Supramolecular Architecture in Some 4-Halophenylboronic Acids

Crystal structures of 4-chloro- and 4-bromophenylboronic acids (1 and 2) and hydrates of 2 and 4-iodophenylboronic acid in two different forms (2a, 3a, and 3b), which were characterized by single-crystal X-ray diffraction methods, are reported. In structures 1 and 2, −B(OH)2 forms a syn−anti conformation, but it exists in syn−syn as well as anti−anti conformations in the hydrated structures 2a, 3a, and 3b. In all the structures, the molecules are held together by O−H···O interactions formed by −B(OH)2 groups. The C−H···X (X = Cl, Br, and I) interactions play an important role in crystal packing. In 2, Br···Br interactions are also observed. Interestingly, all the three hydrates form similar types of three-dimensional structures with the formation of channels, which are occupied by water molecules. The two hydrates of 4-iodophenylboronic acid (3a and 3b) are distinguishable on the basis of O···O short contacts, with an identical host lattice of the boronic acid.本研究报道了4-氯苯硼酸、4-溴苯硼酸（分别记为1和2），以及2的水合物2a、4-碘苯硼酸的两种不同形式水合物3a和3b的晶体结构，所有结构均通过单晶X射线衍射法进行了表征。在1和2的晶体结构中，-B(OH)₂基团呈顺式-反式（syn-anti）构象；而在水合物结构2a、3a和3b中，该基团同时存在顺式-顺式（syn-syn）与反式-反式（anti-anti）构象。在所有晶体结构中，分子均通过-B(OH)₂基团形成的O−H···O氢键相互作用结合在一起。C−H···X（X=Cl、Br、I）相互作用对晶体堆积具有重要影响。在化合物2中，还观察到了Br···Br卤键相互作用。值得注意的是，三种水合物均构建了带有通道的三维网状结构，通道内部由水分子占据。4-碘苯硼酸的两种水合物（3a和3b）虽拥有完全相同的硼酸主体晶格，可通过O···O短接触进行区分。