On the Organizing Role of Water Molecules in the Assembly of Boronic Acids and 4,4′-Bipyridine: 1D, 2D and 3D Hydrogen-Bonded Architectures Containing Cyclophane-Type Motifs

4,4′-Bipyridine has been combined with boric acid and four different boronic acids (1,3- and 1,4-benzenediboronic acid, 3-aminophenylboronic acid, 4-acetylphenylboronic acid) to give 1:1 (with boric acid) and 1:2 adducts (with arylboronic acids), which have been characterized by X-ray diffraction analysis. The supramolecular solid-state structures are composed of hydrogen-bonded networks with (B)O−H···N, (B)O−H···O, C−H···O, C−H···N, C−H···π, π···π and C−H···B interactions. The comparative analysis of the boric/boronic acid−4,4′-bipyridine adducts has revealed that water molecules play an important role as spacer molecules in RB(OH)2···py synthons, since their incorporation in the hydrogen-bonding patterns allows optimization of π−π interactions. The structural relationship between the dihydroxyboryl and the carboxyl group has been analyzed, showing that the former can form at least three different hydrogen-bonding patterns with pyridines. This can be attributed to the presence of two acidic hydrogen atoms instead of one (B(OH)2 ↔ C(O)OH). The three motifs have been examined also by ab initio calculations, confirming that for the three cases the (B)O−H···N interaction energies are similar.