Single-Water Microsolvation Promotes Proton Sharing in a Neutral Formic Acid-Ammonia Complex.
5 affiliations
- 1Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui230026, China.
- 2Deutsches Elektronen-Synchrotron DESY , Notkestr. 85, 22607Hamburg, Germany.
- 3Scuola Superiore Meridionale , Largo San Marcellino 10, Napoli80138, Italy.
- 4INSTM , via G. Giusti 9, Firenze50121, Italy.
- 5Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Str. 1, 24118Kiel, Germany.
Abstract
Can single-water microsolvation promote proton sharing in a neutral acid-base complex? We address this question for formic acid-ammonia by isolating its monohydrated complex with broadband rotational spectroscopy and interpreting the resolved 14N hyperfine structure with calibrated high-level quantum chemistry. The observed complex is a single dominant HCOOH-NH3-H2O isomer with effective Cs symmetry, in which NH3 remains the primary proton acceptor, while water closes a cooperative hydrogen-bond cycle by accepting from NH3 and donating to the carbonyl oxygen. Rather than simply stabilizing the binary acid-base contact, this water molecule measurably increases its proton-sharing character. A resolved A/E tunneling pattern from NH3 internal rotation supplies the missing orientation needed to rotate the experimental 14N quadrupole tensor into the local ammonia frame, yielding an experimental χzz component and a quadrupole-derived Townes-Dailey ionicity of approximately 26%. High-level structures show the same directional response: O-H elongation, H···N contraction, and O···N contraction relative to HCOOH-NH3. Together, these results show that one water molecule can promote proton sharing in a neutral formic acid-ammonia complex without producing a separated ion pair.
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BibTeX
@article{xie2026singlewater,
title = {{Single-Water Microsolvation Promotes Proton Sharing in a Neutral Formic Acid-Ammonia Complex.}},
author = {Fan Xie and Luigi Crisci and Wenhao Sun and Federico Lazzari and Vincenzo Barone and Melanie Schnell},
journal = {Journal of the American Chemical Society},
year = {2026},
month = oct,
doi = {10.1021/jacs.6c13418},
url = {https://europepmc.org/article/MED/42912363},
note = {CC BY},
}
RIS
TY - JOUR
TI - Single-Water Microsolvation Promotes Proton Sharing in a Neutral Formic Acid-Ammonia Complex.
AU - Fan Xie
AU - Luigi Crisci
AU - Wenhao Sun
AU - Federico Lazzari
AU - Vincenzo Barone
AU - Melanie Schnell
PY - 2026
DA - 2026/10/01
JO - Journal of the American Chemical Society
DO - 10.1021/jacs.6c13418
UR - https://europepmc.org/article/MED/42912363
AB - Can single-water microsolvation promote proton sharing in a neutral acid-base complex? We address this question for formic acid-ammonia by isolating its monohydrated complex with broadband rotational spectroscopy and interpreting the resolved 14N hyperfine structure with calibrated high-level quantum chemistry. The observed complex is a single dominant HCOOH-NH3-H2O isomer with effective Cs symmetry, in which NH3 remains the primary proton acceptor, while water closes a cooperative hydrogen-bond cycle by accepting from NH3 and donating to the carbonyl oxygen. Rather than simply stabilizing the binary acid-base contact, this water molecule measurably increases its proton-sharing character. A resolved A/E tunneling pattern from NH3 internal rotation supplies the missing orientation needed to rotate the experimental 14N quadrupole tensor into the local ammonia frame, yielding an experimental χzz component and a quadrupole-derived Townes-Dailey ionicity of approximately 26%. High-level structures show the same directional response: O-H elongation, H···N contraction, and O···N contraction relative to HCOOH-NH3. Together, these results show that one water molecule can promote proton sharing in a neutral formic acid-ammonia complex without producing a separated ion pair.
SN - 0002-7863
SN - 1520-5126
ER -