Short π‑Stacking in N‑Rich Ionic Aromatic Compounds

Reaction
of N-rich conjugated bis­(3,4-diamino-1,2,4-triazole)­s
with dilute hydrochloric acid affords bis­(3,4-diamino-1,2,4-triazol-2-ium)­chlorides.
These compounds form layered structures in which planar layers of
molecules are parallelly stacked. The π-stacking distance of
the layers is relatively short, as compared with all-carbon-containing
aromatic compounds, ranging between 3.00 and 3.22 Å at 173 K,
and several contacts shorter than the sum of van der Waals radii are
observed in the crystal structures. The features of the crystal structures
are discussed in terms of the high nitrogen content of the compounds
and of the H-bonding patterns. Periodic ab initio theoretical calculations
of the crystal structures have allowed decomposing the lattice energy
into various contributions in order to put up the relevance of van
der Waals interactions for the π-stacking. In particular, it
is found that van der Waals interactions account for about 10% of
the total lattice energy and about 50% of the stacking energy (interlayer
energy).