organic compounds
1,1,3,3-Tetra-tert-butyl-2,2-diisopropyl-4,4-diphenylcyclotetrasilane
aDepartment of Chemistry and Chemical Biology, Graduate School of Engineering, Gunma University, Kiryu, Gunma 376-8515, Japan
*Correspondence e-mail: kyushin@gunma-u.ac.jp
The molecule in the structure of the title compound, C34H60Si4, lies on a twofold rotation axis that passes through the two Si atoms, resulting in a planar cyclotetrasilane ring. The dihedral angle between the cyclotetrasilane ring and the phenyl ring is 68.20 (5)°. The Si—Si bonds [2.4404 (8) and 2.4576 (8) Å] are longer than a standard Si—Si bond (2.34 Å) and the C—Si—C bond angle [97.07 (14)°] of the phenyl-substituted Si atom is smaller than the tetrahedral bond angle (109.5°). These long bonds and small bond angle are favorable for reducing the among the bulky substituents.
Related literature
For background to and applications of phenyl-substituted oligosilanes, see: Hinch & Krc (1957); Matsumoto & Tanaka (2008). For a related structure of a cyclotetrasilane without phenyl groups, see: Kyushin et al. (1995).
Experimental
Crystal data
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Data collection: CrystalClear (Rigaku, 2003); cell CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SIR2004 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 2012); software used to prepare material for publication: SHELXL97 and Yadokari-XG 2009 (Kabuto et al., 2009).
Supporting information
https://doi.org/10.1107/S160053681205074X/is5224sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S160053681205074X/is5224Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S160053681205074X/is5224Isup3.cml
A mixture of 1,3-dibromo-1,1,3,3-tetra-tert-butyl-2,2-diphenyltrisilane (5.00 g, 7.98 mmol), dichlorodiisopropylsilane (2.24 g, 12.1 mmol) and lithium (0.28 g, 40 mmol) in THF (50 ml) was stirred at room temperature for 1 day. The solvent was removed under reduced pressure. The residue was dissolved in hexane and passed through a short column of silica gel. After the silica gel was washed with hexane, the
was changed to diethyl ether. The diethyl ether was evaporated. Recrystallization of the residue from methanol–THF (ca 1:1) gave 1 (0.956 g, 21%) as colorless crystals. Single crystals were obtained from methanol–THF (ca 1:1) by slow evaporation.M.p.: 210–211 °C. 1H NMR (400 MHz, CDCl3): δ 1.21 (s, 36H), 1.46 (d, 12H, J = 7.4 Hz), 1.94 (sept, 2H, J = 7.4 Hz), 7.14–7.18 (m, 6H), 7.68–7.70 (m, 4H). 13C NMR (76 MHz, CDCl3): δ 17.5, 24.7, 25.4, 32.8, 127.1, 127.4, 138.6, 142.1. 29Si NMR (119 MHz, CDCl3): δ -6.2, 14.0, 20.4. IR (KBr): 3050, 2950, 2920, 2850, 1470, 1420, 1390, 1360, 810, 730, 700 cm-1. MS (EI, 70 eV): m/z 580 (M+, 17), 360 (100).
All hydrogen atoms were generated at calculated positions and refined as riding atoms, with C—H = 0.95 (phenyl), 0.98 (methyl) or 1.00 (methine) Å, and with Uiso(H) = 1.2Ueq(phenyl C), 1.5Ueq(methyl C) or 1.2Ueq(methine C).
Birefringent materials have a wide range of optical applications. Single crystals of calcium carbonate and barium borate have been well known as inorganic birefringent materials. Organic single crystals such as urea have also been known to show birefringence. Since birefringence is related to crystal structures, studies on molecular structures and packing in a crystal are important. In 1957, birefringence of tetrakis(4-phenylphenyl)silane was reported (Hinch & Krc, 1957). Recently, birefringence of single crystals of phenyl-substituted linear oligosilanes and their application to polarizers have been reported (Matsumoto & Tanaka, 2008). From these results, crystals of phenyl-substituted silicon compounds seem interesting as potential optical materials. We report herein the synthesis and X-ray crystal analysis of a phenyl-substituted cyclotetrasilane.
The coupling of 1,3-dibromo-1,1,3,3-tetra-tert-butyl-2,2-diphenyltrisilane and dichlorodiisopropylsilane with lithium in tetrahydrofuran (THF) gave 1,1,3,3-tetra-tert-butyl-2,2-diisopropyl-4,4-diphenylcyclotetrasilane (1) in 21% yield (Fig. 1). The molecular structure of 1 is shown in Fig. 2. Compound 1 has the crystallographic C2 symmetry, and therefore the cyclotetrasilane ring has a completely planar structure. The silicon–silicon bonds [2.4404 (8) and 2.4576 (8) Å] are longer than the standard silicon–silicon bond (2.34 Å). The C1—Si1—C1i bond angle [97.07 (14)°] is smaller than the tetrahedral bond angle (109.5°), while the C7—Si2—C11 [111.39 (10)°] and C15—Si3—C15i [106.97 (15)°] bond angles are within normal values. The long silicon–silicon bonds and the small carbon–silicon–carbon bond angle are favorable for reducing the
among bulky substituents.Packing diagram of 1 is shown in Fig. 3. Four molecules are present in a π–π interaction among phenyl groups.
All cyclotetrasilane rings are oriented toward the same direction with the line through the Si1 and Si3 atoms parallel to the b axis. There is no intermolecularFor background to and applications of phenyl-substituted oligosilanes, see: Hinch & Krc (1957); Matsumoto & Tanaka (2008). For the related structure of a cyclotetrasilane without phenyl groups, see: Kyushin et al. (1995).
Data collection: CrystalClear (Rigaku, 2003); cell
CrystalClear (Rigaku, 2003); data reduction: CrystalClear (Rigaku, 2003); program(s) used to solve structure: SIR2004 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and Yadokari-XG 2009 (Kabuto et al., 2009).C34H60Si4 | F(000) = 1280 |
Mr = 581.18 | Dx = 1.111 Mg m−3 |
Monoclinic, C2/c | Melting point = 483–484 K |
Hall symbol: -C 2yc | Mo Kα radiation, λ = 0.71073 Å |
a = 11.9477 (9) Å | Cell parameters from 7676 reflections |
b = 17.6585 (12) Å | θ = 1.2–28.3° |
c = 17.0422 (13) Å | µ = 0.19 mm−1 |
β = 104.9394 (8)° | T = 173 K |
V = 3474.0 (4) Å3 | Prism, colourless |
Z = 4 | 0.50 × 0.40 × 0.20 mm |
Rigaku R-AXISIV imaging plate diffractometer | 2917 independent reflections |
Radiation source: rotating anode | 2899 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.025 |
Detector resolution: 10.00 pixels mm-1 | θmax = 25.0°, θmin = 2.1° |
ω scans | h = −14→14 |
Absorption correction: multi-scan (REQAB; Jacobson, 1998) | k = −18→20 |
Tmin = 0.910, Tmax = 0.963 | l = −20→20 |
8534 measured reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.048 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.095 | H-atom parameters constrained |
S = 1.24 | w = 1/[σ2(Fo2) + (0.0127P)2 + 7.2943P] where P = (Fo2 + 2Fc2)/3 |
2917 reflections | (Δ/σ)max = 0.001 |
181 parameters | Δρmax = 0.24 e Å−3 |
0 restraints | Δρmin = −0.20 e Å−3 |
C34H60Si4 | V = 3474.0 (4) Å3 |
Mr = 581.18 | Z = 4 |
Monoclinic, C2/c | Mo Kα radiation |
a = 11.9477 (9) Å | µ = 0.19 mm−1 |
b = 17.6585 (12) Å | T = 173 K |
c = 17.0422 (13) Å | 0.50 × 0.40 × 0.20 mm |
β = 104.9394 (8)° |
Rigaku R-AXISIV imaging plate diffractometer | 2917 independent reflections |
Absorption correction: multi-scan (REQAB; Jacobson, 1998) | 2899 reflections with I > 2σ(I) |
Tmin = 0.910, Tmax = 0.963 | Rint = 0.025 |
8534 measured reflections |
R[F2 > 2σ(F2)] = 0.048 | 0 restraints |
wR(F2) = 0.095 | H-atom parameters constrained |
S = 1.24 | Δρmax = 0.24 e Å−3 |
2917 reflections | Δρmin = −0.20 e Å−3 |
181 parameters |
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 > 2σ(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. |
x | y | z | Uiso*/Ueq | ||
Si1 | 0.0000 | 0.32355 (5) | 0.7500 | 0.01350 (19) | |
Si2 | 0.09403 (5) | 0.22594 (3) | 0.68813 (3) | 0.01324 (15) | |
Si3 | 0.0000 | 0.12695 (5) | 0.7500 | 0.01475 (19) | |
C1 | −0.07934 (19) | 0.39557 (13) | 0.67052 (13) | 0.0179 (5) | |
C2 | −0.0078 (2) | 0.45046 (14) | 0.64962 (15) | 0.0269 (6) | |
H1 | 0.0725 | 0.4498 | 0.6763 | 0.032* | |
C3 | −0.0487 (2) | 0.50564 (15) | 0.59179 (17) | 0.0330 (6) | |
H2 | 0.0031 | 0.5416 | 0.5791 | 0.040* | |
C4 | −0.1657 (2) | 0.50818 (15) | 0.55245 (15) | 0.0307 (6) | |
H3 | −0.1947 | 0.5455 | 0.5122 | 0.037* | |
C5 | −0.2392 (2) | 0.45599 (15) | 0.57252 (16) | 0.0313 (6) | |
H4 | −0.3196 | 0.4576 | 0.5462 | 0.038* | |
C6 | −0.1968 (2) | 0.40088 (14) | 0.63102 (15) | 0.0262 (5) | |
H5 | −0.2494 | 0.3659 | 0.6444 | 0.031* | |
C7 | 0.03683 (19) | 0.22973 (13) | 0.56985 (13) | 0.0191 (5) | |
C8 | −0.0961 (2) | 0.23931 (15) | 0.54491 (14) | 0.0259 (5) | |
H6 | −0.1243 | 0.2356 | 0.4857 | 0.039* | |
H7 | −0.1165 | 0.2890 | 0.5629 | 0.039* | |
H8 | −0.1318 | 0.1994 | 0.5703 | 0.039* | |
C9 | 0.0639 (2) | 0.15671 (16) | 0.52878 (15) | 0.0331 (6) | |
H9 | 0.0373 | 0.1622 | 0.4697 | 0.050* | |
H10 | 0.0240 | 0.1139 | 0.5462 | 0.050* | |
H11 | 0.1476 | 0.1476 | 0.5444 | 0.050* | |
C10 | 0.0887 (2) | 0.29704 (15) | 0.53389 (15) | 0.0307 (6) | |
H12 | 0.1716 | 0.2884 | 0.5404 | 0.046* | |
H13 | 0.0779 | 0.3436 | 0.5623 | 0.046* | |
H14 | 0.0497 | 0.3020 | 0.4760 | 0.046* | |
C11 | 0.26218 (18) | 0.23095 (14) | 0.72206 (14) | 0.0204 (5) | |
C12 | 0.3017 (2) | 0.21501 (14) | 0.81400 (14) | 0.0253 (5) | |
H15 | 0.2866 | 0.1618 | 0.8242 | 0.038* | |
H16 | 0.2587 | 0.2477 | 0.8425 | 0.038* | |
H17 | 0.3848 | 0.2254 | 0.8338 | 0.038* | |
C13 | 0.3052 (2) | 0.31047 (16) | 0.70706 (17) | 0.0347 (6) | |
H18 | 0.3880 | 0.3148 | 0.7340 | 0.052* | |
H19 | 0.2621 | 0.3486 | 0.7291 | 0.052* | |
H20 | 0.2929 | 0.3186 | 0.6486 | 0.052* | |
C14 | 0.3208 (2) | 0.17278 (18) | 0.67839 (17) | 0.0379 (7) | |
H21 | 0.3064 | 0.1865 | 0.6209 | 0.057* | |
H22 | 0.2889 | 0.1223 | 0.6830 | 0.057* | |
H23 | 0.4044 | 0.1724 | 0.7034 | 0.057* | |
C15 | 0.0992 (2) | 0.06194 (13) | 0.82929 (15) | 0.0241 (5) | |
H24 | 0.1364 | 0.0948 | 0.8766 | 0.029* | |
C16 | 0.0306 (3) | 0.00034 (16) | 0.86183 (17) | 0.0387 (7) | |
H25 | 0.0068 | −0.0395 | 0.8209 | 0.058* | |
H26 | −0.0382 | 0.0231 | 0.8734 | 0.058* | |
H27 | 0.0798 | −0.0215 | 0.9118 | 0.058* | |
C17 | 0.1985 (2) | 0.02186 (16) | 0.80303 (19) | 0.0387 (7) | |
H28 | 0.2509 | −0.0020 | 0.8504 | 0.058* | |
H29 | 0.2414 | 0.0591 | 0.7796 | 0.058* | |
H30 | 0.1662 | −0.0170 | 0.7624 | 0.058* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Si1 | 0.0139 (4) | 0.0121 (4) | 0.0151 (4) | 0.000 | 0.0047 (3) | 0.000 |
Si2 | 0.0127 (3) | 0.0149 (3) | 0.0133 (3) | −0.0005 (2) | 0.0055 (2) | −0.0008 (2) |
Si3 | 0.0165 (4) | 0.0118 (4) | 0.0169 (4) | 0.000 | 0.0061 (4) | 0.000 |
C1 | 0.0219 (11) | 0.0167 (12) | 0.0162 (11) | 0.0022 (9) | 0.0072 (10) | −0.0007 (9) |
C2 | 0.0260 (12) | 0.0273 (14) | 0.0279 (14) | 0.0013 (10) | 0.0081 (11) | 0.0074 (10) |
C3 | 0.0415 (15) | 0.0258 (14) | 0.0367 (15) | −0.0008 (11) | 0.0189 (13) | 0.0106 (11) |
C4 | 0.0465 (16) | 0.0230 (14) | 0.0230 (13) | 0.0109 (11) | 0.0101 (12) | 0.0100 (10) |
C5 | 0.0273 (13) | 0.0336 (15) | 0.0298 (14) | 0.0095 (11) | 0.0012 (12) | 0.0062 (11) |
C6 | 0.0227 (12) | 0.0271 (14) | 0.0276 (13) | 0.0002 (10) | 0.0044 (11) | 0.0060 (10) |
C7 | 0.0236 (12) | 0.0209 (12) | 0.0143 (11) | 0.0012 (9) | 0.0078 (10) | −0.0023 (9) |
C8 | 0.0242 (12) | 0.0346 (15) | 0.0179 (12) | 0.0005 (10) | 0.0033 (10) | 0.0002 (10) |
C9 | 0.0410 (15) | 0.0343 (16) | 0.0232 (13) | 0.0076 (12) | 0.0070 (12) | −0.0095 (11) |
C10 | 0.0375 (14) | 0.0359 (16) | 0.0219 (13) | −0.0041 (11) | 0.0135 (12) | 0.0068 (11) |
C11 | 0.0144 (10) | 0.0271 (13) | 0.0210 (12) | −0.0006 (9) | 0.0068 (10) | −0.0040 (9) |
C12 | 0.0192 (11) | 0.0299 (14) | 0.0240 (13) | 0.0013 (10) | 0.0005 (10) | −0.0042 (10) |
C13 | 0.0288 (13) | 0.0431 (17) | 0.0327 (15) | −0.0176 (12) | 0.0086 (12) | 0.0011 (12) |
C14 | 0.0210 (13) | 0.058 (2) | 0.0355 (16) | 0.0079 (12) | 0.0092 (12) | −0.0157 (14) |
C15 | 0.0289 (12) | 0.0170 (12) | 0.0243 (13) | 0.0059 (10) | 0.0029 (11) | 0.0024 (9) |
C16 | 0.0570 (18) | 0.0254 (15) | 0.0335 (15) | −0.0005 (13) | 0.0113 (14) | 0.0090 (12) |
C17 | 0.0319 (14) | 0.0246 (15) | 0.058 (2) | 0.0119 (11) | 0.0084 (14) | 0.0004 (13) |
Si1—C1 | 1.921 (2) | C9—H11 | 0.9800 |
Si1—Si2 | 2.4404 (8) | C10—H12 | 0.9800 |
Si2—C11 | 1.944 (2) | C10—H13 | 0.9800 |
Si2—C7 | 1.956 (2) | C10—H14 | 0.9800 |
Si2—Si3 | 2.4576 (8) | C11—C14 | 1.539 (3) |
Si3—C15 | 1.929 (2) | C11—C13 | 1.539 (3) |
C1—C6 | 1.394 (3) | C11—C12 | 1.541 (3) |
C1—C2 | 1.398 (3) | C12—H15 | 0.9800 |
C2—C3 | 1.382 (3) | C12—H16 | 0.9800 |
C2—H1 | 0.9500 | C12—H17 | 0.9800 |
C3—C4 | 1.386 (4) | C13—H18 | 0.9800 |
C3—H2 | 0.9500 | C13—H19 | 0.9800 |
C4—C5 | 1.376 (4) | C13—H20 | 0.9800 |
C4—H3 | 0.9500 | C14—H21 | 0.9800 |
C5—C6 | 1.392 (3) | C14—H22 | 0.9800 |
C5—H4 | 0.9500 | C14—H23 | 0.9800 |
C6—H5 | 0.9500 | C15—C17 | 1.543 (3) |
C7—C10 | 1.539 (3) | C15—C16 | 1.548 (3) |
C7—C9 | 1.541 (3) | C15—H24 | 1.0000 |
C7—C8 | 1.544 (3) | C16—H25 | 0.9800 |
C8—H6 | 0.9800 | C16—H26 | 0.9800 |
C8—H7 | 0.9800 | C16—H27 | 0.9800 |
C8—H8 | 0.9800 | C17—H28 | 0.9800 |
C9—H9 | 0.9800 | C17—H29 | 0.9800 |
C9—H10 | 0.9800 | C17—H30 | 0.9800 |
C1i—Si1—C1 | 97.07 (14) | H10—C9—H11 | 109.5 |
C1i—Si1—Si2 | 125.03 (7) | C7—C10—H12 | 109.5 |
C1—Si1—Si2 | 111.19 (6) | C7—C10—H13 | 109.5 |
Si2i—Si1—Si2 | 90.13 (4) | H12—C10—H13 | 109.5 |
C11—Si2—C7 | 111.39 (10) | C7—C10—H14 | 109.5 |
C11—Si2—Si1 | 113.26 (7) | H12—C10—H14 | 109.5 |
C7—Si2—Si1 | 110.10 (7) | H13—C10—H14 | 109.5 |
C11—Si2—Si3 | 117.16 (8) | C14—C11—C13 | 108.4 (2) |
C7—Si2—Si3 | 112.93 (7) | C14—C11—C12 | 108.2 (2) |
Si1—Si2—Si3 | 90.27 (3) | C13—C11—C12 | 107.92 (19) |
C15i—Si3—C15 | 106.97 (15) | C14—C11—Si2 | 112.95 (16) |
C15i—Si3—Si2 | 112.89 (7) | C13—C11—Si2 | 110.84 (17) |
C15—Si3—Si2 | 117.23 (7) | C12—C11—Si2 | 108.42 (14) |
Si2i—Si3—Si2 | 89.33 (4) | C11—C12—H15 | 109.5 |
C6—C1—C2 | 115.8 (2) | C11—C12—H16 | 109.5 |
C6—C1—Si1 | 129.59 (18) | H15—C12—H16 | 109.5 |
C2—C1—Si1 | 114.57 (17) | C11—C12—H17 | 109.5 |
C3—C2—C1 | 122.9 (2) | H15—C12—H17 | 109.5 |
C3—C2—H1 | 118.6 | H16—C12—H17 | 109.5 |
C1—C2—H1 | 118.6 | C11—C13—H18 | 109.5 |
C2—C3—C4 | 119.7 (2) | C11—C13—H19 | 109.5 |
C2—C3—H2 | 120.2 | H18—C13—H19 | 109.5 |
C4—C3—H2 | 120.2 | C11—C13—H20 | 109.5 |
C5—C4—C3 | 119.1 (2) | H18—C13—H20 | 109.5 |
C5—C4—H3 | 120.4 | H19—C13—H20 | 109.5 |
C3—C4—H3 | 120.4 | C11—C14—H21 | 109.5 |
C4—C5—C6 | 120.6 (2) | C11—C14—H22 | 109.5 |
C4—C5—H4 | 119.7 | H21—C14—H22 | 109.5 |
C6—C5—H4 | 119.7 | C11—C14—H23 | 109.5 |
C5—C6—C1 | 121.9 (2) | H21—C14—H23 | 109.5 |
C5—C6—H5 | 119.1 | H22—C14—H23 | 109.5 |
C1—C6—H5 | 119.1 | C17—C15—C16 | 107.4 (2) |
C10—C7—C9 | 108.18 (19) | C17—C15—Si3 | 116.68 (18) |
C10—C7—C8 | 107.3 (2) | C16—C15—Si3 | 112.50 (17) |
C9—C7—C8 | 106.7 (2) | C17—C15—H24 | 106.6 |
C10—C7—Si2 | 111.55 (16) | C16—C15—H24 | 106.6 |
C9—C7—Si2 | 112.41 (16) | Si3—C15—H24 | 106.6 |
C8—C7—Si2 | 110.42 (14) | C15—C16—H25 | 109.5 |
C7—C8—H6 | 109.5 | C15—C16—H26 | 109.5 |
C7—C8—H7 | 109.5 | H25—C16—H26 | 109.5 |
H6—C8—H7 | 109.5 | C15—C16—H27 | 109.5 |
C7—C8—H8 | 109.5 | H25—C16—H27 | 109.5 |
H6—C8—H8 | 109.5 | H26—C16—H27 | 109.5 |
H7—C8—H8 | 109.5 | C15—C17—H28 | 109.5 |
C7—C9—H9 | 109.5 | C15—C17—H29 | 109.5 |
C7—C9—H10 | 109.5 | H28—C17—H29 | 109.5 |
H9—C9—H10 | 109.5 | C15—C17—H30 | 109.5 |
C7—C9—H11 | 109.5 | H28—C17—H30 | 109.5 |
H9—C9—H11 | 109.5 | H29—C17—H30 | 109.5 |
C1i—Si1—Si2—C11 | −3.63 (12) | C3—C4—C5—C6 | −0.6 (4) |
C1—Si1—Si2—C11 | 112.02 (11) | C4—C5—C6—C1 | −0.9 (4) |
Si2i—Si1—Si2—C11 | −119.92 (8) | C2—C1—C6—C5 | 2.0 (4) |
C1i—Si1—Si2—C7 | −129.08 (11) | Si1—C1—C6—C5 | −177.9 (2) |
C1—Si1—Si2—C7 | −13.43 (11) | C11—Si2—C7—C10 | −51.24 (19) |
Si2i—Si1—Si2—C7 | 114.63 (8) | Si1—Si2—C7—C10 | 75.27 (16) |
C1i—Si1—Si2—Si3 | 116.29 (8) | Si3—Si2—C7—C10 | 174.50 (14) |
C1—Si1—Si2—Si3 | −128.06 (7) | C11—Si2—C7—C9 | 70.49 (19) |
Si2i—Si1—Si2—Si3 | 0.0 | Si1—Si2—C7—C9 | −163.01 (15) |
C11—Si2—Si3—C15i | −124.05 (11) | Si3—Si2—C7—C9 | −63.78 (18) |
C7—Si2—Si3—C15i | 7.41 (11) | C11—Si2—C7—C8 | −170.44 (16) |
Si1—Si2—Si3—C15i | 119.45 (8) | Si1—Si2—C7—C8 | −43.93 (18) |
C11—Si2—Si3—C15 | 0.95 (12) | Si3—Si2—C7—C8 | 55.30 (18) |
C7—Si2—Si3—C15 | 132.41 (11) | C7—Si2—C11—C14 | −51.3 (2) |
Si1—Si2—Si3—C15 | −115.55 (9) | Si1—Si2—C11—C14 | −176.05 (16) |
C11—Si2—Si3—Si2i | 116.50 (8) | Si3—Si2—C11—C14 | 80.87 (19) |
C7—Si2—Si3—Si2i | −112.04 (8) | C7—Si2—C11—C13 | 70.59 (18) |
Si1—Si2—Si3—Si2i | 0.0 | Si1—Si2—C11—C13 | −54.17 (17) |
C1i—Si1—C1—C6 | −127.9 (2) | Si3—Si2—C11—C13 | −157.25 (14) |
Si2i—Si1—C1—C6 | −5.8 (3) | C7—Si2—C11—C12 | −171.14 (15) |
Si2—Si1—C1—C6 | 100.2 (2) | Si1—Si2—C11—C12 | 64.11 (17) |
C1i—Si1—C1—C2 | 52.17 (16) | Si3—Si2—C11—C12 | −38.97 (18) |
Si2i—Si1—C1—C2 | 174.29 (14) | C15i—Si3—C15—C17 | 74.54 (19) |
Si2—Si1—C1—C2 | −79.77 (18) | Si2i—Si3—C15—C17 | −155.06 (17) |
C6—C1—C2—C3 | −1.9 (4) | Si2—Si3—C15—C17 | −53.4 (2) |
Si1—C1—C2—C3 | 178.1 (2) | C15i—Si3—C15—C16 | −50.24 (16) |
C1—C2—C3—C4 | 0.5 (4) | Si2i—Si3—C15—C16 | 80.16 (18) |
C2—C3—C4—C5 | 0.7 (4) | Si2—Si3—C15—C16 | −178.14 (15) |
Symmetry code: (i) −x, y, −z+3/2. |
Experimental details
Crystal data | |
Chemical formula | C34H60Si4 |
Mr | 581.18 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 173 |
a, b, c (Å) | 11.9477 (9), 17.6585 (12), 17.0422 (13) |
β (°) | 104.9394 (8) |
V (Å3) | 3474.0 (4) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.19 |
Crystal size (mm) | 0.50 × 0.40 × 0.20 |
Data collection | |
Diffractometer | Rigaku R-AXISIV imaging plate |
Absorption correction | Multi-scan (REQAB; Jacobson, 1998) |
Tmin, Tmax | 0.910, 0.963 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 8534, 2917, 2899 |
Rint | 0.025 |
(sin θ/λ)max (Å−1) | 0.595 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.048, 0.095, 1.24 |
No. of reflections | 2917 |
No. of parameters | 181 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.24, −0.20 |
Computer programs: CrystalClear (Rigaku, 2003), SIR2004 (Burla et al., 2005), ORTEP-3 (Farrugia, 2012), SHELXL97 (Sheldrick, 2008) and Yadokari-XG 2009 (Kabuto et al., 2009).
Acknowledgements
This work was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan, and the Japan Society for the Promotion of Science. This work was also supported by the Element Innovation Project of Gunma University.
References
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This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.
Birefringent materials have a wide range of optical applications. Single crystals of calcium carbonate and barium borate have been well known as inorganic birefringent materials. Organic single crystals such as urea have also been known to show birefringence. Since birefringence is related to crystal structures, studies on molecular structures and packing in a crystal are important. In 1957, birefringence of tetrakis(4-phenylphenyl)silane was reported (Hinch & Krc, 1957). Recently, birefringence of single crystals of phenyl-substituted linear oligosilanes and their application to polarizers have been reported (Matsumoto & Tanaka, 2008). From these results, crystals of phenyl-substituted silicon compounds seem interesting as potential optical materials. We report herein the synthesis and X-ray crystal analysis of a phenyl-substituted cyclotetrasilane.
The coupling of 1,3-dibromo-1,1,3,3-tetra-tert-butyl-2,2-diphenyltrisilane and dichlorodiisopropylsilane with lithium in tetrahydrofuran (THF) gave 1,1,3,3-tetra-tert-butyl-2,2-diisopropyl-4,4-diphenylcyclotetrasilane (1) in 21% yield (Fig. 1). The molecular structure of 1 is shown in Fig. 2. Compound 1 has the crystallographic C2 symmetry, and therefore the cyclotetrasilane ring has a completely planar structure. The silicon–silicon bonds [2.4404 (8) and 2.4576 (8) Å] are longer than the standard silicon–silicon bond (2.34 Å). The C1—Si1—C1i bond angle [97.07 (14)°] is smaller than the tetrahedral bond angle (109.5°), while the C7—Si2—C11 [111.39 (10)°] and C15—Si3—C15i [106.97 (15)°] bond angles are within normal values. The long silicon–silicon bonds and the small carbon–silicon–carbon bond angle are favorable for reducing the steric hindrance among bulky substituents.
Packing diagram of 1 is shown in Fig. 3. Four molecules are present in a unit cell. All cyclotetrasilane rings are oriented toward the same direction with the line through the Si1 and Si3 atoms parallel to the b axis. There is no intermolecular π–π interaction among phenyl groups.