Synthesis and structure of 2-amino-4-methylpyridin-1-ium hydrogen squarate

Synthesis and structure of 2-amino-4-methylpyridin-1-ium hydrogen squarate Vanitha Vetrivel https://ror.org/02w7vnb60 Thangavelu Balakrishnan https://ror.org/02w7vnb60 Nishandhini Marimuthu https://ror.org/00tscx035

The title salt (systematic name: 2-amino-4-methylpyridin-1-ium 2-hydroxy-3,4-dioxocyclobut-1-en-1-olate), C 6 H 9 N 2 + ·C 4 HO 4 − , 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—H...O, O—H...O, and C—H...O hydrogen bonds, forming infinite layers. These layers are consolidated by π–π 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.
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