5,8-Bis[bis(pyridin-2-yl)amino]-1,3,4,6,7,9,9b-heptaazaphenalen-2(1H)-one dimethyl sulfoxide monosolvate dihydrate

In the asymmetric unit of the title compound, C26H17N13O·C2H6OS·2H2O, there is one independent heptazine-based main molecule, one dimethyl sulfoxide molecule and two water molecules as solvents. The tri-s-triazine unit is substituted with two dipyridyl amine moieties and a carbonylic O atom. As indicated by the bond lengths in this acid unit of the heptazine derivative [C=O = 1.213 (2) Å, while the adjacent C—N(H) bond = 1.405 (2) Å] it is best described by the keto form. The cyameluric nucleus is close to planar (r.m.s. deviation = 0.061 Å) and the pyridine rings are inclined to its mean plane by dihedral angles varying from 47.47 (5) to 70.22 (5)°. The host and guest molecules are connected via N—H⋯O, O—H⋯O and O—H⋯N hydrogen bonds, forming a four-membered inversion dimer-like arrangement enclosing an R 4 4(24) ring motif. These arrangements stack along [1-10] with a weak π–π interaction [inter-centroid distance = 3.8721 (12) Å] involving adjacent pyridine rings. There are also C—H⋯N and C—H⋯O hydrogen bonds and C—H⋯π interactions present within the host molecule and linking inversion-related molecules, forming a three-dimensional structure.

In the asymmetric unit of the title compound, C 26 H 17 N 13 OÁ-C 2 H 6 OSÁ2H 2 O, there is one independent heptazine-based main molecule, one dimethyl sulfoxide molecule and two water molecules as solvents. The tri-s-triazine unit is substituted with two dipyridyl amine moieties and a carbonylic O atom. As indicated by the bond lengths in this acid unit of the heptazine derivative [C O = 1.213 (2) Å , while the adjacent C-N(H) bond = 1.405 (2) Å ] it is best described by the keto form. The cyameluric nucleus is close to planar (r.m.s. deviation = 0.061 Å ) and the pyridine rings are inclined to its mean plane by dihedral angles varying from 47.47 (5) to 70.22 (5) . The host and guest molecules are connected via N-HÁ Á ÁO, O-HÁ Á ÁO and O-HÁ Á ÁN hydrogen bonds, forming a four-membered inversion dimer-like arrangement enclosing an R 4 4 (24) ring motif. These arrangements stack along [110] with a weakinteraction [inter-centroid distance = 3.8721 (12) Å ] involving adjacent pyridine rings. There are also C-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds and C-HÁ Á Á interactions present within the host molecule and linking inversion-related molecules, forming a three-dimensional structure.

Experimental
Cg1 and Cg2 are the centroids of the N12/C17-C21 and N13/C22-C26 rings, respectively. Cyameluric acid is described to crystallize with water (Sattler & Schnick, 2006), dimethylsulfoxide (Wagler et al., 2006) and free of solvent (Seyfarth et al., 2008). All structures reveal the keto form of the cyameluric nucleus independent of the co-crystallizing solvent. Molecular derivatives are rarely described especially unsymmetrically substituted ones.
Herein, we describe the crystal structure of an unsymmetrically substituted cyameluric acid derivative.
The molecular structure of the host and guest molecules of the title compound are illustrated in Fig. 1. The bond lengths (Allen et al., 1987) and angles are in the range of expected values. As indicated by the C-N bond lengths of the heptazine core the keto form is preferred rather than the hydroxyl form. The C1-O1 bond length [1.213 (2) Å] is a typical C═O bond while the adjacent C1-N1 bond length [1.405 (2) Å] represents a typical C-N single bond. Besides, the bond length of C1-N6 [1.371 (2) Å] is close to a single C-N bond but still indicates the conjugation as expected for the C 6 N 7 core. Additionally, the C-N bond lengths of the inner heptazine core (N7-C2/C4/C6) are significantly shorter on the protonated site of the molecule [1.375 (2) Å in contrast to 1.401 (2) and 1.410 (2) Å]. Furthermore, the N1 hydrogen atom was clearly visible in a difference electron-density map.
Neither the unsymmetrical substitution of the C 6 N 7 core nor the keto form and the adjacent C-N single bond character influence the planarity of the host molecule. The fit of the 13-membered ring system to a plane leads to a r.m.s. deviation of 0.061 Å indicating nearly perfect planarity. The pyridyl moieties reveal a twisting relating to the heptazine ring The crystal packing does not represent a layered structure as it is known for other heptazine derivatives (Schwarzer et al., 2013). This is indicated by the distances between adjacent C 6 N 7 -cores and the great offset to one another. A weak π···π interaction occurs between adjacent pyridyl units. The centroid Cg5 of the ring N10/C12-C16 reveals a distance of 3.8721 (12) Å to the centroid Cg7 of the ring N13/C22-26 (symmetry code: -x, -y, -z+2). To sum up, the title cyameluric compound occurs in its keto form as it is known from other derivatives. In the crystal the interactions of the host-guest compound include O-H···O/N, N-H···O, C-H···O/N/π/ and π···π stacking.

Experimental
α,α′-Dipyridylamine (0.12 g, 0.7 mmol) in 20 ml THF was added to cyameluric chloride (0.1 g, 0.36 mmol) dessolved in 15 ml THF. The mixture was refluxed for 8 h and stirred overnight at room temperature to give a yellow solution and a pale white precipitate. The solid (α,α′-dipyridylamine hydrochloride) was separated via suction filtration. Adding aqueous THF leads to a crystalline solid which was seperated via filtration and dried under air. Colourless prismatic crystals suitable for X-ray diffraction analysis were taken from that batch. Spectroscopic data for the title compound are available in the archived CIF.

Refinement
The NH and OH H atoms were located in a difference Fourier map and freely refined. The C-bound H atoms were positioned geometrically and allowed to ride on their parent atoms: C-H = 0.95 and 0.98 Å for aryl and aliphatic H atom, respectively, with U iso (H) =1.2U eq (C).

Figure 1
A view of the molecular structure of the title compound, with atom labelling. The displacement ellipsoids are drawn at the 50% probability level. The hydrogen bonds are shown as dashed lines (see Table 1 for details).

Figure 2
A partial view along the c axis of the crystal packing of the title compound. Hydrogen bonds are shown as dashed lines (see Table 1 for details; H atoms not involved in hydrogen bonding have been omitted for clarity). Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles 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.