The aromaticity of dicupraannulenes
An extensive theoretical investigation of the electronic structure of a tested fair model dicupraannulene compound, based on the analysis of atom-pair delocalization indices, Bader's molecular graph, the inspection of the canonical molecular orbitals, the z components of their Nuclear Independent Chemical Shifts, NICS(0)zz, and the normalized Giambiagi multicenter delocalization indices, concludes that the perimeter aromaticity of the dicupraannulene ring is consistent with both 10 and 14 π-electron Hückel aromatic 10-membered rings. In either case, the 10-membered ring encloses two 6 π-electron aromatic inner rings, hinged at the Cu–Cu bond. This work demonstrates that the aromaticity of dicupraannulenes closely resembles that of naphthalene. Hence, they are best regarded as metalla-polyacenes, which could make the building blocks of extended structures such as metalated nanotubes.