Salt forms of the pharmaceutical amide dihydrocarbamazepine

Buist, Amanda and Kennedy, Alan (2016) Salt forms of the pharmaceutical amide dihydrocarbamazepine. Acta Crystallographica Section C: Structural Chemistry, 72 (2). pp. 155-160. ISSN 2053-2296 (

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Reaction of the pharmaceutical amide dihydrocarbamazepine with strong acids results in protonation of the amide functionality at the O atom and gives the salt forms dihydrocarbamazepine hydrochloride, dihydrocarbamazepine hydrochloride monohydrate and dihydrocarbamazepine hydrobromide monohydrate (formal names [(10,11-dihydro-5Hdibenzo[b.f]azepin-5-yl)(hydroxy)methylidene]azanium chloride, C15H15ClN2O, [(10,11-dihydro-5Hdibenzo[b.f]azepin-5-yl)(hydroxy)methylidene]azanium chloride monohydrate, C15H17ClN2O2, and [(10,11-dihydro-5Hdibenzo[b.f]azepin-5-yl)(hydroxy)methylidene]azanium bromide monohydrate, C15H17BrN2O2, respectively). The anhydrous hydrochloride has a structures with two crystallographically independent ion pairs (Z′ = 2) wherein both cations adopt syn conformations, whilst the two hydrated species are mutually isostructural and have cations with anti conformations. Compared to neutral dihydrocarbamazepine structures, protonation of the amide is shown to cause changes to both molecular structure (C=O lengthening and C–N shortening) and to supramolecular structure. The amide to amide and dimeric hydrogen bonding motifs seen for neutral polymorphs and cocrystalline species are replaced here by onedimensional polymeric constructs with no direct amide to amide bonds. The structures are also compared with, and shown to be closely related to, those of salt forms of the structurally similar pharmaceutical carbamazepine.