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首页> 外文期刊>Acta Crystallographica, Section B. Structural science, crystal engineering and materials >Resonance-stabilized partial proton transfer in hydrogen bonds of incommensurate phenazine– chloranilic acid
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Resonance-stabilized partial proton transfer in hydrogen bonds of incommensurate phenazine– chloranilic acid

机译：共振稳定的不相称吩嗪-氯苯甲酸氢键中的部分质子转移

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摘要

The co-crystal of phenazine (Phz) and chloranilic acid (H2ca) becomes ferroelectric upon cooling through the loss of inversion symmetry. Further cooling results in the development of an incommensurate ferroelectric phase, followed by a lock-in transition towards a twofold superstructure. Here we present the incommensurately modulated crystal structure of Phz-H2ca at T = 139 K with a symmetry given by the superspace group P2_1(1/2 σ_2 1/2)0 and σ_2 = 0.5139. The modulation mainly affects the positions of the protons within half of the intermolecular hydrogen bonds that are responsible for the spontaneous polarization in all three low-temperature phases. Evidence for proton transfer in part of the hydrogen bonds is obtained from the correlated dependence on the phase of the modulation of the lengths of bonds involved in resonance stabilization of the acidic anion, and much smaller variations of bond lengths of atoms not involved in the resonance mechanism. Incommensurability is explained as competition between proton transfer favored for single hydrogen bonds on the basis of pK_a values and avoiding unfavorable Coulomb repulsion within the lattice of the resulting ionic molecules.
机译：吩嗪（Phz）和氯苯甲酸（H2ca）的共晶体在冷却后由于失去反对称性而变成铁电体。进一步的冷却导致形成不相称的铁电相，随后发生向双重上部结构的锁定过渡。在这里，我们介绍了在T = 139 K处具有非对称调制的Phz-H2ca晶体结构，其对称性由超空间组P2_1（1/2σ_21/2）0和σ_2= 0.5139给出。调制主要影响质子在所有三个低温相中自发极化的分子间氢键的一半内的位置。质子转移部分氢键的证据来自对酸性阴离子共振稳定化所涉及的键长调制相位的相关依赖性，以及与共振无关的原子键长的小得多的变化。机制。不可通约性被解释为基于pK_a值有利于单个氢键的质子转移与避免所得离子分子晶格内的库仑排斥反应之间的竞争。

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