Bis(4-methoxypyridin-3-yl)diazene

The asymmetric unit of the title compound, C12H12N4O2, consists of one half-molecule, which is located on a center of inversion. The molecule has a step-like shape; the azo group adopting a trans configuration, with the pyridine rings being parallel-displace.

The asymmetric unit of the title compound, C 12 H 12 N 4 O 2 , consists of one half-molecule, which is located on a center of inversion. The molecule has a step-like shape; the azo group adopting a trans configuration, with the pyridine rings being parallel-displace.  supplementary materials Acta Cryst. (2012). E68, o1568 [doi:10.1107/S1600536812018326] Bis(4-methoxypyridin-3-yl)diazene

Steffen Thies, Christian Näther and Rainer Herges Comment
We recently reported about a change of the spin state by association/dissociation of photodissociable ligands (PDL's) at square planar Ni(II) porphyrine complexes (Thies et al. 2010, Thies et al. 2011, Venkataramani et al., 2011. Within this project the title compound was synthesized as potential PDL and its structure was determined by single-crystal X-ray diffraction. In the crystal structure of the title compound, the azo group is in a trans configuration with an torsion angle C2-N2-N2 i -C2 i (i = -x + 1, -y + 2, -z + 1) of 180° due to symmetry. The pyridine rings are not coplanar with the central C-N-N-C unit with torsion angles of 32.9 (2)° for C1-C2-N2-N2 i and 151.5 (2)° for C3-C2-N2-N2 i (i = -x + 1, -y + 2, -z + 1).

Experimental
3-Nitro-4-methoxypyridine (1.14 g, 7.41 mmol) was dissolved in ethanol (30 ml) and heated to 80°C. Barium hydroxide (3.50 g, 20.8 mmol) dissolved in 20 ml hot water was added. Zinc powder (6.00 g, 91,7 mmol) was added in small portions within 20 min. The reaction mixture was stirred at 80 °C for 3 h and filtered over celite&reg;. 200 ml dichloromethane were added to the filtrate and air was bubbled through the solution for 2 h. The organic layer was dried over magnesium sulfate and the solvent was removed under reduced pressure. The crude product was dissolved in ethanol and two spoons of activated charcoal were added. After stirring at 80°C for 20 min the mixture was filtered over celite&reg; and the product was crystallized from ethyl acetate. An orange solid (120 mg, 0.49 mmol, 13.2%) was afforded (mp:

Refinement
All H atoms were positioned with idealized geometry (methyl H atoms allowed to rotate but not to tip) and were refined isotropically with U iso (H) = 1.2 U eq (C) for aromatic H atoms (1.5 for methyl H atoms) using a riding model.  Crystal structure of the title compound with labeling and displacement ellipsoids drawn at the 50% probability level.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.