Planar Tetracoordinate Carbon with Triple C≡C Bonding in C2Li3H and C2Li4H2 Clusters

Abstract

Planar hypercoordinate carbon species have attracted sustained interest from chemists due to their unconventional bonding, yet instances featuring localized multiple bonding remain rare. Here, we report that C₂Li₃H and C₂Li₄H₂ adopt planar tetracoordinate carbon (ptC) geometries with C_s and C_2h symmetry as global minima, wherein the C-C unit preserves its C≡C triple-bond character (WBI ∼3.0) and is ionically coordinated by a bent Li-H framework featuring bridging hydrogen atoms. Energy decomposition analysis reveals that the C₂^2- unit interacts with the surrounding Li-H framework predominantly through electrostatic attraction (90.8%), supplemented by directional dative contributions (9.1%). Born-Oppenheimer molecular dynamics simulations at 300 and 400 K confirm kinetic robustness over 20 ps, identifying these global-minimum ptC clusters as plausible targets for gas-phase synthesis. These findings extend the structural diversity of planar hypercoordinate carbon systems to include species featuring preserved C≡C triple bonding.