N 1,N 2-Bis(2-pyridyl)formamidine

In the crystal structure of the title compound, C11H10N4, the dihedral angle between the two pyridyl rings is 36.1 (1)°. The molecules are connected via two strong N—H⋯N and two weak C—H⋯N hydrogen bonds into dimers, which are located on centers of inversion. This compound adopts the s–trans–anti–s–cis conformation in the solid state.

In the crystal structure of the title compound, C 11 H 10 N 4 , the dihedral angle between the two pyridyl rings is 36.1 (1) . The molecules are connected via two strong N-HÁ Á ÁN and two weak C-HÁ Á ÁN hydrogen bonds into dimers, which are located on centers of inversion. This compound adopts the strans-anti-s-cis conformation in the solid state.
Data collection: SMART (Bruker, 1997); cell refinement: SAINT (Bruker, 1997); data reduction: SAINT and SHELXTL (Sheldrick, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL. The title compound and its anion have been used as bridging ligands in coordination chemistry (Liang et al., 2003;Yang et al., 2000;Radak et al., 2001;Cotton et al., 1998). In the present work, the structure of the title compound ( Fig. 1) has been determined to explore its ligand conformation. In the crystal structure of the title compound the molecule is in a strans-anti-s-cis conformation. This conformation is different from that in the Re complex, which is s-cis-syn-s-cis (Liang et al., 2003).
Thus, the conformation of the free ligand has been changed upon coordination to the metal center. The molecules are connected via two strong N-H-N and two weak C-H-N hydrogen bonds into dimers, which are located on centres of inversion (Fig. 2),

S2. Experimental
The title compound was prepared according to a published procedure (Roberts, 1949). 2-Aminopyridine (11.28 g, 0.12 mol) and triethyl orthoformate (8.88 g, 0.06 mol) were placed in a flask under nitrogen. The mixture was then refluxed for 8 h to give a brown solid. Dichloromethane was then added to dissolve the solid and then hexanes added to induce the precipitate. The precipitate was filtered and dried under vacuum to give a light yellow solid with a yield of 82 %. Crystals suitable for X-ray crystallography were obtained by dissolving the product in dichloromethane, followed by slow evaporation of the solvent.

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. 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 > 2sigma(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.