1 research outputs found
Proton Transfer, Hydrogen Bonding, and Disorder: Nitrogen Near-Edge X-ray Absorption Fine Structure and X-ray Photoelectron Spectroscopy of Bipyridine-Acid Salts and Co-crystals
The sensitivity of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to BrĂžnsted donation and the protonation state of nitrogen in the solid state is investigated through a series of multicomponent bipyridineâacid systems alongside X-ray photoelectron spectroscopy (XPS) data. A large shift to high energy occurs for the 1s â 1Ï* resonance in the nitrogen K-edge NEXAFS with proton transfer from the acid to the bipyridine base molecule and allows assignment as a salt (CâNH+), with the peak ratio providing the stoichiometry of the types of nitrogen species present. A corresponding binding energy shift for CâNH+ 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 (CâN) 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 potential to distinguish variations in hydrogen bond length to nitrogen