C-H...[pi] inter­actions in cocrystals of bis­(trimethyl­silyl)acetyl­ene and diphenyl­acetyl­ene with benzene

We present here the crystal structures of two acetyl­ene derivatives cocrystallized with benzene, namely bis­(trimethyl­silyl)acetyl­ene benzene solvate, C₈H₁₈Si₂·C₆H₆, (I), and diphenyl­acetyl­ene benzene solvate, C₁₄H₁₀·C₆H₆, (II). In (I), both mol­ecules belong to the symmetry point group C_2h and are located about special positions with site symmetry 2/m. In (II), both mol­ecules show crystallographic inversion symmetry. In both structures, there are C-H...[pi] contacts between aromatic H atoms and the [pi]-electrons of the triple bond. In addition to these, in (II) there are C-H...[pi] contacts between aromatic H atoms and the [pi]-electron cloud of the benzene mol­ecules.

S1. Comment

The structures of co-crystals of compounds which interact via the π-system with other molecules have received increased attention in recent years. As reported by Kirchner et al. (2010) the structure of the co-crystals of acetylene, HC≡CH, and different arenes feature a structural arrangement with C—H···π contacts as shown in Fig. 1. In all these cases (Figs. 1a, 1b, 1c) the H atoms of the acetylene molecule form C—H···π interactions with the π-system of the arene rings. It is interesting to note that unusually short triple bonds are reported for the acetylene molecules in these co-crystals.

In this paper we describe co-crystals of benzene with the alkines Me₃SiC≡ CSiMe₃ and PhC≡CPh, (I) and (II), respectively. In contrast to the acetylene arene complexes, the structures of the benzene co-crystals of the alkines (I) and (II) reveal C—H···π interactions of H atoms of the aromatic rings with the π-system of the alkine.

Very recently, we have shown that the degradation of Cl₃SiSiCl₃ and Cl₃SiSiCl₂SiCl₃ in the presence of catalytic amounts of donors, such as amines, in the first step gives dichlorosilylene (SiCl₂₎ and ultimately produces the perchlorinated neopentasilane [Si(SiCl₃)_4]. Moreover, we have verified that the donor-induced degradation of Cl₃SiSiCl₃ or Cl₃SiSiCl₂SiCl₃ in the presence of the silylene-trapping agent 2,3-dimethyl-1,3-butadiene gives the [4+1] cycloadduct (Meyer-Wegner et al., 2009). We are currently interested in cluster compounds consisting of group 14 elements (Wiberg, Lerner, Nöth & Ponikwar, 1999; Wiberg, Lerner, Wagner et al., 1999; Wiberg, Lerner, Vasisht et al., 1999; Lerner, 2005; Lerner et al., 2010) especially those which are composed of two different group 14 elements. To this end, we thought that such cluster compounds can be prepared using the reaction between SiCl₂ and PhC≡CPh or Me₃SiC≡CSiMe₃. However, the amine-induced degradation reaction of Cl₃SiSiCl₃ in the presence of PhC≡CPh or Me₃SiC≡CSiMe₃ gives in both cases exclusively the neopentasilane Si(SiCl₃)₄. Apparently, no trapping product and therefore no cluster was formed. The perchlorinated neopentasilane Si(SiCl₃)₄ was identified unambiguously by ²⁹Si NMR spectroscopy. Otherwise single crystals composed of one molecule of benzene and one molecule of PhC≡CPh and Me₃SiC≡CSiMe₃, respectively, could be isolated from these reaction solutions.

(I) crystallizes with just a quarter of both molecules in the asymmetric unit (Fig. 2). The crystal packing is illustrated in Fig. 3, which shows the C—H···π contacts as dashed lines. There are two symmetry-equivalent contacts. The distance from the H atom (H4) to the centre of the triple bond is 3.013 Å, and the angle at the H atom is exactly 180°.

(II) crystallizes with two half molecules in the asymmetric unit, both of which are located on a centre of inversion (Fig. 4). As for (I), there are C—H···π contacts between aromatic H atoms and the π-electrons of the triple bond (Fig. 5), but in contrast to (I), in this structure, there are four C—H···π contacts, two of which are symmetry equivalent. The contact from the benzolic H atom H8 to the centre of the triple bond has a distance of 3.268 Å and the angle at the H atom is 146°. The second, slightly longer, contact links the phenylic H atom H5 at a distance of 3.555 Å to the centre of the triple bond. The angle at the H atom is 155°. Furthermore, in this structure a C—H···π contact to the centre of the benzene molecule can be observed. The distance from H4 to the centre of the aromatic ring is 2.789° and the angle at H4 is 1440°.

In order to compare the length of the C≡C bond in (I) and (II) with other structures, two searches of the Cambridge Structural Database (CSD, Version 5.3 of November 2008, plus four updates; Allen, 2002) were performed. For the fragment C₃Si—C≡C—SiC₃, which was found 27 times, a mean bond length of 1.20 (2) Å was found. This is in good agreement with the value of 1.211 (4) Å found for (I). A second search for diphenylacetylene in which the triple bond does not coordinate to any other atom yielded 34 entries. The mean value of the C≡C bond in these structures was 1.19 (3) Å which agrees well with the value of 1.201 (2) Å found for (II).

It is interesting to note that there are no π···π stacking interactions between aromatic rings in either of the two structures. In (I) the benzene molecules which are the only aromatic rings in this structure are perfectly shielded from each other and in (II) there is no aromatic ring located above another one.

Since neither C atom of the acetylene moiety in (I) and (II) carries a H atom, no C—H···π interaction of the kind encountered by Kirchner et al. (2010) could be found either in (I) nor in (II). Whereas the distance between an acetylenic H atom and the centre of an aromatic ring was found to be less than 3 Å, all C—H···π contacts to the C≡C bond in (I) and (II) are longer than 3 Å.

Both crystal structures presented here show a similar hydrogen-bonding pattern. There are C—H···π contacts from a H atom bonded to an aromatic C atom to the electron cloud of an acetylenic C≡C bond. Whereas in (I) there are no C—H···π interactions between two aromatic rings, this kind of interaction can be observed in (II). The reason for the occurrence of these contacts might be that (II) contains significantly more aromatic rings than (I). Both structures lack π···π stacking interactions between aromatic rings.

Related literature

For related literature, see: Allen (2002); Kirchner et al. (2010); Lerner (2005); Lerner et al. (2010); Meyer-Wegner, Scholz, Sänger, Schödel, Bolte, Wagner & Lerner (2009); Wiberg, Lerner, Nöth & Ponikwar (1999); Wiberg, Lerner, Vasisht, Wagner, Karaghiosoff, Nöth & Ponikwar (1999); Wiberg, Lerner, Wagner, Nöth & Seifert (1999).

S2. Experimental

For the synthesis of (I): a solution of Cl₃SiSiCl₃ (0.08 g, 0.29 mmol), N,N,N',N'-tetramethylethylenediamine (0.03 g, 0.29 mmol) and Me₃SiC≡CSiMe₃ (0.30 g, 1.74 mmol) in 1 ml benzene was heated for 110 h to 323 K. After cooling to room temperature, single crystals of the 1:1 adduct of benzene and Me₃SiC≡CSiMe₃ were obtained (yield 55%). In the ²⁹Si NMR spectrum of the reaction solution signals were observed which can be assigned to the perchlorinated neopentasilane Si(SiCl₃)₄.

For the synthesis of (II): a mixture of Cl₃SiSiCl₃ (0.08 g, 0.29 mmol), Me₂NEt (0.01 g, 0.15 mmol) and PhC≡ CPh (0.32 g, 1.78 mmol) were dissolved 1 ml benzene. After 48 h at room temperature single crystals of the 1:1 adduct of benzene and PhC≡CPh were obtained (yield 60%). In the ²⁹Si NMR spectrum of the reaction solution signals were observed which can be assigned to the perchlorinated neopentasilane Si(SiCl₃)₄. ²⁹Si NMR (C₆D₆): δ 3.5 [Si(SiCl₃)_4], δ -82.0 [Si(SiCl₃)₄].

S3. Refinement

H atoms were located in a difference Fourier map but were included in calculated positions [C_aromatic—H = 0.95 Å and C_methyl—H = 0.98 Å] and refined as riding with U_iso(H) = 1.2U_eq(C_aromatic) or U_iso(H) = 1.5U_eq(C_methyl).

Computing details

For both compounds, 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 (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. Structural arrangement with C—H···π contacts.
	Fig. 2. A perspective view of the two molecules of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. Symmetry operators for generating equivalent atoms: (A) -x, -y, -z+1; (B) x, -y, z; (C) -x, y, -z+1; (D) -x, -y+1, -z+1; (E) x, -y+1, z; (F) -x, y , -z+1;
	Fig. 3. The crystal packing of (I). C—H···π contacts are shown as dashed lines.
	Fig. 4. A perspective view of the two molecules of (II), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. Symmetry operators for generating equivalent atoms: (A) -x, -y, -z+1 and (B) -x+1, -y+1, -z+1.
	Fig. 5. The crystal packing of (II). C—H···π contacts are shown as dashed lines.

(I) bis(trimethylsilyl)acetylene benzene solvate

Crystal data

C8H18Si2·C6H6	F(000) = 272
Mr = 248.51	Dx = 1.004 Mg m^−3
Monoclinic, C2/m	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2y	Cell parameters from 1358 reflections
a = 14.0831 (14) Å	θ = 3.9–25.2°
b = 10.6487 (12) Å	µ = 0.19 mm^−1
c = 5.7225 (6) Å	T = 173 K
β = 106.739 (7)°	Block, colourless
V = 821.82 (15) Å^3	0.43 × 0.38 × 0.35 mm
Z = 2

Data collection

Stoe IPDS II two-circle diffractometer	808 independent reflections
Radiation source: fine-focus sealed tube	754 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.029
ω scans	θmax = 25.6°, θmin = 3.8°
Absorption correction: multi-scan (MULABS: Spek, 2003; Blessing, 1995)	h = −17→17
Tmin = 0.921, Tmax = 0.935	k = −12→12
2358 measured reflections	l = −5→6

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.033	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.090	H-atom parameters constrained
S = 1.07	w = 1/[σ^2(Fo^2) + (0.050P)^2 + 0.4354P] where P = (Fo^2 + 2Fc^2)/3
808 reflections	(Δ/σ)max < 0.001
42 parameters	Δρmax = 0.21 e Å^−3
0 restraints	Δρmin = −0.25 e Å^−3

Special details

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.

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 (Ų)

	x	y	z	Uiso*/Ueq
Si1	0.15254 (4)	0.0000	0.37340 (10)	0.0290 (2)
C1	0.03694 (14)	0.0000	0.4661 (4)	0.0313 (4)
C2	0.15443 (13)	0.14371 (15)	0.1900 (3)	0.0457 (4)
H2A	0.2153	0.1450	0.1396	0.069*
H2B	0.1523	0.2183	0.2888	0.069*
H2C	0.0967	0.1436	0.0451	0.069*
C3	0.25731 (16)	0.0000	0.6575 (4)	0.0434 (5)
H3A	0.3201	0.0000	0.6160	0.065*
H3C	0.2536	0.0751	0.7533	0.065*
C4	0.0000	0.3721 (2)	0.5000	0.0591 (8)
H4	0.0000	0.2829	0.5000	0.071*
C5	0.04258 (13)	0.4362 (2)	0.7113 (3)	0.0570 (5)
H5	0.0721	0.3916	0.8579	0.068*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Si1	0.0278 (3)	0.0275 (3)	0.0347 (4)	0.000	0.0140 (2)	0.000
C1	0.0306 (9)	0.0274 (9)	0.0369 (11)	0.000	0.0113 (8)	0.000
C2	0.0507 (9)	0.0385 (8)	0.0549 (10)	0.0023 (7)	0.0263 (8)	0.0085 (7)
C3	0.0316 (11)	0.0567 (14)	0.0435 (12)	0.000	0.0135 (9)	0.000
C4	0.0596 (15)	0.0332 (11)	0.104 (2)	0.000	0.0543 (16)	0.000
C5	0.0425 (9)	0.0818 (13)	0.0514 (10)	0.0170 (9)	0.0211 (8)	0.0264 (9)

Geometric parameters (Å, º)

Si1—C1	1.852 (2)	C3—H3A	0.9800
Si1—C3	1.854 (2)	C3—H3C	0.9800
Si1—C2	1.8600 (16)	C4—C5^iii	1.367 (2)
Si1—C2^i	1.8600 (16)	C4—C5	1.367 (2)
C1—C1^ii	1.211 (4)	C4—H4	0.9500
C2—H2A	0.9800	C5—C5^iv	1.358 (4)
C2—H2B	0.9800	C5—H5	0.9500
C2—H2C	0.9800
C1—Si1—C3	106.98 (10)	H2A—C2—H2C	109.5
C1—Si1—C2	108.55 (6)	H2B—C2—H2C	109.5
C3—Si1—C2	110.95 (7)	Si1—C3—H3A	109.5
C1—Si1—C2^i	108.55 (6)	Si1—C3—H3C	109.5
C3—Si1—C2^i	110.95 (7)	H3A—C3—H3C	109.5
C2—Si1—C2^i	110.72 (11)	C5^iii—C4—C5	120.1 (2)
C1^ii—C1—Si1	178.1 (2)	C5^iii—C4—H4	120.0
Si1—C2—H2A	109.5	C5—C4—H4	120.0
Si1—C2—H2B	109.5	C5^iv—C5—C4	119.95 (12)
H2A—C2—H2B	109.5	C5^iv—C5—H5	120.0
Si1—C2—H2C	109.5	C4—C5—H5	120.0
C5^iii—C4—C5—C5^iv	0.0

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

(II) 1,2-diphenylacetylene benzene solvate

Crystal data

C14H10·C6H6	F(000) = 272
Mr = 256.35	Dx = 1.157 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 3675 reflections
a = 5.7078 (6) Å	θ = 3.7–25.9°
b = 9.0681 (7) Å	µ = 0.07 mm^−1
c = 14.4212 (16) Å	T = 173 K
β = 99.741 (9)°	Block, colourless
V = 735.66 (13) Å^3	0.41 × 0.35 × 0.32 mm
Z = 2

Data collection

Stoe IPDS II two-circle diffractometer	1182 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.037
Graphite monochromator	θmax = 25.6°, θmin = 3.6°
ω scans	h = −6→6
3831 measured reflections	k = −9→10
1358 independent reflections	l = −17→14

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.036	H-atom parameters constrained
wR(F^2) = 0.099	w = 1/[σ^2(Fo^2) + (0.0589P)^2 + 0.0469P] where P = (Fo^2 + 2Fc^2)/3
S = 1.08	(Δ/σ)max < 0.001
1358 reflections	Δρmax = 0.15 e Å^−3
92 parameters	Δρmin = −0.12 e Å^−3
0 restraints	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.096 (13)

Special details

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.

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 (Ų)

	x	y	z	Uiso*/Ueq
C1	0.13042 (18)	0.04408 (11)	0.37996 (8)	0.0375 (3)
C2	0.33428 (19)	−0.02787 (11)	0.36153 (8)	0.0398 (3)
H2	0.4127	−0.0978	0.4051	0.048*
C3	0.42178 (19)	0.00262 (12)	0.27999 (8)	0.0423 (3)
H3	0.5592	−0.0474	0.2674	0.051*
C4	0.3110 (2)	0.10532 (12)	0.21656 (8)	0.0439 (3)
H4	0.3724	0.1261	0.1607	0.053*
C5	0.1106 (2)	0.17776 (12)	0.23461 (8)	0.0447 (3)
H5	0.0353	0.2491	0.1913	0.054*
C6	0.01914 (18)	0.14701 (12)	0.31526 (8)	0.0411 (3)
H6	−0.1202	0.1962	0.3267	0.049*
C7	0.03862 (19)	0.01323 (12)	0.46466 (9)	0.0436 (3)
C8	0.30705 (18)	0.59454 (12)	0.48945 (8)	0.0387 (3)
H8	0.1747	0.6595	0.4822	0.046*
C9	0.51688 (19)	0.63321 (11)	0.54720 (8)	0.0390 (3)
H9	0.5284	0.7248	0.5797	0.047*
C10	0.70988 (18)	0.53882 (12)	0.55776 (8)	0.0400 (3)
H10	0.8539	0.5656	0.5974	0.048*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0377 (5)	0.0321 (5)	0.0441 (6)	−0.0097 (4)	0.0105 (4)	−0.0077 (4)
C2	0.0419 (6)	0.0303 (5)	0.0478 (6)	−0.0013 (4)	0.0089 (5)	0.0003 (4)
C3	0.0413 (6)	0.0354 (6)	0.0530 (7)	−0.0014 (4)	0.0155 (5)	−0.0054 (5)
C4	0.0520 (7)	0.0399 (6)	0.0413 (6)	−0.0060 (5)	0.0123 (5)	−0.0043 (5)
C5	0.0487 (6)	0.0379 (6)	0.0442 (7)	−0.0009 (5)	−0.0013 (5)	−0.0018 (5)
C6	0.0333 (5)	0.0370 (6)	0.0519 (7)	−0.0021 (4)	0.0043 (4)	−0.0101 (5)
C7	0.0423 (6)	0.0375 (6)	0.0531 (7)	−0.0077 (4)	0.0137 (5)	−0.0063 (5)
C8	0.0388 (6)	0.0357 (6)	0.0428 (6)	0.0016 (4)	0.0105 (4)	0.0033 (4)
C9	0.0467 (6)	0.0315 (5)	0.0401 (6)	−0.0061 (4)	0.0115 (4)	−0.0039 (4)
C10	0.0377 (5)	0.0418 (6)	0.0398 (6)	−0.0071 (4)	0.0042 (4)	−0.0013 (4)

Geometric parameters (Å, º)

C1—C6	1.3946 (16)	C5—H5	0.9500
C1—C2	1.3982 (15)	C6—H6	0.9500
C1—C7	1.4358 (16)	C7—C7^i	1.201 (2)
C2—C3	1.3810 (16)	C8—C10^ii	1.3831 (16)
C2—H2	0.9500	C8—C9	1.3833 (15)
C3—C4	1.3814 (17)	C8—H8	0.9500
C3—H3	0.9500	C9—C10	1.3829 (16)
C4—C5	1.3814 (16)	C9—H9	0.9500
C4—H4	0.9500	C10—C8^ii	1.3831 (16)
C5—C6	1.3814 (17)	C10—H10	0.9500
C6—C1—C2	118.99 (10)	C4—C5—H5	119.8
C6—C1—C7	120.61 (10)	C5—C6—C1	120.28 (10)
C2—C1—C7	120.40 (10)	C5—C6—H6	119.9
C3—C2—C1	120.06 (10)	C1—C6—H6	119.9
C3—C2—H2	120.0	C7^i—C7—C1	179.67 (16)
C1—C2—H2	120.0	C10^ii—C8—C9	119.95 (10)
C2—C3—C4	120.52 (10)	C10^ii—C8—H8	120.0
C2—C3—H3	119.7	C9—C8—H8	120.0
C4—C3—H3	119.7	C10—C9—C8	120.12 (10)
C3—C4—C5	119.78 (11)	C10—C9—H9	119.9
C3—C4—H4	120.1	C8—C9—H9	119.9
C5—C4—H4	120.1	C9—C10—C8^ii	119.93 (10)
C6—C5—C4	120.37 (11)	C9—C10—H10	120.0
C6—C5—H5	119.8	C8^ii—C10—H10	120.0
C6—C1—C2—C3	−0.42 (15)	C4—C5—C6—C1	0.97 (16)
C7—C1—C2—C3	−179.86 (10)	C2—C1—C6—C5	−0.44 (15)
C1—C2—C3—C4	0.76 (16)	C7—C1—C6—C5	179.00 (10)
C2—C3—C4—C5	−0.24 (17)	C10^ii—C8—C9—C10	0.06 (18)
C3—C4—C5—C6	−0.63 (17)	C8—C9—C10—C8^ii	−0.06 (18)

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