Methane-sulfonic acid salt forms of carbamazepine and 10,11-di-hydro-carbamazepine

Acta Cryst. (2013). C69, 1260–1266 (http://doi.org/qdc)

Difference Fourier map for the trifluoroacetic acid carbamazepine complex at 100 K showing the position of the acidic hydrogen at the mid-point between the acid and base; contour level = 0.05 e Å⁻³.

Methanesulfonic acid salt forms of carbamazepine and 10,11-dihydrocarbamazepine were characterized by single-crystal X-ray diffraction. The impact of salt formation on the carbamazepine framework is revealed through an examination of the C=O and C-N bond lengths. Similar analyses of 83 carbamazepine complexes from the CSD led to a re-examination of the trifluoroacetic acid complex, which was determined to be an intermediate-type complex with the acidic hydrogen at the mid-point between the acid and the base. This result has implications for the recent FDA guidelines on the development of pharmaceutical cocrystals. This paper forms part of the special issue on Pharmaceuticals, drug discovery and natural products.