6-Chloro-N 4,N 4-dimethylpyrimidine-2,4-diamine

The asymmetric unit of the title compound, C6H9ClN4, contains four independent molecules (A, B, C and D). Their main difference is the torsion angles, ranging from 1.6 (5) to 5.9 (5)°, between the methyl group and the pyrimidine plane. A pair of intermolecular N—H⋯N hydrogen bonds link molecules A and C into a twisted dimer with a dihedral angle of 32.9 (1)° between the two pyrimidine rings, creating an R 2 2(8) motif. In the packing, each two molecules of B, C and D form centrosymmetric dimers through two intermolecular N—H⋯N hydrogen bonds, locally creating R 2 2(8) motifs. The dimers of C and D are alternately bridged by A into an infinite zigzag strip, locally creating two different R 2 2(8) motifs with dihedral angles of 32.9 (1) and 63.4 (1)° between the pyrimidine rings. Finally, these strips together with the dimers of B associate into a complicated three-dimensional framework.

The title compound, C 6 H 9 ClN 4 , contains four crystallographically independent molecules ( Fig. 1), A, B, C and D, in the asymmetric unit, among which A and C are connected into a twisted dimer by two intermolecular N3-H3A···N9 and N11-H11B···N1 hydrogen bonds (Table 1), with a dihedral angle of 32.9 (1)° between the two pyrimidine rings. The bond lengths and angles of all molecules are similar except for the torsion angles between the methyl groups and the pyrimidine rings, ranging from 1.6 (5) to 5.9 (5)°.
In the packing of the title compound, each inversion-related two molecules of B, C and D form a centrosymmetric dimer through two intermolecular N-H···N hydrogen bonds (Table 1), locally creating an R 2 2 (8) motif (Bernstein et al., 1995). For example, in the dimer of D (Fig. 2), hydrogen bonds arise from atoms N7-H7B at (x, y, z) and (-x + 1, -y + 1, -z), which act as hydrogen-bond donors, respectively, to atoms N5 at (-x + 1, -y + 1, -z) and (x, y, z). The dimers of C and D are alternately arranged and bridged by the molecule A, creating an infinite zigzag strip (Cetina et al., 2005) (Fig. 3). In such a strip, the amino group of each molecule acts as a dual donor in N-H···N hydrogen bonds, while the pyrimidine ring serves as a dual acceptor. Interestingly, two different R 2 2 (8) motifs are formed with dihedral angles of 32.9 (1) and 63.4 (1)° between two adjacent pyrimidine rings. Finally, these strips together with the dimers of B are packed into a complicated three dimensional framework.
Experimental 2-Amino-4,6-dichloropyrimidine (0.082 g, 0.5 mmol) and K 2 CO 3 (0.276 g, 2 mmol) were dissolved in DMF (2 ml) and H 2 O (2 ml), the mixture was heated at 343 K for 0.5 h and then cooled to room temperature. The resulting mixture was extracted with ethyl acetate. The organic layer was separated and washed with brine, then dried over anhydrous MgSO 4 .
Removal of the solvent under reduced pressure gave the title compound as a yellow solid (yield 85%). Single crystals suitable for X-ray diffraction analysis were obtained by liquid-liquid diffusion from hexane and CH 2 Cl 2 at 298 K.

Refinement
All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms attached to anisotropically refined atoms were placed in geometrically idealized positions and included as riding atoms with C-H = 0.93 Å and U iso (H) = 1.2 U eq (C) (aromatic); C-H = 0.96 Å and U iso (H) = 1.5 U eq (C) (methyl); N-H = 0.87-0.88 Å and supplementary materials

Figure 1
The molecular structure of the title compound, with displacement ellipsoids drawn at the 30% probability level. Dashed lines indicate hydrogen bonds.   An infinite zigzag strip formed by a combination of A, C and D through hydrogen bonds, showing different R 2 2 (8) motifs.
For the sake of clarity, H atoms not involved in the motifs have been omitted [symmetry codes: (ii) -x + 1, -y + 1, -z + 1; (iii) -x, -y, -z + 1]. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.27 e Å −3 Δρ min = −0.32 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.