Acta Cryst. (2007). B63, 303-308 [ doi:10.1107/S0108768106055212 ]
Abstract: A new polymorph of 2,4-dihydroxybenzoic acid is reported. The structure was characterized by multiple-temperature X-ray diffraction and solid-state DFT computations. The material shows a geometric pattern of hydrogen bonding consistent with cooperativity between the intermolecular carboxylic acid dimer and intramolecular hydrogen bonds. The presence of proton disorder within this hydrogen-bond system, which would support such a cooperative model, was not fully ruled out by the initial X-ray studies. However, solid-state calculations on the three possible end-point tautomers indicate that the dominant crystallographically observed configuration is substantially lower in energy than the other tautomers (by at least 9 kJ mol-1), indicating that no disorder should be expected. It is therefore concluded that no disorder is observed either in the intra- or intermolecular hydrogen bonds of the title compound and that the cooperativity between the hydrogen bonds is not present within the temperature range studied.
Keywords: hydrogen bonding; single-crystal X-ray diffraction; polymorphism; solid-state computations; cooperative disorder.
 |   Structure factor file (CIF format) (103.4 kbytes) |
| Structure factor file (CIF format) (100.4 kbytes) |
| Structure factor file (CIF format) (100.4 kbytes) |
| Structure factor file (CIF format) (98.9 kbytes) |
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