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In the course of work on main-group silyl compounds, crystals of the title compound, [Hg(C3H9Si)2]2, were prepared. An earlier X-ray analysis of this compound failed to give a full structural characterization. Here, the title compound is found to consist of dimers with 222 crystallographic symmetry formed by two molecules of (Me3Si)2Hg linked by a weak Hg...Hg interaction with an interatomic distance of 3.1463 (6) Å. Each Si—Hg—Si frame is nearly linear and has an Hg—Si distance of 2.4913 (18) Å.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270199016339/bk1496sup1.cif
Contains datablocks global, (I)

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270199016339/bk1496Isup2.hkl
Contains datablock I

CCDC reference: 144608

Comment top

Mercury–bis-silyl compounds have been known for many years and have been used extensively as silylating agents in the preparation of main group silyl compounds. A single-crystal X-ray structural determination was previously undertaken on the title compound, bis(trimethylsilyl)mercury, (Me3Si)2Hg, (I); however, only a partial solution was obtained (Bleckmann et al., 1976). The only other mercury–bis-silyl compounds to have been structurally characterized include bis(triphenylsilyl)mercury, (Ph3Si)2Hg, (II) (Ilsley et al., 1980), bis(tri-t-butylsilyl)mercury, (tBu3Si)2Hg, (III) (Wiberg et al., 1997), in which tBu3Si is a supersily ligand, and bis[tris(trimethylsilyl)silyl]mercury, [(SiMe3)Si]2Hg, (IV), containing the hypersilyl ligand (SiMe3)Si (Klinkhammer & Weidlein 1996). Like bis(trimethylsilyl)mercury, compounds (II), (III) and (IV) all adopt a linear configuration about the mercury. Also worth mentioning is the related cyclic compound 2,2,4,4,6,6,8,8-octamethyl-2,4,6,8-tetrasila-1,5-mercuracyclooctane, (V), which is a centrosymmetric molecule containing two linear Si—Hg—Si moieties linked by methylene groups (Ilsley et al., 1980).

The title compound, (I), was prepared according to the literature method (Rösch & Erb, 1979) from the reaction of chlorotrimethylsilane with mercury and aluminium in tetrahydrofuran. Bright-yellow crystals suitable for an X-ray structural determination were grown by keeping saturated pentane solutions of bis(trimethylsilyl)mercury at 238 K for several days. The results of a single-crystal X-ray analysis are shown in Fig. 1. The molecular structure of (I) consists of dimers formed by two molecules of (Me3Si)2Hg linked by a weak Hg···Hg interaction with an interatomic distance of 3.1463 (6) Å, the midpoint of this interaction having crystallographic 222 symmetry. Each Si—Hg—Si frame is nearly linear [178.04 (8)°] about the Hg atom. The Hg—Si interatomic distance of 2.4913 (8) Å is in good agreement with that determined by the original data collection [2.500 (5) Å]. This value is close to the Hg—Si interatomic distances seen in (II), (III), (IV) and (V) [2.490 (4), 2.495 (2), 2.469 (2) and 2.501 (4)/2.505 (4) Å, respectively]. Surprisingly, (I) and (V), possessing the less bulky silyl ligands, have the longest Hg—Si interatomic distances; these differences can most likely can be attributed to the electron-withdrawing effect of the triphenylsilyl ligands in (II), the supersilyl ligands in (III) and the hypersilyl ligands in (IV). The Si—C interatomic distances seen in (I) [1.876 (9), 1.872 (7) and 1.866 (8) Å] are very similar to those of Si—C bonds adjacent to an Hg atom in other mercury–bis-silyl compounds.

The geometry about the Si atom deviates very slightly from that of an ideal tetrahedron, with angles ranging from 106.9 (5) to 112.9 (3)°. The Hg—Si—C angles are all larger than ideal angles, while all the C—Si—C angles are somewhat smaller than the ideal. A similar effect has also been noted in previously structurally characterized mercury–bis-silyl compounds and is due to the large size of the Hg atom. One further point of interest, within the crystal structure two molecules of bis(trimethylsilyl)mercury are in very close proximity, with the two Si—Hg—Si planes of neighbouring molecules lying perpendicular to each other about the Hg atoms, as shown in Fig. 1. The Hg···Hg interatomic distance [3.1463 (6) Å] appears to be close to the sum of the covalent radii for two Hg atoms [the reported atomic radius of Hg is 1.57 (Ilsley et al., 1980)]. For most structurally characterized compounds possessing an Hg—Hg bond, the interatomic distance is of the order of 2.5–2.7 Å; however, there are also reports of compounds posessing abnormally long Hg···Hg interactions, as in the case of the dimercury platinum cluster [Pt3Hg(CO)3(PPh-iPr2)3]2 (Albinati et al., 1982), which has a slightly longer distance [3.225 (1) Å] than that seen in (I). Due to the cyclic nature of (V), this compound also possesses a close Hg···Hg interaction, albeit an intramolecular interaction. On the basis of other structurally characterized compounds containing Hg···Hg interactions, the Hg···Hg interaction in (V) [3.286 (2) Å], which is slightly longer than the sum of the atomic radii, and that in (I), are considered to constitute real Hg—Hg bonds.

Experimental top

Aluminium powder (20.0 g), mercury (20.0 g) and 130 ml of SiMe3Cl were placed in a 500 ml round-bottom flask and 130 ml of tetrahydrofuran was added. The resulting reaction solution was allowed to reflux for 5 h, while stirring. The solvent volume was removed, by vacuum pump, and the residue redissolved in pentane. The solution was filtered through Celite and the solvent volume reduced. After keeping at 238 K for several days, a crop of bright-yellow crystals was obtained. 1H NMR (300 MHz, C6D6): δ = 0.200 p.p.m. (s, H, SiMe3).

Computing details top

Data collection: SMART (Siemens, 1995); cell refinement: SAINT (Siemens, 1995); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 1995); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL.

Figures top
[Figure 1] Fig. 1. Displacement ellipsoid (30% probability) representation of the solid-state structure of (I), as determined by single-crystal X-ray diffraction analysis. All H atoms have been omitted from the representation for clarity.
Bis(trimethylsilyl)mercury top
Crystal data top
[Hg(C3H9Si)2]2F(000) = 1296
Mr = 693.94Dx = 1.941 Mg m3
Orthorhombic, CccaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2b 2acCell parameters from 3392 reflections
a = 14.9958 (10) Åθ = 2.3–25.0°
b = 17.5356 (12) ŵ = 13.10 mm1
c = 9.0327 (6) ÅT = 173 K
V = 2375.2 (3) Å3Plate, bright yellow
Z = 40.27 × 0.12 × 0.10 mm
Data collection top
Siemens SMART 1K CCD
diffractometer
764 reflections with I > 2σ(I)
ω scanRint = 0.054
Absorption correction: multi-scan
(Blessing, 1995)
θmax = 25.0°
Tmin = 0.125, Tmax = 0.348h = 1716
5829 measured reflectionsk = 2013
1058 independent reflectionsl = 1010
Refinement top
Refinement on F2 w = 1/[σ2(Fo2) + (0.0441P)2]
where P = (Fo2 + 2Fc2)/3.
R[F2 > 2σ(F2)] = 0.028(Δ/σ)max < 0.001
wR(F2) = 0.074Δρmax = 2.14 e Å3
S = 0.99Δρmin = 1.02 e Å3
1058 reflectionsExtinction correction: SHELXTL (Sheldrick, 1995)
46 parametersExtinction coefficient: 0.00033 (6)
Mixed (riding; one variable Uiso per methyl)
Crystal data top
[Hg(C3H9Si)2]2V = 2375.2 (3) Å3
Mr = 693.94Z = 4
Orthorhombic, CccaMo Kα radiation
a = 14.9958 (10) ŵ = 13.10 mm1
b = 17.5356 (12) ÅT = 173 K
c = 9.0327 (6) Å0.27 × 0.12 × 0.10 mm
Data collection top
Siemens SMART 1K CCD
diffractometer
1058 independent reflections
Absorption correction: multi-scan
(Blessing, 1995)
764 reflections with I > 2σ(I)
Tmin = 0.125, Tmax = 0.348Rint = 0.054
5829 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.02846 parameters
wR(F2) = 0.074Mixed (riding; one variable Uiso per methyl)
S = 0.99Δρmax = 2.14 e Å3
1058 reflectionsΔρmin = 1.02 e Å3
Special details top

Experimental. A crystal of the title compound was selected and mounted on a glass fibre, while in a stream of cold argon gas, and placed immediately on a Siemens SMART 1 K CCD diffractometer at 173 K under a stream of cold nitrogen gas. Reflections were collected with a frame width of 0.3° in ω and a counting time of 30 s per frame at a crystal-to-detector distance of 4.911 cm. The double-pass method of scanning was used to exclude any noise.

The first 50 frames of data were recollected at the conclusion of data collection to monitor crystal decay. Insignificant (less than 0.5% in both cases) deterioration of the crystal quality was detected.

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*/Ueq
Hg10.104905 (19)0.25000.75000.02829 (18)
Si20.10774 (12)0.14400 (12)0.9336 (2)0.0440 (5)
C10.0008 (5)0.1322 (5)1.0335 (10)0.065 (3)
H1A0.00650.09671.11210.098*
H1B0.04470.11380.96650.098*
H1C0.01920.17991.07250.098*
C20.1948 (7)0.1609 (5)1.0773 (11)0.115 (5)
H2A0.18140.20701.13020.172*
H2B0.25210.16571.03060.172*
H2C0.19590.11881.14520.172*
C30.1331 (6)0.0508 (4)0.8406 (12)0.082 (3)
H3A0.13700.01170.91300.123*
H3B0.18820.05470.78920.123*
H3C0.08690.03900.77240.123*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Hg10.0274 (2)0.0292 (3)0.0283 (2)0.0000.0000.01007 (14)
Si20.0431 (10)0.0422 (11)0.0467 (12)0.0108 (9)0.0145 (10)0.0263 (10)
C10.088 (7)0.066 (6)0.042 (5)0.010 (4)0.005 (4)0.025 (4)
C20.115 (9)0.118 (8)0.112 (8)0.066 (7)0.084 (7)0.082 (7)
C30.070 (6)0.048 (5)0.129 (9)0.008 (5)0.027 (7)0.036 (6)
Geometric parameters (Å, º) top
Hg1—Si22.4913 (18)Si2—C21.866 (8)
Hg1—Si2i2.4913 (18)Si2—C11.872 (7)
Hg1—Hg1ii3.1463 (6)Si2—C31.876 (9)
Si2—Hg1—Si2i178.04 (8)C1—Si2—C3107.2 (4)
Si2—Hg1—Hg1ii90.98 (4)C2—Si2—Hg1110.9 (3)
Si2i—Hg1—Hg1ii90.98 (4)C1—Si2—Hg1112.9 (3)
C2—Si2—C1106.9 (5)C3—Si2—Hg1110.8 (3)
C2—Si2—C3108.0 (5)
Symmetry codes: (i) x, y+1/2, z+3/2; (ii) x, y+1/2, z.

Experimental details

Crystal data
Chemical formula[Hg(C3H9Si)2]2
Mr693.94
Crystal system, space groupOrthorhombic, Ccca
Temperature (K)173
a, b, c (Å)14.9958 (10), 17.5356 (12), 9.0327 (6)
V3)2375.2 (3)
Z4
Radiation typeMo Kα
µ (mm1)13.10
Crystal size (mm)0.27 × 0.12 × 0.10
Data collection
DiffractometerSiemens SMART 1K CCD
diffractometer
Absorption correctionMulti-scan
(Blessing, 1995)
Tmin, Tmax0.125, 0.348
No. of measured, independent and
observed [I > 2σ(I)] reflections
5829, 1058, 764
Rint0.054
(sin θ/λ)max1)0.595
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.028, 0.074, 0.99
No. of reflections1058
No. of parameters46
No. of restraints?
H-atom treatmentMixed (riding; one variable Uiso per methyl)
Δρmax, Δρmin (e Å3)2.14, 1.02

Computer programs: SMART (Siemens, 1995), SAINT (Siemens, 1995), SAINT, SHELXTL (Sheldrick, 1995), SHELXTL.

Selected geometric parameters (Å, º) top
Hg1—Si22.4913 (18)Si2—C11.872 (7)
Hg1—Hg1i3.1463 (6)Si2—C31.876 (9)
Si2—C21.866 (8)
Si2—Hg1—Si2ii178.04 (8)C1—Si2—C3107.2 (4)
Si2—Hg1—Hg1i90.98 (4)C2—Si2—Hg1110.9 (3)
C2—Si2—C1106.9 (5)C1—Si2—Hg1112.9 (3)
C2—Si2—C3108.0 (5)C3—Si2—Hg1110.8 (3)
Symmetry codes: (i) x, y+1/2, z; (ii) x, y+1/2, z+3/2.
 

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