Structures of Li-Doped Alkali Clusters are Dictated by AO-Hybridization

TL;DR

This study reveals that atomic orbital hybridization significantly influences the shapes of small alkali metal clusters, with different hybridization behaviors leading to distinct geometries and bonding characteristics.

Contribution

It demonstrates how AO hybridization dictates cluster structures, highlighting differences between LiNa4- and LiK4- due to varying 2s-2p hybridization responses.

Findings

LiNa4- is a distorted pentagon due to pseudo Jahn-Teller effect

LiK4- adopts a symmetric square structure with ionic character

Hybridization differences are linked to electronegativity and orbital overlap

Abstract

Hybridization of atomic orbitals is a widely appreciated phenomenon whose impact on the structure and properties of, for example, organic molecules is well-established. Here, we demonstrate that hybridization also dramatically impacts the shapes of small alkali metal clusters. The seemingly similar and valence-iso-electronic LiNa4- and LiK4- clusters adopt very different global minimum structures: LiNa4- is a planar C2v (1A1) species distorted from the perfect pentagon due to the pseudo Jahn-Teller effect, and LiK4- 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. Li inside the Na cluster exhibits a strong 2s-2p mixing, to achieve stronger covalent bonding. In contrast, Li inside of the K cluster does not show any hybridization, and the LiK4- cluster is reminiscent of an ionic salt. These differences are tied to the relative electronegativities of Li, Na, and K, and overlap of the valence atomic orbitals of Li with those of Na versus those of K. Atomic orbital hybridization is thus a pronounced effect in clusters, the understanding of which is important for the use of clusters in material science or catalysis, and designing clusters of desired shapes.