Stabilizing carbon-lithium stars

Abstract

We have explored in silico the potential energy surfaces of the C₅Li_nⁿ⁻⁶ (n = 5, 6, and 7) clusters using the Gradient Embedded Genetic Algorithm (GEGA) and other computational strategies. The most stable forms of C₅Li₅⁻ and C₅Li₆ are two carbon chains linked by two lithium atoms in a persistent seven membered ring capped by two Li atoms. The other Li atoms are arrayed on the edge of the seven membered ring. In contrast, the global minimum structure for C₅Li₇⁺ is a bicapped star of D_5h symmetry. The molecular orbital analysis and computed magnetic field data suggest that electron delocalization, as well as the saturation of the apical positions of the five-membered carbon ring with lithium atoms in C₅Li₇⁺ plays a key role in the stabilization of the carbon-lithium star. In fact, the planar star sub-structure for the carbon ring are unstable without the apical caps. This is also what has been found for the Si analogues. The split of the B^ind_z in its σ- and π-contribution indicates that C₅Li₇⁺ is a π-aromatic and σ-nonaromatic system.