CTHIoN+.C1 -, monoclinic, P2~/a, a = 17.474 (4), b = 13.718 (4), c = 7.639 (2) A, fl = 96.03 (2) °, V = 1820.9/~3, Z = 8, D m = 1.46 (1), D e = 1.46 Mg m -3. Full-matrix least-squares refinement (nonhydrogen atoms anisotropic, H atoms included but not refined) based on 3439 counter-collected Fo'S led to final R and weighted R values of 0.076 and 0.054 respectively. The two crystallographically independent 1,9-dimethyladeninium cations are related by a pseudo center of symmetry and form

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... bonded dimers in the crystal. The exocyclic amino group of one of the cations donates a hydrogen bond to the imidazole-ring nitrogen atom N(7) of the other cation and vice versa. Several interactions of the type D-H... C1-are noted between the purine cations and the chloride anions.