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 center dot center dot center dot N, (B)O-H center dot center dot center dot O, C-H center dot center dot center dot O, C-H center dot center dot center dot N, C-H center dot center dot center dot pi, pi center dot center dot center dot pi and C-H center dot center dot center dot 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)center dot center dot center dot py synthons, since their incorporation in the hydrogen-bonding patterns allows optimization of pi,pi 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 center dot center dot center dot N interaction energies are similar.