MNgCCH (M = Cu, Ag, Au; Ng = Xe, Rn): The First Set of Compounds with M–Ng–C Bonding Motif

Although Ng–M (M = Cu, Ag, Au; Ng = noble gas) and Ng–C bonds are known to exist in different viable species, we report here a series of systems with formula MNgCCH (Ng = Xe, Rn) in which both bonds coexist. These compounds possess reasonably high kinetic stability (free energy barrier, Δ<i>G</i>^‡ of 14.0–34.8 kcal/mol) along an exergonic isomerization channel, MNgCCH → NgMCCH. For a given M, the Δ<i>G</i>^‡ associated with this channel increases from Xe to Rn, whereas for a given Ng, it increases along Ag < Cu < Au. No other possible dissociation channel is feasible at standard condition, except for the Ag–Xe analogue, where one three-body neutral dissociation channel, AgXeCCH → Ag + Xe + CCH, is slightly exergonic by 2.4 kcal/mol. Examination of the thermochemical stability of the Ng–M bonds in noninserted compounds against the dissociation, NgMCCH → Ng + MCCH reveals that Kr–Rn bound Cu and Au analogues, and Xe and Rn bound Ag analogues would be viable at 298 K. The natural bond order analysis indicates the formation of M–Ng covalent bond and Ng–C ionic bonds in these compounds having an ionic representation of (MNg)⁺(CCH)⁻. Energy decomposition analysis reveals a significant contribution of the electrostatic term in the M–Ng covalent bonds