(E)-7-[(4-Nitrophenyl)diazenyl]-3a-(p-tolyl)-2,3,3a,4-tetrahydro-1H-benzo[d]pyrrolo[1,2-a]imidazol-1-one 0.58-dimethyl sulfoxide 0.42-acetonitrile solvate: crystal structure, Hirshfeld analysis and DFT estimation of the energy of intermolecular interactions

In the crystal structure of the title compound, C23H19N5O3·0.58C2H6OS·0.42C2H3N, prepared by the azo coupling of the 4-nitrophenyldiazonium salt with 3a-(p-tolyl)-2,3,3a,4-tetrahydro-1H-benzo[d]pyrrolo[1,2-a]imidazol-1-one, the azo molecules are linked by N—H⋯O hydrogen bonds into chains along the a-axis direction, and by the π–π interaction into [101] chains.


Chemical context
Compounds prepared by azo coupling of aryldiazonium salts with 3a-aryl-2,3,3a,4-tetrahydro-1H-benzo[d]pyrrolo[1,2-a]imidazol-1-one (1) are crystalline substances with deep color varying from yellow to red, depending on the structure of the initial diazonium cation. Since several nucleophilic centers in 1 can be attacked by the electrophilic diazonium cation, it was of interest to study the effect of heteroatoms, as well as other molecular fragments, on the molecular reactivity. The presence of the secondary amino group allows the formation of triazene derivatives. However, the most likely site of electrophilic attack is a fused aromatic ring activated by N heteroatoms. The azo dye molecules constructed in this way can exist in two forms, E and Z, depending on the presence or absence of certain stabilizing factors: bulky substituents, intramolecular hydrogen bonds, non-covalent interactions, etc. One of the representatives of the synthesized series is 7-[(4nitrophenyl)diazenyl]-3a-(p-tolyl)-2,3,3a,4-tetrahydro-1Hbenzo [d]pyrrolo [1,2-a]imidazol-1-one (2), which was prepared from 4-nitrophenyldiazonium chloride and 1. For the final determination of the structure of the azo product, an X-ray diffraction study of a crystal grown from DMSO-acetonitrile solution as a mixed DMSO/acetonitrile solvate of 2 was performed. ISSN 2056-9890

Structural commentary
The asymmetric unit of the title compound is shown in Fig. 1. The molecules of 2 have the E-configuration that was expected because of the para position of the nitro group in the aryldiazenyl fragment. Part of the molecule of 2, including the 4-nitrophenyl and benzimidazole fragments linked by the azo group, is close to planar, with the dihedral angle formed by two aromatic rings being 2.73 (7) . The largest deviation from the mean plane of the benzimidazole ring system is 0.1300 (9) Å for C4. The 1H-imidazole ring adopts an envelope conformation with C4 atom as the flap, thus introducing some non-planarity into the conjugated part of the molecule. The pyrrolidone ring is twisted with respect to the C2-C3 bond, thus the environment of the N2 amide atom becomes non-planar and this atom deviates by 0.267 (1) Å from the plane formed by the three neighboring C atoms. As as result, the C1-N2 distance [1.3737 (17) Å ] is larger than average for -lactams [1.347 (14) Å ; Allen et al., 1987]. The relatively long N2-C10 distance [1.4091 (17) Å ] indicates weak -conjugation and gives an insight into why substitution takes place at the 8 position.

Supramolecular features
In the crystal, molecules of 2 are linked by N-HÁ Á ÁO hydrogen bonds into chains along the a-axis direction (Table 1, Fig. 2). These molecules are also linked byinteractions between the aromatic rings of the benzimidazole fragments and 4-nitrophenyl substituents as well as between p-tolyl substituents (

Figure 1
The asymmetric unit of the title compound with overlapping solvent molecules of DMSO and acetonitrile. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
The packing diagram viewed along the b axis. N-HÁ Á ÁO hydrogen bonds are represented by dotted lines.
The Hirshfeld surface diagram, d norm , with transparency ( Fig. 4), indicates (in red) locations of the strongest intermolecular contacts with participation of atoms H6A, H2A and H2B (Fig. 4). The HÁ Á ÁH, HÁ Á ÁC, HÁ Á ÁS and HÁ Á ÁO contributions to the crystal packing are shown as two-dimensional fingerprint plots with blue dots (Fig. 5). The d e (y axis) and d i (x axis) values represent the closest external and internal distances (Å ), respectively, from the given points on the Hirshfeld surface (Wolff et al., 2012). The intermolecular hydrogen bonds are indicated by the HÁ Á ÁO contacts (21.2%) on the dotted diagram ( Fig. 5c). Two sharp spikes with d e + d i = $2.0 Å visualize the experimentally obtained value of 2.04 (2) Å for the HÁ Á ÁO distance corresponding to a hydrogen bond between azo molecules. The CÁ Á ÁC contacts (3.8%) reflectinteractions between the mentioned above aromatic rings (Figs. 4,5f). In addition, there are some HÁ Á Á contacts (HÁ Á ÁC), which are mostly located at hydrogen atoms of the CH 3 group of the p-tolyl substituent of one molecule and the -system of the same substituent of the neighboring molecule ( Fig. 5e).

Quantum chemical DFT calculations
To compare the energies of the two types of intermolecular interactions found in the title crystal, we performed quantum chemical modeling of this system at the level of Density Functional Theory (DFT). All DFT calculations were made using GAUSSIAN09 package (Frisch et al., 2010) and high-performance computing cluster of National Research Saratov State University. Crystallographic coordinates were used as a starting point, and full geometry optimization of monomer and dimers was performed using an mPW1B95 functional with a 6-31g (d)  Hirshfeld surface diagram for the asymmetric unit of the title compound.

Figure 3
Diagram showinginteractions between molecules of 2 (a) between the aromatic rings of the benzimidazole group and the 4-nitrophenyl substituent, (b) between the aromatic rings of two p-tolyl substituents.

Figure 5
Diagrams showing (a) the full two-dimensional fingerprint plot, and those functional theory (HMDFT) method based on the modified Perdew and Wang exchange functional (mPW) and Becke's 1995 correlation functional (B95) gives good results for the systems with non-covalent interactions, such as hydrogen bonding and weak van der Waals interactions (Zhao & Truhlar, 2004). The energy of theinteraction was estimated using the following simple equation: A comparison of some parameters of non-covalent interactions for the optimized geometry of 2 and for the crystallographic data is presented in Table 2. The chosen level of theory reproduces the geometrical parameters of the intermolecular interactions quite well. Thus, the energies ofinteractions of both types, between the aromatic rings of the benzimidazole fragment and of the 4-nitrophenyl substituent and between the two aromatic p-tolyl substituents at the 3a positions, can be estimated to be equal to À16.5 and À3.0 kcal mol-1, respectively.

Synthesis and crystallization
The synthesis of 2 was carried out according to the procedure, proposed by Gavkus et al., 2012, starting from 4-nitroaniline and 1. The product was isolated with 87% yield and recrystallized from acetonitrile as ruby-red prisms. A suitable single crystal was obtained by slow cooling of the saturated solution of 2 in DMSO-acetonitrile mixture at 1:1 ratio.

Refinement
Crystal data, details of data collection and structure refinement details are summarized in    program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: publCIF (Westrip, 2010). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.46 e Å −3 Δρ min = −0.50 e Å −3 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 > 2sigma(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.

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