Crystal and Molecular Structures of Three Co-crystals from 1,3-Dimethyl-3,7-dihydro-1H-purine-2,6-dione and Carboxylic Acids

The preparation, X-ray crystal structure, Fourier Transform infrared (FTIR) spectroscopy, and elemental analysis of the three complexes (1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione): (2,6-dichlorobenzoic acid)2: H2O [(tp)· (Hbza)2 · H2O, Hdcba = 2,6-dichlorobenzoic acid] (1) (1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione): (2-pyrazinecarboxylic acid) [(tp) · (Hpyca), Hpyca = 2-pyrazinecarboxylic acid] (2) and (1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione): (3-nitrophthalic acid) [(tp) · (Hntpa)] (3) based on 1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione, 2,6-dichlorobenzoic acid 2-pyrazinecarboxylic acid, and 3-nitrophthalic acid are reported. XRD and FTIR analysis indicated that they are all co-crystal. 1 crystallizes in the monoclinic, space group P21/n, with a = 7.1019(7) Å, b = 12.9494(12) Å, c = 26.253(3) Å, β = 93.536(3)°, V = 2409.8(4) Å3, Z = 4. 2 crystallizes in the monoclinic, space group P21/c, with a = 6.9863(7) Å, b = 25.437(3) Å, c = 7.3987(7) Å, β = 95.152(2)°, V = 1309.5(2) Å3, Z = 4. 3 crystallizes in the monoclinic, space group P21/n, with a = 14.2133(15) Å, b = 8.2333(9) Å, c = 15.3860(17) Å, β = 117.236(5)º, V = 1600.9(3) Å3, Z = 4. The imidazole-carboxylic acid synthon of the CO2H···N type is observed in all the co-crystal. The imidazole H–N also donated the N–H···O hydrogen bonds in all cases. Apart from the classical hydrogen bonds, the auxiliary expanding interactions as CH···O, CH3···O, CH···Cl, O···O, Cl···O, Cl···Cl, Cl···π, O···π, and π···π also play important roles in the structure extension. For the coexistence of the various weak interactions these structures adopted the most common R22(7) supramolecular synthon. In conclusion, we have shown that 2D–3D connections can be constructed by the collective non-covalent interactions. In the three prepared supramolecular assemblies there are plenty of weak nonbonding interactions such as directional hydrogen bonds of O–H···N, N-H···O, O–H···O, intra- and interchain CH···O, CH3···O, CH···Cl, O···O, Cl···O, Cl···Cl, Cl···π, O···π, and π···π interactions, on account of these collective weak interactions, these compounds displayed the 2D–3D framework structures.