Intermolecular Interaction, Electronic Structure and Aromaticity of Possible Dimers of Cyclo[18]Carbon (C18)

The optimized structures in the configuration space of cyclo[18]carbon (C₁₈) dimers, most of which haven't been studied in detail or even discovered yet, were explored here, and their electronic structure, aromaticity and intermolecular interaction between monomers were thoroughly investigated based on quantum chemistry and various electronic wavefunction analyses. For the dimers bound by weak interaction, their dimerization interactions are contributed mainly by dispersion and less significantly by electrostatic attraction. For those bound by covalent bonds, the symmetry of their geometric structures and hence the degeneracy of out-of-plane and in-plane $$ orbitals ($$ and $$ ) are broken after dimerization. Also predicted are the interesting phenomena including their aromaticity or anti-aromaticity, as well as the spin polarization of their singlet ground states as a result of the distortion of their carbon rings.