Crystal structures and Hirshfeld surface analyses of 2-[(4,6-diaminopyrimidin-2-yl)sulfanyl]-N-(pyridin-2-yl)acetamide and 2-[(4,6-diaminopyrimidin-2-yl)sulfanyl]-N-(pyrazin-2-yl)acetamide

The conformation of the title diaminopyrimidine sulfanly acetamides, (I) and (II), have similar conformations, with the pyrimidine ring being inclined to the pyridine ring in (I) by 71.10 (9) °, and by 62.93 (15) ° to the pyrazine ring in (II).

In the title compounds, C 11 H 12 N 6 OS (I) and C 10 H 11 N 7 OS (II), the diaminopyrimidine ring makes dihedral angles of 71.10 (9) with the pyridine ring in (I) and 62.93 (15) with the pyrazine ring in (II). The ethanamine group, -CH 2 -C( O)-NH-lies in the plane of the pyridine and pyrazine rings in compounds (I) and (II), respectively. In both compounds, there is an intramolecular N-HÁ Á ÁN hydrogen bond forming an S(7) ring motif and a short C-HÁ Á ÁO interaction forming an S(6) loop. In the crystals of both compounds, molecules are linked by pairs of N-HÁ Á ÁN hydrogen bonds, forming inversion dimers with R 2 2 (8) ring motifs. In (I), the dimers are linked by N-HÁ Á ÁO and N-HÁ Á ÁN hydrogen bonds, forming layers parallel to (111). The layers are linked by offset interactions [intercentroid distance = 3.777 (1) Å ], forming a threedimensional supramolecular structure. In (II), the dimers are linked by N-HÁ Á ÁO, N-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds, also forming a threedimensional supramolecular structure.

Figure 1
The molecular structure of the compound (I), showing the atom labelling and displacement ellipsoids drawn at the 50% probability level. The intramolecular N-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds (see Table 1) are shown as dashed lines.
In the crystal of (II), the dimers are linked by N1-H1AÁ Á ÁO ii , N2-H2AÁ Á ÁN7 iii and C9-H9Á Á ÁO1 iv hydrogen bonds (Table 2), forming a three-dimensional supramolecular structure (Fig. 4). In contrast, in the crystal of (II) there are no interactions present. In these eight compounds, the diaminopyrimidine and benzene rings are inclined to one another by dihedral angles varying from ca 42.25 to 78.33 . The dihedral angle between the diaminopyrimidine and the pyridine ring in (I) is 71.10 (9) and with the pyrazine ring in (II) is 62.93 (15) , well within these limits. As in the title compounds, there is also an intramolecular N-HÁ Á ÁN hydrogen bond present in all eight compounds, stabilizing the folded conformation of each molecule. In the crystals of all but two compounds ( A view along the a axis of the crystal packing of compound (II). The hydrogen bonds (see Table 2) are shown as dashed lines, and C-bound H atoms have been omitted for clarity.

Figure 3
A view normal to the (111) plane of the crystal packing of compound (I). The hydrogen bonds (see Table 1) are shown as dashed lines and C-bound H atoms have been omitted for clarity. hydrogen bonds, involving the 4,6-diaminopyrimidine moieties, forming inversion dimers with R 2 2 (8) ring motifs, as for compounds (I) and (II).

Hirshfeld surface analysis
In Figs. 5 and 6, the ball and stick model of the front and back views of the compounds (I) and (II), respectively, and the intermolecular contacts are shown by conventional mapping of d norm on the molecular Hirshfeld surfaces, where the redspot areas denote intermolecular contacts involved in the hydrogen-bonding interactions (McKinnon et al., 2007). The electrostatic potential is mapped on the Hirshfeld surface using the STO-3G basis set at the Hartree-Fock theory over the range of AE0.025 a.u. The positive electrostatic potential (blue region) over the surface shows hydrogen-donor potential, and the hydrogen-bond acceptors are shown by negative electrostatic potential (red regions); see Figs. 5 and 6. The twodimensional fingerprint plots [ Fig. 7 for (I) and Fig. 8 for (II)] are deconvoluted to highlight atom-pair close contacts by which different atomic types, overlapping the full fingerprint can be separated based on different interaction types. For compound (I), intermolecular HÁ Á ÁH contacts of 39.1% are the most significant, followed by 17.7% for NÁ Á ÁH/HÁ Á ÁN, 12% for CÁ Á ÁH/HÁ Á ÁC, 9.3% for OÁ Á ÁH/HÁ Á ÁO, 8.4% for SÁ Á ÁH/ HÁ Á ÁS and 4.1% for CÁ Á ÁC contacts. In contrast, for compound (II) the HÁ Á ÁH contacts at 28.2% are significantly lower than in (I), while the NÁ Á ÁH/HÁ Á ÁN contacts at 27% are significantly higher than in (I). The CÁ Á ÁC contacts at only 1.9% are much lower than in (I) where offsetinteractions are observed in the crystal structure.

Synthesis and crystallization
Compound (I): To a solution of 4, 6-diamino-pyrimidine-2thiol (0.5 g; 3.52 mmol) in 25 ml of ethanol, (0.2g; 3.52 mmol) potassium hydroxide was added and refluxed for about 30 min. Then an equimolar quantity of 2-chloro-N-(pyridin-2yl)acetamide (3.52 mmol) was added to the above reaction mixture and it was refluxed for 5 h. Evaporation of the organic layer under vacuum provided compound (I). After purification, the compound was crystallized from ethanol solution by slow evaporation of the solvent giving yellow block-like crystals.

Figure 7
The 2D fingerprint plot for all the intermolecular contacts for compound (I).

Figure 8
The 2D fingerprint plot for all the intermolecular contacts for compound (II).

Figure 5
Ball and stick, Hirshfeld surface and electrostatic potential surface diagrams for compound (I).
30 min. Then an equimolar quantity of 2-chloro-N-(pyrazin-2yl)acetamide (3.52 mmol) was added to the above reaction mixture and it was refluxed for 5.5 h. Evaporation of the organic layer under vacuum resulted in compound (II). After purification, the compound was crystallized from ethanol solution by slow evaporation of the solvent giving yellow block-like crystals.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. For both compounds, the NH 2 and NH H atoms were located in difference-Fourier maps and freely refined, and the C-bound H atoms were placed in calculated positions and refined in the riding model: C-H = 0.93-0.97 Å with U iso (H) = 1.2U eq (C).  Computer programs: APEX2 and SAINT (Bruker, 2008), SHELXS97 (Sheldrick, 2008), SHELXL2016 (Sheldrick, 2015), PLATON (Spek, 2009)

Computing details
For both structures, data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2016 (Sheldrick, 2015); molecular graphics: PLATON (Spek, 2009) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL2016 (Sheldrick, 2015) and PLATON (Spek, 2009). Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq S1 0.77107 (