Spectroscopic, Structural, and Theoretical Studies of Halide Complexes with a Urea-Based Tripodal Receptor

A urea-based tripodal receptor L substituted with p-cyanophenyl groups has been studied for halide anions using 1H NMR spectroscopy, density functional theory (DFT) calculations, and X-ray crystallography. The 1H NMR titration studies suggest that the receptor forms a 1:1 complex with an anion, showing a binding trend in the order of fluoride > chloride > bromide > iodide. The interaction of a fluoride anion with the receptor was further confirmed by 2D NOESY and 19F NMR spectroscopy in DMSO-d6. DFT calculations indicate that the internal halide anion is held by six NH···X interactions with L, showing the highest binding energy for the fluoride complex. Structural characterization of the chloride, bromide, and silicon hexafluoride complexes of [LH+] reveals that the anion is externally located via hydrogen bonding interactions. For the bromide or chloride complex, two anions are bridged with two receptors to form a centrosymmetric dimer, while for the silicon hexafluoride complex, the anion is located within a cage formed by six ligands and two water molecules.本研究采用核磁共振氢谱（1H NMR spectroscopy）、密度泛函理论（DFT）计算与X射线晶体学方法，对经对氰苯基取代的尿素基三脚架型受体L与卤族阴离子的相互作用展开了系统性探究。核磁共振氢谱滴定实验结果表明，该受体与阴离子可形成1:1型配合物，其结合亲和力遵循氟离子＞氯离子＞溴离子＞碘离子的顺序。在氘代二甲基亚砜（DMSO-d6）溶剂中，二维核Overhauser效应谱（2D NOESY）与核磁共振氟谱（19F NMR spectroscopy）进一步验证了氟离子与该受体之间的相互作用。密度泛函理论计算结果显示，包埋于受体内部的卤族阴离子通过六组NH···X氢键与受体L结合，其中氟离子配合物的结合能最高。对[LH+]的氯离子、溴离子与六氟硅配合物的结构表征结果表明，阴离子通过氢键相互作用位于受体外部。在溴离子或氯离子配合物中，两个阴离子与两个受体桥连形成中心对称的二聚体；而在六氟硅配合物中，阴离子位于由六个配体与两个水分子构成的笼状结构内部。