High-Level ab Initio Predictions for the Ionization Energies, Bond Dissociation Energies, and Heats of Formation of Vanadium Methylidene, Vanadium Methyl Species, and Their Cations (VCH₂/VCH₂⁺, VCH₃/VCH₃⁺)

Abstract

The ionization energies of VCH 2 and VCH 3 , the various 0 K bond dissociation energies (D 0 s) in their neutrals and cations, and their respective heats of formation at 0 and 298 K are computed by the single-reference, wave functionbased CCSDTQ/CBS procedure. The core of the composite method is the approximation to the complete basis set (CBS) limit at the coupled cluster (CC) level which includes up to full quadruple excitations. The zero-point vibrational energy, core−valence correlation, spin−orbit coupling, and scalar relativistic effects have their contributions incorporated in an additive manner. For the species in the current study, this protocol requires geometry optimizations and harmonic frequency calculations practically no higher than the CCSD(T)/aug-cc-pwCVTZ and CCSD(T)/aug-cc-pVTZ levels, respectively. The present calculations successfully predict D 0 (V + −CH 3 ) = 2.126 eV and D 0 (V + −CH 2 ) = 3.298 eV in remarkable agreement with the data recently measured by a spin−orbit state selected V + + CH 4 collision experiment (Phys. Chem. Chem. Phys. 2021, 23, 273−286). The good accord encourages the use of CCSDTQ/CBS protocol in thermochemical predictions of various feasible product channels identified in methane activation by transition metal species.

Ferrocene/ferrocenium, cobaltocene/cobaltocenium and nickelocene/nickelocenium: from gas phase ionization energy to one-electron reduction potential in solvated medium

“…Given the fact that advanced electronic structure methods, e.g. , CCSD(T)/CBS 43–46 or other composite methods, 47–50 have been shown to give accurate predictions for the gas-phase IE values of main-group compounds 51–60 and 3d- and 4d-transition-metal diatomics and triatomics, 61–71 the accuracy in the prediction of the value is largely dependent on the two Δ G solv quantities, or simply their difference given by “Δ G solv (Cp 2 Fe + ) − Δ G solv (Cp 2 Fe)”. As expected, the value prediction could be improved if we can maximize the cancellation of errors in the “Δ G solv (Cp 2 Fe + ) − Δ G solv (Cp 2 Fe)” term.…”