1-Hydroxy-1,1,3,3,3-pentaphenyldisiloxane, [Si2O(OH)(Ph)5], at 100 K

In the crystal structure of the title compound, C30H26O2Si2, one Si(Ph)3 residue is bound to another Si(OH)(Ph)2 residue via a non-linear Si—O—Si bridge. The asymmetric unit is composed of two such molecules which interact, on the one hand, via a strong and highly directional O—H⋯O hydrogen bond involving the two neighbouring Si—OH units and, on the other, via an O—H⋯π contact connecting the second hydroxyl group with an adjacent phenyl group.

We are grateful to Fundaçã o para a Ciê ncia e a Tecnologia (FCT, Portugal) for their general financial support and also for specific funding toward the purchase of the single-crystal diffractometer.
centre is bound to a hydroxyl group are unknown as revealed by a search of the literature in conjunction with another of the Cambridge Structural Database (CSD, Version 5.28 with three updates -August 2007; Allen, 2002). Moreover, disiloxanes having one of the two Si centres bound to three phenyl groups are scarce, with only a handful of compounds being available in the literature (Glidewell & Liles, 1978;Hönle et al., 1990;Morosin & Harrah, 1981;Suwińska et al., 1986;Wojnowski et al., 2004). Following our on-going research toward the synthesis, structural characterization and catalytic application of novel triphenylsiloxy derivatives (Abrantes et al., 2002;Bruno et al., 2006Bruno et al., , 2007Nunes et al., 2003), we have recently isolated the unprecedented [Si 2 O(OH)(Ph) 5 ] disiloxane, in which one Si(Ph) 3 residue is bound to another Si(OH)(Ph) 2 residue via a non-linear Si-O-Si bridge.
The crystal structure of the title compound, (I), at the low temperature of 100 K is fully described in the triclinic P1 space group with the asymmetric unit being composed of two crystallographically independent [Si 2 O(OH)(Ph) 5 ] molecular units,  Table 1. Within each binuclear unit, the two Si centres exhibit distinct coordination environments, even though the µ 2 -bridging oxo group is common to the two Si centres. While one Si is coordinated to three phenyl groups, {SiC 3 O}, the other is bound to two phenyl groups plus a hydroxyl moiety,{SiC 2 O 2 }. For the two independent molecular units, the Si-C and Si-O bond lengths were found in the 1.841 (5)-1.861 (5) and 1.605 (3)-1.637 (3) Å ranges, respectively, in good agreement with those found in related materials.
It is of considerable importance to note that while for the disiloxanes which have identical coordination environments for the Si centres the internal Si-O-Si bridge is almost linear, such as for the compounds reported by Glidewell & Liles (1978), Hönle et al. (1990 and Suwińska et al. (1986), the presence of distinct coordinating chemical moieties and their interaction with adjacent species in (I) induces a kink in this µ 2 -bridge. Indeed, the Si-O-Si bond angles for (I) range from 147.7 (2)° to 166.0 (2)°, values which are consistent with that reported by Wojnowski et al. (2004) for [Si 2 O(H)(Ph) 5 ] (ca 163°). We also note the markedly distinct nature of the bridging angles for the two molecular units, a structural feature which can be rationalized taking into consideration the strongest intermolecular interactions present. Indeed, besides the very strong and linear O-H···O hydrogen bonding interaction connecting adjacent [Si 2 O(OH)(Ph) 5 ] units, the O2-hydroxyl group is further engaged in a O-H···π interaction with the neighbouring C55→C60 phenyl group, Table 2. Consequently, in order to maximize these two interactions the Si3-O3-Si4 angle decreases, while the Si1-O1-Si2 approaches linearity so to minimize steric hindrance between coordinating moieties.
The two interactions described above (O-H···O and O-H···π) create a supramolecular entity ( Fig. 1) which packs in a parallel fashion in the ab plane of the unit cell forming layers (Fig. 2). Adjacent layers alternate along the [001] direction of the unit cell with a number of C-H···π contacts mediating the interactions between adjacent phenyl groups (not shown).

supplementary materials sup-2 Experimental
The title compound was isolated as a secondary product during our synthetic attempts to isolate organometallic vanadium(V) oxides from AgVO 3 and triphenylchlorosilane (Ph 3 SiCl, 97.0%, Fluka). Standard Schlenk line techniques were employed.
To a solution of AgVO 3 (0.31 g) in dried 1,2-dichloroethane, another solution of Ph 3 SiCl (0.44 g) was added dropwise, and the resulting mixture was allowed to react over a period of 87 h under reflux in an oil bath at 263 K. After reacting, the obtained precipitate was separated from the yellow mother liquor by using dried Celite 545 (Aldrich). The isolated solution was then concentrated to an oil by slowly evaporating 1,2-dichloroethane in a water bath, under vacuum for 5 h. The title compound (a secondary product) was separated from the desired synthesized product by washing with ca 10 ml of n-hexane

Refinement
Crystals of the title compound were manually harvested from the crystallization vial and mounted on CryoLoops purchased from Hampton Research using FOMBLIN Y perfluoropolyether vacuum oil (LVAC 25/6) purchased from Aldrich, with the help of a Stemi 2000 stereomicroscope equipped with Carl Zeiss lenses. Different crystals from the same batch systematically diffracted very weakly at high angle. A full data set was collected at the low temperature of 100 (2) K with a long exposure time per frame, revealing the existence of a poorly defined spot shape which ultimately had a strong influence in the high value of R int . Nevertheless, the structure was readily solved using Patterson synthesis which allowed the immediate location of the four crystallographically unique Si centres. All remaining non-H atoms were located from difference Fourier maps calculated from successive least-squares refinements cycles. Non-H atoms were successfully refined using anisotropic displacement parameters. H atoms bound to C and the terminal Si-OH groups were located at their idealized positions and allowed to ride on their parent atoms with C-H = 0.95Å and O-H = 0.84 Å, and with U iso = 1.2 or 1.5×U eq of the parent atoms (C and O, respectively).