Spherical aromaticity in inorganic chemistry

After more than 150 years since the Kekule's conceptualization of the benzene structure, this small hexagonal hydrocarbon indubitably remains the most prototypical example of aromaticity. Recent developments revealed that aromaticity is not limited by canonical carbon, hydrogen, or nearby elements but also covers almost all periodic table. Moreover, aromaticity paradigms and features (π-electron precession or noble gas-like electronic configuration, stability, etc.) do not purely belong to the realm of planarity but are also applicable to three-dimensional (3D) structures, ranging from homometal clusters to complex multilayer arrangements. In this chapter, we summarize recent findings extending aromaticity to a plethora of 3D spherical aromatic (or superatomic) inorganic systems bearing homo- and heteronuclear backbones, with elements across the periodic table from hydrogen to gold. These observations are based on bonding and magnetic response properties given by the adaptive natural density partitioning (AdNDP) analysis and induced magnetic field tools. These recent insights contribute to the continuous blooming of nontrivial aromatic species, which are of broad interest for chemical and physical and material science communities. This chapter is organized in the following sequence. First, information about the origin of spherical aromaticity concept and its evolution is provided. Second, we discuss the AdNDP tool and magnetic response technique which are among aromaticity criteria. Third, detailed consideration of systems possessing spherical aromaticity that correspond to filled S-shell and then P-shell are discussed. Fourth, a short discussion of spherical antiaromaticity concept is provided.