The π Complex of the Hydronium Ion Frozen on the Pathway of Electrophilic Aromatic Substitution

A very rare crystal was prepared consisting of a 2D aromatic (toluene) together with a weakly coordinating 3D aromatic (closo-1-CB11H12 –) and a hydronium ion, and this crystal was analyzed by using X-ray diffraction and high-level quantum-mechanical calculations. The nature of the crystal arrangement made it possible to detect the frozen π complex that would originate during protonation of toluene by the acidic hydronium ion.