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).