(HS) (HT, high temperature structure; LT, low temperature structure; HS, high spin) phase transition (PT), which is associated with conformational changes of the bbtre molecules and with deformation of the polymeric skeleton. In the LT phase incomplete and reversible LT(HS) ⇄ LT(HS/LS) spin crossover occurs (LS, low spin). In contrast, rapid cooling (of a sample not previously thermally treated) allows the HT(HS) → LT(HS) phase transition to be avoided, and so complete HT(HS) → HT1(LS) SCO occurs. This means that the PT plays the role of a switch, which allows a choice of one of two ways in which the SCO will proceed. After rapid cooling, further heating to 150 K and subsequent cooling results in a reversible HT1(HS) ⇄ HT1(LS) spin crossover (T↓1/2 = 130 K, T↑1/2 = 131 K). However, raising the temperature to 170-200 K leads to formation of a modulated structure HT2(HS) exhibiting the next reversible HT2(HS) ⇄ HT2(LS) SCO (T↓1/2 = 121 K, T↑1/2 = 123 K). Finally, heating above 200 K involves the HT2(HS) → LT(HS) PT and results in a LT(HS) structure exhibiting incomplete LT(HS) ⇄ LT(HS/LS) spin crossover.
1,4-二（1-乙基-1,2,3-三唑-5-基）丁烷（bbtre）通过1-乙基-1,2,3-三唑的锂化反应制备，随后与1,4-二溴丁烷进行烷基化反应。配体bbtre与Fe（II）形成三维网络Fe(bbtre)32·2CH3CN，其表现出热诱导自旋交叉（SCO）。温度变化或自旋状态变化会导致各种类型的结构转变，从而产生在严格定义的温度范围内稳定的不同结构。结果，通过两条不同路径排列了三个自旋交叉转变。因此，冷却至280 K以下涉及HT(HS)→LT(HS)（HT，高温结构；LT，低温结构；HS，高自旋）相变（PT），这与bbtre分子的构象变化以及聚合物骨架的变形有关。在LT相中发生不完全且可逆的LT(HS)⇄LT(HS/LS)自旋交叉（LS，低自旋）。相反，快速冷却（对先前未进行热处理的样品）可避免HT(HS)→LT(HS)相变，从而发生完全的HT(HS)→HT1(LS) SCO。这意味着PT起到了开关的作用，它允许在SCO进行的两种方式中选择一种。快速冷却后，进一步加热至150 K并随后冷却会导致可逆的HT1(HS)⇄HT1(LS)自旋交叉（T↓1/2 = 130 K，T↑1/2 = 131 K）。然而，将温度升至170 - 200 K会导致形成调制结构HT2(HS)，其表现出下一个可逆的HT2(HS)⇄HT2(LS) SCO（T↓1/2 = 121 K，T↑1/2 = 123 K）。最后，加热至200 K以上涉及HT2(HS)→LT(HS) PT，并导致形成表现出不完全LT(HS)⇄LT(HS/LS)自旋交叉的LT(HS)结构。
