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Clear crystals of anhydrous theophylline (3,7-dihydro-1,3-dimethyl-1H-purine-2,6-dione), C7H8N4O2, were grown by sublimation and the X-ray structure determined. The planar molecules are stacked in columns along 010 and are inclined at an angle of 26.05 (10)° relative to (010). The melting point has been determined to be 548.8 (5) K.
Ebisuzaki et al. (Sun,) studied this question.