Theophylline monohydrate

The crystal structure of the title compound, 3,7-dihydro-1,3-dimethyl-1H-purine-2,6-dione monohydrate, C7H8N4O2.H2O, was determined by single-crystal X-ray diffractometry using direct methods. Water molecules in the crystals form infinite chains, through hydrogen-bonded chains running through tunnels formed by surrounding theophylline molecules along the a axis. The water chains are also crosslinked through hydrogen bonds by hydrogen-bonded theophylline dimers, and form a two-dimensional hydrogen-bonded structure parallel to the ab plane. The previously reported structure [Suctor (1958), Acta Cryst. 11, 83-87] in space group P2(1), with Z = 4, appears to be incorrect.