The Corannulene Dianion

Distribution of the two additional electrons to 8 required for dianion formation among the degenerate LUMO orbitals of E, symmetry gives rise to four new states, since, within the 5v symmetry group, the direct product Ej Ej may be reduced to a sum of Aj, and 2 irreducible representations. The A2 state represents a triplet, while Aj and 2 are singlet states. 

The degenerate 2 state for the dianion of C5V symmetry is expected to be distorted into two singlet states of lower symmetry, most probably due to the Jahn-Teller effect. Inspection of the topology of the wavefunctions associated with the degenerate LUMO orbitals in 8 suggests a distortion to symmetry which splits the y LUMO into a pair of orbitals of A and A symmetry, respectively.  

From the pair of Ay and A2 states, the latter is expected to be of lower energy. If Hund s rule is applicable to this system, then the higher spin system is preferred. Also, AM 1 calculations prefer the triplet state at both the HF level and various levels of Cl treatment. 

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It also appears that the addition of alkali metals may have an effect on the bowl-to-bowl inversion of 1. An interesting study of the alkali metal reduction of S9, in which two corannulene moieties are tethered by an eight carbon atom chain, allowed for the estimation of inversion barriers in the corannulene dianion [49]. The barrier for the doubly charged corannulene moieties (8.8 and 9.2 kcal mol at 186 and 196 K for K and Cs salts, respectively) is significantly lower than for neutral corannulene (ca. 11 kcal mol ), and closely agrees with our theoretical prediction (7.9-9.2 kcal mol [48]) published earlier. 

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