Mono‐reduced Corannulene: To Couple and Not to Couple in One Crystal

One‐electron reduction of corannulene, C 20 H 10 , with Li metal in diglyme resulted in crystallization of [{Li + (diglyme) 2 } 4 (C 20 H 10 .− ) 2 (C 20 H 10 ‐C 20 H 10 ) 2− ] ( 1 ), as revealed by single‐crystal X‐ray diffraction. This hybrid product contains two corannulene monoanion‐radicals along with a dianionic dimer, crystallized with four Li + ions wrapped by diglyme molecules. The dimeric (C 20 H 10 ‐C 20 H 10 ) 2− anion provides the first crystallographically confirmed example of spontaneous radical dimerization for C 20 H 10 .− . The C−C bond length between the two C 20 H 10 .− bowls of 1.588(5) Å is consistent with the single σ‐bond character of the linker. The trans ‐disposition of two bowls in the centrosymmetric (C 20 H 10 ‐C 20 H 10 ) 2− dimer is observed with the torsion angle around the central C−C bond of 180°. Comprehensive theoretical analysis of formation/decomposition processes of the dimeric dianion has been carried out in order to evaluate the nature of bonding and energetics of the C 20 H 10 .− coupling. It is found that such σ‐bonded dimers are thermodynamically unstable due to large preparation energy and repulsive Pauli component of the bonding, but kinetically persistent due to a high energy barrier provided by the existing spin‐crossing point.