Supramolecular interactions in 2,6-diamino-4-chloropyrimidin-1-ium 5-chlorosalicylate and bis(2,6-diamino-4-chloropyrimidin-1-ium) naphthalene-1,5-disulfonate

Two new salts – 2,6-diamino-4-chloropyrimidin-1-ium 5-chlorosalicylate and bis(2,6-diamino-4-chloropyrimidin-1-ium) naphthalene-1,5-disulfonate – have been synthesized and characterized by single-crystal X-ray diffraction. The supramolecular interactions such as hydrogen bonding, halogen bonding, C—Cl⋯π and π–π interactions are investigated for these crystal structures.


Chemical context
The study of supramolecular interactions in the crystals of pyrimidinium salts continues to be an active field since the pyrimidine fragment is a component of nucleobases and many drug molecules. The pyrimidine group offers two protonation sites (the two ring nitrogens) and the site of protonation depends on the nature of the substituents. Tautomerism of the pyrimidinium cation has also been reported recently (Rajam et al., 2017). The pyrimidinium-carboxylate interaction is also of fundamental importance in biology since it is involved in protein-nucleic acid interactions and drug-receptor recognition (Hunt et al., 1980;Baker & Santi, 1965). The molecules are often self-assembled by hydrogen bonding, halogen bonding, cationÁ Á Á, anionÁ Á Á andstacking interactions. Among these interactions, halogen bonding is of particular current interest (Cavallo et al., 2016). Various substituted pyrimidines and their interactions with different acids have been studied systematically in our laboratory. The variation in supramolecular architectures resulting from the different substituents in the base and the acid is being investigated, and ISSN 2056-9890 crystal structures of 2,6-diamino-4-chloropyrimidinium salts with carboxylate/sulfonate have been reported recently from our laboratory (Mohana et al., 2017). The same pyrimidine derivative has been used to prepare the title compounds in order to further study the supramolecular architectures and the role of the halogen bond.

Structural commentary
The salt of compound (I) crystallizes with one CDAPY (2,6diamino-4-chloropyrimidinium) cation and one CSA (5chlorosalicylate) anion in the asymmetric unit (Fig. 1). The pyrimidinium cation is protonated at the N1 position (see Fig. 1 for atom numbering) and this is confirmed by an increase in the internal bond angle. The C2-N3-C4 angle at the unprotonated N3 atom is 115.1 (2) , while for the protonated N1 atom, the C2-N1-C6 angle is 121.8 (2) . The ion-pair (CDAPY and CSA) is almost planar [dihedral angle = 4.22 (11) ]. The carboxylate group of CSA is twisted slightly with respect to the remainder of the anion [dihedral angle= 3.9 (3) ]. The salt of compound (II) crystallizes with one CDAPY (2,6-diamino-4-chloropyrimidinium) cation and half a molecule of NSA (naphthalene-1,5-disulfonate) anion in the asymmetric unit (Fig. 2), the other half of NSA being generated by an inversion centre. A crystallographic inversion centre coinciding with the inversion centre of the NSA ion has also been reported earlier (Liu, 2012;Xu, 2012;Liu & Chen, 2012). The pyrimidinium cation is again protonated at the N1 position (see Fig. 2 for atom numbering) and this is confirmed by an increase in the internal bond angle. The C2-N3-C4 angle at the unprotonated N3 atom is 115.40 (16) , while the angle at the protonated N1 atom (C2-N1-C6) is 121.84 (16) . All of the sulfonate oxygen atoms of the NSA anion are involved in hydrogen bonding. The S1-O1, S1-O2 and S1-O3 distances are similar [1.4550 (15), 1.4584 (15) and 1.4431 (16) Å respectively].

Figure 3
Supramolecular layered structure extended as a chain via ClÁ Á ÁCl interactions in (I).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Formation of a quadruple DDAA array in (II) via N-HÁ Á ÁO hydrogen bonds.

Figure 6
A view of thestacking interactions between the pyrimidinium cation and the anion.    Mercury (Macrae et al., 2008); software used to prepare material for publication: PLATON (Spek, 2009).

2,6-Diamino-4-chloropyrimidin-1-ium 2-chloro-6-hydroxybenzoate (I)
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.29 e Å −3 Δρ min = −0.40 e Å −3 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 where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.49 e Å −3 Δρ min = −0.59 e Å −3 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.