Evaluating Halogen-Bond Strength as a Function of Molecular Structure Using Nuclear Magnetic Resonance Spectroscopy and Computational Analysis
Evaluating Halogen-Bond Strength as a Function of Molecular Structure Using Nuclear Magnetic Resonance Spectroscopy and Computational Analysis
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DOI：
10.1021/acs.jpca.1c07554
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发表时间：
2021-10-18
影响因子：
2.9
通讯作者：
Leopold, Michael C.
中科院分区：
文献类型：
--
作者：
Dang, Quang Minh;Simpson, Jeffrey H.;Leopold, Michael C.
卤素键（XB）是一种高度定向的、非共价的分子间相互作用，在一个分子（XB供体）和一个富电子或刘易斯碱分子（XB受体）之间形成一个缺电子区或西格玛空穴（sigma空穴）。本文系统地、实验地和理论地研究了溶液相XB强度与XB供体和受体分子结构的关系。使用F-19和H-1核磁共振（NMR）滴定来确定缔合常数，密度泛函理论计算相互作用能和键长，以及F-19-H-1 HOESY核磁共振测量相互作用的XB供体-受体加合物之间的分子间交叉弛豫，评估特定结构特征的影响。对于XB给体分子（全氟卤化苯），结果表明碘与吸电子实体偶联的重要性。XB受体分子的主要结构成分包括一个中心原子与一个刘易斯碱原子结合，在s空穴处呈现高电子密度（例如，氧化三烷基膦）。此外，周围较大的脂肪族R基团（例如，丁基和辛基）被发现可以显著稳定强XB，特别是在促进相互作用的溶剂中。随着对结构优化XB的更深入了解，人们可以设想在优化材料和化学应用的特定设计中更有策略地利用XB相互作用。
Halogen bonding (XB) is a highly directional, non-covalent intermolecular interaction between a molecule (XB donor) presenting a halogen with an electron-deficient region or sigma hole (sigma-hole) and an electron-rich or Lewis-base molecule (XB acceptor). A systematic, experimental, and theoretical study of solution-phase XB strength as a function of the molecular structure for both XB donor and acceptor molecules is presented. The impact of specific structural features is assessed using F-19 and H-1 nuclear magnetic resonance (NMR) titrations to determine association constants, density functional theory calculations for interaction energies and bond lengths, as well as F-19-H-1 HOESY NMR measurements of intermolecular cross-relaxation between the interacting XB donor-acceptor adducts. For XB donor molecules (perfluoro-halogenated benzenes), results indicate the critical importance of iodine coupled with electron-withdrawing entities. Prominent structural components of XB acceptor molecules include a central atom working in conjunction with a Lewis-base atom to present high electron density directed at the s-hole (e.g., tributylphosphine oxide). Additionally, larger surrounding aliphatic R groups (e.g., butyl and octyl) were found to significantly stabilize strong XB, particularly in solvents that promote the interaction. With a more thorough understanding of structure-optimized XB, one can envision harnessing XB interactions more strategically for specific design of optimal materials and chemical applications.