Bonding and uneven charge distribution in infinite pyrene π-stacks

Abstract

Unusual intermolecular π-stacking in a new charge transfer salt of pyrene (Py), (Py)₂⁺(Ga₂Cl₇)⁻, has been observed. The structure obtained by single crystal X-ray crystallography indicates π-stacks of pyrene which were analyzed using a combination of density functional theory and the analysis of the bond length alternation patterns in the pyrene molecules in different charge states. There are relatively few crystal structures of charge transfer salts of pyrene in the literature, and this structure shows a unique charge separation in which half of the pyrenes are nearly neutral while the other half carry approximately +1 charge in an alternating fashion along the 1D stacks balancing one electron charge transfer to each (Ga₂Cl₇)⁻ anion. The charge localization is attributed to the incomplete inter-pyrene overlap of the singly occupied molecular orbitals.