Crystal structure of rac-(3aR*,9aS*)-4,4,4-trichloro-1,2,3,3a,4,9a-hexahydro-4λ5,9λ4-cyclopenta[4,5][1,3]tellurazolo[3,2-a]pyridine

The title compound, C10H12Cl3NTe, crystallizes with two crystallographically independent molecules (A and B) in the asymmetric unit. In each case, the coordination around the Te atom is distorted square-pyramidal, with the equatorial plane composed of the three Cl atoms and the C atom of the pyridinium ring. The Te atom is displaced from the mean-square plane by 0.1926 (7) and 0.1981 (8) Å, in molecules A and B, respectivly, away from the apical C atom. The bond lengths from the Te atom to the two Cl atoms arranged trans to each other [2.5009 (7)/2.5145 (7) and 2.5184 (7)/2.5220 (8) Å in molecules A and B, respectivly] are substantially shorter than the third Te—Cl distance [2.8786 (7) and 2.8763 (7) Å in molecules A and B, respectivly]. The 1,3-tellurazole ring is almost planar (r.m.s. deviations of 0.042 and 0.045 Å in molecules A and B, respectivly). The cyclopentane rings in both molecules A and B adopt envelope conformations with the carbon atom opposed to the (Te)C—C(N) bond as the flap. In the crystal, molecules form centrosymmetric 2 + 2 associates via Te⋯Cl interactions [3.3993 (7) and 3.2030 (7) Å]. As a result of these secondary interactions, the Te atom attains a strongly distorted 5 + 1 octahedral environment. Further, the 2 + 2 associates are bound by weak C—H⋯Cl hydrogen bonds into a three–dimensional framework.


S1. Structural commentary
It is known that the reaction of arenetellurium trihalides ArTeHal 3 with alkenes and acetylenes usually gives the products of 1,2-addition at the multiple bonds, β-haloalkyl(vinyl)tellurium dihalides or the products of transannular cyclization with the ring closure by the electron-donating center of the functional group containing in the molecule of the unsaturated substrate, lactones, ordinary cyclic ethers, pyrrolidine and piperidine derivatives (Petragnani & Stefani, 2007).
This work reports the structural characterization of a product of reaction of 2-pyridinetellurium trichloride -the first representative of hetarenetellurium trihalides containing a nitrogen base as the hetaryl substituent (Borisov et al., 2013) with cyclopentene ( Figure 1).
Compound (I), C 10 H 12 Cl 3 NTe, crystallizes with two crystallographically independent molecules in the asymmetric unit ( Figure 2). These crystallographically independent molecules are geometrically very similar. The coordination around the tellurium atom is a distorted square-pyramidal. The equatorial plane is composed of the three chlorine atoms and the carbon atom of pyridinium ring. The tellurium atom is displaced from the mean square plane by 0.1926 (7) and 0.1981 (8) Å for the two crystallographically independent molecules, respectively, away from the apical carbon atom.
The bond lengths from the tellurium atom to the two chlorine atoms arranged trans to each other [2.5009 (7)/2.5145 (7) and 2.5184 (7)/2.5220 (8) Å for the two crystallographically independent molecules, respectively] are close to those in related complexes (Singh et al., 1990;Sundberg et al., 1994;Zukerman-Schpector et al., 2000;Kandasamy et al., 2003;Raghavendra et al., 2006;Dutton et al., 2009;Lee et al., 2010;Rakesh et al., 2012). The third Te-Cl distance (2.8786 (7) and 2.8763 (7) Å for the two crystallographically independent molecules, respectively) is substantially longer than the other two Te-Cl distances. This geometry is apparently determined by the zwitterionic nature of the complex and the hypervalent configuration of the tellurium atom. The analogous geometry was observed previously for trichloro- (Sundberg et al., 1994). The Te-C distances are in good agreement with typical values found in tellurium(IV) complexes, which range from 2.11 to 2.16 Å. The 1,3-tellurazole ring in (I) is almost planar (r.m.s. deviation is 0.042 and 0.045 Å for the two crystallographically independent molecules, respectively). The cyclopentane ring adopts the usual envelope conformation.
The molecule of (I) possesses two asymmetric centers at the C3A and C9A carbon atoms and can have potentially four diastereomers. The crystal of (I) is racemic and consists of enantiomeric pairs with the following relative configuration of the centers: rac-3AR*,9AS*.

S2. Synthesis and crystallization
Complex (I) was prepared according to the procedure described by us earlier (Borisov et al., 2013). The single crystals of (I) suitable for an X-ray diffraction analysis were obtained after recrystallization of the crude product from methylene chloride.

Figure 1
The reaction of 2-pyridinetellurium trichloride with cyclopentene. The centrosymmetrical 2+2-associates of (I  Crystal packing of (I). The thick dashed lines indicate the intermolecular non-valent attractive Te···Cl interactions, and the thin dashed lines indicate the intermolecular C-H···Cl hydrogen bonds.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes.