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.