Anion Binding of One-, Two-, and Three-Armed Thiourea Receptors Examined via Photoelectron Spectroscopy and Quantum Computations

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.

Determinants for proton location and electron coupled proton transfer in hydrogen bonded pentafluorophenol–anion clusters

This work reveals the determinant factors for proton locations and electron coupled proton transfer (ECPT) in biologically relevant hydrogen bonded systems.

Spectroscopic Signature of Proton Location in Proton Bound HSO4-·H+·X- (X = F, Cl, Br, and I) Clusters

Proton transfer plays a vital role in a variety of chemical and biological processes. The proton location in proton bound clusters, specifically, in the anions of HSO₄^-·H⁺·X^- (X = F, Cl, Br, and I), has been studied by negative ion photoelectron spectroscopy and ab initio theoretical calculations. The measured photoelectron spectra of HSO₄^-·H⁺·X^- (X = Cl, Br, and I) closely resemble those of X^- by simply shifting to higher electron binding energies, suggesting that X^- is the chromophore of the electron photodetachment, a fact clearly violating gas-phase acidity predictions. However, in the X = F case, the spectrum of HSO₄^-·H⁺·F^- is more similar to that of HSO₄^-, indicating that H⁺ stays with F^- and that the HSO₄^- moiety carries the extra electron. Accompanying theoretical analyses are in excellent agreement with the experimental measurements and observations. This work provides direct spectroscopic evidence of the proton locations, clearly showing cases in which proton affinities of the constituent bases cannot correctly predict the right chemistry involving proton transfer processes.

Hydrogen-bonding cyclodiphosphazanes: superior effects of 3,5-(CF3)2-substitution in anion-recognition and counter-ion catalysis

Syntheses, X-ray characterization and employment of new cyclodiphosph(v)azane hydrogen-bonding catalysts in experimental and computational anion recognition and the N-acyl-Mannich reaction.