Abstract
The sensitivity of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to Bronsted donation and the protonation state of nitrogen in the solid state is investigated through a series of multicomponent bipyridine–acid systems alongside X-ray photoelectron spectroscopy (XPS) data. A large shift to high energy occurs for the 1s → 1π* resonance in the nitrogen K-edge NEXAFS with proton transfer from the acid to the bipyridine base molecule and allows assignment as a salt (C═NH+), with the peak ratio providing the stoichiometry of the types of nitrogen species present. A corresponding binding energy shift for C═NH+ is observed in the nitrogen XPS, clearly identifying protonation and formation of a salt. The similar magnitude shifts observed with both techniques relative to the unprotonated nitrogen of co-crystals (C═N) suggest that the chemical state (initial-state) effects dominate. Results from both techniques reveal the sensitivity to identify proton transfer, hydrogen bond disorder, and even the...
Highlights
Proton transfer can be thought of as one of the simplest chemical reactions, ranging from complete transfer from an acidic to a basic moiety to varying degrees of sharing through hydrogen bonding
Comparison of X-ray powder diffraction patterns with those simulated from previously reported single crystal structures.[35−37] The new 4BPY/sulfo system was revealed as a 1:1 salt and 4BPY/butanetetracarboxylic acid (buTA) system as a 1:1 co-crystal initially by X-ray photoelectron spectroscopy (XPS), and this was confirmed by both Nearedge X-ray absorption fine structure (NEXAFS) and single crystal X-ray diffraction
XPS yields nitrogen 1s spectra with the binding energy (EB) specific to the nitrogen chemical and local electronic environment and has recently been shown to be adept at identifying the nature of intermolecular interactions in two-component base/acid systems.[14,18,19]
Summary
Proton (hydrogen) transfer can be thought of as one of the simplest chemical reactions, ranging from complete transfer from an acidic to a basic moiety (protonation through Brønsted donation) to varying degrees of sharing through hydrogen bonding. Whether Brønsted proton transfer occurs has a profound effect on the location of protons in crystal structures and influences chemical and physical properties. This reflects the influence of the local chemical state on the core level binding energy,[19,23−25] resulting in a large positive chemical shift due to proton transfer to nitrogen.[14,18−21] Nearedge X-ray absorption fine structure (NEXAFS) is likewise highly dependent on the local electronic structure, as excitation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
