Crystal structure and spectroscopic properties of (E)-1,3-dimethyl-2-[3-(4-nitrophenyl)triaz-2-enylidene]-2,3-dihydro-1H-imidazole

The triazene derivative, (E)-1,3-dimethyl-2-[(4-nitrophenyl)triaz-2-enylidene]-2,3-dihydro-1H-imidazole was synthesized by coupling 1,3-dimethylimidazolium iodide with 1-azido-4-nitro benzene. The title compound has monoclinic (C2/c) symmetry and an E conformation about the –N= N– bond.

The title compound (E)-1,3-dimethyl-2-[3-(4-nitrophenyl)triaz-2-enylidene]-2,3dihydro-1H-imidazole, C 11 H 12 N 6 O 2 , has monoclinic (C2/c) symmetry at 100 K. This triazene derivative was synthesized by the coupling reaction of 1,3-dimethylimidazolium iodide with 1-azido-4-nitro benzene in the presence of sodium hydride (60% in mineral oil) and characterized by 1 H NMR, 13 C NMR, IR, mass spectrometry, and single-crystal X-ray diffraction. The molecule consists of six-membered and five-membered rings, which are connected by a triazene moiety (-N N-N-). In the solid-state, the molecule is found to be planar due to conjugation throughout the molecule. The extended structure shows two layers of molecules, which present weak intermolecular interactions that facilitate the stacked arrangement of the molecules forming the extended structure. Furthermore, there are several weak pseudo-cyclical interactions between the nitro oxygen atoms and symmetry-adjacent H atoms, which help to arrange the molecules.

Chemical context
Triazenes are versatile compounds in preparative chemistry because of their stable and highly modular nature (Patil & Bugarin, 2016). Triazene derivatives have been studied for their potential anticancer properties (Rouzer et al., 1996;Connors et al., 1976), used as a protecting group in natural product synthesis (Nicolaou et al., 1999) and combinatorial chemistry (Brase et al., 2000), incorporated into polymers (Jones et al., 1997) and oligomer synthesis (Moore, 1997), and used to prepare heterocycles (Wirschun et al., 1998). Their modular nature allows triazenes to be converted into a different functional group after treatment with the appropriate reagents. For example, aryl triazenes can be transformed to useful cross-coupling reagents (iodoarenes) via iodomethane-induced decomposition (Zollinger, 1994). Further, aryl triazenes have been studied for their unique structural and chemical properties (Cornali et al., 2016;Knyazeva et al., 2017). They have been used in medicinal, combinatorial chemistry, in natural synthesis and as organometallic ligands (Kimball et al., 2002). In chemical biology, masked diazonium ions (triazabutadienes) have found use on protein surfaces for identifying host proteins that interact ISSN 2056-9890 during early stages of viral entities (Jensen et al., 2016;Shadmehr et al., 2018). In addition, triazabutadienes have shown tunable reactivity under specific conditions. For example, unique transformations of triazabutadienes have been affected via water solubility, pH Guzman et al., 2016;He et al., 2017), and photoinduced isomerization (He et al., 2015). In synthesis, these triazenes have been used as starting materials for aldehydes, ketones, ethers, and sulfides, under mild reaction conditions (Barragan & Bugarin, 2017;Cornali et al., 2016). Furthermore, natural sunlight has been utilized to activate those triazenes to produce bisaryls and anilides (Noonikara-Poyil et al., 2019;Barragan et al., 2020).
There are no lattice-held water molecules or organic solvent molecules in the unit cell of the determined structure, a potential issue since the starting material 1,3-dimethylimidazolium iodide is hydroscopic. The bond lengths and angles in 1 are similar to those reported for analogous structures (Khramov & Bielawski, 2005;Jishkariani et al., 2013). The C-C bond lengths in the phenyl rings are in the normal range of 1.33-1.40 Å , which is characteristic of delocalized phenyl rings. The C-C-C bond angles are around 120 , with the variation being less than 2 , which is characteristic of sp 2hybridized carbons.

Supramolecular features
Figs. 2 and 3 show a perspective view of the crystal packing of the title compound. The packing diagram shows two layers of molecules, which are independently arranged in the unit cell without intra-and inter molecular hydrogen bonds. In each layer, the molecules are alternately parallel.

Database survey
The first X-ray structure of a -conjugated triazene was reported by Khramov & Bielawski (2005). The current WebCSD structural database includes the structures of only 18 -conjugated triazenes. However, there is only one structure, reported by our research group , that utilizes the small molecule (1,3-dimethylimidazolium iodide) as the carbene coupling partner, and one more that bears an electron-deficient aryl group in combination with the small Perspective view of the molecular packing of 1 (there are no hydrogen atoms involved in hydrogen-bonding interactions. Dotted lines represent weak non-covalent C-HÁ Á ÁN and C-HÁ Á ÁO interactions, which direct the packing.

Figure 3
Extended network of the structure of compound 1 viewed from (001). There are two layers of molecules, which are arranged independently in the unit cell without intra-and/or intermolecular hydrogen bonds. Dotted lines represent weak non-covalent C-HÁ Á ÁN and C-HÁ Á ÁO interactions, which direct the packing. carbene precursor . Those characteristics highlight the novelty and uniqueness of the compound reported herein.

(E)-1,3-Dimethyl-2-[3-(4-nitrophenyl)triaz-2-enylidene]-2,3-dihydro-1H-imidazole
Crystal data 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.