A unique trimeric triphenylene radical cation: stacking aggregation, bonding, and stability

Abstract

A new and unique π-stacking triphenylene trimer cation radical unit appears in the crystal structure of a newly synthesized salt with an oligomeric gallium(III) chloride, [(C₁₈H₁₂)₃]˙⁺(Ga₃Cl₁₀)⁻, which is the first triphenylene aggregate observed. The structure is attributed to a shared electron distributed over the trimer displaying π-stacking pancake bonding. Computational modeling rationalizes the appearance of a “chain-shaped” rather than a “star-shaped” gallium chloride anion as well as the reasons why the trimer, rather than a radical cation aggregate of different size, is preferred in this system. Moreover, the calculations allowed evaluation of larger cationic triphenylene radical π-stacked aggregates. Additional stabilization due to the shared single unpaired electron is calculated to remain significant at 5–7 kcal mol⁻¹ for aggregates as large as 5–6 units.