Usefulness of the σ-Aromaticity and σ-Antiaromaticity Concepts for Clusters and Solid-State Compounds.

In this Review we present examples of clusters, molecules, and solid-state compounds, for which the use of σ-aromaticity and σ-antiaromaticity concepts is essential for understanding of chemical bonding. We show that the bonding patterns in these σ-aromatic and σ-antiaromatic compounds are similar to those of the corresponding π-aromatic and π-antiaromatic chemical systems, respectively. Undoubtedly, σ-aromaticity helps us understand why the high symmetry isomers are the most stable among myriads of other potential structures. We also show that besides systems exhibiting either σ- or π-aromatic features, there are species, which can possess multiple aromaticity/antiaromaticity, or conflicting aromaticity patterns. We believe that the σ-aromaticity and σ-antiaromaticity concepts will be helpful in rationalizing chemical bonding, structure, stability, and molecular properties of chemical species in both organic and inorganic chemistry. We hope that they will also be useful for other areas of science such as material science, catalysis, nanotechnology, and biochemistry.