Structural Evidence of Interanionic Hydrogen Bonding in Phosphoric Acid Solutions

Kim, Pyeongeun [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Chemical Sciences Division] (ORCID:0000000247184770); Kang, Richard [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Chemical Sciences Division; University of California, Berkeley, CA (United States)] (ORCID:0000000189011723); Carter-Fenk, Kevin [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Chemical Sciences Division; University of California, Berkeley, CA (United States); Univ. of Pittsburgh, PA (United States)]; Wilson, Kevin R. [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Chemical Sciences Division] (ORCID:0000000302640872); Head-Gordon, Martin [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Chemical Sciences Division; University of California, Berkeley, CA (United States)] (ORCID:0000000243096669); Ahmed, Musahid [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Chemical Sciences Division] (ORCID:000000031216673X)

doi:10.1021/jacs.5c12699

DOE OSTI · 3375162

Structural Evidence of Interanionic Hydrogen Bonding in Phosphoric Acid Solutions

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Abstract

Interanionic hydrogen bonding (IAHB) is a noncovalent interaction between like-charged ions that challenges conventional electrostatic understanding. This study provides direct structural evidence of IAHB in concentrated aqueous phosphoric acid (PA) solutions, which exhibit >60% dissociation under these conditions. Oxygen K-edge X-ray absorption fine structure spectroscopy, combined with electron affinity time-dependent density functional theory calculations, reveals the formation of stable, cyclic phosphate-phosphate IAHB dimers at PA concentrations ≥7 M. Extended X-ray absorption fine structure data show distinct long-range ordering consistent with these dimers, and near-edge X-ray absorption fine structure spectra confirm a concentration-dependent transition from monomeric to dimeric species. Energy decomposition analysis through density functional theory shows that the formation of solution-phase IAHB is energetically favored and is attributed to polarization of and the charge transfer between the two fragments driven by the surrounding solvent molecules, in addition to the permanent electrostatics. These findings offers crucial structural insights into the H-bonded networks in concentrated PA, highlighting the critical role of solvent in facilitating anion–anion association.

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY Extended X-ray absorption fine structure Noncovalent interactions Oligomers Solvation X-ray absorption near edge spectroscopy

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Kim, Pyeongeun [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Chemical Sciences Division] (ORCID:0000000247184770), Kang, Richard [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Chemical Sciences Division; University of California, Berkeley, CA (United States)] (ORCID:0000000189011723), Carter-Fenk, Kevin [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Chemical Sciences Division; University of California, Berkeley, CA (United States); Univ. of Pittsburgh, PA (United States)], Wilson, Kevin R. [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Chemical Sciences Division] (ORCID:0000000302640872), Head-Gordon, Martin [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Chemical Sciences Division; University of California, Berkeley, CA (United States)] (ORCID:0000000243096669), Ahmed, Musahid [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Chemical Sciences Division] (ORCID:000000031216673X). 2025-11-24. Structural Evidence of Interanionic Hydrogen Bonding in Phosphoric Acid Solutions. https://doi.org/10.1021/jacs.5c12699

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