Carbyne‐Terminated Carbon‐Flanked Noble‐Gas Cations: Stability and Asymmetric C–Ng–C Bonding (NgHe–Rn)

Carbyne‐terminated, carbon‐flanked noble‐gas cations CH 2 NgCR + (Ng = He–Rn; R = CH, N, P, As) serve as a minimal platform for carbon‐only coordination of noble gases and for tuning asymmetric C–Ng–C bonding. Geometry optimizations and thermochemistry were performed at the MP2/def2‐TZVPP level. Most systems adopt a C 2v Y‐shaped structure, with CH 2 HeCCH + and CH 2 NeCCH + as C s exceptions. In contrast, no bound minima were located for CH 2 HeCN + and CH 2 NeCN + at the MP2 level, although Y‐shaped structures were obtained at the DFT level. The singlet is the lowest electronic state for most bound systems, although CH 2 NeCCH + and CH 2 ArCP + have lower‐energy triplet states, while CH 2 ArCCH + and CH 2 XeCP + show near‐degenerate spin states. A dissociation network considering different fragmentation limits and the CH 2 spin state was used to assess thermodynamic stability. The bound He and Ne complexes are destabilized by three‐body homolytic fragmentation, whereas dissociation into CH 2 (t) + NgCR + generally provides the most relevant dissociation limit for the heavier analogues. Several Ar and Kr derivatives remain close to thermoneutrality or are slightly unstable at 298 K, while the Xe and Rn systems are thermodynamically protected with respect to the dissociation pathways considered. NPA, Mayer bond‐order, QTAIM, and AdNDP analyses reveal pronounced asymmetry: the H 2 C–Ng contact is weak and becomes closed‐shell for Ne, whereas Ng–CR exhibits shared‐shell character and near‐single‐bond Mayer indices for Ar–Rn. EDA, performed at the ωB97X–D3/def2–TZVPP level, indicates predominantly electrostatic H 2 C–Ng stabilization and a larger orbital contribution to the Ng–CR interaction in the heavier noble‐gas systems.