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) ų, 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) ų, 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) ų, 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.

Graphical Abstract

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.