2,2′-(Diselane-1,2-diyl)dinicotinamide N,N′-dimethylformamide disolvate

The asymmetric unit of the title compound, C12H10N4O2Se2·2C3H7NO, contains two solvent molecules and two half molecules of the dinicotinamide, each of which sits on a center of symmetry passing through the middle of the Se—Se bond. In each molecule, the two pyridyl groups and diseleno group are approximately coplanar (r.m.s. deviations from planarity for all non-H atoms = 0.011 and 0.008 Å in the two molecules). Intermolecular N—H⋯O hydrogen bonds stablilize the crystal packing.


Comment
Organoselenium compounds have attracted much atention because of their potential applications in organic synthesis, precursors for semiconducting materials, ligand chemistry and biochemistry (Mugesh et al., 2001). During the past decade, many organoselenium compounds have been synthesized and well characterized. In contrast to alkyl, aryl, and mixed alkylaryl senium compounds, the pyridyl selenium compounds are still rare.
The unit cell contains two nicotinamide molecules and four of the solvent molecules. The asymmetric unit contains two solvent molecules and two half molecues of the nicotinamide each of which sits on a center of symmetry passing through the middle of the Se-Se bond (Fig. 1). In (I),the two independent nicotinamides (molecule A containing Se1 and molecule B containing Se2) have comparable conformations. In each nicotinamide, the two pyridyl groups and the diseleno group are approximately coplanar (r.m.s. deviations from planarity for all non-H atoms are 0.011 and 0.008Å for molecules A and B, respectively while the two CONH 2 groups are rotated out of this plane by 11.0 (5)° and 18.6 (5)° for molecules A and B, respectively. Fig. 2 shows the sheets of molecules formed by intermolecular N-H···O hydrogen-bond interactions between the nicotinamides and neighbouring solvents with distances between 2.869 (5) and 3.081 (4) Å (Table 1).
The structure of (I) is similar to that of other diselenide compounds (Kienitz, et al. 1996;Bhasin and Singh 2002).The two neighbouring pyridyl groups can be brought into register by rotation about the Se-Se bond. The commonly observed approximate coplanarity of the rings and the Se-Se bonds (C-C-Se-Se or N-C-Se-Se torsion angles ca. 0°) in these molecules has been explained in terms of a minimization of Se···Se lone pair repulsion.

Experimental
To a vigorously stirred solution of selenium powder (1.19 g, 15 mmol) and absolute ethanol (30 ml), sodium borohydride (0.40 g, 10.6 mmol) was added at 0 °C. The mixture was warmed to room temperature and stirred for 2 h. 2-Chloro-nicotinamide (1.56 g, 10 mmol) was added and stirred for 7 days. O 2 was passed through the solution slowly for 2 h after the reaction mixture was acidfied by glacial acetic. The solvents were removed in vacuo and the residue was extracted with hot dimethyl sulphoxide (DMSO) and filtered. The filtrate was poured into water( 200 ml, cooled to 0 °C). The precipitate was separated by filtration and recrystallized from DMSO-CH 3 OH(1:2) to give the product as yellow crystals, yield:

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 > σ(F 2 ) is used only for calculating Rfactors(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.