C₂₁H₉^Z (Z=−3 to +3): a theoretical study on the redox behaviour of C₃ symmetric fragment of C₆₀

Abstract

B3LYP/6-31G* calculations were done on seven C₂₁H₉^Z . fragments, where the charge, Z, is varied from −3 to +3; doublet states of the open shell systems and both singlet and triplet states of closed shell species are considered. Among them, only the D_3h and C_3v forms of the singlet states of C₂₁H₉³⁻ and C₂₁H₉¹⁺, and triplet-C₂₁H₉¹⁻ correspond to the bowl-to-bowl inversion transition states and minimum energy structures, respectively. 6-31+G* basis set, which employs a set of diffuse functions on the non-hydrogen atoms, was employed on anionic systems. The rest encountered symmetry breaking problem, which necessitated us to go for lower symmetry structures to obtain the local minima and the bowl-to-bowl inversion transition states. The curvature, ascertained by π-orbital axis vector angles (POAV), is lowest for the trianion and highest for the cations. The triplet states of the closed shell species are found to be competitive in energy with the singlet states when Z=−1 and +3, whereas for Z=−3 and +1, the triplet states lie above the corresponding singlet states over 30 kcal/mol. The inversion barriers vary from 12.2 to 40.2 kcal/mol with C₂₁H₉³⁻ and C₂₁H₉²⁺ having the lowest and highest inversion barriers, respectively. The electron affinities and ionization energies were calculated to assess the electron receiving and donating ability of the C₃-fragment in comparison to corannulene. The curvature and redox behavior of the C₂₁H₉ fragment are compared to those of C₆₀.