A charge density study of π-delocalization and intermolecular interactions

The compound trans-4,4'-azo-1,2,4-triazole (atrz) is a planar molecule with two planar triazole rings bridged by an azo group. The molecule is a good donor ligand and has an interesting π-delocalized character. In addition, intermolecular interactions in the crystalline state through π-π stacking are found between triazole rings with a very short inter-planar distance of 3.17 Å. The electron density distribution is obtained from both high resolution X-ray diffraction data at 100 K and density functional theory (DFT) calculations using the ωB97X-D functional. Bond characterization is performed in terms of the charge density distribution and the associated topological properties. The Laplacian distribution around each atom reveals the shape of the valence-shell charge concentration and demonstrates a sp(2) hybrid orbital shape for each atom in the molecule. The π-delocalization of the planar molecule is further illustrated by the Fermi-hole distribution. The weak intermolecular π-π interactions and hydrogen bonds are further illustrated by the Hirshfeld surface. The energies of weak intermolecular π-π interactions and hydrogen bonds have been calculated using ωB97X-D/6-311++G(3df,2p) at experimental geometry.