Valence tautomeric complexes (VT) are promising systems for creating molecular devices. From this viewpoint, valence tautomeric complexes with a hysteresis loop on the magnetic curve are of special interest as potential memory elements. The hysteresis loop is a consequence of retarded structural rearrangements which investigation is an actual problem. Recently, we have described a new VT transition taking place in a bis-dioxolene cobalt complex with imino-pyridine having a TEMPO substituent (A. A. Zolotukhin, et al., Inorg. Chem., 2017, 56, 14751–14754). Valence tautomeric transformation occurs with a hysteresis loop and is accompanied by a phase transition. The phase transition taking place during cooling is accompanied by crystal destruction. This fact makes it impossible to monitor the structural changes responsible for the hysteresis loop. The current research attempts to resolve this problem. A nickel compound of the same composition (TEMPO-imino-pyridine)Ni(3,6-DBSQ)₂ was synthesized and characterized. It was established to be isostructural with the cobalt complex. It was used as an inert matrix for the dilution of the VT cobalt complex. The number of solid solutions with Co/Ni ratios of 1 : 1, 1 : 2, 1 : 4, and 1 : 8 was obtained. Variable temperature magnetic susceptibility measurements show that VT transformation with a hysteresis loop takes place in all solid solutions. The hysteresis loop is shifted to low temperatures primarily due to the shifting of its low-temperature boundary with dilution. The hysteresis width does not change significantly with dilution. DSC detected that transformations are accompanied by phase transitions at different temperatures at cooling and heating. The phase transition at the first cooling occurs at slightly lower temperatures compared with subsequent cycles. These temperatures correspond to the transition temperatures detected from the magnetic curves. The phase transition during the first cooling is accompanied by crystal destruction. Physical destruction takes place in the crystals of all solid solutions. X-ray diffraction powder patterns confirm that phase transition is accompanied by considerable reorganization of the crystal structure typical for the first order transitions. The unit cell volume of solid solutions is larger than that of pure complexes. Especially calculated crystal invariom indicated that the “lattice energy” in a solid solution is the lowest compared with that in “pure” nickel and cobalt complexes.

中文翻译：

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双二氧杂环戊烯钴配合物与 TEMPO 部分功能化的亚氨基吡啶在固溶体中与同构镍类似物的价互变异构：相变和单晶破坏

价互变异构体（VT）是用于创建分子器件的有前景的系统。从这个角度来看，磁曲线上具有磁滞回线的价互变异构体作为潜在的存储元件特别令人感兴趣。磁滞回线是延迟结构重排的结果，其研究是一个实际问题。最近，我们描述了具有 TEMPO 取代基的双二氧杂环戊烯钴配合物与亚氨基吡啶中发生的新 VT 转变（AA Zolotukhin, et al. , Inorg. Chem. , 2017, 56 , 14751–14754）。价互变异构体的发生伴随着磁滞回线并伴随着相变。冷却过程中发生的相变伴随着晶体破坏。这一事实使得不可能监测导致磁滞回线的结构变化。目前的研究试图解决这个问题。合成并表征了具有相同组成的镍化合物(TEMPO-亚氨基-吡啶)Ni(3,6-DBSQ) ₂ 。它被确定为与钴络合物同构。它被用作稀释 VT 钴络合物的惰性基质。获得Co/Ni比为1:1、1:2、1:4和1:8的固溶体的数量。变温磁化率测量表明，所有固溶体中都会发生带有磁滞回线的 VT 转变。磁滞回线向低温移动主要是由于其低温边界随着稀释而移动。滞后宽度不会因稀释而发生显着变化。 DSC 检测到，在冷却和加热的不同温度下，转变伴随着相变。与后续循环相比，第一次冷却时的相变发生温度略低。这些温度对应于从磁曲线检测到的转变温度。第一次冷却期间的相变伴随着晶体破坏。所有固溶体的晶体都会发生物理破坏。 X 射线衍射粉末图案证实，相变伴随着一级转变典型的晶体结构的大量重组。固溶体的晶胞体积大于纯配合物的晶胞体积。特别计算的晶体不变量表明，与“纯”镍和钴配合物相比，固溶体中的“晶格能”是最低的。