Key indicators: single-crystal X-ray study; T = 298 K; mean (C-C) = 0.011 Å; R factor = 0.047; wR factor = 0.095; data-to-parameter ratio = 16.5.The title compound, (C 6 H 9 N 2 ) 2 [Sb 2 Cl 6 O], consists of one triple-bridged [Sb 2 Cl 6 O] 2À anion and two 2-amino-6-methylpyridinium cations that undergo aminium-iminium tautomerism. The counter-ion pair are linked together by N-HÁ Á ÁO and N-HÁ Á ÁCl hydrogen bonds. ExperimentalCrystal data (C 6 H 9 N 2 ) 2 [Sb 2 Cl 6 O] M r = 690.52 Monoclinic, P2 1 =n a = 10.0746 (10) Å b = 15.1972 (16) Å c = 15.4631 (14) Å = 101.597 (6) V = 2319.2 (4) Å 3 Z = 4 Mo K radiation = 3.03 mm À1 T = 298 (2) K 0.30 Â 0.30 Â 0.30 mm Data collection Bruker APEX area-detector diffractometer Absorption correction: multi-scan (SADABS; Bruker, 2000) T min = 0.419, T max = 0.419 12055 measured reflections 4137 independent reflections 3876 reflections with I > 2(I) R int = 0.026 Refinement R[F 2 > 2(F 2 )] = 0.048 wR(F 2 ) = 0.095 S = 1.24 4137 reflections 250 parameters 8 restraints H atoms treated by a mixture of independent and constrained refinement Á max = 0.86 e Å À3 Á min = À0.50 e Å À3 metal-organic compounds m1786 # 2007 International Union of Crystallography

Key indicatorsSingle-crystal X-ray study T = 293 K Mean (C-C) = 0.007 Å R factor = 0.042 wR factor = 0.100 Data-to-parameter ratio = 16.2 For details of how these key indicators were automatically derived from the article, see

The title compound, di‐μ‐chloro‐bis­[aqua­chloro­(3,7‐dihydro‐1,3,7‐trimethyl‐1H‐purine‐2,6‐dione)copper(II)], [Cu2Cl4(C8H10N3O2)2(H2O)2], has the same chemical empirical formula as another compound [Bandoli et al. (1976). Inorg. Chim. Acta, 20, 71–78]. However, the title compound is a dimer arranged around an inversion centre, whereas Bandoli's compound is a chiral polymer. In the title compound, the CuII atom has a distorted tetra­gonal pyramidal coordination, formed by three Cl atoms, one N atom of the caffeine ligand and one O atom of a water mol­ecule.

Key indicators: single-crystal X-ray study; T = 273 K; mean (C-C) = 0.004 Å; disorder in main residue; R factor = 0.069; wR factor = 0.169; data-to-parameter ratio = 12.2.The title compound, C 11 H 14 N 4 O 4 ÁC 3 H 4 O 2 , a 1:1 doxofyllineacrylic acid complex, forms via O-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds in the solid state. Dimers of (I) aggregate via methyl-acid C-HÁ Á ÁO interactions about inversion centres, and the three-dimensional structure arises fromstacking interactions of the purine molecules.

Key indicatorsSingle-crystal X-ray study T = 273 K Mean (C-C) = 0.002 Å R factor = 0.025 wR factor = 0.065 Data-to-parameter ratio = 24.3For details of how these key indicators were automatically derived from the article, see