Nonlocal electronic distribution in metallic clusters: a critical examination of aromatic stabilization

All-metal clusters, such as Al(4)M(4) (M = alkali metal ion), exhibit interesting features of multi-fold aromaticity/antiaromaticity. Such characteristics arise particularly because of the poor sigma-pi separation in this class of systems. This Account presents computational strategies to unambiguously determine the aromaticity/antiaromaticity characteristics of such clusters. Computations of the linear and nonlinear optical responses show that all-metal clusters are orders of magnitude more polarized than the conventional pi-conjugated molecules. We also propose new strategies to stabilize all-metal antiaromatic systems through complexation to transition metals and discuss mechanisms for substitution reactions within the conventional organometallic systems by Al(4)M(4). Additionally, we find that these all-metal clusters form stacked superclusters that are extremely stable and aromatic.