Accurate Quantum Chemical Prediction of Gas-Phase Anion Binding Affinities and Their Structure-Binding Relationships

This
paper systematically examines the performance of contemporary
wavefunction and density functional theory methods to identify robust
and cost-efficient methods for predicting gas-phase anion binding
energies. This includes the local coupled cluster LNO-CCSD­(T) and
DLPNO-CCSD­(T), as well as double-hybrid DSD-PBEP86-D3­(BJ) and various
hybrid functionals M06-2X, B3LYP-D3­(BJ), ωB97M-V, and ωB97X-V.
The focus is on dual-hydrogen-bonding anion receptors that are commonly
found in supramolecular chemistry and organocatalysis, namely, (thio)­ureas,
deltamides, (thio)­squaramides, and croconamides as well as the yet-to-be-explored
rhodizonamides. Of the methods examined, M06-2X emerged as the overall
best performing method as the other functionals including DSD-PBEP86-D3­(BJ)
and the local coupled cluster DLPNO-CCSD­(T) method displayed systematic
errors that increase with the degree of carbonylation of the receptors.
Hybrid ONIOM models that employed semiempirical methods (PM7, GFN1-xTB,
and GFN2-xTB) and “threefold”-corrected small-basis
set potentials (HF-3c, B97-3c, and PBEh-3c) were explored, and the
best models resulted in 50- to 500-fold reduction in CPU time compared
to W1-local. These calculations provide important insight into the
structure-binding relationships where there is a direct correlation
between Brønsted acidity and anion binding affinity, though the
strength of the correlation also depends on other factors such as
hydrogen-bonding geometry and the geometrical distortion that the
receptor needs to undergo to bind the anion.