Triclinic polymorph of bis(triphenylsilyl) oxide toluene disolvate

A new polymorph of the title compound, C36H30OSi2·2C7H8, is reported, which is triclinic (P-1) instead of possessing the previously reported rhombohedral symmetry [Hönle et al. (1990). Acta Cryst. C46, 1982–1984]. Each of the –SiPh3 units are related by the inversion center. The Si—O—Si moiety is linear with the O atom sitting on an inversion center, and the O—Si—(toluene ring centroid) angle is 3.69 (15)°. Each toluene molecule is 5.622 (2) Å from the Si atom and has its closest contacts with the phenyl rings outside of the van der Waals radii.


Related literature
For the rhombohedral polymorph of the title compound and its benzene analog, see: Hö nle et al. (1990). For the structures of related compounds, see: Glidewell & Liles (1978); Morosin & Harrah (1981); Suwiń ska et al. (1986). For the determination by IR spectroscopy of silylcarbonate in the reaction product, see: Yildirimyan & Gattow (1984 Table 1 Selected geometric parameters (Å , ). A rhombohedral polymorph of the title compound and its benzene analog have been reported by Hönle et al. (1990). The triclinic unsolvated molecule was reported by Glidewell & Liles (1978) and repeated by Morosin & Harrah (1981), who also determined the entire series of Ge and Sn analogs. A benzene and a piperidine adduct of (Ph 3 Si) 2 O were also determined by Suwińska et al. (1986).
The core geometry (Table 1) of the title compound is almost identical to the previously reported rhombohedral polymorph. The main difference is the rhombohedral form was collected at room temperature, and has rotational disorder in the toluene. Our structure was collected at -150°C, and the toluene is not disordered. This difference could account for the lower symmetry of our structure. In our structure, the centroid of the toluene is slightly offset (3.69 (15)° versus 0°) from the linear Si-O-Si axis, and slightly closer (5.622 (5) versus 5.672 (2) Å) than it is in the rhombohedral form.

Experimental
All chemicals were handled inside a dry box under Ar or N 2 . A Ph 3 SiOK solution was prepared by dissolving KH (0.28 g) with Ph 3 SiOH (2.0 g) in 30 g of dry ether, and filtering to remove the small amount of undissolved solids. The solution was put in a 1" diameter test tube which was inserted into a Newport Scientific 2" OD pressure vessel and pressurized with CO 2 at tank pressure. After 1 day, the pressure was released and the resulting voluminous white solid (presumably Ph 3 SiOCO 2 K) was isolated by filtration and washing with ether, and pumped dry under vacuum. An infrared spectrum of the white solid shows a broad peak at 1660 cm -1 and is consistent (Yildirimyan & Gattow, 1984) with the presence of silylcarbonate. Attempts were made to crystallize the silylcarbonate from numerous solvents. In one attempt, a portion of the white solid was mixed in a vial with toluene and 18-crown-6. Over several weeks small crystals formed on the walls of the vial. One crystal was mounted in Cargill #2 oil and frozen in the diffractometer.

Refinement
H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with a C-H distance of 0.95 and 0.98 Å U iso (H) = 1.2U eq (C) [1.5U eq (C) for CH 3 ]. During data collection it was found that the previous crystal (a completely unrelated material) was still present on the MiTiGen mount. However since its cell constants were different from those of the current compound, there was very little overlap of the reflections. The unit cell for the title compound was determined using the twinning routine cell_now and integration proceeded smoothly.  Structural diagram of the title compound. Atomic displacement parameters are at the 30% probability level. Unlabelled atoms are related to the labelled atoms by the symmetry operation 1-x, 1-y, 1-z. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 1.38 e Å −3 Δρ min = −0.52 e Å −3 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.

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