Conclusion
The reactions of CO2 with 20 anions were computed with
the wavefunction MP2/aug-cc-pvtz method. To test for convergence of the
results, we also employed an extrapolation procedure using the CBS
approach, as reported in previous studies. Solvent effects were computed
using the IEFPCM method with water, tetrahydrofuran and toluene as
solvents. In the gas-phase the computed reactions are exergonic without
any activation energy. In the condensed phase the anions are more
stabilized than the adducts, reducing the reaction spontaneity and
inducing an activation barrier for some systems. Interestingly, although
the dielectric constant of tetrahydrofuran is closer to that of toluene
than to the dielectric constant of water, results obtained with
tetrahydrofuran are closer to results obtained with water than with
toluene. For some anions we observe a change in the reaction spontaneity
in the different solvents, allowing to think of a medium where
CO2 sequestration and regeneration could be done
depending only on the medium composition. Alkyl sulfide anions emerge as
an interesting candidate for CO2 sequestration because
they combine suitable thermodynamics with low activation barrier for
both the direct and the reverse reactions.
When comparing the trends obtained with the different methods, we
observe that the MP2 and CBS approaches yield results that are close to
each other within 3 kcal mol-1. Comparing to results
obtained previously with the B3LYP-D3 and M06-2X functionals we found
that B3LYP-D3 follows the same trends as MP2, while M06-2X tends to
diverge from the wavefunction results.