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.

基于尿素的三脚受体L，经p-氰基苯基取代，已被用于研究卤素阴离子。本研究采用1H NMR光谱、密度泛函理论（DFT）计算以及X射线晶体学进行分析。1H NMR滴定研究结果表明，该受体与阴离子形成1:1的复合物，其结合趋势为氟化物 > 氯化物 > 溴化物 > 碘化物。通过2D NOESY和19F NMR光谱在DMSO-d6中的进一步研究，证实了氟阴离子与受体的相互作用。DFT计算表明，内部卤素阴离子由L通过六个NH···X相互作用固定，其中氟化物复合物显示出最高的结合能。对[LH+]的氯化物、溴化物和六氟硅烷复合物的结构表征揭示，阴离子通过氢键相互作用外部定位。对于溴化物或氯化物复合物，两个阴离子通过两个受体桥接形成中心对称的二聚体，而六氟硅烷复合物中，阴离子位于由六个配体和两个水分子形成的笼状结构内部。