Diphenyl(pyridin-2-yl)phosphane selenide

In the title compound, C17H14NPSe, the P atom has a distorted tetrahedral environment resulting in an effective cone angle of 163°. In the crystal, C—H⋯Se/N/π interactions are observed.

In the title compound, C 17 H 14 NPSe, the P atom has a distorted tetrahedral environment resulting in an effective cone angle of 163 . In the crystal, C-HÁ Á ÁSe/N/ interactions are observed.
Cg1 is the centroid of the C1-C6 ring. Financial assistance from the Research Fund of the University of Johannesburg is gratefully acknowledged.

Wade L. Davis and Alfred Muller Comment
As part our systematic investigation on the steric and electronic properties of phosphorus containing ligands, we are also utilizing the 1 J( 31 P-77 Se) multi-nuclear NMR coupling in Se-P bond as a probe (see Muller et al., 2008). The advantage of this approach is that there is no steric crowding effect, albeit crystal packing effects, as normally found in transition metal complexes with bulky ligands, e.g. in trans-[Rh(CO)Cl{P(OC 6 H 5 ) 3 } 2 ] cone angles variation from 156° to 167° was observed for the two phosphite ligands (Muller et al., 2006). Herein we report here the single-crystal structure of SePPh 2 py, where Ph = C 6 H 5 and py = C 5 H 4 N as part of our investigation.
Molecules of the title compound ( Fig. 1) adopts a distorted tetrahedral arrangement about the P atom with average C-P -C and Se-P-C angles of 105.47° and 113.20° respectively. Describing the steric demand of phosphane ligands has been the topic of many studies and a variety of models have been developed. The Tolman cone angle (Tolman, 1977) is still the most commonly used model. Applying this model to the geometry obtained for the title compound (and adjusting the Se-P bond distance to 2.28 Å) we calculated an effective cone angle from the geometry found in the crystal structure of 163° (Otto, 2001). The angle calculated is 9° larger than that of the free phosphine (Charland et al., 1989; effective cone angle calculated as 154°), and could be ascribed to C-H···Se/N/π intra-and interactions observed in the title compound (Table 1, Fig. 2), whereas the free phosphine shows C-H···N/π interactions only. The difference in the orientation of the substituents for these two structures can be illustrated by superimposing their coordinates (Fig. 3); root mean squared deviation calculated as 0.0468 Å for P and ipso C atoms only using Mercury (Macrae et al., 2008;Weng et al., 2008a,b).

Experimental
Diphenyl-2-pyridylphosphine and KSeCN were purchased from Sigma-Aldrich and used without purification. Eqimolar amounts of KSeCN (5.8 mg, 0.04 mmol) and the diphenylpyridylphosphine (10.5 mg, 0.04 mmol) were dissolved in the minimum amounts of methanol (10 ml). The KSeCN solution was added dropwise (5 min) to the phosphine solution with stirring at room temperature. The final solution was left to evaporate slowly until dry to give crystals suitable for a singlecrystal X-ray study. Analytical data: 31 P {H} NMR (CDCl 3 , 161.99 MHz): δ = 31.47 (t, 1 J( 31 P-77 Se) = 734 Hz).

Refinement
The aromatic H atoms were placed in geometrically idealized positions with C-H = 0.95 Å, and allowed to ride on their parent atoms, with U iso (H) = 1.2U eq (C).

Figure 1
A view of (1). Displacement ellipsoids are drawn at the 50% probability level.

Special details
Experimental. The intensity data was collected on a Bruker Apex DUO 4 K CCD diffractometer using an exposure time of 5 s/frame. A total of 287 frames were collected with a frame width of 4° covering up to θ = 66.62° with 96.7% completeness accomplished. 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