N-(5-Nitropyridin-2-yl)-5H-dibenzo[d,f][1,3]diazepine-6-carboxamide

The title compound, C19H13N5O3, can be obtained from the corresponding α-amido-α-aminonitrone in a reaction with biphenyl-2,2′-diamine. The amido–amidine core has distinctive geometrical parameters including: an outstandingly long Csp 2—Csp 2 single bond of 1.5276 (13) Å and an amidine N—C—N angle of 130.55 (9)°. Intramolecular N—H⋯O, N—H⋯N and C—H⋯O hydrogen bonds occur. In the crystal, molecules form layers parallel to (001) via weak intermolecular C—H⋯N interactions. The layers are linked via N—H⋯O hydrogen bonds and π–π interactions along [001] [benzene–pyridine centroid–centroid distance = 3.672 (2) Å].


Comment
The current report is a continuation of an earlier joint theoretical and X-ray study upon the versatile reactivity of α-amidoα-aminonitrones, having several reactivity centers of different types and yielding various products in reactions with electrophilic and nucleophilic reagents (Trzewik et al., 2008). Among them 5H-dibenzo[d,f][1,3]diazepines, the synthesis and structures of which were described elsewhere (Trzewik et al., 2008(Trzewik et al., , 2010, are unique from the viewpoint of their geometrical features. The overall shape of the title molecule is shown in Figure 1. The two benzene rings within the diazepine moiety are twisted by torsion angle C25-C26-C36-C35 = -28.63 (13) o . The r.m.s. deviation for the best plane through atoms C21-C26 is significantly greater than that for C31-C36 (0.0166 and 0.0040 Å, respectively) due to steric hindrance between H25 and H35 (H25···H35 distance 2.12 Å).
The rest of the molecule is almost perfectly planar (r.m.s. deviation of fitted atoms equals 0.0181 Å). The fragment of the molecule, relevant from both crystallographic and chemical perspectives, is the amido-amidine core Within the core distinctive geometrical features of the molecule can be seen: a long C3(sp 2 )-C4(sp 2 ) bond of 1.528 (1) Å and N2-C3-N3 angle of 130.55 (9)°. We expect that the planarity of the core moiety possibly results from intramolecular interactions: N5-H5···N3, N2-H2···O4 and C55-H55···O4 (Table   1). In order to verify the existence of such interactions the analysis of topological properties of electron density distribution is in progress and will be published elsewhere.
The N-H···O hydrogen bond together with its centrosymmetric counterpart form a ring motif with descriptor R 2 2 (10) according to graph-set theory (Bernstein et al., 1995). The ring motif is marked in Figure 4.
The title compound was synthesized using the procedure already described in literature (Trzewik et al., 2008). Single crystals suitable for X-ray diffraction were grown by slow evaporation from the mixture of methanol and acetonitrile (1:2) solution at ambient conditions.

Refinement
All hydrogen atoms of N-H groups were found in difference Fourier maps and refined in a riding model assuming N-H = 0.88 (2) Å and U iso = 1.2U eq of the parent atom. Aromatic hydrogen atoms were found in difference Fourier maps and refined from geometrical positions assuming C-H = 0.95 Å and using riding model with U iso = 1.2U eq .      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 > 2σ(F 2 ) is used only for calculating Rfactors(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.