Heavy icosagens embedded in a plane of lithium: Can multicentric bonding reinforce planarity?

Planar hypercoordination of main group elements has attracted chemists due to their structural peculiarity. Herein, we present global minimum structure featuring planar pentacoordinate indium and thallium (ppIn and ppTl) in Li₅M²⁺ (M = In, Tl) clusters. The clusters are found to be stabilized by multicentric bonding without any aromaticity. Although aromaticity plays a major role in stabilizing such planar hypercoordinate species, this study reveals that the presence of aromaticity in not the sole criterion to achieve planar hypercoordination. The presence of multicentre bonding is enough to provide stability to the planar geometry. Energy decomposition analysis reveals significant covalent character in the Li-In and Tl-In bonds. The clusters stable towards dissociation, suggesting their kinetic stability. Interestingly, the planarity of the clusters is maintained in ligand supported neutral complexes, Li₂M(Cp)₂ (Cp = C₅H₅^-) as well.