5,7-syn-Bis(trimethyl­silyl)-5-nor­bornene-2,3-endo-dicarboxylic acid: a rare co-existence of dimeric and catemeric synthons

The crystal and mol­ecular structure of the title compound, C₁₅H₂₆O₄Si₂, reveals a self-assembly facilitated via the rare co-existence of dimeric and catemeric patterns, which is attributed to the influence of the trimethyl­silyl groups. The structure is dicussed in the context of a database search and subsequent analysis of structures of cis-1,2-dicarboxylic acids.

S1. Comment

Carboxylic acid groups have been shown to self-assemble via dimeric and catemeric arrangements (Duchamp & Marsh, 1969; Leiserowitz, 1976; Ermer, 1988; Holy et al., 1999). The latter may be formed in different ways (see scheme) (Duchamp & Marsh, 1969; Das & Desiraju, 2006). An analysis of entries in the Cambridge Structural Database (CSD, Version?; Allen, 2002) reveals that the centrosymmetric dimer pattern is found in more than 90% and the catemeric pattern in less than 5% of the structures analysed (Das & Desiraju, 2006; Kolotuchin et al., 1995)

In recent investigations on cyclic cis-1,2-dicarboxylic acids, we observed that a hydrophobic moiety such as the trimethylsilyl (TMS) group at position 7 in syn-7-trimethylsilyl-5-norbornene-endo-2,3-dicarboxylic acid, (I), induces helicity (Begum et al., 2004). This and the novel self-assembly observed in the analogous cyclic cis-1,2-diols (Begum et al., 2005) led us to explore the consequences of introducing an additional TMS group, which led to the present work on the title compound, (II). Here, we report the co-existence of dimeric and catemeric assemblies in the crystal structure of (II). From the structure of (II), in conjunction with analyses of the structures of cis-1,2-dicarboxylic acids reported in the CSD, it appears that both steric factors and the hydrophobic nature of the TMS group are responsible for the rare occurrence of the catemeric pattern together with the centrosymmetric dimer motif.

The geometry of the two carboxyl groups in (II) is found to be syn (Fig. 1). The vicinal dicarboxylic acids are anti with respect to each other, i.e. the two carbonyl O atoms and the hydroxyl groups are oriented in opposite directions. Furthermore, the two carboxyl groups are not parallel, forming a dihedral angle of 58.2 (1)°. This presumably minimizes dipolar repulsions. Apart from this, there are no exceptional geometric features.

The crystal packing (Fig. 2) includes two modes of self-assembly for the carboxyl groups. The first is a centrosymmetric head-to-head dimer motif formed between the carboxylic acid group at C14 (O4—H17···O3ⁱ) and the equivalent group in the molecule at (1 - x, -y, 2 - z). The second is formed by molecules related by the 2₁ screw axis and hydrogen bonded in a syn-catemeric fashion, as shown schematically in the scheme. The chain is propagated by the 2₁ axis, with the molecule at (x, y, z) donating an O2—H16···O1ⁱⁱ hydrogen bond to its neighbour at (1 - x, 1/2 + y, 3/2 - z). The base molecule (x, y, z) accepts an equivalent hydrogen bond from its 2₁-related neighbour at (1 - x, -1/2 + y, 3/2 - z).

Given the rarity of the concurrence of the two aggregation patterns observed for (II), a search of the CSD was conducted to shed light on other factors that might play an important role. We retrieved 353 structures for 1,2-dicarboxylic acids. A total of 21 hits were distilled from the initial set for 1,2-cis-dicarboxylic acids, with subsequent elimination of cases for which the two carboxylic acids are geometrically anti, as well as those cases for which there is potential interference by interactions due to other functional groups present in the molecules. In Table 2 are shown the most relevant cases and the pattern of association observed for each; Fig. 3 defines each compound. As can be seen, the predominant pattern observed for 1,2-dicarboxylic acids, with the exception of 3,3-dimethylcyclopropane-1,2-dicarboxylic acid, is dimeric; to the best of our knowledge, the latter is the only example in addition to the diacid (II) of the present study in which the co-existence of both dimeric and catemeric motifs has been found.

In (II), the O—H···O hydrogen-bonded catemeric assembly is supported by weak C—H···O hydrogen bonds (Fig. 4), in this case involving atom C3 and the C15 carboxyl O atom, C3—H3···O1ⁱⁱⁱ [symmetry code: (iii) 1-x, -1/2+y, 3/2-z]. It has been proposed that the catemeric motif arises due to auxiliary/supporting weak interactions such as C—H···O hydrogen bonds (Duchamp & Marsh, 1969; Das & Desiraju, 2006; Kuduva et al., 1999). Evidently, an increase in hydrophobicity through further TMS substitution in (II) compared with diacid (I) (Begum et al., 2004), as well as weak C—H···O hydrogen bonds, lead to the appearance of a catemeric motif in diacid (II), a motif not present in (I) nor in the other simple cis-norbornene-1,2-carboxylic acids (Table 2). That the hydrophobic factor itself does appear to play a role in the generation of the catemeric motif can be clearly inferred from the comparison of the crystal packings of cis-cyclopropane-1,2- dicarboxylic acid (CSD refcode FOJRAX) and its 3,3-dimethyl analogue (KOJZEO; Table 2). While the dimeric motif is common to both carboxylic acids, it is the dimethyl substitution in cis-cyclopropane-1,2-dicarboxylic acid that causes the co-existence of two patterns. The tendency for increased hydrophobic aggregation in the crystal structures appears to have a decisive effect in the overall crystal packing, leading to the observation of the co-existence of the two patterns in (II).

The co-existence of dimeric and catemeric motifs observed for the title compound, for which we found just one precedent in the CSD, thus appears to be directed by the hydrophobic aggregation of the TMS groups. Though not uncommon, this aggregation influences the usual dimeric motif in favour of the further formation of the chain. This is another instance of how weak interactions may potentially influence the molecular association based on strongly directional supramolecular synthons/motifs.

S2. Experimental

To a suspension of small pieces (1 mm) of sodium (6.1 g, 0.265 mol) in dry tetrahydrofuran (100 ml) in a 500 ml three-necked round-bottomed flask fitted with a mechanical stirrer, a dropping funnel and a condenser, under a nitrogen atmosphere, was added freshly distilled 1,3-cyclopentadiene (16.5 g, 0.25 mol) over a period of 45 min. The dark-red reaction mixture was stirred for 2 h at room temperature. Then chlorotrimethylsilane (27.25 g, 0.25 mol) was added dropwise over a period of 1 h, during which the mixture became warm and changed colour from dark-red to blue to white with copious precipitation of NaCl. The stirring was continued for 3 h more, and then the mixture was filtered through glass wool and the precipitate was washed with tetrahydrofuran (2 × 10 ml). The combined filtrates were cooled in an ice–water bath and carefully treated with water (75 ml). The layers were then separated. The aqueous layer was washed with ether (3 × 50 ml), and the organic layers were combined, washed with water (3 × 75 ml), dried (Na₂SO₄) and concentrated. The residue was distilled under vacuum on a spinning band column. The fraction collected at 341–344 K and 20 Torr (1 Torr = 133.322 Pa) was 99.9% pure (by gas chromatography) 2,5-bistrimethylsilylcyclopentadiene.

To finely powdered maleic anhydride (2.44 g, 0.025 mol) in a 25 ml conical flask was added 2,5-bistrimethylsilylcyclopentadiene (5.16 g, 0.025 mol) dropwise over a period of 15 min with shaking and occasional cooling in water. The mixture was allowed to stand for 3 h and then stirred with CH₂Cl₂ (20 ml). The solution was filtered, and the filtrate was concentrated to obtain 2,7-anti-bistrimethylsilylbicyclo[2.2.1]hept-2-ene-5,6-endo-dicarboxylic acid anhydride (m.p. 360–361 K). A portion of this (1.0 g) was stirred in water (10 ml) for 3 h and then filtered, and the title dicarboxylic acid was recrystallized from chloroform (m.p. 399 K).

S3. Refinement

Methyl H atoms were treated using a riding model, with C—H = 0.93–0.97 Å and U_iso(H) = 1.2U_eq(C). The remaining H atoms were refined freely. [Please give ranges of refined C—H and O—H distances. Values in CIF do not match those in the hydrogen-bond table - please check]

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SAINT-Plus (Bruker, 1998); data reduction: SAINT-Plus (Bruker, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

Fig. 1. The molecular structure of (II), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. Fig. 2. The two modes of self-assembly in (II), showing both dimeric and catemeric motifs. Fig. 3. The structures of the compounds in Table 2. Fig. 4. The catemeric associations of the diacid (II). Note that auxiliary C—H···O hydrogen bonds compliment the strongly directional O—H···O hydrogen bonds.

5,syn-7-Bis(trimethylsilyl)-5-norbornene-endo-2,3-dicarboxylic acid

Crystal data

C15H26O4Si2	F(000) = 704
Mr = 326.54	Dx = 1.143 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 16.9370 (4) Å	Cell parameters from 21556 reflections
b = 6.8184 (16) Å	θ = 1.2–25.0°
c = 16.5770 (4) Å	µ = 0.20 mm^−1
β = 97.667 (4)°	T = 293 K
V = 1897.3 (4) Å^3	Rectangular, white
Z = 4	0.3 × 0.2 × 0.15 mm

Data collection

Bruker SMART CCD area-detector diffractometer	2641 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.034
Graphite monochromator	θmax = 25°, θmin = 1.2°
ϕ and ω scans	h = −20→20
17324 measured reflections	k = −8→8
3338 independent reflections	l = −19→19

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F^2 > 2σ(F^2)] = 0.068	w = 1/[σ^2(Fo^2) + (0.1196P)^2 + 0.2522P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.182	(Δ/σ)max = 0.001
S = 1.12	Δρmax = 1.16 e Å^−3
3338 reflections	Δρmin = −0.33 e Å^−3
228 parameters

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.72385 (15)	0.0546 (4)	0.80717 (16)	0.0412 (6)
C2	0.63487 (14)	−0.0112 (4)	0.79371 (15)	0.0389 (6)
C3	0.62864 (14)	−0.1429 (4)	0.86913 (16)	0.0383 (6)
C4	0.71722 (14)	−0.1380 (4)	0.91435 (16)	0.0379 (6)
C5	0.73298 (13)	0.0689 (4)	0.94826 (15)	0.0370 (6)
C6	0.73620 (14)	0.1802 (4)	0.88270 (16)	0.0387 (6)
C7	0.76375 (15)	−0.1372 (4)	0.84053 (17)	0.0429 (6)
C8	0.9253 (2)	0.0922 (6)	0.8759 (3)	0.0956 (14)
H8A	0.9811	0.0792	0.8717	0.143*
H8B	0.9188	0.1396	0.9292	0.143*
H8C	0.9016	0.1832	0.8356	0.143*
C9	0.9061 (2)	−0.3098 (8)	0.9487 (4)	0.1113 (18)
H9A	0.9628	−0.328	0.9557	0.167*
H9B	0.8802	−0.4348	0.94	0.167*
H9C	0.8907	−0.2498	0.9966	0.167*
C10	0.9091 (3)	−0.2585 (11)	0.7670 (4)	0.147 (3)
H10A	0.8881	−0.1832	0.7201	0.221*
H10B	0.8901	−0.391	0.7608	0.221*
H10C	0.9663	−0.2581	0.7723	0.221*
C11	0.6803 (3)	0.3816 (5)	1.0615 (2)	0.0896 (14)
H11A	0.6244	0.352	1.0537	0.134*
H11B	0.6922	0.4698	1.0196	0.134*
H11C	0.6944	0.442	1.1137	0.134*
C12	0.7000 (3)	−0.0400 (6)	1.1200 (2)	0.0772 (11)
H12A	0.7252	−0.1628	1.1111	0.116*
H12B	0.6434	−0.0526	1.1055	0.116*
H12C	0.7115	−0.0042	1.1764	0.116*
C13	0.8441 (3)	0.1998 (8)	1.0969 (3)	0.0976 (14)
H13A	0.8474	0.2485	1.1516	0.146*
H13B	0.8656	0.2955	1.0634	0.146*
H13C	0.8739	0.0802	1.0967	0.146*
C14	0.57027 (14)	−0.0795 (4)	0.92443 (16)	0.0409 (6)
C15	0.57271 (15)	0.1469 (4)	0.77608 (16)	0.0416 (6)
O1	0.50192 (11)	0.1119 (3)	0.75801 (15)	0.0628 (6)
O2	0.60012 (12)	0.3253 (3)	0.77698 (14)	0.0547 (6)
O3	0.55174 (13)	0.0884 (3)	0.93425 (14)	0.0594 (6)
O4	0.54348 (14)	−0.2273 (3)	0.96336 (16)	0.0671 (7)
Si2	0.73810 (5)	0.15205 (11)	1.05643 (4)	0.0469 (3)
Si1	0.87633 (5)	−0.14913 (13)	0.85926 (6)	0.0574 (3)
H1	0.7404 (16)	0.108 (4)	0.7624 (18)	0.040 (7)*
H2	0.6279 (16)	−0.092 (4)	0.7481 (17)	0.040 (7)*
H3	0.6186 (15)	−0.276 (4)	0.8527 (16)	0.037 (7)*
H4	0.7257 (15)	−0.235 (4)	0.9500 (16)	0.035 (7)*
H6	0.7401 (15)	0.320 (4)	0.8796 (15)	0.029 (6)*
H7	0.7468 (16)	−0.263 (4)	0.8064 (17)	0.047 (7)*
H16	0.555 (2)	0.409 (5)	0.762 (2)	0.077 (11)*
H17	0.518 (2)	−0.177 (6)	1.002 (3)	0.084 (12)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0324 (13)	0.0563 (16)	0.0363 (14)	0.0005 (11)	0.0098 (11)	0.0027 (12)
C2	0.0331 (13)	0.0479 (14)	0.0353 (13)	0.0009 (11)	0.0030 (10)	−0.0033 (11)
C3	0.0304 (13)	0.0407 (14)	0.0443 (14)	0.0000 (10)	0.0063 (11)	−0.0018 (11)
C4	0.0315 (13)	0.0445 (14)	0.0375 (13)	0.0031 (10)	0.0042 (10)	0.0039 (11)
C5	0.0284 (12)	0.0461 (14)	0.0365 (13)	0.0023 (10)	0.0043 (10)	−0.0011 (11)
C6	0.0298 (12)	0.0459 (15)	0.0410 (14)	−0.0026 (10)	0.0073 (10)	0.0017 (11)
C7	0.0314 (13)	0.0552 (16)	0.0432 (14)	0.0047 (11)	0.0093 (11)	−0.0061 (12)
C8	0.0441 (19)	0.097 (3)	0.149 (4)	−0.011 (2)	0.027 (2)	−0.009 (3)
C9	0.060 (2)	0.121 (4)	0.145 (5)	0.016 (2)	−0.015 (3)	0.042 (3)
C10	0.064 (3)	0.238 (7)	0.147 (5)	0.016 (4)	0.041 (3)	−0.098 (5)
C11	0.142 (4)	0.067 (2)	0.058 (2)	0.027 (2)	0.004 (2)	−0.0113 (17)
C12	0.112 (3)	0.076 (2)	0.0462 (18)	−0.008 (2)	0.0218 (19)	0.0049 (16)
C13	0.073 (3)	0.148 (4)	0.067 (2)	−0.020 (3)	−0.007 (2)	−0.022 (3)
C14	0.0279 (12)	0.0488 (15)	0.0463 (14)	−0.0017 (11)	0.0066 (10)	0.0037 (12)
C15	0.0347 (14)	0.0493 (15)	0.0393 (14)	0.0004 (11)	−0.0004 (11)	−0.0009 (11)
O1	0.0358 (11)	0.0525 (12)	0.0940 (17)	−0.0016 (9)	−0.0140 (11)	0.0020 (11)
O2	0.0363 (10)	0.0500 (12)	0.0761 (15)	−0.0028 (9)	0.0009 (10)	0.0106 (10)
O3	0.0598 (13)	0.0510 (12)	0.0756 (14)	0.0055 (10)	0.0397 (11)	0.0070 (10)
O4	0.0713 (15)	0.0539 (12)	0.0864 (17)	0.0045 (11)	0.0489 (13)	0.0119 (12)
Si2	0.0529 (5)	0.0525 (5)	0.0346 (4)	−0.0002 (3)	0.0037 (3)	−0.0027 (3)
Si1	0.0308 (4)	0.0722 (6)	0.0699 (6)	0.0082 (3)	0.0092 (4)	−0.0104 (4)

Geometric parameters (Å, º)

C1—C6	1.508 (4)	C9—H9B	0.96
C1—C7	1.541 (4)	C9—H9C	0.96
C1—C2	1.560 (3)	C10—Si1	1.852 (5)
C1—H1	0.90 (3)	C10—H10A	0.96
C2—C15	1.508 (4)	C10—H10B	0.96
C2—C3	1.554 (4)	C10—H10C	0.96
C2—H2	0.93 (3)	C11—Si2	1.854 (4)
C3—C14	1.499 (4)	C11—H11A	0.96
C3—C4	1.586 (3)	C11—H11B	0.96
C3—H3	0.95 (3)	C11—H11C	0.96
C4—C5	1.529 (4)	C12—Si2	1.851 (3)
C4—C7	1.541 (4)	C12—H12A	0.96
C4—H4	0.89 (3)	C12—H12B	0.96
C5—C6	1.333 (4)	C12—H12C	0.96
C5—Si2	1.872 (3)	C13—Si2	1.859 (4)
C6—H6	0.96 (3)	C13—H13A	0.96
C7—Si1	1.892 (3)	C13—H13B	0.96
C7—H7	1.04 (3)	C13—H13C	0.96
C8—Si1	1.847 (4)	C14—O3	1.203 (3)
C8—H8A	0.96	C14—O4	1.310 (3)
C8—H8B	0.96	C15—O1	1.220 (3)
C8—H8C	0.96	C15—O2	1.301 (3)
C9—Si1	1.859 (5)	O2—H16	0.96 (4)
C9—H9A	0.96	O4—H17	0.89 (4)
C6—C1—C7	100.3 (2)	H9A—C9—H9C	109.5
C6—C1—C2	107.9 (2)	H9B—C9—H9C	109.5
C7—C1—C2	100.1 (2)	Si1—C10—H10A	109.5
C6—C1—H1	115.5 (17)	Si1—C10—H10B	109.5
C7—C1—H1	117.8 (17)	H10A—C10—H10B	109.5
C2—C1—H1	113.4 (17)	Si1—C10—H10C	109.5
C15—C2—C3	116.6 (2)	H10A—C10—H10C	109.5
C15—C2—C1	117.3 (2)	H10B—C10—H10C	109.5
C3—C2—C1	102.67 (19)	Si2—C11—H11A	109.5
C15—C2—H2	104.8 (16)	Si2—C11—H11B	109.5
C3—C2—H2	107.2 (17)	H11A—C11—H11B	109.5
C1—C2—H2	107.6 (17)	Si2—C11—H11C	109.5
C14—C3—C2	116.5 (2)	H11A—C11—H11C	109.5
C14—C3—C4	111.4 (2)	H11B—C11—H11C	109.5
C2—C3—C4	101.92 (19)	Si2—C12—H12A	109.5
C14—C3—H3	110.0 (16)	Si2—C12—H12B	109.5
C2—C3—H3	110.3 (16)	H12A—C12—H12B	109.5
C4—C3—H3	106.0 (15)	Si2—C12—H12C	109.5
C5—C4—C7	101.9 (2)	H12A—C12—H12C	109.5
C5—C4—C3	107.5 (2)	H12B—C12—H12C	109.5
C7—C4—C3	100.2 (2)	Si2—C13—H13A	109.5
C5—C4—H4	116.2 (17)	Si2—C13—H13B	109.5
C7—C4—H4	118.4 (17)	H13A—C13—H13B	109.5
C3—C4—H4	111.0 (16)	Si2—C13—H13C	109.5
C6—C5—C4	104.5 (2)	H13A—C13—H13C	109.5
C6—C5—Si2	127.4 (2)	H13B—C13—H13C	109.5
C4—C5—Si2	127.97 (18)	O3—C14—O4	123.5 (3)
C5—C6—C1	109.7 (2)	O3—C14—C3	124.2 (2)
C5—C6—H6	128.5 (15)	O4—C14—C3	112.3 (2)
C1—C6—H6	121.5 (15)	O1—C15—O2	121.5 (2)
C1—C7—C4	92.40 (19)	O1—C15—C2	123.1 (2)
C1—C7—Si1	118.64 (19)	O2—C15—C2	115.3 (2)
C4—C7—Si1	118.70 (19)	C15—O2—H16	106 (2)
C1—C7—H7	115.1 (15)	C14—O4—H17	107 (3)
C4—C7—H7	107.2 (16)	C12—Si2—C11	110.2 (2)
Si1—C7—H7	104.6 (15)	C12—Si2—C13	108.2 (2)
Si1—C8—H8A	109.5	C11—Si2—C13	109.0 (2)
Si1—C8—H8B	109.5	C12—Si2—C5	110.88 (14)
H8A—C8—H8B	109.5	C11—Si2—C5	109.99 (15)
Si1—C8—H8C	109.5	C13—Si2—C5	108.56 (16)
H8A—C8—H8C	109.5	C8—Si1—C10	107.7 (3)
H8B—C8—H8C	109.5	C8—Si1—C9	109.7 (2)
Si1—C9—H9A	109.5	C10—Si1—C9	110.0 (3)
Si1—C9—H9B	109.5	C8—Si1—C7	114.15 (16)
H9A—C9—H9B	109.5	C10—Si1—C7	106.78 (18)
Si1—C9—H9C	109.5	C9—Si1—C7	108.46 (17)
C6—C1—C2—C15	64.1 (3)	C5—C4—C7—C1	−51.1 (2)
C7—C1—C2—C15	168.5 (2)	C3—C4—C7—C1	59.4 (2)
C6—C1—C2—C3	−65.2 (3)	C5—C4—C7—Si1	73.6 (2)
C7—C1—C2—C3	39.2 (2)	C3—C4—C7—Si1	−175.90 (17)
C15—C2—C3—C14	−9.8 (3)	C2—C3—C14—O3	−29.4 (4)
C1—C2—C3—C14	119.9 (2)	C4—C3—C14—O3	86.9 (3)
C15—C2—C3—C4	−131.2 (2)	C2—C3—C14—O4	152.8 (2)
C1—C2—C3—C4	−1.6 (2)	C4—C3—C14—O4	−90.9 (3)
C14—C3—C4—C5	−55.4 (3)	C3—C2—C15—O1	−63.9 (4)
C2—C3—C4—C5	69.5 (2)	C1—C2—C15—O1	173.8 (3)
C14—C3—C4—C7	−161.5 (2)	C3—C2—C15—O2	119.8 (3)
C2—C3—C4—C7	−36.5 (2)	C1—C2—C15—O2	−2.5 (3)
C7—C4—C5—C6	34.4 (2)	C6—C5—Si2—C12	162.1 (2)
C3—C4—C5—C6	−70.4 (2)	C4—C5—Si2—C12	−12.3 (3)
C7—C4—C5—Si2	−150.22 (19)	C6—C5—Si2—C11	40.0 (3)
C3—C4—C5—Si2	105.0 (2)	C4—C5—Si2—C11	−134.4 (3)
C4—C5—C6—C1	−0.4 (3)	C6—C5—Si2—C13	−79.2 (3)
Si2—C5—C6—C1	−175.86 (17)	C4—C5—Si2—C13	106.4 (3)
C7—C1—C6—C5	−33.5 (3)	C1—C7—Si1—C8	23.9 (3)
C2—C1—C6—C5	70.8 (3)	C4—C7—Si1—C8	−86.8 (3)
C6—C1—C7—C4	49.7 (2)	C1—C7—Si1—C10	−95.0 (3)
C2—C1—C7—C4	−60.7 (2)	C4—C7—Si1—C10	154.3 (3)
C6—C1—C7—Si1	−75.1 (2)	C1—C7—Si1—C9	146.5 (3)
C2—C1—C7—Si1	174.51 (18)	C4—C7—Si1—C9	35.9 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O4—H17···O3^i	0.88 (4)	1.79 (4)	2.666 (4)	167 (4)
O2—H16···O1^ii	0.95 (3)	1.69 (3)	2.622 (3)	161 (3)
C3—H3···O1^iii	0.95 (2)	2.66 (2)	3.299 (3)	124 (2)

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