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

摘要

A urea-based tripodal receptor L substituted with p-cyanophenyl groups hasbeen studied for halide anions by $^1$H NMR spectroscopy, density functionaltheory (DFT) calculations and X-ray crystallography. The $^1$H NMR titrationstudies suggest that the receptor forms a 1:1 complex with an anion, showingthe binding trend in the order of fluoride > chloride > bromide > iodide. Theinteraction of fluoride anion with the receptor was further confirmed by 2DNOESY and $^{19}$F NMR spectroscopy in DMSO-d$_6$. DFT calculations indicatethat the internal halide anion is held by six NH...X interactions with L,showing the highest binding energy for the fluoride complex. Structuralcharacterization of the chloride, bromide, and silicon hexafluoride complexesof $[LH^+]$ reveals that the anion is externally located via hydrogen bondinginteractions. For the bromide or chloride complex, two anions are bridged withtwo receptors to form a centrosymmetric dimer, while for the siliconhexafluoride complex, the anion is located within a cage formed by six ligandsand two water molecules.