The structures of three ortho-alkoxyphenylboronic acids (2-methoxy-, 2-ethoxy-, 2-isobutoxy-), and three diortho-alkoxyphenylboronic acids (2,6-dimethoxy-, 2,6-diethoxy-and 2-isobutoxy-6-methoxy) were determined by single crystal X-ray diffraction. The study was undertaken with the intention of designing a novel boronic acid having a monomeric structure, which to date has been an unavailable building block for crystal engineering. This motif can be enhanced by involving two hydroxyl groups at the boron atom in intramolecular hydrogen bonds. Although monosubstituted systems form typical dimers in the crystal lattice, disubstituted species reveal a much bigger variety of possible interactions. Among the analyzed compounds, 2,6-dimethoxyphenylboronic acid and 2,6diethoxyphenylboronic acid crystallize in two polymorphic forms each. The unprecedented packing with monomers as the dominant structural motif has been found in the crystal structure of 2-isobutoxy-6-methoxyphenylboronic acid and one of the polymorphs of both 2,6dimethoxyphenylboronic acid and 2,6-diethoxyphenylboronic acid. This description of the molecular packing is also supported by the analysis of fingerprint 2-D plots based on the Hirshfeld surfaces. The variety of possible types of interactions either within a single moiety or between moieties in dimers were additionally analyzed on the basis of the interaction energies, which have been estimated by ab initio calculations at the MP2/6-31+G* and B3LYP/6-311+G** level of theory.

Nine new cocrystals of para-phenylenediboronic or para-hydroxyphenylboronic acids with a series of aromatic N-oxides are reported. All of the complexes form centrosymmetric crystal structures. They are stabilized by an extended net of hydrogen bonds further supported by effective π-stacking interactions. In the studied structures four main synthons were distinguished. Only in the 3,10-phenanthroline-3-N-oxide and 3,10-N,N-dioxide cocrystals from the series, an acid–acid dimeric motif characteristic for arylboronic acid crystals was observed. The majority of the obtained cocrystals exhibit layered architectures, where the N-oxide molecules are separated by boronic acid slabs. Furthermore, most of the cocrystals form hydrates, where water molecules play the role of a “molecular glue”. Water contribution to the lattice stability is significant, and energy gain per water molecule ranges from 66.8 to 117.6 kJ·mol–1. The cocrystal cohesive energies seem to be more favorable when compared to the corresponding values for crystals of their components. However, the presence of various asymmetric unit contents and numerous hydrated crystal structures indicates that the crystallization process and the final products are highly dependent on kinetic and entropy factors. Finally, the calculated energetic features are compared with the experimental thermogravimetric analysis–differential scanning calorimetry results obtained for selected cocrystals.

In the search for biological agents, a series of new N-substituted ethyl 11-ethyl-7-methyl-3,5,10-trioxo-4-azatricyclo[5.2.2.02,6]undecane-8-carboxylates 3, 9-methyl-3,5,8-trioxo-4-azatricyclo[5.2.1.02,6]dec-1-yl acetates 6 and 1,3-dioxo-4,5,6,7-tetraphenyl-2,3,3a,4,5,7a-hexahydro-1H-isoindole-4-carboxylic acids 9 were prepared. All compounds were characterized by 1H NMR, ESI-MS, and elemental analyses. Moreover, for intermediate products 2, 5, and 8, X-ray structural analyses were conducted. Compounds 3a–e, 6a, 6b, 9a–e were tested for their cytotoxic properties in K562 and HeLa cells.

1,4,5,8-Naphthalene bisimides react as dipolarophiles with in situ formed azomethine ylides. Double 1,3-dipolar cycloaddition is followed by unique ring rearrangement and leads to the formation of two six-membered rings. The formation of hexacyclic products is rationalized based on DFT calculations.