Tetrakis[3,5-bis(trifluoromethyl)phenyl]tin(IV)

The title molecule, [Sn(C8H3F6)4], lies on a twofold rotation axis with the SnIV ion in a distorted tetrahedral coordination environment. Both –CF3 groups attached to one of the unique benzene rings are disordered over two sets of sites, with the ratios of refined occupancies being 0.719 (14):0.281 (14) and 0.63 (5):0.37 (5).

The title molecule, [Sn(C 8 H 3 F 6 ) 4 ], lies on a twofold rotation axis with the Sn IV ion in a distorted tetrahedral coordination environment. Both -CF 3 groups attached to one of the unique benzene rings are disordered over two sets of sites, with the ratios of refined occupancies being 0.719 (14):0.281 (14) and 0.63 (5):0.37 (5).

Related literature
For synthesis of the title compound, see King et al. (1986). Additional preparative details of similar compounds are given by Lu & Tilley (2000). For related crystal structures, see: Young et al. (2005); Smith et al. (1994); Wharf & Simard (1997). For further details of geometric distortions in related compounds, see Charissé et al. (1998).

S1. Comment
The preparation of polymerizable dialkyl or diaryl tin monomers bearing either chlorine or hydride groups (Lu & Tilley, 2000) is accessed through the initial comportionation reactions involving the tetraalkyl-or tetraryltin(IV) compounds and tin(IV) tetrachloride. The incorporation of perfluorinated species in the backbone of polystannanes should by design impart an improved stability towards nucleophilic attack. Our interest in the distortions from tetrahedral geometry of other tin aryl compounds (Charissé et al., 1998), prompted us to determine the crystal structure of the title compound which was previously synthesized by King et al. (1986).
The title molecule ( Fig. 1) lies on a twofold rotation axis. The Sn IV ion is in a distorted tetrahedral coordination environment ( Table 1). The angular disortion from the ideal values of 109.5° is most likely a consequence of the steric crowding caused by the 3,5 substitution of the bulky trifluoromethyl groups on the benzene rings. The Sn-C bond distances in the title compound are the same within experimental error and are comparable to those in the parasubstituted and meta-substituted tetrakis[(trifluoromethyl)phenyl]stannane structures (Young et al., 2005;Smith et al., 1994) but are significantly longer than the Sn-C bonds in the related triaryltin(IV)chloride compounds (Wharf & Simard, 1997).

S2. Experimental
The title compound was prepared from the refluxing Grignard reaction of 3,5-trifluoromethylphenyl magnesium bromide (12.5 mmol) in ether with anhydrous tin tetrachloride (3.125 mmol). The reaction mixture was refluxed overnight, cooled and filtered to remove salts. The crude compound was purified first by sublimation, and then recrystallization from ether to yield long large needles suitable for X-ray diffraction. Yield 1.33 g, 44%. m.p. 426 K (literature 436 K; King et al., 1986).

S3. Refinement
H atoms were placed in calculated positions with C-H = 0.95 Å and included in a riding-motion approximation with U iso (H) = 1.2U eq (C). Both -CF 3 groups attached to one of the unique benzene rings are disordered over two sets of sites with the ratios of refined occupancies being 0.719 (14)  The molecular structure of the title compound with displacement ellipsoids drawn at the 30% probabilty level. The minor comonent of disorder is not shown [symmetry code (a): -x + 1, y, -z + 1/2].

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.