{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,30]],"date-time":"2026-07-30T14:23:31Z","timestamp":1785421411733,"version":"3.56.0"},"reference-count":41,"publisher":"International Union of Crystallography (IUCr)","issue":"12","license":[{"start":{"date-parts":[[2025,11,28]],"date-time":"2025-11-28T00:00:00Z","timestamp":1764288000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/legalcode"},{"start":{"date-parts":[[2025,11,28]],"date-time":"2025-11-28T00:00:00Z","timestamp":1764288000000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/legalcode"}],"content-domain":{"domain":["iucr.org","wiley.com","iucrj.org"],"crossmark-restriction":true},"short-container-title":["Acta Crystallogr E Cryst Commun","Acta Cryst E","Acta Cryst Sect E","Acta Crystallogr E","Acta Crystallogr Sect E","Acta Cryst E Cryst Commun","Acta Cryst Sect E Cryst Commun"],"accepted":{"date-parts":[[2025,11,21]]},"published-print":{"date-parts":[[2025,12,1]]},"abstract":"<jats:p>\n                    The title salt (systematic name: 2-amino-4-methylpyridin-1-ium 2-hydroxy-3,4-dioxocyclobut-1-en-1-olate), C\n                    <jats:sub>6<\/jats:sub>\n                    H\n                    <jats:sub>9<\/jats:sub>\n                    N\n                    <jats:sub>2<\/jats:sub>\n                    <jats:sup>+<\/jats:sup>\n                    \u00b7C\n                    <jats:sub>4<\/jats:sub>\n                    HO\n                    <jats:sub>4<\/jats:sub>\n                    <jats:sup>\u2212<\/jats:sup>\n                    , was obtained by the proton-transfer reaction between 2-amino-4-methylpyridine and squaric acid in aqueous solution: protonation occurs at the pyridine nitrogen atom, while squaric acid is singly deprotonated. In the crystal, the cations and anions are linked by N\u2014H...O, O\u2014H...O, and C\u2014H...O hydrogen bonds, forming infinite layers. These layers are consolidated by \u03c0\u2013\u03c0 stacking interactions, resulting in a columnar packing arrangement. Hirshfeld surface analysis reveals that O...H\/H...O contacts dominate the intermolecular interactions, consistent with the hydrogen-bonding network observed in the crystal structure.\n                  <\/jats:p>","DOI":"10.1107\/s205698902501045x","type":"journal-article","created":{"date-parts":[[2025,11,24]],"date-time":"2025-11-24T10:37:12Z","timestamp":1763980632000},"page":"1189-1194","update-policy":"https:\/\/doi.org\/10.1107\/cm_01","source":"Crossref","is-referenced-by-count":1,"title":["Synthesis and structure of 2-amino-4-methylpyridin-1-ium hydrogen squarate"],"prefix":"10.1107","volume":"81","author":[{"given":"Vanitha","family":"Vetrivel","sequence":"first","affiliation":[{"id":[{"id":"https:\/\/ror.org\/02w7vnb60","id-type":"ROR","asserted-by":"publisher"}]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Thangavelu","family":"Balakrishnan","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/02w7vnb60","id-type":"ROR","asserted-by":"publisher"}]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nishandhini","family":"Marimuthu","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/00tscx035","id-type":"ROR","asserted-by":"publisher"}]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"329","published-online":{"date-parts":[[2025,11,28]]},"reference":[{"key":"hb8170_bb1","doi-asserted-by":"crossref","first-page":"317","DOI":"10.1021\/mp060126o","volume":"4","author":"Aaker\u00f6y","year":"2007","journal-title":"Mol. 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