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No crystal structure at ambient pressure is known for tetramethylsilane, Si(CH3)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 (Pa\overline{3}, 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_3)_4, 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 Pa\overline{3}, Z = 8.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768110003423/og5040sup1.cif
Contains datablocks I, global

fcf

Structure factor file (CIF format) https://doi.org/10.1107/S0108768110003423/og5040Isup2.fcf
Contains datablock I

CCDC reference: 775212

Computing details top

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.

; top
Crystal data top
C4H12SiDx = 0.860 Mg m3
Mr = 88.23Melting point: 174 K
Orthorhombic, PnmaMo Kα radiation, λ = 0.71073 Å
a = 13.131 (3) ÅCell parameters from 1789 reflections
b = 8.198 (3) Åθ = 3.6–25.6°
c = 6.329 (1) ŵ = 0.21 mm1
V = 681.3 (3) Å3T = 100 K
Z = 4Block, colourless
F(000) = 2000.40 × 0.40 × 0.40 mm
Data collection top
STOE IPDS II two-circle-
diffractometer
635 independent reflections
Radiation source: fine-focus sealed tube466 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.143
ω scansθmax = 25.0°, θmin = 3.6°
Absorption correction: multi-scan
MULABS (Spek, 2003; Blessing, 1995)
h = 1511
Tmin = 0.920, Tmax = 0.920k = 98
1818 measured reflectionsl = 76
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.123Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.355H-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 parametersΔρmax = 0.61 e Å3
0 restraintsΔρmin = 0.69 e Å3
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
xyzUiso*/UeqOcc. (<1)
Si10.34452 (15)0.25000.6446 (3)0.0466 (11)
C10.4109 (5)0.4368 (8)0.7457 (7)0.0597 (17)
H1A0.40900.43730.90050.090*
H1B0.37640.53430.69180.090*
H1C0.48180.43640.69770.090*
C20.2095 (6)0.25000.7334 (13)0.058 (2)
H2A0.20700.25000.88820.087*
H2B0.17510.15240.67950.087*0.50
H2C0.17510.34760.67950.087*0.50
C30.3484 (6)0.25000.3501 (11)0.057 (2)
H3A0.41940.25000.30250.086*
H3B0.31390.34760.29660.086*0.50
H3C0.31390.15240.29660.086*0.50
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Si10.0569 (16)0.0485 (16)0.0345 (13)0.0000.0003 (8)0.000
C10.067 (4)0.063 (4)0.049 (3)0.007 (3)0.002 (3)0.008 (2)
C20.062 (5)0.049 (4)0.063 (4)0.0000.004 (4)0.000
C30.082 (6)0.052 (5)0.037 (4)0.0000.000 (3)0.000
Geometric parameters (Å, º) top
Si1—C21.861 (9)C2—H2A0.9800
Si1—C31.864 (7)C2—H2B0.9800
Si1—C11.874 (6)C2—H2C0.9800
Si1—C1i1.874 (6)C3—H3A0.9800
C1—H1A0.9800C3—H3B0.9800
C1—H1B0.9800C3—H3C0.9800
C1—H1C0.9800
C2—Si1—C3109.1 (4)Si1—C2—H2A109.5
C2—Si1—C1109.9 (2)Si1—C2—H2B109.5
C3—Si1—C1109.2 (2)H2A—C2—H2B109.5
C2—Si1—C1i109.9 (2)Si1—C2—H2C109.5
C3—Si1—C1i109.2 (2)H2A—C2—H2C109.5
C1—Si1—C1i109.6 (4)H2B—C2—H2C109.5
Si1—C1—H1A109.5Si1—C3—H3A109.5
Si1—C1—H1B109.5Si1—C3—H3B109.5
H1A—C1—H1B109.5H3A—C3—H3B109.5
Si1—C1—H1C109.5Si1—C3—H3C109.5
H1A—C1—H1C109.5H3A—C3—H3C109.5
H1B—C1—H1C109.5H3B—C3—H3C109.5
Symmetry code: (i) x, y+1/2, z.
 

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