A quantum crystallographic approach to short hydrogen bonds

Abstract

Mapped electron density and ab initio modelling reveal how H-atom position and molecular environment tune short hydrogen bond characteristics and properties.

Importance of Nuclear Quantum Effects for Molecular Cocrystals with Short Hydrogen Bonds

“…At a high temperature, the electron density in the H1O position corresponding to the cocrystal of LUNNAJ is 1.38× higher than in the H1N position (corresponding to the salt), whereas at 100 K, the R OF value is slightly less than 1. These results thus confirm the temperature-induced hydrogen atom shift from the nitrogen atom to the oxygen atom in a gradual trend (salt–cocrystal continuum) . The R OF values of SEDJUI and AJAKEB also increase with increasing temperature, but they are higher than 2 in the whole temperature range, indicating a higher proportion of the cocrystal form.…”

“…These results thus confirm the temperature-induced hydrogen atom shift from the nitrogen atom to the oxygen atom in a gradual trend (salt−cocrystal continuum). 43 The R OF values of SEDJUI and AJAKEB also increase with increasing temperature, but they are higher than 2 in the whole temperature range, indicating a higher proportion of the cocrystal form. Furthermore, we selected the SEDJUI system for variable temperature diffuse reflectance measurements because we expected significant absorbance changes of the phenolic component upon protonation/deprotonation during the cocrystal/salt transformation.…”

Proton Transfer on the Edge of the Salt/Cocrystal Continuum: X-Ray Photoelectron Spectroscopy of Three Isonicotinamide Salts

“…Systems in which the donor–acceptor distance is short (up to ∼2.6 Å) allow strong potential well overlap, resulting in a low barrier or even a single well without any barrier . Often referred to as short hydrogen bonds (SHBs) or SSHBs, their classification into salts and cocrystals is not clear-cut when the barrier is so low that the protons are able to populate a continuum of positions and with a distribution that responds to temperature variations. ,,, In line with this, XPS distinguished a quasi-centered population of hydrogens in a low-barrier SHB between an oxygen donor and a nitrogen acceptor unequivocally . Compared to the N 1s emission from protonated and hydrogen-bonded functional groups, broadening of the N 1s emission line reflected the dynamic disorder in the quasi-single potential well, and the N 1s emission line centroid was at an intermediate BE, neither characteristic for protonation nor for a hydrogen bond …”

X-ray wavefunction refinement and comprehensive structural studies on bromo-substituted analogues of 2-deoxy-d-glucose in solid state and solution

“… 32 Such refined structural information is useful for investigating thermodynamical properties of the crystal 33 as well as intermolecular interactions. 34 In this study, the crystal structures of both 2-BG and 2-BM have been established by X-ray crystallography using HAR to obtain models of improved quality when compared to the classical IAM approach. We described their supramolecular architecture focusing on analysis of the H-bond network.…”