Reversible Control of Crystalline Rotors by Squeezing Their Hydrogen Bond Cloud Across a Halogen Bond-Mediated Phase Transition

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• 作者：Cyprien Lemouchi ; Hiroshi M. Yamamoto ; Reizo Kato ; Sergey Simonov ; Leokadiya Zorina ; Antonio Rodr铆guez-Fortea ; Enric Canadell ; Pawel Wzietek ; Konstantinos Iliopoulos ; Denis Gindre ; Michael Chrysos ; Patrick Batail
• 刊名：Crystal Growth & Design
• 出版年：2014
• 出版时间：July 2, 2014
• 年：2014
• 卷：14
• 期：7
• 页码：3375-3383
• 全文大小：558K
• ISSN：1528-7505

文摘

We report on a crystalline rotor that undergoes a reversible phase transition at 145 K. Variable-temperature X-ray and ¹H spin鈥搇attice relaxation experiments, and calculations of rotational barriers, provide a description (i) of the way in which the rotators鈥?dynamics changes back and forth at the onset of the phase transition and (ii) of the mechanism responsible for the abrupt switching of the crystalline rotors from a very low-energy 4-fold degenerate equilibrium state, in which the rotation is ultrafast (9.6 GHz at 145 K), to a single higher-energy state associated with a slower motion (2.3 GHz at 145 K). Our results provide evidence that the reversible change observed in the rotational barriers at the transition is due to a cooperative modulation of the C鈥揌_rotator路路路I_stator hydrogen bond cloud across a C鈥揑_stator路路路I_stator鈥揅 halogen bond-mediated phase transition. In addition, we report evidence for second-harmonic generation from this material, thereby confirming with a second example the benefit of using polarized light to probe the torsional degree of freedom of chiral helix blades, as well as symmetry and dimensionality of large collections of chiral rotors in the solid state.