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.