Trichloroacetic acid at 105 K

Acta Cryst. (2003). E59, o316–o318

Packing of the molecules, viewed down the a axis.

Crystal structures of a number of simple compounds remain unknown for a variety of reasons. The answer to 'Why has the crystal structure of trichloroacetic acid, a simple and yet an important compound, not been reported until now?' lies perhaps in its highly deliquescent nature. This low-temperature x-ray study reveals that the molecules form centrosymmetric pairs leading to hydrogen-bonded dimers. In the absence of 'scope' for other strong intermolecular interactions, Cl···O and Cl···Cl interactions presumably play a role in stabilizing the crystal structure. Interestingly, there is another dimension to simple crystal structures of these types: trichloroacetic acid represents a class of simple organic molecules of the type R-COOH and accurate x-ray crystallographic investigations on such molecules may prove to be useful in the design of crystals, assuming a 'direct' relationship between the nature of R and the difficulty of design.