Alhameedi Khidhir, Karton Amir, Jayatilaka Dylan, Thomas Sajesh P
School of Molecular Sciences, University of Western Australia, 35 Stirling Highway, Perth 6009, Australia.
College of Education for Pure Science, University of Karbala, Karbala, Iraq.
IUCrJ. 2018 Aug 29;5(Pt 5):635-646. doi: 10.1107/S2052252518010758. eCollection 2018 Sep 1.
The question of whether intermolecular interactions in crystals originate from localized atom⋯atom interactions or as a result of holistic molecule⋯molecule close packing is a matter of continuing debate. In this context, the newly introduced Roby-Gould bond indices are reported for intermolecular 'σ-hole' interactions, such as halogen bonding and chalcogen bonding, and compared with those for hydrogen bonds. A series of 97 crystal systems exhibiting these interaction motifs obtained from the Cambridge Structural Database (CSD) has been analysed. In contrast with conventional bond-order estimations, the new method separately estimates the ionic and covalent bond indices for atom⋯atom and molecule⋯molecule bond orders, which shed light on the nature of these interactions. A consistent trend in charge transfer from halogen/chalcogen bond-acceptor to bond-donor groups has been found in these intermolecular interaction regions Hirshfeld atomic partitioning of the electron populations. These results, along with the 'conservation of bond orders' tested in the interaction regions, establish the significant role of localized atom⋯atom interactions in the formation of these intermolecular binding motifs.
晶体中的分子间相互作用是源于局部的原子⋯原子相互作用还是整体的分子⋯分子紧密堆积，这一问题仍在持续争论中。在此背景下，本文报道了新引入的用于分子间“σ-空穴”相互作用（如卤键和硫族元素键）的罗比-古尔德键指数，并与氢键的键指数进行了比较。对从剑桥结构数据库（CSD）获得的一系列97个呈现这些相互作用模式的晶体系统进行了分析。与传统的键级估计不同，新方法分别估计了原子⋯原子和分子⋯分子键级的离子键和共价键指数，这有助于揭示这些相互作用的本质。在这些分子间相互作用区域，通过赫希菲尔德原子电子布居划分，发现了从卤/硫族元素键受体到键供体基团的电荷转移的一致趋势。这些结果，连同在相互作用区域测试的“键级守恒”，确立了局部原子⋯原子相互作用在这些分子间结合模式形成中的重要作用。
