The monohydrate of the title phenolic diacid (C8H 6O5-H2O, 2-hydroxybenzene-1,3-dioic acid or 3-carboxysalicylic acid) adopts a planar conformation, with the phenol hydrogen internally hydrogen-bonded to the carbonyl of one highly ordered carboxyl, which, in turn, donates a hydrogen bond to the oxygen of water. The second carboxyl is disordered and hydrogen-bonded both to water and to the disordered carboxyl of a centrosymmetrically related neighbor in a static disorder arrangement extending over two full asymmetric units. The water accepts either one or two hydrogen bonds and donates a long bifurcated hydrogen bond shared equally by O atoms of the phenol and the disordered carboxyl. The hydrogen bonding includes no standard carboxyl pairing and is entirely two-dimensional. The resulting planar ribbons stack translationally at a distance of 3.413 (8) Å, in an offset arrangement having non-translational interplanar distances of 0.821 (5) and 2.592 (6) Å. This structure is compared with two previously reported for this compound. The title compound forms a monoanion, whose tetraphenylphosphonium salt is described (C32H 25O5P, tetraphenylphosphonium 2,6-dicarboxyphenolate, tetraphenylphosphonium 2-oxidoisophthalic acid or tetraphenylphosphonium 3-carboxy-salicylate). The, phenol oxygen is the site of formal negative charge on the anion, which is stabilized in a planar arrangement by symmetrical hydrogen bonds from both ortho-carboxyl groups. The energetics of this arrangement, the phenol and carboxyl acidities, and factors affecting those acidities and providing anion stabilization are discussed.
|Original language||English (US)|
|Number of pages||9|
|Journal||Acta Crystallographica Section B: Structural Science|
|State||Published - Aug 1 2004|
All Science Journal Classification (ASJC) codes
- Biochemistry, Genetics and Molecular Biology(all)