Bis[(4-methylphenyl)ethynyl] telluride

The tellurium atom in the title bis-ethynyl telluride, Te(C9H7)2 or C18H14Te, is located on a crystallographic twofold axis, the C—Te—C angle being 92.23 (15)°. The dihedral angle between the rings is 87.27 (7)°. In the crystal structure, molecules are connected in chains parallel to the b axis and mediated by C—H⋯π interactions.

The tellurium atom in the title bis-ethynyl telluride, Te(C 9 H 7 ) 2 or C 18 H 14 Te, is located on a crystallographic twofold axis, the C-Te-C angle being 92.23 (15) . The dihedral angle between the rings is 87.27 (7) . In the crystal structure, molecules are connected in chains parallel to the b axis and mediated by C-HÁ Á Á interactions.
Cg is the centroid of the C3-C8 ring.

Comment
Carbon-carbon bond formation for the preparation of symmetrical and unsymmetrical 1,3-diyne compounds is one of the most useful and important tools in modern organic chemistry. The construction of 1,3-diynes can be achieved either by intermolecular or intramolecular coupling of two similar or dissimilar alkynylic functionalities in the presence of organometallic complexes. However, the synthesis and use of bis-ethynyl tellurides are scarcely described in the literature (Gedridge et al., 1992, Engman & Stern, 1993 and their use in the detelluration reaction to afford 1,3-diynes is unknown until now. As part of our ongoing research into tellurium chemistry (Petragnani & Stefani, 2007;Zukerman-Schpector et al., 2008), the title compound, (I), was synthesized and its crystal structure determined.
The C-Te-C in (I), Fig. 1 (Jones & Ruthe, 2006). A search in the CSD (Bruno et al. 2002) showed 225 hits for related compounds and a mean value of 96.0 ° for the C-Te(II)-C angle.
The molecules are linked in chains parallel to the b axis mediated in a large part through C-H···π interactions, Table   1

Experimental
To a stirred solution of 1-ethynyl-4-methylbenzene (0.35 g, 3.0 mmol) in THF (10 ml), n-BuLi (1.2 ml, 2.5 M, 3.0 mmol) was added dropwise at 195 K. After 20 min., freshly crushed tellurium powder (0.38 g, 3.0 mmol) was added in one lot while a stream of argon was passed through the open flask. The cooling bath was then removed to bring the reaction medium to room temperature. When almost all the tellurium was consumed, the reaction mixture was again cooled to 195 K. Then a solution of bromine (0.48 g, 3.0 mmol) in dry benzene (5 ml) was added dropwise, and stirring was continued for 15 min.

Refinement
The H atoms were geometrically placed (C-H = 0.95-0.98 Å) and refined as riding with U iso (H) = 1.2-1.5U eq (C). Fig. 1. The molecular structure of (I) showing atom labelling scheme and displacement ellipsoids at the 50% probability level (arbitrary spheres for the H atoms). Symmetry operation i:x, y, 3/2-z.

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.
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.

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