Crystal structure of N-[(8E)-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]hydroxylamine 1,4-dioxane hemisolvate

In the title solvate, C19H13N5O·0.5C4H8O2, the main molecule is almost planar (r.m.s. deviation for the non-H atoms = 0.066 Å). The hydroxylamine group is disordered over two orientations in a 0.761 (4):0.239 (4) ratio. The complete dioxane solvent molecule is generated by a crystallographic inversion centre. In the crystal, both disorder components of the hydroxylamine group form O—H⋯N hydrogen bonds to the same N-atom acceptor, thereby generating [010] chains. The chains encompass [010] channels occupied by the solvent molecules. Aromatic π–π stacking is also observed [shortest centroid–centroid separation = 3.3394 (19) Å].


S1. Comment
Heterocyclic compounds containing pyrolo-or pyrazino-pyrazole core structures represent a relatively little-explored group with interesting pharmaceutical properties. They have been described as vasodilators (Nyeki et al., 2002), fibrinogen receptor antagonists with antiplatelet activity (Askew et al., 1997), vitronectin-receptor antagonists (Wehner et al., 1998 and herbicidal agents (Zimmerman, 1995). In a continuation of our efforts towards the synthesis of bio-active pyrazinopyrazines, we report here the synthesis and crystal structure of the title compound.
The fused, four-ring core of the title molecule ( Fig. 1) is nearly planar with only a 3.0 (2)° dihedral angle between the C14-C19 and C7/C9/C10/N1/N2 rings while the dihedral angle between the latter ring and the pendant phenyl ring is 5.2 (2)°. The values of the geometric parameters of the title molecule are normal and are comparable to those reported for a similar structure (Mague et al., 2014).
The molecules form stacks via π-π interactions between the C7/C9/C10/N1/N2 ring in one molecule with the C11-C15 ring in the molecule at x, -1 + y, z (centroid-centroid distance = 3.34 Å, Fig. 2). Two screw-axis-related stacks are associated via O1-H1···N4 hydrogen bonds forming columns running parallel to the b axis (Table 1 and Fig. 3). In each column, the mean planes of the molecules in one stack are inclined to those of the second by 73.3°. The solvent dioxane molecules lie adjacent to the hydroxylamine groups and fill channels between the columns.

S3. Refinement
H-atoms attached to carbon atoms were placed in calculated positions (C-H = 0.95 -0.98 Å) while that attached to the oxygen atom was placed in a location derived from a difference map and its parameters adjusted to give O-H = 0.84 Å.
All were included as riding contributions with isotropic displacement parameters 1.2 -1.5 times those of the attached atoms. The {N-OH} unit is disordered over two resolved sites in a 3:1 ratio and was refined subject to restraints that the geometries of the two components be comparable. The solvent molecule of dioxane located on a center of symmetry supporting information sup-2 Acta Cryst. (2015). E71, o75-o76 appeared to be slightly disordered on the basis of the size and shape of its displacement ellipsoids but attempts to refine it with a split atom model were unsuccessful.

Figure 1
The title molecule showing 50% probability ellipsoids. Only the major componenet of the disordered hydroxylamine substituent is shown.

Figure 2
Packing showing the π-π interactions as green dotted lines.  is disordered over two resolved sites in a 3:1 ratio and was refined subject to restraints that the geometries of the two components be comparable. The molecule of lattice dioxane located on a center of symmetry appeared to be slightly disordered on the basis of the size and shape of its displacement ellipsoids but attempts to refine it with a split atom model were unsuccessful.

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