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No crystal structure at ambient pressure is known for tetramethylsilane, Si(CH
3)
4, which is used as a standard in NMR spectroscopy. Possible crystal structures were predicted by global lattice-energy minimizations using force-field methods. The lowest-energy structure corresponds to the high-pressure room-temperature phase (
,
Z = 8). Low-temperature crystallization at 100 K resulted in a single crystal, and its crystal structure has been determined. The structure corresponds to the predicted structure with the second lowest energy rank. In X-ray powder analyses this is the only observed phase between 80 and 159 K. For tetramethylgermane, Ge(CH
)
, no experimental crystal structure is known. Global lattice-energy minimizations resulted in 47 possible crystal structures within an energy range of 5 kJ mol
−1. The lowest-energy structure was found in
,
Z = 8.
Supporting information
CCDC reference: 775212
Data collection: X-AREA (Stoe & Cie, 2001); cell refinement: X-AREA (Stoe & Cie, 2001); data reduction: X-AREA (Stoe & Cie, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL-Plus (Sheldrick, 1991); software used to prepare material for publication: SHELXL97.
Crystal data top
C4H12Si | Dx = 0.860 Mg m−3 |
Mr = 88.23 | Melting point: 174 K |
Orthorhombic, Pnma | Mo Kα radiation, λ = 0.71073 Å |
a = 13.131 (3) Å | Cell parameters from 1789 reflections |
b = 8.198 (3) Å | θ = 3.6–25.6° |
c = 6.329 (1) Å | µ = 0.21 mm−1 |
V = 681.3 (3) Å3 | T = 100 K |
Z = 4 | Block, colourless |
F(000) = 200 | 0.40 × 0.40 × 0.40 mm |
Data collection top
STOE IPDS II two-circle- diffractometer | 635 independent reflections |
Radiation source: fine-focus sealed tube | 466 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.143 |
ω scans | θmax = 25.0°, θmin = 3.6° |
Absorption correction: multi-scan MULABS (Spek, 2003; Blessing, 1995) | h = −15→11 |
Tmin = 0.920, Tmax = 0.920 | k = −9→8 |
1818 measured reflections | l = −7→6 |
Refinement top
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)] = 0.123 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.355 | H-atom parameters constrained |
S = 1.21 | w = 1/[σ2(Fo2) + (0.2P)2] where P = (Fo2 + 2Fc2)/3 |
635 reflections | (Δ/σ)max < 0.001 |
28 parameters | Δρmax = 0.61 e Å−3 |
0 restraints | Δρmin = −0.69 e Å−3 |
Special details top
Experimental. ; |
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 (Å2) top | x | y | z | Uiso*/Ueq | Occ. (<1) |
Si1 | 0.34452 (15) | 0.2500 | 0.6446 (3) | 0.0466 (11) | |
C1 | 0.4109 (5) | 0.4368 (8) | 0.7457 (7) | 0.0597 (17) | |
H1A | 0.4090 | 0.4373 | 0.9005 | 0.090* | |
H1B | 0.3764 | 0.5343 | 0.6918 | 0.090* | |
H1C | 0.4818 | 0.4364 | 0.6977 | 0.090* | |
C2 | 0.2095 (6) | 0.2500 | 0.7334 (13) | 0.058 (2) | |
H2A | 0.2070 | 0.2500 | 0.8882 | 0.087* | |
H2B | 0.1751 | 0.1524 | 0.6795 | 0.087* | 0.50 |
H2C | 0.1751 | 0.3476 | 0.6795 | 0.087* | 0.50 |
C3 | 0.3484 (6) | 0.2500 | 0.3501 (11) | 0.057 (2) | |
H3A | 0.4194 | 0.2500 | 0.3025 | 0.086* | |
H3B | 0.3139 | 0.3476 | 0.2966 | 0.086* | 0.50 |
H3C | 0.3139 | 0.1524 | 0.2966 | 0.086* | 0.50 |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Si1 | 0.0569 (16) | 0.0485 (16) | 0.0345 (13) | 0.000 | 0.0003 (8) | 0.000 |
C1 | 0.067 (4) | 0.063 (4) | 0.049 (3) | −0.007 (3) | −0.002 (3) | −0.008 (2) |
C2 | 0.062 (5) | 0.049 (4) | 0.063 (4) | 0.000 | 0.004 (4) | 0.000 |
C3 | 0.082 (6) | 0.052 (5) | 0.037 (4) | 0.000 | 0.000 (3) | 0.000 |
Geometric parameters (Å, º) top
Si1—C2 | 1.861 (9) | C2—H2A | 0.9800 |
Si1—C3 | 1.864 (7) | C2—H2B | 0.9800 |
Si1—C1 | 1.874 (6) | C2—H2C | 0.9800 |
Si1—C1i | 1.874 (6) | C3—H3A | 0.9800 |
C1—H1A | 0.9800 | C3—H3B | 0.9800 |
C1—H1B | 0.9800 | C3—H3C | 0.9800 |
C1—H1C | 0.9800 | | |
| | | |
C2—Si1—C3 | 109.1 (4) | Si1—C2—H2A | 109.5 |
C2—Si1—C1 | 109.9 (2) | Si1—C2—H2B | 109.5 |
C3—Si1—C1 | 109.2 (2) | H2A—C2—H2B | 109.5 |
C2—Si1—C1i | 109.9 (2) | Si1—C2—H2C | 109.5 |
C3—Si1—C1i | 109.2 (2) | H2A—C2—H2C | 109.5 |
C1—Si1—C1i | 109.6 (4) | H2B—C2—H2C | 109.5 |
Si1—C1—H1A | 109.5 | Si1—C3—H3A | 109.5 |
Si1—C1—H1B | 109.5 | Si1—C3—H3B | 109.5 |
H1A—C1—H1B | 109.5 | H3A—C3—H3B | 109.5 |
Si1—C1—H1C | 109.5 | Si1—C3—H3C | 109.5 |
H1A—C1—H1C | 109.5 | H3A—C3—H3C | 109.5 |
H1B—C1—H1C | 109.5 | H3B—C3—H3C | 109.5 |
Symmetry code: (i) x, −y+1/2, z. |
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