Short strong hydrogen bonds in multi-component organic acid molecular crystals exhibit temperature dependent proton migration for certain HB donor–acceptor distances.
X-ray
photoelectron spectroscopy (XPS) has emerged as a technique
that allows for characterization and classification of hydrogen bonding
and proton transfer interactions in organic crystal structures, in
a way that is complementary to crystallography by X-ray or neutron
diffraction. Here, we analyze the nitrogen 1s core-level binding energies
(BEs) of isonicotinamide (IN) systems with proton transfer between
donor and acceptor groups at short distances. We show how a careful
calibration of the BE scale places these salt systems correctly on
the edge of the so-called salt–cocrystal continuum. We show
how performing a fitting analysis of the data that is consistent with
elemental analysis, expected stoichiometry, and quantification of
adventitious carbon contamination facilitates the determination of
absolute BEs with accuracy and reproducibility within ±0.1 eV.
The determined N 1s core-level BEs of the protonated IN acceptors
suggest that the local geometric arrangements of the donor, acceptor,
and proton can influence the N 1s core-level BE significantly.
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