5,7-Dimethyl-2,3-dihydro-1H-1,4-diazepin-4-ium picrate

In the cation of the title compound, C7H13N2 +·C6H2N3O7 −, the seven-membered 1,4-diazepine ring forms a twist chair conformation. The two o-nitro groups in the anion are twisted by 35.0 (7) and 36.0 (9)° from the benzene ring. In the crystal, N—H⋯O hydrogen bonds between the cation and anion along with weak C—H⋯O hydrogen bonds produce chains along the b axis. C—H⋯O hydrogen bonds connecting the chains are also present.

In the cation of the title compound, C 7 H 13 N 2 + ÁC 6 H 2 N 3 O 7 À , the seven-membered 1,4-diazepine ring forms a twist chair conformation. The two o-nitro groups in the anion are twisted by 35.0 (7) and 36.0 (9) from the benzene ring. In the crystal, N-HÁ Á ÁO hydrogen bonds between the cation and anion along with weak C-HÁ Á ÁO hydrogen bonds produce chains along the b axis. C-HÁ Á ÁO hydrogen bonds connecting the chains are also present.
Today many diazepine derivatives are widely used as daytime sedatives, tranquilizers, sleep inducers, anesthetics, anticonvulsants and muscle relaxants (Moroz, 2004). The use of this class of compounds with therapeutic purposes is not only confined to anxiety and stress conditions, given that minor changes in their structures can produce a host of different biological activities, and novel applications are continuously emerging (Andrews et al., 2001;Carp, 1999). Five-atom heterocyclic fused benzodiazepine ring systems occupy a prominent place among drugs for treatment of CNS disorders (Walser et al., 1978). The introduction of alprazolam, triazolam and midazolam in chemotherapy has enhanced the interest in the preparation of novel five-atom heterocyclic fused benzodiazepine ring systems. Numerous analogs of alprazolam, triazolam and midazolam have been described, and they have shown different pharmacological profiles related to those of their parent compounds (Carlos et al., 2004). In continuation of our work on picrates of biologically important molecules, we have prepared a new picrate of 5,7-dimethyl-2,3-dihydro-1H-1,4-diazepine, C 7 H 13 N 2 + .C 6 H 2 N 3 O 7 -, and its crystal structure is reported.
The title compound, C 13 H 15 N 5 O 7 , crystallizes as a salt with one C 7 H 13 N 2 + .C 6 H 2 N 3 O 7 cation-anion pair in the asymmetric unit (Fig. 1). The dihedral angle between the mean planes of the benzene and 1,4-diazepine rings is 4.4 (6)°. In the cation, the seven membered 1,4-diazepine ring forms a twist chair conformation with Cs asymmetry parameters of -0.4004 and 0.3553°, for the sp 3 hybridized C1B and C2B atoms, respectively. The two o-nitro groups in the anion are twisted by 35.0 (7) and 36.0 (9)° from the mean plane of the benzene ring. Bond distances and angles in both the cation and anion are in normal ranges. Cation-anion N-H···O hydrogen bonds [N1B-H1BC···O1A & N2B-H2BC···O42A] along with weak C-H···O intermolecular interactions (Table 1) produce a network of infinite N1B-H1BC···O1A/N2B-H2BC···O42A chains along the b axis which helps to establish crystal packing (Fig. 2).
A density functional theory (DFT) geometry optimization molecular orbital calculation (Schmidt & Polik, 2007) was performed on the independent cation-anion pair (C 7 H 13 N 2 + .C 6 H 2 N 3 O 7 -) within the asymmetric unit with the B3LYP/6-311+G(d,p) basis set (Hehre et al., 1986). Starting geometries were taken from X-ray refinement data. The dihedral angle between the mean planes of the benzene and 1,4-diazepine rings increases to 30.9 (5)°. In the anion, the mean planes of the two o-nitro groups each become twisted by 35.5 (3)°, from the mean plane of the benzene ring. The mean plane of the p-nitro group remains planar to the benzene ring. These observations suggest that the N-H···O hydrogen bonds and weak C-H···O intermolecular interactions play a significant role in crystal stability.

Refinement
All of the H atoms were placed in their calculated positions and then refined using the riding model, with C-H = 0.95-0.99 Å and N-H = 0.88 Å, and with U iso (H) = 1.18-1.51U eq (C, N). Fig. 1

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.
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 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.