A.N.Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28, Vavilov Street, 119991 Moscow, Russian Federation.
Inorg Chem. 2012 Oct 15;51(20):10590-602. doi: 10.1021/ic300814w. Epub 2012 Sep 20.
Three thermochromic phases (α, green; β, red; γ, yellow) and six polymorphic modifications (α(1), monoclinic, P2(1)/n, Z = 2; β(1), monoclinic, P2(1)/c, Z = 4; β(2), triclinic, P1[overline], Z = 4; β(3), monoclinic, P2(1)/n, Z = 4; γ(1) and γ(2), tetragonal, P4(2)/n, Z = 4) have been found and structurally characterized for copper(II) diiminate CuCF(3)-C(NH)-CF═C(NH)-CF(3) (1). The α phase is stable under normal conditions, whereas the high-temperature β and γ phases are metastable at room temperature and transform slowly into the more stable α phase over several days or even weeks. X-ray diffraction study revealed that the title molecules adopt different conformations in the α, β, and γ phases, namely, staircase-like, twisted, and planar, respectively. The investigation of the α, β, and γ phases by differential scanning calorimetry showed that the three endothermic peaks in the range 283, 360, and 438 K are present on their thermograms upon heating/cooling. The two peaks at 283 and 360 K correspond to the solid-solid phase transitions, and the high-temperature peak at 438 K belongs to the melting process of 1. The temperature and thermal effect of all the observed transitions depend on the prehistory of the crystalline sample obtained. A reversible thermochromic single-crystal-to-single-crystal α(1)<--> β(1) phase transition occurring within a temperature interval of 353-358 K can be directly observed using a CCD video camera of the X-ray diffractometer. A series of other solid-solid α(1)→γ(1), β(2)→γ(1), β(3)→γ(1), and γ(1)<-->γ(2) phase transitions can be triggered in 1 by temperature. It has been suggested that, under equilibrium conditions, the α(1)→γ(1) and β(2)→γ(1) phase transitions should proceed stepwise through the α(1)→β(1)→β(2)→β(3)→γ(1) and β(2)→β(3)→γ(1) stages, respectively. The mechanism of the phase transitions is discussed on the basis of experimental and theoretical data.
已发现并结构表征了铜（II）二亚胺 CuCF3-C(NH)-CF═C(NH)-CF3（1）的三种热致变色相（α，绿色；β，红色；γ，黄色）和六种多晶型变体（α(1)，单斜，P2(1)/n，Z=2；β(1)，单斜，P2(1)/c，Z=4；β(2)，三斜，P1[overline]，Z=4；β(3)，单斜，P2(1)/n，Z=4；γ(1)和γ(2)，四方，P4(2)/n，Z=4）。在正常条件下，α 相稳定，而高温β和γ相在室温下为亚稳相，并在数天甚至数周内缓慢转变为更稳定的α相。X 射线衍射研究表明，标题分子在α、β和γ相中分别采用不同的构象，即阶梯状、扭曲状和平面状。通过差示扫描量热法研究α、β和γ相表明，在加热/冷却时，其热图谱中存在三个在 283、360 和 438 K 范围内的吸热峰。283 和 360 K 处的两个峰对应于固-固相转变，而 438 K 处的高温峰属于 1 的熔融过程。所有观察到的转变的温度和热效应取决于所获得的结晶样品的预处理历史。使用 X 射线衍射仪的 CCD 摄像机可以直接观察到在 353-358 K 温度间隔内发生的可逆热致变色单晶-单晶α(1)<-->β(1)相转变。通过温度可以在 1 中引发一系列其他固-固α(1)→γ(1)、β(2)→γ(1)、β(3)→γ(1)和γ(1)<-->γ(2)相转变。有人建议，在平衡条件下，α(1)→γ(1)和β(2)→γ(1)相转变应该分别通过α(1)→β(1)→β(2)→β(3)→γ(1)和β(2)→β(3)→γ(1)阶段逐步进行。基于实验和理论数据讨论了相转变的机制。
