Hydrogen Bond Patterns of Dipyridone and Bis(Hydroxypyridinium) Cations

Dipyridonyl-substituted
derivatives 2–4 of
benzene, pyridine, and pyrazine, respectively, were synthesized to
examine the ability of 2-pyridone and its protonated species to direct
the self-assembly by hydrogen bonding. Structural analysis by single-crystal
X-ray diffraction (SCXRD) of 2 and 4 in
trifluoroacetic acid demonstrated that salts are formed as a result
of the transfer of protons from the acid to the base (organic species)
to generate a bis­(hydroxypyridinium) dication. However, if no proton
transfer takes place like in the case of crystals of 3 grown from DMSO/H2O, the self-assembly is mainly directed
by the typical R22(8) hydrogen bond motif of 2-pyridone. These
results indicate that the process of converting a neutral 2-pyridonyl
group into a hydroxypyridinium cation makes structure prediction difficult.
Consequently, examination of proton transfer and assembly of dipyridone
and its protonated species are of interest. In combination with SCXRD,
Hirshfeld surface analysis (HSA) was also used to have a better understanding
on the nature of intermolecular interactions within crystal structures
of 2–4. The large number of F···H/H···F,
H···O/O···H, H···H, and
H···C/C···H contacts revealed by HSA
indicates that hydrogen bonding and van der Waals interactions mainly
contribute to crystal packing.