The low-temperature phase of di-tert-butylsilanediol

The crystal structure of di-tert-butyl­silanediol, C₈H₂₀O₂Si, has a reversible phase transition at 211 (2) K. The orthorhombic high-temperature structure has space group Ibam, with Z' = , and shows a disordered hydrogen-bonding system. The low-temperature structure, determined at 143 (2) K, has a twinned monoclinic cell, with space group C2/c and Z' = 2, and shows an ordered hydrogen-bonding system.

S1. Comment

During the study of the chemical behaviour of 1,3-dichloro-1,1,3,3-tetra-tert-butyldisilazane, crystals of di-tert-butylsilanediol, (I), were obtained. Crystal structure determinations of (I) at room temperature have been reported by Graalmann et al. (1984) and Buttrus et al. (1985). Possible hydrogen-bonding schemes were proposed, but no H-atom positions were reported in those studies. Due to the symmetry of the structure of (I) at room temperature, any hydrogen-bonding system must be disordered. We have remeasured (I) at a temperature of 224 K and confirmed the structure previously reported. Compound (I) crystallizes in the orthorhombic space group Ibam. The cell constants at 224 K are a = 16.336 (2), b = 12.699 (3) and c = 10.4918 (15) Å. The molecule has m symmetry. A difference Fourier synthesis showed the H atom of the hydroxyl group to be disordered over two possible positions. Recently, this structure was also reported to occur at 173 K (Bolte & Lerner, 2001). By lowering the temperature, however, we found a reversible phase transition at 211 (2) K. Here, we report the low-temperature phase of (I) determined at 143 K. \sch

On cooling (I) through the phase transition, additional reflections appear, resulting in a doubling of the ab diagonal of the high-temperature Ibam cell. The low-temperature reflection data can be interpreted either by an orthorhombic C-centred unit cell or a twinned monoclinic unit cell. The structure can indeed be determined and refined in the orthorhombic space group Ccca (see Experimental); however, the resulting value of S and the residual density are larger than expected. Moreover, one tert-butyl group of this solution has displacement parameters larger than those observed for the high-temperature structure at 224 K, making this solution suspect. The structure can also be determined and refined in the monoclinic space group C2/c. In this case, the crystal is twinned and each reflection h k l coincides with reflection l k h of the twin domain. Reflections with h+k and k+l odd should be absent for both twin domains. An inspection of the measured reflections shows this indeed to be the case. The structure was refined with SHELXL97 (Sheldrick, 1997) using reflections from both twin domains simultaneously (see Experimental). The R values and residual density in C2/c are significantly better than those in Ccca. Thus, C2/c was adopted as the correct space group.

The low-temperature structure of (I) has two independent molecules, A and B (Fig. 1). The dimensions of both molecules are very similar. Molecule A shows a small deviation from the mirror-symmetrical conformation observed in the high-temperature phase: the C2—C1—Si1—C5 and C1—Si1—C5—C6 torsion angles are 178.48 (9) and -176.01 (10)°, respectively, rather than 180°. Molecule B remains approximately mirror-symmetric: the C10—C9—Si2—C13 and C9—Si2—C13—C14 torsion angles are 179.86 (11) and 179.38 (10)°, respectively. The C—Si—C angles are rather large, at 119.20 (11) and 119.97 (11)°, due to intramolecular steric interactions between the tert-butyl groups. The shortest intramolecular H···H contacts are H3B···H7C 2.28, H4C···H8B 2.25, H11C···H15B 2.28 and H12B···H16C 2.27 Å.

The crystal packing of (I) at 143 K is shown in Fig. 2, which also shows the relationship between the high-temperature Ibam cell and the low-temperature C2/c cell. The molecules are connected by intermolecular hydrogen bonds (Table 1) to form a twisted ladder structure along the b direction. This hydrogen-bonded structure is shown in more detail in Fig. 3. Each molecule is connected by two almost straight O—H···O hydrogen bonds to a centrosymmetric counterpart to form a dimer. AA dimers are found at (1/4,3/4,1/2) and symmetry-related positions, while BB dimers are found at (1/4,1/4,1/2) and symmetry-related positions. The dimers are connected by additional O—H···O hydrogen bonds to form a ladder structure along b, with the sequence ···AA—BB—AA—BB···.. These latter hydrogen bonds have O—H—O angles of 148.2 (17) and 153.2 (17)° and are less straight than the hydrogen bonds in the dimers. It is interesting to note that the Si—O—H angles are also clearly affected by the hydrogen-bonding environment, with Si1—O1—H01 113.6 (14), Si2—O3—H03 113.2 (17), Si1—O2—H02 124.2 (13) and Si2—O4—H04 122.5 (14)°. A refinement with the X—O—H angle constrained to the tetrahedral value, as generally applied in crystal structure refinements, appears to be inappropriate in the present case. The O1—H01···O2 hydrogen bond is rotated by an angle of 38° about the b axis with respect to the O3—H03···O4 hydrogen bond, resulting in a twisted rather than a straight ladder.

In the high-temperature phase of (I), the molecules are situated about mirror planes and the hydrogen-bonded ladders have internal crystallographic symmetry ccm. Both OH groups of each molecule are symmetry-related, and consequently the H atoms must be distributed over two possible positions in each hydrogen bond. This was confirmed by our structure refinement at 224 K. Below the phase transition temperature, the crystallographic m symmetry is lost. Molecules A and B are tilted by angles of 3.6 and 6.8°, respectively, with respect to the (010) plane. Hydrogen bonds with ordered H-atom positions are found in the low-temperature phase. The internal symmetry of the hydrogen-bonded ladders is reduced to 1. The AA and BB dimers are related only by a pseudo-c glide plane perpendicular to the ac diagonal. The hydrogen-bonded chain about (1/4,y,1/2) is related to similar chains about (3/4,y,1/2), (1/4,y,0) and (3/4,y,0) by the crystallographic symmetry operations C, c and n, respectively. The pseudo-mirror symmetry about y = 1/4 and 3/4, combined with the c glide plane, results in pseudo-A centring of the crystal structure.

At this point, one question still has to be answered. The cell constants do not show the structure of (I) below the phase transition temperature to be monoclinic. The lattice parameters a and c are equal, and the observed unit cell can be transformed within experimental uncertainty to a C-centred unit cell with orthorhombic geometry. As the value of the twin fraction is almost 1/2, the low-temperature structure of (I) may actually be orthorhombic and perhaps the best solution has not been found. To clear this point, a smaller crystal of (I), with dimensions 0.20 × 0.24 × 0.30 mm, was measured at 145 K. The twin fraction of this second crystal refined to 0.323 (1). From this additional experiment, the crystal system of the low-temperature phase of (I) is definitely shown to be monoclinic.

S2. Experimental

A solution of 1,3-dichloro-1,1,3,3-tetra-tert-butyl-disilazane (0.203 g, 0.55 mmol) in C₆D₆ (1 ml) was hydrolysed with wet air. Colourless crystals (rods) of (I) were obtained from this solution at ambient temperature (Lerner, 1994).

S3. Refinement

The reflections observed for (I) at 143 K are perfectly fitted by a C-centred orthorhombic unit cell, with a = 25.195 (4), b = 32.385 (3) and c = 10.4557 (8) Å. Systematic absences are in agreement with space group Ccca. R_int = 0.050 for orthorhombic symmetry. Structure determination and refinement in Ccca proceeded smoothly. The H atoms of the methyl groups were geometrically positioned and refined as riding atoms. The H atoms of the hydroxyl groups were taken from a difference synthesis and were refined with individual isotropic displacement parameters. The H atoms of the hydroxyl groups of one molecule were disordered over two possible positions. Refinement in Ccca converged at wR(F²) = 0.192, R[F²>2σ(F²)] = 0.080 and S = 2.01, with residual density between -1.11 and 0.64 e Å^-3. The cell constants of the twinned monoclinic structure were determined from reflections with contributions from only a single twin domain. For the structure refinement in C2/c, the reflections were divided into four classes: reflections with h+k and k+l odd are absent and were omitted from the refinement, reflections with h+k even and k+l odd only have intensity contributions from domain 1, reflections with h+k odd and k+l even only have intensity contributions from domain 2, reflections with h+k and k+l even have intensity contributions from both twin domains. Refinement was performed with the HKLF 5 option in SHELXL97 (Sheldrick, 1997). The H atoms of the methyl groups were geometrically positioned and refined with fixed individual displacement parameters [U_iso(H) = 1.5U_eq(C)], using a riding model with a fixed C—H distance of 0.98 Å. The torsion angles about the C—C bonds of the methyl groups were refined. The H atoms of the hydroxyl groups were taken from a difference synthesis and were refined with individual isotropic displacement parameters. The O—H distances were restrained to 0.84 (1) Å. The twin fraction refined to 0.468 (1). Refinement in C2/c converged at wR(F²) = 0.130, R[F²>2σ(F²)] = 0.051 and S = 1.22, with residual density between -0.34 and 0.41 e Å^-3.

Computing details

Data collection: SMART (Siemens, 1995); cell refinement: SMART; data reduction: SAINT (Siemens, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97; molecular graphics: XP in SHELXTL (Sheldrick, 1996); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The molecular structure of (I) with 50% probability displacement ellipsoids, (a) molecule A, (b) molecule B. H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. The crystal packing of (I) as a projection on [010]. The small rectangular cell with labels O', a' and b' represents the high-temperature Ibam cell.
	Fig. 3. The hydrogen-bonded ladder structure of (I) viewed along the b direction (horizontal direction). Meaning left-right or into the paper? [Symmetry code: (i) 1/2 - x, 3/2 - y, 1 - z.] Is this correct?

di-tert-butylsilanediol

Crystal data

C8H20O2Si	F(000) = 1568
Mr = 176.33	Dx = 1.098 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 179 reflections
a = 20.515 (3) Å	θ = 3–23°
b = 10.4596 (11) Å	µ = 0.18 mm^−1
c = 20.517 (3) Å	T = 143 K
β = 104.223 (13)°	Block, colourless
V = 4267.5 (10) Å^3	0.45 × 0.42 × 0.35 mm
Z = 16

Data collection

Siemens SMART CCD area-detector diffractometer	12235 independent reflections
Radiation source: normal-focus sealed tube	9107 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.041
ω scans	θmax = 34.0°, θmin = 2.0°
Absorption correction: numerical (SHELXTL; Sheldrick, 1996)	h = −31→30
Tmin = 0.923, Tmax = 0.947	k = −16→16
71887 measured reflections	l = −31→32

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.051	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.130	w = 1/[σ^2(Fo^2) + (0.04P)^2 + 2P] where P = (Fo^2 + 2Fc^2)/3
S = 1.22	(Δ/σ)max = 0.001
12235 reflections	Δρmax = 0.41 e Å^−3
229 parameters	Δρmin = −0.34 e Å^−3
4 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.00056 (12)

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 F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² 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 (Ų)

	x	y	z	Uiso*/Ueq
Si1	0.28894 (4)	0.75857 (3)	0.61303 (3)	0.01686 (10)
O1	0.29256 (7)	0.62510 (10)	0.57150 (6)	0.0220 (2)
O2	0.28272 (7)	0.87597 (10)	0.55817 (6)	0.0243 (2)
C1	0.20773 (13)	0.75941 (12)	0.64191 (14)	0.0255 (4)
C2	0.15099 (14)	0.74981 (14)	0.57661 (15)	0.0411 (6)
H2A	0.1073	0.7493	0.5879	0.062*
H2B	0.1563	0.6707	0.5529	0.062*
H2C	0.1535	0.8233	0.5477	0.062*
C3	0.20292 (13)	0.6452 (2)	0.68682 (14)	0.0461 (5)
H3A	0.1577	0.6415	0.6946	0.069*
H3B	0.2362	0.6544	0.7299	0.069*
H3C	0.2118	0.5662	0.6647	0.069*
C4	0.19823 (12)	0.8838 (2)	0.67781 (14)	0.0435 (5)
H4A	0.1523	0.8876	0.6836	0.065*
H4B	0.2061	0.9569	0.6508	0.065*
H4C	0.2303	0.8865	0.7219	0.065*
C5	0.37161 (9)	0.77310 (14)	0.67750 (8)	0.0224 (3)
C6	0.42666 (8)	0.77918 (16)	0.63855 (9)	0.0315 (3)
H6A	0.4708	0.7866	0.6704	0.047*
H6B	0.4190	0.8537	0.6087	0.047*
H6C	0.4253	0.7012	0.6118	0.047*
C7	0.38473 (8)	0.65676 (14)	0.72479 (8)	0.0340 (3)
H7A	0.4298	0.6635	0.7550	0.051*
H7B	0.3817	0.5783	0.6981	0.051*
H7C	0.3511	0.6544	0.7514	0.051*
C8	0.37483 (8)	0.89540 (13)	0.71960 (8)	0.0308 (3)
H8A	0.4206	0.9067	0.7477	0.046*
H8B	0.3433	0.8884	0.7484	0.046*
H8C	0.3627	0.9691	0.6896	0.046*
Si2	0.36300 (3)	0.25476 (2)	0.53898 (4)	0.01686 (11)
O3	0.31860 (6)	0.12732 (10)	0.54759 (6)	0.0230 (2)
O4	0.31156 (6)	0.37871 (10)	0.52694 (6)	0.0240 (2)
C9	0.39095 (14)	0.23835 (13)	0.45899 (14)	0.0267 (4)
C10	0.32752 (12)	0.2239 (2)	0.40104 (12)	0.0391 (4)
H10A	0.3406	0.2139	0.3585	0.059*
H10B	0.2993	0.3002	0.3988	0.059*
H10C	0.3022	0.1484	0.4089	0.059*
C11	0.43529 (13)	0.1200 (2)	0.45887 (12)	0.0448 (5)
H11A	0.4421	0.1073	0.4137	0.067*
H11B	0.4131	0.0446	0.4719	0.067*
H11C	0.4789	0.1326	0.4909	0.067*
C12	0.42987 (13)	0.3567 (2)	0.44440 (12)	0.0404 (5)
H12A	0.4368	0.3503	0.3989	0.061*
H12B	0.4736	0.3609	0.4771	0.061*
H12C	0.4040	0.4341	0.4479	0.061*
C13	0.42720 (8)	0.27410 (14)	0.62140 (8)	0.0220 (3)
C14	0.38811 (8)	0.28635 (16)	0.67618 (8)	0.0305 (3)
H14A	0.4198	0.2998	0.7199	0.046*
H14B	0.3624	0.2079	0.6776	0.046*
H14C	0.3572	0.3592	0.6659	0.046*
C15	0.47417 (7)	0.15735 (14)	0.63764 (8)	0.0310 (3)
H15A	0.5041	0.1673	0.6826	0.046*
H15B	0.5011	0.1509	0.6043	0.046*
H15C	0.4472	0.0796	0.6363	0.046*
C16	0.46982 (8)	0.39531 (13)	0.62209 (8)	0.0323 (3)
H16A	0.4986	0.4085	0.6674	0.049*
H16B	0.4401	0.4692	0.6092	0.049*
H16C	0.4980	0.3854	0.5901	0.049*
H01	0.2684 (8)	0.6254 (19)	0.5330 (6)	0.050 (6)*
H02	0.3032 (8)	0.9433 (11)	0.5658 (9)	0.045 (5)*
H03	0.2788 (6)	0.132 (2)	0.5256 (11)	0.073 (8)*
H04	0.3165 (10)	0.4396 (14)	0.5533 (9)	0.057 (6)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Si1	0.0216 (3)	0.01234 (16)	0.0155 (3)	0.00028 (11)	0.00241 (18)	0.00015 (10)
O1	0.0305 (5)	0.0143 (4)	0.0183 (5)	0.0028 (3)	0.0007 (4)	−0.0022 (3)
O2	0.0346 (6)	0.0142 (4)	0.0205 (5)	−0.0051 (4)	−0.0001 (4)	0.0029 (3)
C1	0.0239 (10)	0.0267 (7)	0.0275 (10)	0.0010 (5)	0.0095 (7)	−0.0015 (5)
C2	0.0212 (9)	0.0600 (13)	0.0421 (14)	−0.0046 (5)	0.0076 (9)	−0.0045 (6)
C3	0.0521 (12)	0.0443 (10)	0.0508 (12)	−0.0017 (8)	0.0295 (9)	0.0129 (8)
C4	0.0404 (10)	0.0408 (9)	0.0541 (12)	0.0062 (7)	0.0206 (8)	−0.0132 (8)
C5	0.0265 (7)	0.0191 (4)	0.0195 (6)	−0.0008 (6)	0.0016 (5)	−0.0018 (6)
C6	0.0234 (7)	0.0353 (6)	0.0343 (8)	−0.0010 (6)	0.0044 (6)	−0.0031 (7)
C7	0.0421 (9)	0.0274 (7)	0.0257 (7)	0.0037 (6)	−0.0046 (6)	0.0052 (6)
C8	0.0360 (8)	0.0256 (6)	0.0273 (7)	−0.0040 (6)	0.0008 (6)	−0.0073 (5)
Si2	0.0172 (3)	0.01248 (17)	0.0202 (3)	0.00021 (9)	0.00327 (19)	0.00024 (9)
O3	0.0214 (5)	0.0157 (4)	0.0291 (6)	−0.0020 (3)	0.0009 (4)	0.0030 (4)
O4	0.0224 (5)	0.0153 (4)	0.0307 (6)	0.0031 (3)	−0.0003 (4)	−0.0033 (4)
C9	0.0293 (10)	0.0232 (6)	0.0296 (11)	0.0012 (5)	0.0108 (8)	0.0004 (5)
C10	0.0395 (12)	0.0527 (8)	0.0243 (9)	−0.0004 (9)	0.0064 (8)	−0.0084 (8)
C11	0.0525 (11)	0.0411 (9)	0.0471 (12)	0.0162 (8)	0.0245 (9)	−0.0036 (8)
C12	0.0468 (11)	0.0412 (9)	0.0388 (9)	−0.0094 (7)	0.0210 (8)	0.0042 (7)
C13	0.0199 (6)	0.0192 (4)	0.0244 (7)	−0.0014 (6)	0.0009 (5)	0.0005 (6)
C14	0.0339 (8)	0.0331 (7)	0.0233 (7)	−0.0022 (7)	0.0046 (6)	−0.0021 (6)
C15	0.0246 (7)	0.0275 (7)	0.0358 (8)	0.0035 (5)	−0.0021 (6)	0.0037 (6)
C16	0.0274 (7)	0.0263 (6)	0.0393 (8)	−0.0087 (5)	0.0003 (6)	−0.0027 (6)

Geometric parameters (Å, º)

Si1—O1	1.6467 (12)	Si2—O3	1.6483 (12)
Si1—O2	1.6492 (12)	Si2—O4	1.6516 (12)
Si1—C5	1.8833 (18)	Si2—C9	1.875 (3)
Si1—C1	1.901 (3)	Si2—C13	1.8817 (17)
O1—H01	0.824 (9)	O3—H03	0.832 (9)
O2—H02	0.816 (9)	O4—H04	0.825 (9)
C1—C3	1.527 (3)	C9—C11	1.537 (3)
C1—C4	1.531 (3)	C9—C10	1.539 (4)
C1—C2	1.547 (4)	C9—C12	1.542 (3)
C2—H2A	0.9800	C10—H10A	0.9800
C2—H2B	0.9800	C10—H10B	0.9800
C2—H2C	0.9800	C10—H10C	0.9800
C3—H3A	0.9800	C11—H11A	0.9800
C3—H3B	0.9800	C11—H11B	0.9800
C3—H3C	0.9800	C11—H11C	0.9800
C4—H4A	0.9800	C12—H12A	0.9800
C4—H4B	0.9800	C12—H12B	0.9800
C4—H4C	0.9800	C12—H12C	0.9800
C5—C8	1.536 (2)	C13—C16	1.538 (2)
C5—C6	1.537 (2)	C13—C14	1.538 (2)
C5—C7	1.538 (2)	C13—C15	1.540 (2)
C6—H6A	0.9800	C14—H14A	0.9800
C6—H6B	0.9800	C14—H14B	0.9800
C6—H6C	0.9800	C14—H14C	0.9800
C7—H7A	0.9800	C15—H15A	0.9800
C7—H7B	0.9800	C15—H15B	0.9800
C7—H7C	0.9800	C15—H15C	0.9800
C8—H8A	0.9800	C16—H16A	0.9800
C8—H8B	0.9800	C16—H16B	0.9800
C8—H8C	0.9800	C16—H16C	0.9800
O1—Si1—O2	106.49 (8)	O3—Si2—O4	107.53 (8)
O1—Si1—C5	106.53 (7)	O3—Si2—C9	108.40 (7)
O2—Si1—C5	108.94 (7)	O4—Si2—C9	105.22 (8)
O1—Si1—C1	108.64 (7)	O3—Si2—C13	105.89 (7)
O2—Si1—C1	106.41 (8)	O4—Si2—C13	109.30 (7)
C5—Si1—C1	119.20 (11)	C9—Si2—C13	119.97 (11)
Si1—O1—H01	113.6 (14)	Si2—O3—H03	113.2 (17)
Si1—O2—H02	124.2 (13)	Si2—O4—H04	122.5 (14)
C3—C1—C4	109.9 (2)	C11—C9—C10	107.95 (18)
C3—C1—C2	108.99 (18)	C11—C9—C12	108.1 (2)
C4—C1—C2	108.31 (18)	C10—C9—C12	108.0 (2)
C3—C1—Si1	112.09 (15)	C11—C9—Si2	112.56 (15)
C4—C1—Si1	112.27 (14)	C10—C9—Si2	107.63 (19)
C2—C1—Si1	105.1 (2)	C12—C9—Si2	112.39 (14)
C1—C2—H2A	109.5	C9—C10—H10A	109.5
C1—C2—H2B	109.5	C9—C10—H10B	109.5
H2A—C2—H2B	109.5	H10A—C10—H10B	109.5
C1—C2—H2C	109.5	C9—C10—H10C	109.5
H2A—C2—H2C	109.5	H10A—C10—H10C	109.5
H2B—C2—H2C	109.5	H10B—C10—H10C	109.5
C1—C3—H3A	109.5	C9—C11—H11A	109.5
C1—C3—H3B	109.5	C9—C11—H11B	109.5
H3A—C3—H3B	109.5	H11A—C11—H11B	109.5
C1—C3—H3C	109.5	C9—C11—H11C	109.5
H3A—C3—H3C	109.5	H11A—C11—H11C	109.5
H3B—C3—H3C	109.5	H11B—C11—H11C	109.5
C1—C4—H4A	109.5	C9—C12—H12A	109.5
C1—C4—H4B	109.5	C9—C12—H12B	109.5
H4A—C4—H4B	109.5	H12A—C12—H12B	109.5
C1—C4—H4C	109.5	C9—C12—H12C	109.5
H4A—C4—H4C	109.5	H12A—C12—H12C	109.5
H4B—C4—H4C	109.5	H12B—C12—H12C	109.5
C8—C5—C6	108.81 (13)	C16—C13—C14	108.77 (13)
C8—C5—C7	109.11 (13)	C16—C13—C15	109.11 (13)
C6—C5—C7	108.89 (14)	C14—C13—C15	108.59 (13)
C8—C5—Si1	111.66 (11)	C16—C13—Si2	111.57 (11)
C6—C5—Si1	106.75 (11)	C14—C13—Si2	106.86 (11)
C7—C5—Si1	111.53 (11)	C15—C13—Si2	111.82 (10)
C5—C6—H6A	109.5	C13—C14—H14A	109.5
C5—C6—H6B	109.5	C13—C14—H14B	109.5
H6A—C6—H6B	109.5	H14A—C14—H14B	109.5
C5—C6—H6C	109.5	C13—C14—H14C	109.5
H6A—C6—H6C	109.5	H14A—C14—H14C	109.5
H6B—C6—H6C	109.5	H14B—C14—H14C	109.5
C5—C7—H7A	109.5	C13—C15—H15A	109.5
C5—C7—H7B	109.5	C13—C15—H15B	109.5
H7A—C7—H7B	109.5	H15A—C15—H15B	109.5
C5—C7—H7C	109.5	C13—C15—H15C	109.5
H7A—C7—H7C	109.5	H15A—C15—H15C	109.5
H7B—C7—H7C	109.5	H15B—C15—H15C	109.5
C5—C8—H8A	109.5	C13—C16—H16A	109.5
C5—C8—H8B	109.5	C13—C16—H16B	109.5
H8A—C8—H8B	109.5	H16A—C16—H16B	109.5
C5—C8—H8C	109.5	C13—C16—H16C	109.5
H8A—C8—H8C	109.5	H16A—C16—H16C	109.5
H8B—C8—H8C	109.5	H16B—C16—H16C	109.5
O1—Si1—C1—C3	58.9 (2)	O3—Si2—C9—C11	−60.6 (2)
O2—Si1—C1—C3	173.20 (17)	O4—Si2—C9—C11	−175.45 (17)
C5—Si1—C1—C3	−63.28 (18)	C13—Si2—C9—C11	61.02 (19)
O1—Si1—C1—C4	−176.87 (17)	O3—Si2—C9—C10	58.20 (13)
O2—Si1—C1—C4	−62.6 (2)	O4—Si2—C9—C10	−56.61 (13)
C5—Si1—C1—C4	61.0 (2)	C13—Si2—C9—C10	179.86 (11)
O1—Si1—C1—C2	−59.35 (11)	O3—Si2—C9—C12	176.95 (17)
O2—Si1—C1—C2	54.96 (10)	O4—Si2—C9—C12	62.1 (2)
C5—Si1—C1—C2	178.48 (9)	C13—Si2—C9—C12	−61.38 (19)
O1—Si1—C5—C8	179.57 (10)	O3—Si2—C13—C16	−176.51 (10)
O2—Si1—C5—C8	65.06 (13)	O4—Si2—C13—C16	−60.94 (13)
C1—Si1—C5—C8	−57.21 (13)	C9—Si2—C13—C16	60.60 (13)
O1—Si1—C5—C6	60.77 (12)	O3—Si2—C13—C14	−57.73 (12)
O2—Si1—C5—C6	−53.75 (12)	O4—Si2—C13—C14	57.84 (12)
C1—Si1—C5—C6	−176.01 (10)	C9—Si2—C13—C14	179.38 (10)
O1—Si1—C5—C7	−58.05 (13)	O3—Si2—C13—C15	60.97 (13)
O2—Si1—C5—C7	−172.57 (11)	O4—Si2—C13—C15	176.54 (10)
C1—Si1—C5—C7	65.16 (13)	C9—Si2—C13—C15	−61.92 (13)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H01···O2^i	0.82 (1)	1.91 (1)	2.7284 (18)	176 (2)
O2—H02···O3^ii	0.82 (1)	2.00 (1)	2.7530 (16)	153 (2)
O3—H03···O4^iii	0.83 (2)	1.91 (2)	2.7324 (18)	173 (2)
O4—H04···O1	0.83 (2)	2.06 (2)	2.7937 (16)	148 (2)

Symmetry codes: (i) −x+1/2, −y+3/2, −z+1; (ii) x, y+1, z; (iii) −x+1/2, −y+1/2, −z+1.