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.

Infinite chains of spirocyclic water hexamers are included in the crystal lattice of a tin complex with a curved, hydrophobic surface and only weak intermolecular bonding interactions between the host molecules, so that the enclosed water clusters might be reminiscent of the solvation sphere in solution.

Thermal and microwave reactions between [PcSn(IV)Cl2] (1) and the potassium salts of eight fatty acids (2 a-h) led to cis-[(RCO2)2Sn(IV)Pc] compounds (3 a-h) in yields ranging from 54 to 90 %. Compounds 3 a-h were fully characterized by elemental analysis, spectroscopy (IR, UV/Vis, multinuclear NMR), and seven X-ray diffraction structures, whereby two different allotropes were observed in two cases. The two carboxylates in 3 have a cis anisobidentate binding mode, octacoordination of the tin atoms with square-antiprismatic geometry, and pi-electron-rich nanocap shapes. On account of the latter characteristics, 3 a-h compounds have anticorrosion properties. LPR and Tafel electrochemical methods were used to characterize the behavior of these derivatives in naturally aerated sour brine, which is a common environment in petroleum production and refinery operations. The measurement of the corrosion rate of carbon steel AISI 1018 in the presence of 3 a-h (500 ppm) gave efficiencies of 61-87 % for the inhibitor performance. Of the different derivatives examined, compounds 3 e and 3 h were the most effective corrosion inhibitor prototypes.

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