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Critical Evaluation of C-H…X Hydrogen Bonding in the Crystalline State

机译：晶体状态下C-H…X氢键的严格评估

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摘要

Contacts of the type C-H…X where X = F, Cl, Br, I, O, S, or N were analyzed statistically using structures available in the Cambridge Structural Database. For this analysis, the cone correction method was extended to an isotropic density correction. This method corrects for both angular and distance effects by normalizing isotropic contact densities from the experimental distributions. It was possible to show the widespread occurrence of C-H…X interactions in the crystalline state using this method. Distances of highest incidence, at which the largest number of contacts were sampled after normalization of isotropic distribution, were determined for each interaction type. These distances were compared to the classically accepted van der Waals cutoff radii, often used to distinguish between hydrogen-bonded interactions and van der Waals contacts. Generally, distances of highest incidence did not occur at the sum of van der Waals cutoff radii but occurred either below or above that distance depending on the specific interaction analyzed. This methodology, while of course not yielding quantitative data on hydrogen bond strength, allowed for a qualitative ordering of the interactions studied, in terms of expected interaction strengths.
机译：使用剑桥结构数据库中可用的结构，对X = F，Cl，Br，I，O，S或N的C-H…X类型的接触进行统计分析。对于此分析，将圆锥校正方法扩展到各向同性密度校正。该方法通过根据实验分布归一化各向同性接触密度来校正角度和距离影响。用这种方法可能显示出在晶体状态下C-H…X相互作用的广泛发生。确定每种交互作用类型的最高入射距离，即各向同性分布归一化后采样到最多接触点的距离。将这些距离与经典接受的范德华截止半径进行了比较，范德华截止半径通常用于区分氢键相互作用和范德华接触。通常，最高发生率的距离不是发生在范德华截断半径的总和上，而是发生在该距离以下或之上，这取决于所分析的特定相互作用。这种方法虽然不能得出有关氢键强度的定量数据，但可以根据预期的相互作用强度对所研究的相互作用进行定性排序。

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