Low-temperature determination of theophylline dimethyl sulfoxide solvate

The title solvate, C7H8N4O2·C2H6OS, was obtained unintentionally from a cocrystal screen involving theophylline and isophthalic acid. One mol­ecule each of theophylline and dimethyl sulfoxide is present in the asymmetric unit. The packing consists of mol­ecular sheets lying parallel to the (040) series of lattice planes, in which each theophylline mol­ecule is hydrogen bonded to one dimethyl sulfoxide mol­ecule through an N—H⋯O [2.7658 (15) A] hydrogen bond. This particular hydrogen-bond donor was found to be used in this type of inter­action in a variety of other crystal structures of theophylline.