STRUCTURAL STUDIES ON COMPLEXES .4. CRYSTAL STRUCTURE OF A 1 - 1 5-CHLOROSALICYLIC ACID AND THEOPHYLLINE COMPLEX

Single crystal X‐ray diffraction methods were utilized in obtaining the crystal and molecular structure of a 1:1 association complex between 5‐chlorosalicylic acid and theophylline. The crystals are monoclinic (space group P 21/c) with cell parameters of a = 7.845 Å b = 9.636 Å c = 21.185 Å and β = 92.20° The crystals contain a significant fraction of the impurities 3,5‐dichloro‐ and 3‐chlorosalicylic acid. Hydrogen bonds are the major attractive forces between the components of the complex. A relatively strong hydrogen bond exists between the carboxyl group of 5‐chlorosalicylic acid and N(9) of theophylline (2.682 A.). The theophylline molecules are in a dimeric arrangement by virtue of centrosymmetrically related hydrogen bonds between N(7) and TO(10). The packing arrangement of the molecules suggests that the stacking forces are similar to those in a caffeine: 5‐chlorosalicylic acid complex. Copyright © 1969 Wiley‐Liss, Inc., A Wiley Company