The anion-binding properties of two tripodal-based hexaureas appended with the m-nitrophenyl (1) and pentafluorophenyl (2) groups have been studied both experimentally and theoretically, showing strong affinities for sulfate over other inorganic oxoanions such as hydrogen sulfate, dihydrogen phosphate, bicarbonate, nitrate, and perchlorate. The structural analysis of the sulfate complex with 1 reveals that the receptor organizes all urea-binding sites toward the cavity at precise orientations around a tetrahedral sulfate anion to form an ideal C₃-symmetric sulfate complex that is stabilized by 12 hydrogen-bonding interactions. The receptor and the encapsulated sulfate are located on the threefold axis passing through the bridgehead nitrogen of 1 and the sulfur atom of the anionic guest. The high-level density functional theory calculations support the crystallographic results, demonstrating that the C₃-symmetric conformation of the sulfate complex is achieved due to the complementary NH···O between the receptor and sulfate.

中文翻译：

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一个理想的Ç ₃ -对称硫酸盐复合物：含氧阴离子的分子识别由米-Nitrophenyl-和五氟苯官能化Hexaurea受体

所附两个基于三足-hexaureas的阴离子结合性质米硝基苯（1）和五氟苯基（2）基团已被实验和理论研究，示出了用于过硫酸盐等无机含氧阴离子诸如硫酸氢亲和力强，磷酸二氢，碳酸氢盐，硝酸盐和高氯酸盐。具有1的硫酸盐配合物的结构分析表明，该受体在四面体硫酸盐阴离子周围以精确的方向将所有尿素结合位点组织到腔中，形成了理想的C _3。对称的硫酸盐配合物，通过12个氢键相互作用得以稳定。受体和包封的硫酸盐位于三重轴上，穿过1的桥头氮和阴离子客体的硫原子。高层密度泛函理论计算支持了晶体学结果，表明硫酸盐配合物的C ₃对称构象是由于受体和硫酸盐之间互补的NH···O而实现的。