title: Four salt phases of theophylline.
abstract: The structures of two anhydrous salt phases of theophylline, namely 1,3-dimethyl-2,6-dioxo-7H-purin-9-ium tetrafluoroborate, C7H9N4O2(+)·BF4(-), and 1,3-dimethyl-2,6-dioxo-7H-purin-9-ium chloride, C7H9N4O2(+)·Cl(-), are reported together with the structures of two monohydrate salt forms, namely 1,3-dimethyl-2,6-dioxo-7H-purin-9-ium chloride monohydrate, C7H9N4O2(+)·Cl(-)·H2O, and 1,3-dimethyl-2,6-dioxo-7H-purin-9-ium bromide monohydrate, C7H9N4O2(+)·Br(-)·H2O. The monohydrate structures are mutually isostructural, with the cations and anions lying on crystallographic mirror planes (Z' = ½). The main intermolecular interaction motif is a hydrogen-bonding network in the same mirror plane. The tetrafluoroborate structure is based on planar hydrogen-bonded theopylline cation dimers; the anions interact with the dimers in a pendant fashion. The anhydrous chloride structure has Z' = 2 and in contrast to the other species it does not form planar hydrogen-bonded constructs, instead one-dimensional chains of cations and anions propagate parallel to the crystallographic c direction. An earlier report claiming to describe an anhydrous structure of theophylline hydrochloride is re-examined in light of these results. It is concluded that the earlier structure has been reported in the wrong space group and that it has been chemically misidentified.
authors: Westchem, Department of Pure & Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, Scotland.
authors: Amanda R
authors: AR
authors: Buist
authors: Westchem, Department of Pure & Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, Scotland.
authors: Alan R
authors: AR
authors: Kennedy
authors: Vale of Leven Academy, Main Street, Alexandria G83 0BH, Scotland.
authors: Craig
authors: C
authors: Manzie
mesh_terms: D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D007477:Ions / Q000737:chemistry*; D015394:Molecular Structure; D012492:Salts / Q000737:chemistry*; D013806:Theophylline / Q000737:chemistry*
chemical_list: D007477:Ions; D012492:Salts; D013806:Theophylline
keywords: 1,3-dimethyl-2,6-dioxo-7H-purin-9-ium; crystal structure; hydrogen bonding; theophylline salts