5-[1-(4-Methylphenyl)-2-nitrobutyl]-4-phenyl-1,2,3-selenadiazole

In the title compound, C19H19N3O2Se, the selenadiazole ring is roughly planar [maximum deviation 0.033 (6) Å]. The attached phenyl ring is twisted away at an angle of 47.5 (1)°. The butyl group is in an extended conformation [C—C—C—C torsion angle = 174.7 (2)°]. In the crystal, C—H⋯O interactions form C(10) chains running aling the c-axis direction.

The ORTEP plot of the molecule is shown in Fig. 1 The tolyl group is oriented to the planar nitro group at an angle of 64.4 (1)°. The butyl group is in an extended conformation, which can be seen from the torsion angle value of [C9-C16-C17-C18 ] 174.7 (2)°. The molecular packing is controlled by C-H···O interactions in addition to van der Waals forces (Fig.2).

Refinement
H atoms were positioned geometrically (N-H=0.88-0.90 Å and C-H=0.93-0.98 Å) and allowed to ride on their parent atoms,with U iso (H) = 1.5U eq (C) for methyl H 1.2U eq (C) for other H atoms.

Figure 1
The molecular structure of the title compound with the displacement ellipsoids drawn at 30% probability level.  The crystal packing of the molecules viewed down a axis.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C1 0.2947 (