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 sigma-aromaticity in defining cluster shapes. The valence-iso-electronic LiNa4- and LiK4- clusters adopt different global minimum structures: LiNa4- is a planar C-2v ((1)A(1)) species distorted from the perfect pentagon, and LiK4- is a planar square D-4h ((1)A(1g)) 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. (C) 2012 Elsevier B. V. All rights reserved.