Ligand-stabilized dilithium (C6F5)2Li2 featuring two planar tetracoordinate lithium and carbon centers

Abstract

The design of planar hypercoordinate Li represents a significant challenge because the stabilization in such molecules arises exclusively from electrostatic interactions, while covalent glue, particularly delocalized π/σ bond, is needed to stabilize a planar conformer. Here, we report a computational study of a novel system, two pentafluorophenyl ligands stabilized dilithium, (C6F5)2Li2, featuring two planar tetracoordinate lithium (ptLi) atoms and two planar tetracoordinate carbon (ptC). The design strategy was inspired by the recent synthesis of tolyl–lithium complexes and refined through systematic structural modifications to achieve a fully planar geometry corresponding to a true minimum on the potential energy surface. Both thermodynamic and kinetic analyses demonstrate that the structure is stable under static and dynamic conditions. A thorough bonding analysis using different methods reveals that the stabilization of the ptLi atoms arises primarily from the electrostatic interactions, while the orbital contributions are comparatively weak. On the other hand, the stabilization of the ptCs is the interplay of both electrostatic and covalent interactions. Aromaticity analysis based on magnetically induced current densities indicates that aromatic character is confined to the benzenoid rings, whereas the Li-containing core is non-aromatic. These findings expand the conceptual framework for hypercoordinate species in s-block elements and highlight the role of selecting proper ligands that can lead to the realization of such planar hypercoordinate Li, not only in the cluster form but also in molecular materials.