Structure and stability of the heteroannulated [8–10]circulenes: A quantum-chemical study

The structure and stability of a new family of heterocyclic [n]circulenes C_nN_nY_n (n = 8–10; Y = N, P, As, BF₂, AlF₂, GaF₂) have been computationally studied using density functional theory (DFT) B3LYP/6-311G* calculations. The geometry of the compounds is determined by the balance of steric factors and effects of aromatic π-electron delocalization depending on the electronegativity of heteroatoms. An increase in the bulkiness of peripheral atoms Y and enlargement of the inner C_n cycle leads to the gradual transformation of the bowl-shaped circulene structure (Y = N, BF₂) to planar and then saddle-shaped forms (Y = P, As, AlF₂, GaF₂). The calculations performed manifest stabilization of the heteroannulated circulenes ensured by the strong aromatic character of the conjugated five-membered rings fringing the central non-aromatic or antiaromatic [8–10] annulene rings.