A C≡C Triple Bond as a Structural Anchor of Planar Pentacoordinate Carbon

High Resolution Image Download MS PowerPoint Slide The potential energy surface of C 2 Li 4 H 3 – was examined to identify stable structures containing planar hypercoordinate carbon centers. The lowest-energy form corresponds to a C 2 v -symmetric arrangement in which a Li 4 H 3 framework encloses a C≡C triple bond. Bonding analyses (NBO, AdNDP, EDA, and IQA) show that the system consists of a C 2 2– fragment interacting mainly through electrostatic attraction and weak covalent contributions with the Li 4 H 3 + unit. Magnetic response calculations indicate localized electron density supported by the C≡C bond, contrasting with the delocalization mechanisms typically invoked for planar hypercoordinate carbons. Born–Oppenheimer molecular dynamics simulations confirm structural stability under thermal conditions. These results outline an alternative electronic route to achieve planar pentacoordination in carbon systems.