A new pseudopolymorph of perchlorinated neo­penta­silane: the benzene monosolvate Si(SiCl3)4·C6H6

Tillmann, J.; Lerner, H.-W.; Bolte, M.

doi:10.1107/S2056989020000900

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Volume 76| Part 2| February 2020| Pages 261-263

https://doi.org/10.1107/S2056989020000900

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A new pseudopolymorph of perchlorinated neopentasilane: the benzene monosolvate Si(SiCl₃)₄·C₆H₆

Jan Tillmann,^a Hans-Wolfram Lerner ^a and Michael Bolte ^a ^*

^aInstitut für Anorganische und Analytische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main, Germany
^*Correspondence e-mail: bolte@chemie.uni-frankfurt.de

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 10 December 2019; accepted 23 January 2020; online 31 January 2020)

A new pseudopolymorph of dodecachloropentasilane, namely a benzene monosolvate, Si₅Cl₁₂·C₆H₆, is described. There are two half molecules of each kind in the asymmetric unit. Both Si₅Cl₁₂ molecules are completed by crystallographic twofold symmetry. One of the benzene molecules is located on a twofold rotation axis with two C—H groups located on this rotation axis. The second benzene molecule has all atoms on a general position: it is disordered over two equally occupied orientations. No directional interactions beyond normal van der Waals contacts occur in the crystal.

Keywords: crystal structure; co-crystal; polymorphism; solvate.

CCDC reference: 1979631

1. Chemical context

Since the 1980s, silicon hydrides, such as Si(SiH₃)₄, have attracted considerable attention as precursors for the liquid phase deposition (LPD) of silicon thin films (Nishimura et al., 1985 ). In this context it should be noted that the perchlorinated neopentasilane Si(SiCl₃)₄ (Si₅Cl₁₂) is easily accessible in large amounts by the amine-induced disproportionation (Meyer-Wegner et al., 2011 ; Tillmann et al., 2012 ) of perchloropolysilanes, e.g. Si₂Cl₆ or Si₃Cl₈ (Meyer-Wegner et al., 2011; Urry, 1970 ). Subsequent hydrogenation of Si(SiCl₃)₄ (I) then yields the neopentasilane Si(SiH₃)₄, which can be used as an LPD agent (Cannady & Zhou, 2008 ) (see Fig. 1).

Figure 1
Amine-induced disproportionation of Si₂Cl₆ and Si₃Cl₈: (i) + NMe₃, or NMe₂Et, or NEt₃ in benzene at room temperature; (ii) + LiAlH₄ in diethyl ether at room temperature

In this paper we describe the structure of a new pseudo-polymorph of perchlorinated neopentasilane (I), namely the benzene monosolvate Si(SiCl₃)₄·C₆H₆, and make a comparison of its structure with those of Si(SiCl₃)₄ (Meyer-Wegner et al., 2011) and Si(SiCl₃)₄·SiCl₄ (Fleming, 1972 ).

2. Structural commentary

There are two half molecules of each kind in the asymmetric unit of (I). Both Si₅Cl₁₂ molecules are completed by crystallographic twofold symmetry, with the rotation axes orientated in the [110] and [ $[\overline{1}]$ 10] directions and the central Si atom located on the axis (Fig. 2). One of the benzene molecules is located on a twofold rotation axis propagating along the a or b axes with two C—H groups located on this rotation axis. The second benzene molecule has all atoms on general positions: it is disordered over two equally occupied orientations about a twofold rotation axis running in the [100] and [010] directions.

Figure 2
A perspective view of the title compound. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: (i) −y, −x, −z + $[{1\over 4}]$ ; (ii) 1 − y, 1 − x, −z + $[{1\over 4}]$ ; (iii) −x, y, −z; (iv) 1 − x, y, −z.

3. Supramolecular features

A view of the molecular packing of (I) (Fig. 3) reveals that the benzene molecules fill the voids between the dodecachloropentasilane molecules. There are no identified directional intermolecular interactions.

Figure 3
Packing diagram of the title compound viewed down [010].

4. Database survey

There are two already known structures of dodecachloropentasilane: first, there is pure Si₅Cl₁₂ (Meyer-Wegner et al., 2011; CCDC deposition number 793308) and second, a co-crystal with silicon tetrachloride (Fleming, 1972; CCDC deposition number 1592571). In each of these structures, the Si₅Cl₁₂ molecule is located on a special position. As noted above, in (I), both molecules in the asymmetric unit are found on a twofold rotation axis. Compound (II) also crystallizes with two molecules in the asymmetric unit. One of them is located on a threefold rotation axis and the other is disordered about a special position of site symmetry $[\overline{3}]$ . In the second molecule, it is noteworthy that only the Si atoms carrying the Cl atoms are disordered: the central Si atom and the Cl atoms themselves are not disordered. In (III), the Si₅Cl₁₂ molecule is located on a special position of site symmetry 23. The central Si atom is located at the intersection of the twofold and the threefold rotation axes (the twofold rotation axis coincides with a $[\overline{4}]$ axis). The Si—Si and Si—Cl bond lengths in all three structures agree well (Table 1).

Table 1
Bond lengths (Å) in the different structures containing Si₅Cl₁₂ molecules

For (I), mean values of the two molecules are given. For (II), mean values of the non-disordered molecule are given. Because of the high symmetry of (III), there is only one value for each bond length.

	Si—Si	Si—Cl
(I)	2.324	2.019
(II)	2.340	2.026
(III)	2.332 (9)	1.994 (7)

5. Synthesis and crystallization

The perchlorinated neopentasilane (I) was synthesized according to a literature procedure (Kaczmarczyk & Urry, 1960 ). Single crystals of Si(SiCl₃)₄·C₆H₆ were grown from a solution of Si(SiCl₃)₄ in benzene after one week at room temperature.

Si(SiCl₃)₄ (I). ²⁹Si{¹H}NMR (C₆D₆, external TMS): δ = −80.9 [Si(SiCl₃)₄], δ = 3.5 [Si(SiCl₃)₄].

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. The H atoms were refined using a riding model with C—H = 0.95 Å and with U_iso(H) = 1.2U_eq(C). One of the benzene molecules is disordered over two equally occupied orientations: its carbon atoms were isotropically refined. The C—C distances in the non-disordered benzene molecule were restrained to 1.390 (2) Å. The crystal chosen for data collection was found to crystallize as a racemic twin.

Table 2
Experimental details

Crystal data
Chemical formula	Cl₁₂Si₅·C₆H₆
M_r	643.96
Crystal system, space group	Tetragonal, P4₁22
Temperature (K)	173
a, c (Å)	11.9633 (4), 33.7848 (16)
V (Å³)	4835.3 (4)
Z	8
Radiation type	Mo Kα
μ (mm⁻¹)	1.62
Crystal size (mm)	0.28 × 0.18 × 0.16

Data collection
Diffractometer	Stoe IPDS II two-circle
Absorption correction	Multi-scan (X-AREA; Stoe & Cie, 2001 )
T_min, T_max	0.803, 1.0
No. of measured, independent and observed [I > 2σ(I)] reflections	39180, 5189, 4790
R_int	0.047
(sin θ/λ)_max (Å⁻¹)	0.642

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.027, 0.075, 1.08
No. of reflections	5189
No. of parameters	207
No. of restraints	5
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.39, −0.42
Absolute structure	Flack x determined using 1905 quotients [(I⁺)−(I⁻)]/[(I⁺)+(I⁻)] (Parsons et al., 2013 )
Absolute structure parameter	0.48 (5)
Computer programs: X-AREA (Stoe & Cie, 2001), SHELXS97 (Sheldrick, 2008 ), XP in SHELXTL-Plus (Sheldrick, 2008), SHELXL2018 (Sheldrick, 2015 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 1979631

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S2056989020000900/hb7874sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989020000900/hb7874Isup2.hkl

checkCIF report

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: SHELXL2018 (Sheldrick, 2015); molecular graphics: XP in SHELXTL-Plus (Sheldrick, 2008); software used to prepare material for publication: SHELXL2018 (Sheldrick, 2015) and publCIF (Westrip, 2010).

Dodecachloropentasilane benzene monosolvate top

Crystal data top

Cl₁₂Si₅·C₆H₆	D_x = 1.769 Mg m⁻³
M_r = 643.96	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, P4₁22	Cell parameters from 62511 reflections
a = 11.9633 (4) Å	θ = 1.9–27.6°
c = 33.7848 (16) Å	µ = 1.62 mm⁻¹
V = 4835.3 (4) Å³	T = 173 K
Z = 8	Block, colourless
F(000) = 2528	0.28 × 0.18 × 0.16 mm

Data collection top

Stoe IPDS II two-circle diffractometer	4790 reflections with I > 2σ(I)
ω scans	R_int = 0.047
Absorption correction: multi-scan (X-AREA; Stoe & Cie, 2001)	θ_max = 27.1°, θ_min = 1.8°
T_min = 0.803, T_max = 1.0	h = −14→15
39180 measured reflections	k = −15→15
5189 independent reflections	l = −43→43

Refinement top

Refinement on F²	Hydrogen site location: mixed
Least-squares matrix: full	H-atom parameters constrained
R[F² > 2σ(F²)] = 0.027	w = 1/[σ²(F_o²) + (0.0375P)² + 2.8317P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.075	(Δ/σ)_max = 0.001
S = 1.08	Δρ_max = 0.39 e Å⁻³
5189 reflections	Δρ_min = −0.42 e Å⁻³
207 parameters	Absolute structure: Flack x determined using 1905 quotients [(I⁺)-(I^-)]/[(I⁺)+(I^-)] (Parsons et al., 2013)
5 restraints	Absolute structure parameter: 0.48 (5)
Primary atom site location: structure-invariant direct methods

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Si1	0.54973 (7)	0.45027 (7)	0.125000	0.0222 (3)
Si2	0.38834 (7)	0.45056 (7)	0.08678 (2)	0.02447 (19)
Si3	0.54972 (8)	0.29277 (8)	0.16530 (3)	0.0264 (2)
Cl21	0.40377 (8)	0.34525 (8)	0.04060 (2)	0.0400 (2)
Cl22	0.25695 (7)	0.39988 (8)	0.11990 (3)	0.0387 (2)
Cl23	0.35776 (8)	0.60671 (7)	0.06658 (3)	0.0384 (2)
Cl31	0.49743 (8)	0.15929 (7)	0.13366 (3)	0.0408 (2)
Cl32	0.70602 (8)	0.26452 (9)	0.18579 (3)	0.0453 (2)
Cl33	0.44514 (8)	0.31660 (9)	0.21128 (3)	0.0412 (2)
Si4	0.04988 (7)	−0.04988 (7)	0.125000	0.0225 (3)
Si5	0.05165 (7)	0.11311 (7)	0.16232 (2)	0.02420 (19)
Si6	0.20502 (8)	−0.05209 (8)	0.08356 (3)	0.0263 (2)
Cl51	−0.05058 (7)	0.09833 (8)	0.20938 (2)	0.0382 (2)
Cl52	−0.00287 (8)	0.24225 (7)	0.12875 (3)	0.0367 (2)
Cl53	0.20867 (7)	0.14553 (8)	0.18124 (3)	0.0379 (2)
Cl61	0.23134 (9)	0.10282 (8)	0.06166 (3)	0.0449 (2)
Cl62	0.17856 (9)	−0.15973 (8)	0.03862 (2)	0.0414 (2)
Cl63	0.34091 (8)	−0.10198 (9)	0.11430 (3)	0.0424 (2)
C1	0.000000	0.3434 (6)	0.000000	0.100 (4)
H1	0.000000	0.263981	0.000000	0.120*
C2	0.0511 (5)	0.4024 (4)	0.03030 (13)	0.094 (2)
H2	0.087169	0.363505	0.051231	0.113*
C3	0.0495 (5)	0.5176 (4)	0.03001 (14)	0.090 (2)
H3	0.083717	0.556596	0.051284	0.107*
C4	0.000000	0.5786 (7)	0.000000	0.087 (3)
H4	0.000000	0.657984	0.000000	0.104*
C5	0.5409 (8)	0.8628 (10)	0.0236 (3)	0.051 (2)*	0.5
H5	0.570943	0.806236	0.040196	0.062*	0.5
C6	0.5561 (8)	0.9738 (11)	0.0335 (3)	0.050 (2)*	0.5
H6	0.594385	0.992910	0.057205	0.059*	0.5
C7	0.5158 (9)	1.0566 (8)	0.0092 (3)	0.054 (3)*	0.5
H7	0.527035	1.132987	0.015732	0.065*	0.5
C5'	0.5145 (10)	0.8339 (8)	0.0086 (3)	0.057 (3)*	0.5
H5'	0.526088	0.757264	0.014687	0.068*	0.5
C6'	0.5559 (9)	0.9177 (12)	0.0335 (3)	0.058 (2)*	0.5
H6'	0.594991	0.897299	0.056942	0.069*	0.5
C7'	0.5410 (10)	1.0290 (11)	0.0247 (4)	0.062 (3)*	0.5
H7'	0.569534	1.085379	0.041783	0.074*	0.5

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Si1	0.0213 (4)	0.0213 (4)	0.0241 (6)	0.0004 (5)	0.0008 (3)	0.0008 (3)
Si2	0.0245 (4)	0.0238 (4)	0.0251 (4)	0.0000 (3)	−0.0010 (3)	0.0009 (3)
Si3	0.0252 (4)	0.0247 (4)	0.0294 (4)	0.0001 (4)	−0.0007 (3)	0.0046 (3)
Cl21	0.0521 (5)	0.0364 (5)	0.0316 (4)	−0.0014 (4)	0.0003 (4)	−0.0084 (3)
Cl22	0.0269 (4)	0.0476 (5)	0.0418 (4)	−0.0054 (4)	0.0051 (3)	0.0042 (4)
Cl23	0.0464 (5)	0.0278 (4)	0.0411 (4)	0.0058 (4)	−0.0079 (4)	0.0060 (3)
Cl31	0.0452 (5)	0.0268 (4)	0.0503 (5)	−0.0048 (4)	−0.0003 (4)	−0.0032 (4)
Cl32	0.0317 (4)	0.0461 (5)	0.0579 (5)	0.0068 (4)	−0.0113 (4)	0.0116 (4)
Cl33	0.0406 (5)	0.0529 (6)	0.0302 (4)	−0.0059 (4)	0.0065 (4)	0.0031 (4)
Si4	0.0214 (4)	0.0214 (4)	0.0245 (6)	0.0000 (5)	0.0006 (3)	0.0006 (3)
Si5	0.0236 (4)	0.0242 (4)	0.0248 (4)	−0.0008 (3)	−0.0010 (3)	−0.0011 (3)
Si6	0.0248 (4)	0.0259 (4)	0.0282 (4)	0.0001 (4)	0.0038 (3)	0.0010 (3)
Cl51	0.0366 (5)	0.0486 (5)	0.0295 (4)	0.0010 (4)	0.0072 (3)	−0.0013 (4)
Cl52	0.0436 (5)	0.0268 (4)	0.0398 (4)	0.0039 (4)	−0.0050 (4)	0.0042 (3)
Cl53	0.0282 (4)	0.0428 (5)	0.0429 (4)	−0.0063 (4)	−0.0069 (3)	−0.0033 (4)
Cl61	0.0489 (5)	0.0325 (4)	0.0533 (5)	−0.0063 (4)	0.0126 (4)	0.0108 (4)
Cl62	0.0520 (5)	0.0404 (5)	0.0317 (4)	0.0053 (4)	0.0022 (4)	−0.0084 (4)
Cl63	0.0274 (4)	0.0505 (5)	0.0494 (5)	0.0067 (4)	−0.0039 (4)	0.0003 (4)
C1	0.074 (6)	0.043 (4)	0.184 (11)	0.000	0.056 (7)	0.000
C2	0.068 (4)	0.147 (7)	0.067 (4)	0.011 (4)	0.001 (3)	0.055 (4)
C3	0.070 (4)	0.138 (6)	0.060 (3)	−0.026 (4)	0.006 (3)	−0.037 (4)
C4	0.067 (5)	0.068 (5)	0.125 (8)	0.000	0.040 (5)	0.000

Geometric parameters (Å, º) top

Si1—Si2	2.3227 (11)	Si6—Cl61	2.0202 (13)
Si1—Si2ⁱ	2.3228 (11)	C1—C2	1.3855 (18)
Si1—Si3ⁱ	2.3246 (11)	C1—C2ⁱⁱⁱ	1.3855 (18)
Si1—Si3	2.3247 (11)	C1—H1	0.9500
Si2—Cl21	2.0138 (12)	C2—C3	1.378 (3)
Si2—Cl23	2.0221 (12)	C2—H2	0.9500
Si2—Cl22	2.0225 (12)	C3—C4	1.3824 (18)
Si3—Cl33	2.0150 (13)	C3—H3	0.9500
Si3—Cl31	2.0209 (13)	C4—H4	0.9500
Si3—Cl32	2.0223 (13)	C5—C6	1.382 (15)
Si4—Si5	2.3221 (11)	C5—H5	0.9500
Si4—Si5ⁱⁱ	2.3222 (11)	C6—C7	1.375 (14)
Si4—Si6	2.3250 (11)	C6—H6	0.9500
Si4—Si6ⁱⁱ	2.3251 (11)	C7—H7	0.9500
Si5—Cl51	2.0138 (12)	C5'—C6'	1.399 (15)
Si5—Cl53	2.0218 (12)	C5'—H5'	0.9501
Si5—Cl52	2.0243 (12)	C6'—C7'	1.376 (15)
Si6—Cl62	2.0158 (13)	C6'—H6'	0.9500
Si6—Cl63	2.0194 (13)	C7'—H7'	0.9500

Si2—Si1—Si2ⁱ	107.85 (6)	C2—C1—C2ⁱⁱⁱ	118.8 (7)
Si2—Si1—Si3ⁱ	110.38 (3)	C2—C1—H1	120.6
Si2ⁱ—Si1—Si3ⁱ	109.07 (3)	C2ⁱⁱⁱ—C1—H1	120.6
Si2—Si1—Si3	109.07 (3)	C3—C2—C1	119.9 (6)
Si2ⁱ—Si1—Si3	110.37 (3)	C3—C2—H2	120.1
Si3ⁱ—Si1—Si3	110.06 (7)	C1—C2—H2	120.1
Cl21—Si2—Cl23	109.46 (5)	C2—C3—C4	122.6 (6)
Cl21—Si2—Cl22	108.20 (6)	C2—C3—H3	118.7
Cl23—Si2—Cl22	108.85 (6)	C4—C3—H3	118.7
Cl21—Si2—Si1	110.71 (5)	C3ⁱⁱⁱ—C4—C3	116.3 (7)
Cl23—Si2—Si1	109.84 (5)	C3ⁱⁱⁱ—C4—H4	121.9
Cl22—Si2—Si1	109.75 (4)	C3—C4—H4	121.9
Cl33—Si3—Cl31	109.11 (6)	C6—C5—C5^iv	106.0 (6)
Cl33—Si3—Cl32	109.50 (6)	C6—C5—H5	119.4
Cl31—Si3—Cl32	109.58 (6)	C5^iv—C5—H5	134.6
Cl33—Si3—Si1	109.69 (5)	C5—C6—C7	120.0 (9)
Cl31—Si3—Si1	109.31 (5)	C5—C6—C7^iv	104.5 (8)
Cl32—Si3—Si1	109.63 (5)	C5—C6—H6	120.0
Si5—Si4—Si5ⁱⁱ	108.07 (6)	C7—C6—H6	120.0
Si5—Si4—Si6	109.22 (3)	C7^iv—C6—H6	135.5
Si5ⁱⁱ—Si4—Si6	110.07 (3)	C7^iv—C7—C6	133.9 (6)
Si5—Si4—Si6ⁱⁱ	110.08 (3)	C6—C7—C6^iv	103.4 (9)
Si5ⁱⁱ—Si4—Si6ⁱⁱ	109.22 (3)	C7^iv—C7—H7	105.9
Si6—Si4—Si6ⁱⁱ	110.15 (7)	C6—C7—H7	120.2
Cl51—Si5—Cl53	109.35 (5)	C6^iv—C7—H7	136.4
Cl51—Si5—Cl52	108.28 (6)	C5'^iv—C5'—C6'	134.3 (6)
Cl53—Si5—Cl52	109.28 (6)	C5'^iv—C5'—H5'	105.1
Cl51—Si5—Si4	110.45 (5)	C6'—C5'—H5'	120.6
Cl53—Si5—Si4	109.95 (5)	C6'^iv—C5'—H5'	136.3
Cl52—Si5—Si4	109.50 (5)	C7'—C6'—C5'	121.1 (10)
Cl62—Si6—Cl63	108.97 (6)	C7'—C6'—H6'	119.4
Cl62—Si6—Cl61	109.56 (6)	C5'—C6'—H6'	119.4
Cl63—Si6—Cl61	109.51 (6)	C5'^iv—C6'—H6'	134.0
Cl62—Si6—Si4	109.60 (5)	C6'—C7'—C7'^iv	104.6 (7)
Cl63—Si6—Si4	109.65 (5)	C6'—C7'—H7'	120.6
Cl61—Si6—Si4	109.54 (5)	C7'^iv—C7'—H7'	134.8

C2ⁱⁱⁱ—C1—C2—C3	0.6 (4)	C7^iv—C6—C7—C6^iv	−1 (2)
C1—C2—C3—C4	−1.2 (9)	C5'^iv—C5'—C6'—C7'	0 (4)
C2—C3—C4—C3ⁱⁱⁱ	0.6 (4)	C6'^iv—C5'—C6'—C7'	0.0 (10)
C5^iv—C5—C6—C7	−1.7 (13)	C6'^iv—C5'—C6'—C5'^iv	0 (3)
C5^iv—C5—C6—C7^iv	−1.2 (10)	C5'—C6'—C7'—C7'^iv	−0.1 (14)
C5—C6—C7—C7^iv	2 (3)	C5'^iv—C6'—C7'—C7'^iv	−0.2 (11)
C5—C6—C7—C6^iv	1.0 (9)

Symmetry codes: (i) −y+1, −x+1, −z+1/4; (ii) −y, −x, −z+1/4; (iii) −x, y, −z; (iv) −x+1, y, −z.

Bond lengths (Å) in the different structures containing Si₅Cl₁₂ molecules top

	Si—Si	Si—Cl
(I)	2.324	2.019
(II)	2.340	2.026
(III)	2.332 (9)	1.994 (7)

References

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