MC6Li6 (M = Li, Na and K): a new series of aromatic superalkalis

Organic superalkalis are carbon-based species possessing lower ionisation energy than alkali atom. We study the MC6Li6 (M = Li, Na, and K) complexes and their cations by decorating hexalithiobenzene with an alkali atom using density functional theory. All MC6Li6 complexes are stable against dissociation into M + C6Li6 fragments, irrespective of their charge. Furthermore, their degree of aromaticity increases monotonically from M = Li to K, unlike MC6Li6+ cations, which are not aromatic as suggested by their NICS values. The adiabatic ionisation energies of MC6Li6 (2.60–2.78 eV) and vertical electron affinities of MC6Li6+ (2.32–2.62 eV) suggest that MC6Li6 species form a new series of aromatic superalkalis. The superalkali nature of MC6Li6+ and its relation with NICS values are explained on the basis of the positive charge delocalisation. We believe that these species will not only enrich the aromatic superalkalis but also their possible applications will be explored.