1,5-Bis(2-methylphenyl)-3-nitroformazan

In the title compound, C15H15N5O2, the nitro O atoms are disordered over two sets of sites with an occupancy ratio of 0.75 (4):0.25 (4). Amine–imine tautomerism is observed in the formazan group. This was evident from the similar C—N bond distances in the formazan [1.319 (2) and 1.332 (3) Å], as well as the distribution of the imine proton in the Fourier difference map which refined to a 0.53 (3):0.47 (3) ratio. C—H⋯O and π–π interactions [centroid–centroid distances = 3.4813 (1) and 3.3976 (1) Å] are observed in the crystal packing.

In the title compound, C 15 H 15 N 5 O 2 , the nitro O atoms are disordered over two sets of sites with an occupancy ratio of 0.75 (4):0.25 (4). Amine-imine tautomerism is observed in the formazan group. This was evident from the similar C-N bond distances in the formazan [1.319 (2) and 1.332 (3) Å ], as well as the distribution of the imine proton in the Fourier difference map which refined to a 0.53 (3):0.47 (3) ratio. C-HÁ Á ÁO andinteractions [centroid-centroid distances = 3.4813 (1) and 3.3976 (1) Å ] are observed in the crystal packing.

Comment
During synthesis of the versatile trace metal analysis dithizone reagent, aniline is first diazotized and then treated with nitromethane to form the bright orange-red nitroformazan product (Pelkis et al., 1957). Ammonia and hydrogen sulfide gas is used to substitute the nitro group with sulfur towards the formation of dithizone, the chemistry of which is extensively described by Irving, 1977. Single crystal X-ray structures of nitroformazan derivatives were determined by Gilroy et al., 2008;Mito et al.,1997, and the dithizone structure by Laing, 1977, while we performed extensive DFT (Von Eschwege et al., 2011) and electrochemistry studies (Von Eschwege & Swarts, 2010) on the free ligand. We recently embarked on a study during which we synthesized a series of electronically altered dithizones for the purpose of investigating its altered redox and structural properties. During this process orange 1,5-bis(2-methylphenyl)-3-nitroformazan crystals suitable for X-ray structure analysis were grown from an acetone solution overlaid with n-hexane.
The structure showed large thermal vibrations at the NO 2 moiety and was treated for disorder. From the Fourier difference map the imine hydrogen was also detected as being disordered over two nitrogen atoms. Details of these can be found in the refinement section.

Experimental
Solvents (AR) purchased from Merck and reagents from Sigma-Aldrich were used without further purification. The orthomethyl derivative of nitroformazan was prepared according to the procedure reported by Pelkis et al., 1957.

Refinement
All hydrogen atoms were positioned in geometrically idealized positions with 0.98 Å (methyl), 0.95 Å (aromatic) and C-H = 0.86 Å (imine). All hydrogen atoms were allowed to ride on their parent atoms with U iso (H) = 1.2U eq , except for the methyl where U iso (H) = 1.5U eq was utilized. The initial positions of methyl hydrogen atoms were located from a Fourier difference map and refined as fixed rotor. The amine hydrogen atom was refined as disordered over N1 and N4. The occupancy was connected to a free variable to add to unity. This refined to a 0.53 (3):0.47 (3) ratio. The NO 2 moiety showed large displacement ellipsoids on O1 and O2. These were also treated for disorder. Geometrical (SADI) and displacement (SIMU and DELU) restraints were applied. A free variable, to refine the disordered sites to unity, gave a distribution of 0.75 (4):0.25 (4). Fig. 1. View of the title compound with labelling and displacement ellipsoids drawn at a 50% probability level. Hydrogen atoms and minor components of disorders not shown for clarity.    For centroids: Cg1 = N 1 -N 2 ═C 8 -N 3 ═N 4 , Cg2 = ring C 2 -C 7 , Cg3 = ring C 9 -C 14 ; Symmetry codes: i = 1/2-X,1/2+Y,Z; Alpha = Dihedral angle between Cg(X) and Cg(Y); Cg(X)perp = Perpendicular distance of Cg(X) on ring Y; Cg(X)perp = Perpendicular distance of Cg(Y) on ring X; Beta = Angle Cg(X)···Cg(Y) vector and normal to ring X; Gamma = Angle Cg(I)···Cg(J) vector and normal to plane Y; Fig. 1 supplementary materials sup-9