Stabilizing carbon-lithium stars.

We have explored in silico the potential energy surfaces of the C(5)Li(n)(n-6) (n = 5, 6, and 7) clusters using the Gradient Embedded Genetic Algorithm (GEGA) and other computational strategies. The most stable forms of C(5)Li(5)(-) and C(5)Li(6) 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 C(5)Li(7)(+) 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 C(5)Li(7)(+) 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 C(5)Li(7)(+) is a π-aromatic and σ-nonaromatic system.