Tug of war between AO-hybridization and aromaticity in dictating structures of Li-doped alkali clusters

Hybridization of atomic orbitals is a widely appreciated phenomenon in organic chemistry. Here, we demonstrate that hybridization also can dramatically impact the shapes of small all-alkali metal clusters, and oppose σ-aromaticity in defining cluster shapes. The valence-iso-electronic LiNa 4 - and LiK 4 - clusters adopt different global minimum structures: LiNa 4 - is a planar C2v (1A1) species distorted from the perfect pentagon, and LiK 4 - is a planar square D4h (1A1g) species with Li being in the centre. This effect is rooted in the different degrees of the 2s–2p hybridization in Li in response to binding to Na versus K.