(E)-1-(4-Nitrophenyl)-2-(4-{[(E)-2-(4-nitrophenyl)hydrazinylidene]methyl}benzylidene)hydrazine dihydrate

The 30 non-H atoms in title dihydrazine compound, C20H16N6O4·2H2O, are close to coplanar, the r.m.s. deviation for these atoms being 0.096 Å. The conformation about each of the C=N bonds is E, and the molecule has non-crystallographic 2/m symmetry. The presence of O—H⋯O and N—H⋯O hydrogen bonding leads to a three-dimensional network in the crystal structure. A highly disordered solvent molecule is present within a molecular cavity defined by the organic and water molecules. Its contribution to the electron density was removed from the observed data in the final cycles of refinement and the formula, molecular weight and density are given without taking into account the contribution of the solvent molecule.


Comment
In connection with on-going studies into the structural chemistry of hydrazones (Baddeley et al., 2009;Ferguson et al., 2005;Glidewell et al., 2006;Low et al., 2006;Wardell et al., 2005;Wardell et al., 2006), we now report the structure of the title compound, (I).
The molecule in (I) is essentially planar with the r.m.s. of the 30 non-hydrogen atoms being 0.096 Å. The maximum deviations from the least-squares plane are 0.243 (2) Å for atom O3 and -0.140 (3) Å for atom C13; the former deviation arises as the N6-nitro group is slightly twisted out of the plane of the benzene ring to which it is attached: the C17-C18-N6-O3 Overall, to a first approximation, the molecule has non-crystallographic 2/m symmetry.
The water molecules are involved in a number of hydrogen bonding interactions and stabilize a double layer arrangement.
As illustrated in Fig. 2, molecules are arranged into a layer being connected by O-H···O and N-H···O hydrogen bonds as well as C-H···O contacts, Table 1. Each of the hydrazine-H atoms forms a donor interaction to a water molecule. The O1w water molecule forms a donor hydrogen bond with a O2w water molecule in the plane, Fig. 2, as well as with a nitro-O4 atom. The O2w water molecule accepts a hydrogen bond from the O1w atom as described above, and forms two donor interactions with the nitro-O1 and O2 atoms via a bifurcated H4w atom. Each of the nitro O1 and O2 atoms forms a C-H···O contact. The aforementioned interactions stabilize a 2-D array. Each of the O1w (acceptor) and O2w (donor) molecules forms one further hydrogen bond to a water molecule of a centrosymmetrically related layer to form a double layer as well as eight-membered {···O-H} 4 synthons. Further stability to the double layers is afforded by weak π···π interactions [ring centroid(C16-C6)···ring centroid(C15-C20) i = 3.6716 (16) Å with a dihedral angle between planes = 2.31 (12) °f or symmetry operation i: 1 -x, -y, 2 -z]. Layers stack in the crystal structure as illustrated in Fig. 3. As noted in the Experimental, ill-defined solvent, most probably methanol, was present in the crystal structure. These are located in the vicinity of the voids within the double layer.

Refinement
The N-and C-bound H atoms were geometrically placed (N-H = 0.88 Å and C-H = 0.95 Å) and refined as riding with U iso (H) = 1.2U eq (C). The O-H atoms were located in a difference map and refined with the distance restraint O-H = 0.84±0.01 and with U iso (H) = 1.5U eq (N). Unresolved disordered solvent was evident in the final cycles of the refinement.
This was modelled with the SQUEEZE option in PLATON (Spek, 2009); the solvent cavity had volume 76 Å 3 . In the final cycles of refinement, this contribution to the electron density was removed from the observed data. The density, the F (000) value, the molecular weight, and the formula are given without taking into account the contribution of the solvent molecule. Fig. 1. The molecular structure of (I) showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level.