Crystal structure of 2-[12-methyl-14-phenyl-10,13,14,16-tetraazatetracyclo[7.7.0.02,7.011,15]hexadeca-1(16),2,4,6,9,11(15),12-heptaen-8-ylidene]propandinitrile

In the title molecule, C22H12N6, the fused tetracyclic core shows a small lengthwise twist as indicated by the dihedral of 2.7 (2)° between the outer rings. In the crystal, molecules stack along the b-axis direction via offset π-stacking [centroid–centroid distances = 3.5282 (13) and 3.5597 (14) Å] with the stacks weakly associated through C—H⋯N hydrogen bonds. The phenyl ring is rotationally disordered over two orientations with an occupancy ratio of 0.516 (4):0.484 (4).


S1. Comment
Over recent years there has been an increasing interest in the chemistry of pyrazine scaffold compounds due to their biological significance. Pyrazine ring is found in numerous pharmaceutically active compounds such as analgesic (Kaliszan et al., 1985), antiallergic (Makino et al., 1990), antibacterial (Emary & Ibrahim 2006), anti-inflammatory (Silva et al., 2010), antiviral (Rusinov et al., 2005, diuretic (Johnston & Kau, 1993), anticancer (Myadaraboina et al., 2010, and anti-HIV (Metobo et al., 2006) medications. Other pyrazine derivatives are also used as fluorescent dyes or dispersed dyes for polyester fibers (Rangnekar & Dhamnaskar, 1990). As part of our investigations of pyrazine derivatives to compare their chemical and biological activities, we have undertaken the X-ray crystal structure analysis of the title compound.
In the title compound, Fig. 1, the fused 4-ring core of the title molecule is nearly planar with only a slight lengthwise twist as indicated by the dihedral angle between the N1/N2/C7/C8/C9 and C12-C17 rings of 2.7 (2)°.
In the crystal, molecules pack in columns along [010] which involve offset π-stacking in which atom N2 is 3.36 (4) Å from the centroid of the N3/C11/C19/N4/C8/C7 ring one unit cell translation in b above it while C17 is 3.41 (4) Å from the centroid of the N3/C11/C19/N4/C8/C7 ring one unit cell translation in b below it (Fig. 2). Adjacent stacks are weakly associated via C-H···N hydrogen bonds ( Fig. 3 and Table 1) and are inclined at ca 43.5° in opposite directions from (010).

S2. Experimental
The title compound was prepared according to the reported procedure (El-Emary & El-Kashef, 2013). Orange crystals suitable for X-ray diffraction were obtained by recrystallization of the reaction product from dimethylformamide (m.p.

S3. Refinement
C-bound H atoms were placed in calculated positions and treated as riding atoms, with C-H = 0.95-0.98 Å and with U iso (H) = 1.5U eq (C) for methyl H atoms and = 1.2U eq (C) for other H atoms. The phenyl ring attached to N1 is rotationally disordered over two sites with an occupancy ratio of 0.516 (4):0.484 (4). The components of the disorder were refined as rigid hexagons.  The molecular structure of the title molecule, showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
Portions of two neighboring stacks showing the offset π-stacking and C-H···N interactions (Table 1) Table 1 for details).

2-{12-Methyl
Special details Experimental. The diffraction data were collected in three sets of 400 frames (0.5° width in ω) at φ = 0, 120 and 240°. A scan time of 90 sec/frame was used. 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. H-atoms attached to carbon were placed in calculated positions (C-H = 0.95 -0.98 Å). All were included as riding contributions with isotropic displacement parameters 1.2 -1.5 times those of the attached atoms. The phenyl ring attached to N1 is rotationally disordered over two sites in approximately equal amounts. The components of the disorder were refined as rigid hexagons.