Highly Flexible Molecule 鈥淐hameleon鈥? Reversible Thermochromism and Phase Transitions in Solid Copper(II) Diiminate Cu[CF3鈥擟(NH)鈥擟F鈺怌(NH)鈥擟F3]2

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• 作者：Victor N. Khrustalev ; Svetlana O. Kostenko ; Mikhail I. Buzin ; Alexander A. Korlyukov ; Yan V. Zubavichus ; Michael A. Kurykin ; Mikhail Yu. Antipin
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：October 15, 2012
• 年：2012
• 卷：51
• 期：20
• 页码：10590-10602
• 全文大小：770K
• 年卷期：v.51,no.20(October 15, 2012)
• ISSN：1520-510X

文摘

Three thermochromic phases (伪, green; 尾, red; 纬, yellow) and six polymorphic modifications (伪₁, monoclinic, P2₁/n, Z = 2; 尾₁, monoclinic, P2₁/c, Z = 4; 尾₂, triclinic, P1̅, Z = 4; 尾₃, monoclinic, P2₁/n, Z = 4; 纬₁ and 纬₂, tetragonal, P4₂/n, Z = 4) have been found and structurally characterized for copper(II) diiminate Cu[CF₃鈥擟(NH)鈥擟F鈺怌(NH)鈥擟F₃]₂ (1). The 伪 phase is stable under normal conditions, whereas the high-temperature 尾 and 纬 phases are metastable at room temperature and transform slowly into the more stable 伪 phase over several days or even weeks. X-ray diffraction study revealed that the title molecules adopt different conformations in the 伪, 尾, and 纬 phases, namely, staircase-like, twisted, and planar, respectively. The investigation of the 伪, 尾, and 纬 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鈥搒olid 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 伪₁尾₁ phase transition occurring within a temperature interval of 353鈥?58 K can be directly observed using a CCD video camera of the X-ray diffractometer. A series of other solid鈥搒olid 伪₁鈫捨?sub>1, 尾₂鈫捨?sub>1, 尾₃鈫捨?sub>1, and 纬₁纬₂ phase transitions can be triggered in 1 by temperature. It has been suggested that, under equilibrium conditions, the 伪₁鈫捨?sub>1 and 尾₂鈫捨?sub>1 phase transitions should proceed stepwise through the 伪₁鈫捨?sub>1鈫捨?sub>2鈫捨?sub>3鈫捨?sub>1 and 尾₂鈫捨?sub>3鈫捨?sub>1 stages, respectively. The mechanism of the phase transitions is discussed on the basis of experimental and theoretical data.