The synthesis and crystal structure of 2-(chloroselanyl)pyridine 1-oxide: the first monomeric organoselenenyl chloride stabilized by an intramolecular secondary Se⋯O interaction

2-(Chloroselanyl)pyridine 1-oxide represents the first monomeric organoselenenyl chloride stabilized by an intramolecular secondary Se⋯O interaction.

The title compound, C 5 H 4 ClNOSe, is the product of the reaction of sulfuryl chloride and 2-selanyl-1-pyridine 1-oxide in dichloromethane. The molecule has an almost planar geometry (r.m.s. deviation = 0.012 Å ), and its molecular structure is stabilized by an intramolecular secondary SeÁ Á ÁO interaction of 2.353 (3) Å , closing a four-membered N-C-SeÁ Á ÁO ring. The title compound represents the first monomeric organoselenenyl chloride stabilized intramolecularly by an interaction of this type. The non-valent attractive SeÁ Á ÁO interaction results in a substantial distortion of the geometry of the ipso-carbon atom. The endo-cyclic N-C-Se [102.1 (3) ] and exo-cyclic C-C-Se [136.9 (3) ] bond angles deviate significantly from the ideal value of 120 for an sp 2 -hybridized carbon atom, the former bond angle being much smaller than the latter. In the crystal, molecules are linked by C-HÁ Á ÁO hydrogen bonds, forming zigzag chains propagating along [010]. The chains, which stack along the a-axis direction, are linked by offsetinteractions [intercentroid distance = 3.960 (3) Å ], forming corrugated sheets parallel to the ab plane.

Chemical context
Organoselenenyl halides RSeX (X = Cl, Br) play an important role in modern organic synthesis and are used as reagents for the functionalization of many classes of compounds, including organoselenium compounds with a broad spectrum of biological activities (Ranganathan et al., 2004;Selvakumar et al., 2010Selvakumar et al., , 2011Ninomiya et al., 2011;Singh & Wirth, 2011;Zade & Singh, 2014;Elsherbini et al., 2016). An essential aspect of the chemistry of selenenyl halides is the factors responsible for the stability of these reagents (Coles, 2006;Mukherjee et al., 2010;Nakanishi et al., 2013;Takaluoma et al., 2015). Recently, we have developed a new effective method for the stabilization of heteroarenselenenyl and -tellurenyl chlorides by the transformation of them to T-shaped zwitterionic adducts with hydrochloric acid (Khrustalev et al., 2012(Khrustalev et al., , 2014(Khrustalev et al., , 2016. Moreover, we have established another stabilization method of heteroarenselenenyl and -tellurenyl chlorides by intermolecular secondary ChÁ Á ÁN (Ch = Se, Te) ISSN 2056-9890 interactions with the formation of dimers (Borisov et al., 2010a,b,c;Khrustalev et al., 2016). Herein, we report on the synthesis and structural characterization of the first monomeric 2-(chloroselanyl)pyridine 1-oxide stabilized by an intramolecular secondary SeÁ Á ÁO interaction.

Synthesis and crystallization
The synthesis of the title compound is illustrated in Fig. 3. It was synthesized according to the procedure described previously by Borisov et al. (2010a,b,c). A solution of sulfuryl chloride (0.27 g, 2 mmol) in dichloromethane (15 ml) was added to a solution of 2-selanyl-1-pyridine 1-oxide (0.35 g, 2 mmol) in dichloromethane (20 ml) at 293 K. After one h it was filtered to give the title compound (yield 0.33 g, 80%). The The molecular structure of the title compound, with atom labelling and displacement ellipsoids drawn at the 50% probability level. The dashed line indicates the intramolecular secondary attractive Se1Á Á ÁO1 interaction. Table 1 Hydrogen-bond geometry (Å , ). Symmetry code: (i) Àx þ 2; y þ 1 2 ; Àz þ 1 2 .

Figure 2
The crystal packing of the title compound viewed along the a axis. The intramolecular secondary SeÁ Á ÁO interactions and the intermolecular C-HÁ Á ÁO hydrogen bonds are shown as dashed lines (see Table 1).
filtrate was evaporated in vacuo and recrystallization of the residue from dichloromethane solution gave an additional 0.06 g (15%) of the title compound. Colourless prismatic crystals of the title compound were obtained after recrystallization of the crude product from dichloromethane (m.

Figure 3
The synthesis of the title compound; the reaction of 2-selanyl-1-pyridine 1-oxide with sulfuryl chloride in dichloromethane.

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.