Crystal structure of 2,5-di­hydroxy­terephthalic acid from powder diffraction data

The crystal structure of anhydrous 2,5-dhy­droxy­terephthalic acid, C(8)H(6)O(6), was solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The published structure of 2,5-di­hydroxy­terephthalic acid dihydrate was also optimized. The carb­oxy­lic acid groups form strong hydrogen bonds, which form centrosymmetric rings with graph set R (2) (2)(8). These hydrogen bonds link the mol­ecules into chains along [011]. There is an intra­molecular O—H⋯O hydrogen bond between the hydroxyl group and the carbonyl group of the carb­oxy­lic acid. The hydrogen bonding in the dihydrate is very different. Although the intra­molecular hy­droxy/carb­oxy­lic acid hydrogen bond is present, the water mol­ecule acts as an acceptor to the carb­oxy­lic acid and a donor to two other oxygen atoms. The carb­oxy­lic acid groups do not inter­act with each other directly.