Crystal structure of 1,2-bis[(1H-imidazol-2-yl)methylidene]hydrazine and its one-dimensional hydrogen-bonding network

In the title compound, two imidazolyl groups are separated by a zigzag –CH=N—N=CH– linkage. Each molecule forms four N—H⋯N hydrogen bonds with two neighbouring molecules to constitute a one-dimensional ladder-like structure along the a axis.


Chemical context
Supramolecular chemistry is a fascinating topic, and molecular assemblies via intermolecular non-covalent binding interactions (i.e. hydrogen bonding, ionic andstacking interactions) have attracted much attentions in the field of crystal engineering over the last decade. In particular, hydrogen bonding, which is a powerful organizing force in designing a variety of supramolecular and solid-state architectures (Subramanian & Zaworotko, 1994), is not only used extensively to generate numerous network structures consisting of discrete organic and organometallic compounds (Desiraju, 2000), but is also responsible for interesting physical properties of these supramolecular arrangements, such as electrical, optical, magnetic, etc. (Bacchi & Pelagatti, 2016;Lindoy & Atkinson, 2000;Lé tard et al., 1998).
Imidazoles, containing two nitrogen atoms, possess both hydrogen-bond donating and accepting sites and are superior building blocks for supramolecular architectures. Many imidazole-containing polydentate ligands derived from hydrazine find a wide range of applications in coordination chemistry owing to their chelating ability (Zhou et al., 2012). In this paper we report the synthesis of 1,2-bis[(1H-imidazol-2-yl)methylene]hydrazine (I), designed to consist of nitrogen donors and acceptors, and the supramolecular architecture it ISSN 2056-9890 gives rise to via hydrogen bonds. The functionality of molecule (I) as a bridge between metal centers for the formation of multi-dimensional structures will be discussed in subsequent publications.

Structural commentary
The molecular structure of the title compound consists of two imidazolyl groups linked by a zigzag -CH N-N CHlinkage ( Fig. 1) and with C5Á Á ÁC5 i = 5.937 (3) Å [the distance between the centroids of the imidazolyl groups is 8.103 (3) Å ]. The molecule possesses an inversion center located in the midpoint of the N-N single bond and the complete molecule is generated by symmetry. The molecule appears in a Z(EE)Z configuration and its geometry is similar to that of 1,2-bis[(1Himidazol-5-yl)methylene]hydrazine (Pinto et al., 2013) and 1,2bis[(thiophene-3-yl)methylene]hydrazine (Kim & Lee, 2008).

Supramolecular features
In the crystal structure of (I), each molecule is involved in four N-HÁ Á ÁN hydrogen bonds (i.e.: two donor and two acceptor interactions) and interacts with two neighboring molecules, resulting in a one-dimensional ladder-like structure along the a axis (Fig. 2). Numerical details of the hydrogen-bonding geometry are tabulated in Table 1.

Figure 1
The molecular structure of (I), showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 50% probability level.
[Symmetry code: (i) Àx, Ày + 1, Àz + 2.] to the (101) plane, as a result of both hydrogen bonding and stacking interactions with adjacent molecules. In the present case of (I), instead, there are no significantstacking interactions.

Synthesis and crystallization
A methanol solution (10 mL) of imidazole-2-carboxaldehyde (2.48 g, 25.8 mmol) was added to a methanol solution (10 mL) of hydrazine monohydrate (0.64 ml, 12.9 mmol). The mixture was stirred for 3 h and the precipitate was collected by filtration. Single crystals suitable for X-ray diffraction studies were obtained by diffusion of diethyl ether into a DMSO solution of the title compound (I). Yield: 2.21 g (91%).

Refinement
Crystal data, data collection and structure refinement details are summarized in