Form IV of carbamazepine

Carbamazepine has been found to crystallize as a new polymorph that is stable at room temperature. We report the crystal structure of this C-centered monoclinic form (space group C2/c, cell parameters: a = 26.609, b = 6.9269, c = 13.957, beta = 109.702), which consists of hydrogen bonded dimers with an anti-disposition. This represents the third modification of carbamazepine that has been crystallographically characterized, and the fourth for which cell parameters have been determined. Thus, it is designated as form IV of carbamazepine. Differences between the packing of the various polymorphs are discussed.