title: In Situ Solid-State Reactions Monitored by X-ray Absorption Spectroscopy: Temperature-Induced Proton Transfer Leads to Chemical Shifts.
abstract: The dramatic colour and phase alteration with the solid-state, temperature-dependent reaction between squaric acid and 4,4'-bipyridine has been probed in situ with X-ray absorption spectroscopy. The electronic and chemical sensitivity to the local atomic environment through chemical shifts in the near-edge X-ray absorption fine structure (NEXAFS) revealed proton transfer from the acid to the bipyridine base through the change in nitrogen protonation state in the high-temperature form. Direct detection of proton transfer coupled with structural analysis elucidates the nature of the solid-state process, with intermolecular proton transfer occurring along an acid-base chain followed by a domino effect to the subsequent acid-base chains, leading to the rapid migration along the length of the crystal. NEXAFS thereby conveys the ability to monitor the nature of solid-state chemical reactions in situ, without the need for a priori information or long-range order.
authors.affiliation: School of Chemical Engineering & Analytical Science, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK. joanna.stevens@manchester.ac.uk.
authors.forename: Joanna S
authors.identifier: http://orcid.org/0000-0002-1013-8447
authors.initials: JS
authors.lastname: Stevens
authors.affiliation: School of Materials, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
authors.forename: Monika
authors.initials: M
authors.lastname: Walczak
authors.affiliation: Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland, 20899, USA.
authors.forename: Cherno
authors.initials: C
authors.lastname: Jaye
authors.affiliation: Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland, 20899, USA.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Fischer
keywords: X-ray absorption spectroscopy; acid-base reactions; protonation; reaction monitoring; solid-state reactions