Acta Crystallographica Section C

Crystal Structure Communications

Volume 57, Part 10 (October 2001)

Acta Cryst. (2001). C57, 1184-1188 [doi:10.1107/S0108270101010757]

Hydrogen bonding in the inner-salt zwitterion and in two different charged forms of 5,6-bis(2-pyridyl)pyrazine-2,3-dicarboxylic acid

M. Alfonso, Y. Wang and H. Stoeckli-Evans

Abstract: 5,6-Bis(2-pyridyl)pyrazine-2,3-dicarboxylic acid exists as an inner-salt zwitterion, 3-carboxy-5-(2-pyridinio)-6-(2-pyridyl)pyrazine-2-carboxylate, (Ia), C₁₆H₁₀N₄O₄. The adjacent pyridine and pyridinium rings are almost coplanar due to the presence of an intramolecular hydrogen bond involving the pyridine N atom and the NH H atom of the pyridinium group. In the crystal of (Ia), symmetry-related molecules are hydrogen bonded via the carboxylic acid OH group and one of the carboxylate O atoms to form a polymer, which exhibits a channel-type structure. In the HCl, HClO₄ and HPF₆ salts, 6-carboxy-5-carboxylatopyrazine-2,3-diyldi-2-pyridinium chloride 2.25-hydrate, (II), C₁₆H₁₁N₄O₄⁺·Cl^-·2.25H₂O, 6-carboxy-5-carboxylatopyrazine-2,3-diyldi-2-pyridinium perchlorate trihydrate, (IIIa), C₁₆H₁₁N₄O₄⁺·ClO₄^-·3H₂O, and 6-carboxy-5-carboxylatopyrazine-2,3-diyldi-2-pyridinium hexafluorophosphate trihydrate, (IIIb), C₁₆H₁₁N₄O₄⁺·PF₆^-·3H₂O, both pyridine rings are protonated. In the perchlorate form, and in the isomorphous hexafluorophosphate form, the molecule possesses C₂ symmetry, with has a symmetrical intramolecular hydrogen bond involving the adjacent carboxylate and carboxylic acid substituents. In the crystals of the chloride and perchlorate (or hexafluorophosphate) salts, hydrogen-bonded polymers are formed which are three-dimensional and one-dimensional, respectively.

Formula: C₁₆H₁₀N₄O₄ and three salts of C₁₆H₁₁N₄O₄⁺

Online 12 October 2001


	Structure factor file (CIF format) (114.8 kbytes) Contains datablock Ia

	Structure factor file (CIF format) (171.1 kbytes) Contains datablock II

	Structure factor file (CIF format) (94.2 kbytes) Contains datablock IIIa

	Structure factor file (CIF format) (95.6 kbytes) Contains datablock IIIb

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