In situ Solid-State Reactions Monitored by X-ray Absorption Spectroscopy: Temperature-Induced Proton Transfer Leads to Chemical Shifts

摘要

The dramatic colour and phase alteration with the solidstate,temperature-dependent reaction between squaric acid and4,4’-bipyridine has been probed in situ with X-ray absorptionspectroscopy. The electronic and chemical sensitivity to the localatomic environment through chemical shifts in the near-edge X-rayabsorption fine structure (NEXAFS) reveals proton transfer from theacid to the bipyridine base through the change in nitrogenprotonation state in the high-temperature form. Direct detection ofproton transfer coupled with structural analysis elucidates the natureof the solid-state process, with intermolecular proton transferoccurring along an acid-base chain followed by a domino effect tothe subsequent acid-base chains leading to the rapid migrationalong the length of the crystal. NEXAFS thereby conveys the abilityto monitor the nature of solid-state chemical reactions in situ, withoutthe need for a priori information or long-range order.