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

摘要

A urea-based tripodal receptor L substitutednwith p-cyanophenyl groups has been studied for halide anionsnusing 1H NMR spectroscopy, density functional theory (DFT)ncalculations, and X-ray crystallography. The 1H NMR titrationnstudies suggest that the receptor forms a 1:1 complex with annanion, showing a binding trend in the order of fluoride >nchloride > bromide > iodide. The interaction of a fluoridenanion with the receptor was further confirmed by 2D NOESYnand 19F NMR spectroscopy in DMSO-d6. DFT calculations indicate that the internal halide anion is held by six NH···Xninteractions with L, showing the highest binding energy for the fluoride complex. Structural characterization of the chloride,nbromide, and silicon hexafluoride complexes of [LH+] reveals that the anion is externally located via hydrogen bondingninteractions. For the bromide or chloride complex, two anions are bridged with two receptors to form a centrosymmetric dimer,nwhile for the silicon hexafluoride complex, the anion is located within a cage formed by six ligands and two water molecules