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首页> 外文期刊>Crystal growth & design >Halogen Bond as Controlling the Crystal Structure of 4-Amino-3,5-Dihalogenobenzoic Acid and Its Effect on the Positional Ordering/Disordering of Acid Protons
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Halogen Bond as Controlling the Crystal Structure of 4-Amino-3,5-Dihalogenobenzoic Acid and Its Effect on the Positional Ordering/Disordering of Acid Protons

机译：卤素键控制4-氨基-3,5-二卤代苯甲酸的晶体结构及其对酸质子位置有序/无序的影响

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摘要

Crystal structures and thermal behaviors of 4-amino-3,5-dihalogenobenzoic acid (AXBA: X = Cl and I) were studied by single-crystal X-ray diffractometry and differential scanning calorimetry. It was found that all the crystal structures of AClBA and AIBA as well as ABrBA at room temperature belong to the same space group with two crystallographically distinguishable dimer units. The dimer was located in a highly symmetric circumstance; for example, its C=O and C-O bonds were indistinguishable due to the presence of 2-fold rotational and mirror symmetry elements so that two hydrogen bonds should be equivalent within each dimer. Such symmetric dimer structures are very rare among carboxylic acid crystals. Stabilization of such a symmetric dimer structure is attributed probably to notably strong and angular-dependent interdimer interactions: halogen bonds and NH center dot center dot center dot O hydrogen bonds. The strength of the halogen bond, among different halogens, was in the order of I > Br > Cl from the interhalogen-atomic length as compared with its ordinary van der Waals diameter. AIBA revealed no phase transition even down to 110 K, while AClBA revealed it at around 140 K. The difference in the thermal behaviors perhaps originates from the different strengths of halogen bonds in the AIBA and AClBA crystals.
机译：通过单晶X射线衍射和差示扫描量热法研究了4-氨基-3,5-二卤代苯甲酸（AXBA：X = Cl和I）的晶体结构和热行为。发现在室温下，AC1BA和AIBA以及ABrBA的所有晶体结构均属于具有两个晶体学上可区分的二聚体单元的相同空间群。二聚体位于高度对称的环境中。例如，由于存在2倍旋转对称和镜像对称元素，其C = O和C-O键无法区分，因此每个二聚体中两个氢键应相等。这种对称的二聚体结构在羧酸晶体中非常罕见。这种对称二聚体结构的稳定可能归因于强烈的和依赖于角度的二聚体相互作用：卤素键和NH中心点中心点中心点O氢键。与卤素的普通范德华直径相比，卤素之间的卤素键强度在卤素间原子长度上的顺序为I> Br> Cl。 AIBA甚至在低至110 K时都没有显示出相变，而AClBA在140 K时却显示出相变。热行为的差异可能源自AIBA和AClBA晶体中卤素键的不同强度。

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