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Experimentally, potential differences between two half\u2010cells connected by an \u201cideal\u201d ionic liquid salt bridge (ILSB) were measured. Here, our established setup with the \u201cideal\u201d Ionic Liquid [N\n                    <jats:sub>2225<\/jats:sub>\n                    ][NTf\n                    <jats:sub>2<\/jats:sub>\n                    ] in the ILSB ([N\n                    <jats:sub>2225<\/jats:sub>\n                    ] = [N(C\n                    <jats:sub>2<\/jats:sub>\n                    H\n                    <jats:sub>5<\/jats:sub>\n                    )\n                    <jats:sub>3<\/jats:sub>\n                    (C\n                    <jats:sub>5<\/jats:sub>\n                    H\n                    <jats:sub>11<\/jats:sub>\n                    )]; Tf = SO\n                    <jats:sub>2<\/jats:sub>\n                    CF\n                    <jats:sub>3<\/jats:sub>\n                    ) was refined to enable measurements of the Gibbs energies of proton transfer \u0394\n                    <jats:sub>tr<\/jats:sub>\n                    <jats:italic>G<\/jats:italic>\n                    \u00b0(H\n                    <jats:sup>+<\/jats:sup>\n                    , S\n                    <jats:sub>1<\/jats:sub>\n                    \u2192 S\n                    <jats:sub>2<\/jats:sub>\n                    ) between different solvents S\n                    <jats:sub>1<\/jats:sub>\n                    and S\n                    <jats:sub>2<\/jats:sub>\n                    , such as water, methanol, ethanol, acetonitrile and methyl formate. These results were further evaluated by extensive theoretical studies using the double\u2010hybrid functional DSD\u2010BLYP for structure optimization and highly accurate coupled cluster DLPNO\u2010CCSD(T) calculations that were extrapolated to the basis set limit (CBS) for the gas phase contributions. Solvation effects were added implicitly with the Conductor\u2010like Polarizable continuum Model (CPCM) in a Cluster Continuum approach, including a scheme to use the CPCM with coupled cluster calculations in ORCA's newest version. A monomer and a cluster thermodynamic cycle were used to calculate the proton's solvation energy from the calculated solvent clusters. The cluster cycle performed well with consistent improvement at higher levels of theory, while the monomer cycle suffered from inadequate error compensation. Yet, the monomer cycle results can be significantly improved by the inclusion of experimental data, such as Gibbs energies of evaporation. However, it remains clear that even when using the most sophisticated of all currently available methods, the error bars of the calculations may at best reach about 10\u201315\u2009kJ mol\n                    <jats:sup>\u20131<\/jats:sup>\n                    and, given low polarity solvents like methyl formate with\n                    <jats:italic>\u03b5<\/jats:italic>\n                    <jats:sub>r<\/jats:sub>\n                    \u2009=\u20098.838, may even substantially exceed this error bar. Analysis shows that one of the largest problems arising for the calculations is the lack of reliable experimental structural data in solution to know how the dissolved particles governing the protochemical potential exactly prevail in solution. The delicate balance of subtle and relatively weak hydrogen bonds or dispersive interactions may lead to large structural differences between the structures known in the solid state (e.g., from single crystal structure determinations) and those actually being thermodynamically relevant in (dynamic) equilibrium in solution. We present some problems encountered during our work on this subject. At least for the more polar \u201cclassical\u201d solvents, experimental ILSB\u2010 as well as computationally obtained results are in good agreement with the known values from the TATB assumption, which is currently one of the most widely used assumptions for determining single\u2010ion transfer energies. However, with none of the described in part rather sophisticated calculations, it is possible to achieve \u201cchemical accuracy\u201d in solution, as one can with the used \u201cgold standard\u201d coupled cluster methods in the gas phase (i.e., \u00b14\u2009kJ mol\n                    <jats:sup>\u20131<\/jats:sup>\n                    ).\n                  <\/jats:p>","DOI":"10.1002\/cphc.202500349","type":"journal-article","created":{"date-parts":[[2026,4,25]],"date-time":"2026-04-25T20:05:06Z","timestamp":1777147506000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Proton Solvation in Water and Selected Organic Solvents: A Critical Assessment of Experimental and Theoretical Approaches to Extend the Solvent\u2010Independent Unified Acidity Scale"],"prefix":"10.1002","volume":"27","author":[{"given":"Regina","family":"Stroh","sequence":"first","affiliation":[{"name":"Institut f\u00fcr Anorganische und Analytische Chemie and Freiburger Materialforschungszentrum (FMF) Universit\u00e4t Freiburg  Freiburg Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Niklas","family":"Gebel","sequence":"additional","affiliation":[{"name":"Institut f\u00fcr Anorganische und Analytische Chemie and Freiburger Materialforschungszentrum (FMF) Universit\u00e4t Freiburg  Freiburg Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Timo","family":"Kienzle","sequence":"additional","affiliation":[{"name":"Institut f\u00fcr Anorganische und Analytische Chemie and Freiburger Materialforschungszentrum (FMF) Universit\u00e4t Freiburg  Freiburg Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5547-1278","authenticated-orcid":false,"given":"Valentin","family":"Radtke","sequence":"additional","affiliation":[{"name":"Institut f\u00fcr Anorganische und Analytische Chemie and Freiburger Materialforschungszentrum (FMF) Universit\u00e4t Freiburg  Freiburg Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7182-4387","authenticated-orcid":false,"given":"Ingo","family":"Krossing","sequence":"additional","affiliation":[{"name":"Institut f\u00fcr Anorganische und Analytische Chemie and Freiburger Materialforschungszentrum (FMF) Universit\u00e4t Freiburg  Freiburg Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2026,4,25]]},"reference":[{"key":"e_1_2_12_2_1","doi-asserted-by":"publisher","DOI":"10.1002\/anie.201000252"},{"key":"e_1_2_12_3_1","doi-asserted-by":"publisher","DOI":"10.1002\/chem.201003164"},{"key":"e_1_2_12_4_1","doi-asserted-by":"publisher","DOI":"10.1002\/chem.201302473"},{"key":"e_1_2_12_5_1","doi-asserted-by":"publisher","DOI":"10.1021\/ed066p403"},{"key":"e_1_2_12_6_1","volume-title":"Single\u2010Ion Solvation. 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