Polymorphs of anhydrous theophylline: Stable form IV consists of dimer pairs and metastable form i consists of hydrogen-bonded chains

Abstract

The structure of a previously unreported polymorph of anhydrous theophylline (1,3-dimethyl-3,7-dihydro-1H-pur-ine-2,6-dione), C 7H8N 4O 2, has been determined at 100 K and shown to have monoclinic symmetry with Z′ = 2. The structure is named form IV and experimental observation indicates that this is the stable form of the material. The mol-ecular packing consists of discrete hydrogen-bonded dimers similar to that observed in the monohydrate structure. The structure of form I has also been determined and consists of hydrogen-bonded chains. © 2011 International Union of Crystallography.