  A sigma-pi separation analysis of the energies in Al4Li4 reveals that the
system is more pi-antiaromatic than the sigma-aromaticity in it. This is true
also for C4H4 and Ga4Li4. Unlike C4H4 that has a very large component of
pi-antiaromaticity, for these all-metal clusters, these energy scales are
comparable though pi-antiaromaticity is the major driving force for the
distortion of the these molecules from the square (sigma-aromatic) structure to
the rectangular (pi-antiaromatic) architecture. For the dianion Al4Li42-, the
sigma-equalization prevails over the pi-distortion in Al4Li4 and for the
dication Al4Li42+, pi-equalization is the driving force for the square
symmetric structure.
