Methanesulfonic acid salt forms of carbamazepine and 10,11-dihydrocarbamazepine.

New methanesulfonic acid salt forms of the anticonvulsant and analgesic active pharmaceutical ingredient carbamazepine and its closely related structural analogue 10,11-dihydrocarbamazepine have been prepared and characterized by single-crystal X-ray diffraction at 120 and 100 K, respectively {namely [(5H-dibenzo[b,f]azepin-5-yl)(hydroxy)methylidene]azanium methanesulfonate, C15H13N2O(+)·CH3SO3(-), and [(10,11-dihydro-5H-dibenzo[b,f]azepin-5-yl)(hydroxy)methylidene]azanium methanesulfonate, C15H15N2O(+)·CH3SO3(-)}. In light of the structural information obtained, the crystal structure of the carbamazepine trifluoroacetic acid monosolvate [dibenzo[b,f]azepine-5-carboxamide-trifluoroacetic acid (1/1), C15H12N2O·CF3COOH] was redetermined at 100 and 270 K, and from this data it was concluded that the protonation state for this solvate species is best described as in an `intermediate state' with the acidic proton located almost at the mid-point between the acid and base.