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The rod-like molecule of the title hydro­carbon, C24H18, is centrosymmetric, with the centroid of the central benzene ring residing on an inversion center. The molecules display a planar conformation of the benzene rings and aggregate into stacks along the [010] direction via Csp3—H...π(arene) interactions, thus forming a stair-like pseudo-two-dimensional network. Each molecule acts as both a C—H hydrogen donor and a π-arene acceptor, forming four hydrogen bonds per molecule.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270105000983/gg1238sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270105000983/gg1238Isup2.hkl
Contains datablock I

CCDC reference: 268127

Comment top

The present work forms part of our studies focused on the structures and reactivities of planar and curved polyaromatic hydrocarbons (Petrukhina et al., 2004). Molecules showing π-extended conjugation attract special attention since they exhibit interesting electroconductive, magnetic and optical properties (Bunz, 2000; Delaire & Nakatani, 2000; Kawase et al., 2003). Knowledge of the intermolecular interactions determining solid-state packing is required in order to understand the influence of crystal structure on the above properties. Here, we present the structural characterization of 1,4-bis(p-tolylethynyl)benzene, (I). The synthesis of (I) was previously reported by Nguyen et al. (1994), but its crystal structure has not been reported to date.

The present X-ray structural analysis shows that all three benzene rings are coplanar in the centrosymmetric molecule of (I) (Fig. 1), with an r.m.s. displacement of the C atoms from the molecular plane of 0.012 Å and a maximum displacement of 0.020 (1) Å for atom C10. The C—C bond lengths within the phenyl rings are very similar and are consistent with values typical for para-substituted aryls. The CC bond length [1.199 (2) Å; Table 1] is virtually identical, as reported for diphenylacetylene, (II), C6H5—CC—C6H5 [1.198 (3) Å; Mavridis & Moustakali-Mavridis, 1977].

In the current study, ab initio calculations have been performed on (I) at the HF/6–31 G(d,p) level (Frisch et al., 1998) in order to estimate the rotation barriers of the phenyl rings. The potential minimum (-918.9296 a.u.) corresponds to the planar conformation. This contrasts with (II), where a conformation with perpendicular phenyl rings is favoured (Liberles & Matlosz, 1971). The rotation barrier for the peripheral phenyl rings in (I) (0.73 kcal mol-1; 1 kcal mol-1 = 4.184 kJ mol-1) is comparable with the rotation barrier in (II) (ca 0.6 kcal mol-1). The rotation barrier for the central phenyl ring located between the two CC triple bonds is only ca 1.6 times greater (1.14 kcal mol-1) than for the terminal phenyl rings, which are constrained by one triple bond.

In the crystal structure of (I), molecules of C24H18 are aligned along the [010] direction in a regular fashion but show a chain slippage of ca 3.45 Å, thus preventing ππ stacking of the phenyl rings of neighbouring molecules (Fig. 2). By contrast, the packing motif for (II) is based on a face-to-face coplanar stacking. The most probable reasons for such a difference in the solid-state structures of (I) and (II) are repulsive interactions of the methyl groups, forcing the molecules of (I) to slip, and the formation of intermolecular hydrogen bridges by means of the Csp3—H···π(arene) bonds, forming a pseudo-two-dimensional stack.

It has been shown previously that methyl groups can function as hydrogen-bond donors towards aromatic π systems (Desiraju, 2002). In the structure of (I), each linear hydrocarbon molecule serves as a two-site hydrogen acceptor using two peripheral phenyl rings, and as a two-site hydrogen donor provided by the methyl groups. The value for these hydrogen bonds [2.605 (19) Å] is noticeably short [estimated as the distance between the H atom and the centroid (Cg1) of the phenyl ring defined by atoms C2–C7]. It is comparable with the distances for the more activated C—H donors, such as those containing ethylene or acetylene moieties (ca 2.5–2.7 Å; Weiss et al., 1997; Gobius du Sart et al., 2004). The angle formed by Csp3—H···Cg1 tends toward linearity and is 164°. It is worth mentioning that the H atom lies almost exactly over the centre of the accepting phenyl ring, with the H—Cg1—Cn angles (Cn is C2–C7) ranging from 86.3 (4) to 93.4 (4)°. Hence, it does not exhibit a preferential interaction with any C atoms.

As a result of hydrogen bonding, the distance between the molecules of (I) in the stacks (3.52 Å) is similar to the intermolecular distance between 3,3',4,4'-tetrakis(phenylethynyl)biphenyl molecules (3.45 Å), held by strong ππ interactions (Perera et al., 2003). This may represent an additional verification for the existence of the hydrogen bridges that are responsible for the solid-state packing of (I).

In summary, an addition of methyl groups to rod-like π systems provides a source for C—H···π(arene) hydrogen bonding, which results in a sliding of the chain of one linear polyaromatic molecule over another in the solid state. This effect can be used to direct the self-assembly of aromatic hydrocarbons and to control their crystal packing.

Experimental top

1,4-Bis(p-tolylethynyl)benzene was synthesized according to the literature procedure of Nguyen et al. (1994). The crude product obtained from this procedure was purified by sublimation to yield a well defined crystalline powder of (I), which was sealed under vacuum in a small glass ampoule. The ampoule was placed in an electric furnace that had a small temperature gradient along the length of the tube. The temperature was set at 428 K. After 2 d, the temperature was gradually lowered at a rate of 5 K h-1. This resulted in the deposition in the coldest part of the ampoule of single crystals of (I) suitable for X-ray analysis.

Refinement top

Space group P21/c was uniquely assigned from the systematic absences. All H atoms were refined independently, and the range of C—H distances is 0.964 (13)–0.992 (12) Å for the aromatic rings and 0.974 (18)–1.000 (18) Å for the methyl group.

Structure description top

The present work forms part of our studies focused on the structures and reactivities of planar and curved polyaromatic hydrocarbons (Petrukhina et al., 2004). Molecules showing π-extended conjugation attract special attention since they exhibit interesting electroconductive, magnetic and optical properties (Bunz, 2000; Delaire & Nakatani, 2000; Kawase et al., 2003). Knowledge of the intermolecular interactions determining solid-state packing is required in order to understand the influence of crystal structure on the above properties. Here, we present the structural characterization of 1,4-bis(p-tolylethynyl)benzene, (I). The synthesis of (I) was previously reported by Nguyen et al. (1994), but its crystal structure has not been reported to date.

The present X-ray structural analysis shows that all three benzene rings are coplanar in the centrosymmetric molecule of (I) (Fig. 1), with an r.m.s. displacement of the C atoms from the molecular plane of 0.012 Å and a maximum displacement of 0.020 (1) Å for atom C10. The C—C bond lengths within the phenyl rings are very similar and are consistent with values typical for para-substituted aryls. The CC bond length [1.199 (2) Å; Table 1] is virtually identical, as reported for diphenylacetylene, (II), C6H5—CC—C6H5 [1.198 (3) Å; Mavridis & Moustakali-Mavridis, 1977].

In the current study, ab initio calculations have been performed on (I) at the HF/6–31 G(d,p) level (Frisch et al., 1998) in order to estimate the rotation barriers of the phenyl rings. The potential minimum (-918.9296 a.u.) corresponds to the planar conformation. This contrasts with (II), where a conformation with perpendicular phenyl rings is favoured (Liberles & Matlosz, 1971). The rotation barrier for the peripheral phenyl rings in (I) (0.73 kcal mol-1; 1 kcal mol-1 = 4.184 kJ mol-1) is comparable with the rotation barrier in (II) (ca 0.6 kcal mol-1). The rotation barrier for the central phenyl ring located between the two CC triple bonds is only ca 1.6 times greater (1.14 kcal mol-1) than for the terminal phenyl rings, which are constrained by one triple bond.

In the crystal structure of (I), molecules of C24H18 are aligned along the [010] direction in a regular fashion but show a chain slippage of ca 3.45 Å, thus preventing ππ stacking of the phenyl rings of neighbouring molecules (Fig. 2). By contrast, the packing motif for (II) is based on a face-to-face coplanar stacking. The most probable reasons for such a difference in the solid-state structures of (I) and (II) are repulsive interactions of the methyl groups, forcing the molecules of (I) to slip, and the formation of intermolecular hydrogen bridges by means of the Csp3—H···π(arene) bonds, forming a pseudo-two-dimensional stack.

It has been shown previously that methyl groups can function as hydrogen-bond donors towards aromatic π systems (Desiraju, 2002). In the structure of (I), each linear hydrocarbon molecule serves as a two-site hydrogen acceptor using two peripheral phenyl rings, and as a two-site hydrogen donor provided by the methyl groups. The value for these hydrogen bonds [2.605 (19) Å] is noticeably short [estimated as the distance between the H atom and the centroid (Cg1) of the phenyl ring defined by atoms C2–C7]. It is comparable with the distances for the more activated C—H donors, such as those containing ethylene or acetylene moieties (ca 2.5–2.7 Å; Weiss et al., 1997; Gobius du Sart et al., 2004). The angle formed by Csp3—H···Cg1 tends toward linearity and is 164°. It is worth mentioning that the H atom lies almost exactly over the centre of the accepting phenyl ring, with the H—Cg1—Cn angles (Cn is C2–C7) ranging from 86.3 (4) to 93.4 (4)°. Hence, it does not exhibit a preferential interaction with any C atoms.

As a result of hydrogen bonding, the distance between the molecules of (I) in the stacks (3.52 Å) is similar to the intermolecular distance between 3,3',4,4'-tetrakis(phenylethynyl)biphenyl molecules (3.45 Å), held by strong ππ interactions (Perera et al., 2003). This may represent an additional verification for the existence of the hydrogen bridges that are responsible for the solid-state packing of (I).

In summary, an addition of methyl groups to rod-like π systems provides a source for C—H···π(arene) hydrogen bonding, which results in a sliding of the chain of one linear polyaromatic molecule over another in the solid state. This effect can be used to direct the self-assembly of aromatic hydrocarbons and to control their crystal packing.

Computing details top

Data collection: SMART (Bruker, 1999); cell refinement: SMART; data reduction: SAINT (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and SHELXTL (Bruker, 1997); software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1. A view of the molecular structure of (I), showing displacement ellipsoids at the 70% probability level and H atoms as spheres of arbitrary radii. Atoms labelled with a symmetry code are symmetrically dependent via an inversion centre [symmetry code: (i) 2 - x, -y, -z Please check added symmetry code].
[Figure 2] Fig. 2. A fragment of the crystal structure of (I), showing the formation of a pseudo-two-dimensional network along the [010] direction through the Csp3—H···π(arene) hydrogen bonds.
1,4-Bis(p-tolylethynyl)benzene top
Crystal data top
C24H18F(000) = 324
Mr = 306.38Dx = 1.280 Mg m3
Monoclinic, P21/cMelting point: 493 K
Hall symbol: -P 2ybcMo Kα radiation, λ = 0.71073 Å
a = 14.5478 (11) ÅCell parameters from 3277 reflections
b = 4.9229 (4) Åθ = 2.4–28.3°
c = 11.3006 (9) ŵ = 0.07 mm1
β = 100.711 (1)°T = 173 K
V = 795.22 (11) Å3Plate, colourless
Z = 20.27 × 0.12 × 0.04 mm
Data collection top
Bruker SMART APEX CCD area-detector
diffractometer
1358 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.034
Graphite monochromatorθmax = 28.3°, θmin = 1.4°
0.3° wide ω exposures scansh = 1919
6512 measured reflectionsk = 66
1863 independent reflectionsl = 1414
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)] = 0.045Hydrogen site location: difference Fourier map
wR(F2) = 0.144All H-atom parameters refined
S = 1.02 w = 1/[σ2(Fo2) + (0.095P)2]
where P = (Fo2 + 2Fc2)/3
1863 reflections(Δ/σ)max < 0.001
145 parametersΔρmax = 0.28 e Å3
0 restraintsΔρmin = 0.22 e Å3
Crystal data top
C24H18V = 795.22 (11) Å3
Mr = 306.38Z = 2
Monoclinic, P21/cMo Kα radiation
a = 14.5478 (11) ŵ = 0.07 mm1
b = 4.9229 (4) ÅT = 173 K
c = 11.3006 (9) Å0.27 × 0.12 × 0.04 mm
β = 100.711 (1)°
Data collection top
Bruker SMART APEX CCD area-detector
diffractometer
1358 reflections with I > 2σ(I)
6512 measured reflectionsRint = 0.034
1863 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0450 restraints
wR(F2) = 0.144All H-atom parameters refined
S = 1.02Δρmax = 0.28 e Å3
1863 reflectionsΔρmin = 0.22 e Å3
145 parameters
Special details top

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
C10.56240 (9)1.3946 (2)0.17290 (11)0.0257 (3)
C20.63033 (7)1.1809 (2)0.14793 (10)0.0196 (3)
C30.62640 (8)1.0805 (2)0.03184 (10)0.0237 (3)
C40.69990 (8)1.0812 (2)0.23902 (10)0.0223 (3)
C50.68910 (8)0.8862 (2)0.00720 (10)0.0237 (3)
C60.76300 (8)0.8860 (2)0.21554 (10)0.0222 (3)
C70.75825 (7)0.7849 (2)0.09897 (10)0.0203 (3)
C80.82239 (8)0.5801 (2)0.07380 (9)0.0216 (3)
C90.87491 (7)0.4075 (2)0.05173 (9)0.0212 (3)
C100.93817 (7)0.2014 (2)0.02552 (9)0.0195 (3)
C110.93330 (8)0.1070 (2)0.09229 (10)0.0218 (3)
C121.00581 (8)0.0917 (2)0.11751 (10)0.0220 (3)
H1A0.5877 (13)1.579 (4)0.1600 (16)0.076 (6)*
H1B0.5533 (11)1.389 (3)0.2561 (17)0.071 (5)*
H1C0.5001 (12)1.375 (4)0.1205 (16)0.071 (5)*
H30.5775 (9)1.142 (3)0.0349 (12)0.035 (4)*
H40.7049 (9)1.152 (2)0.3221 (12)0.033 (3)*
H50.6839 (8)0.818 (3)0.0762 (12)0.033 (3)*
H60.8107 (9)0.821 (3)0.2801 (12)0.034 (3)*
H110.8859 (9)0.180 (3)0.1569 (11)0.031 (3)*
H121.0106 (8)0.154 (2)0.2018 (11)0.030 (3)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0272 (7)0.0222 (7)0.0298 (7)0.0051 (5)0.0106 (5)0.0005 (5)
C20.0213 (6)0.0160 (5)0.0233 (6)0.0003 (4)0.0085 (4)0.0013 (4)
C30.0235 (6)0.0250 (6)0.0223 (6)0.0041 (4)0.0034 (5)0.0027 (5)
C40.0256 (6)0.0213 (6)0.0207 (6)0.0002 (4)0.0058 (5)0.0025 (5)
C50.0274 (6)0.0242 (6)0.0204 (6)0.0021 (5)0.0064 (5)0.0023 (4)
C60.0214 (6)0.0217 (6)0.0227 (6)0.0025 (4)0.0018 (5)0.0012 (4)
C70.0205 (6)0.0162 (5)0.0259 (6)0.0000 (4)0.0082 (5)0.0001 (4)
C80.0217 (6)0.0196 (6)0.0243 (6)0.0009 (4)0.0063 (5)0.0003 (4)
C90.0207 (6)0.0193 (6)0.0244 (6)0.0005 (4)0.0062 (5)0.0001 (4)
C100.0182 (5)0.0164 (6)0.0253 (6)0.0004 (4)0.0075 (4)0.0000 (4)
C110.0210 (6)0.0212 (6)0.0229 (6)0.0020 (4)0.0034 (5)0.0018 (4)
C120.0238 (6)0.0213 (6)0.0216 (6)0.0005 (4)0.0063 (5)0.0018 (4)
Geometric parameters (Å, º) top
C1—C21.5054 (15)C6—C71.3978 (15)
C1—H1A1.000 (18)C6—H60.964 (13)
C1—H1B0.974 (18)C7—C81.4378 (14)
C1—H1C0.990 (18)C8—C91.1992 (15)
C2—C41.3921 (15)C9—C101.4372 (14)
C2—C31.3932 (15)C10—C111.3995 (15)
C3—C51.3853 (15)C10—C121.4002 (15)
C3—H30.984 (13)C11—C12i1.3842 (15)
C4—C61.3883 (15)C11—H110.975 (13)
C4—H40.991 (13)C12—C11i1.3842 (15)
C5—C71.3958 (15)C12—H120.992 (12)
C5—H50.989 (13)
C2—C1—H1A109.6 (10)C4—C6—C7120.52 (10)
C2—C1—H1B112.0 (10)C4—C6—H6119.6 (7)
H1A—C1—H1B106.5 (14)C7—C6—H6119.9 (7)
C2—C1—H1C112.2 (10)C5—C7—C6118.41 (10)
H1A—C1—H1C108.8 (14)C5—C7—C8120.53 (9)
H1B—C1—H1C107.5 (13)C6—C7—C8121.05 (10)
C4—C2—C3117.91 (10)C7—C8—C9179.10 (12)
C4—C2—C1121.35 (10)C8—C9—C10179.76 (14)
C3—C2—C1120.73 (10)C11—C10—C12118.84 (10)
C5—C3—C2121.40 (11)C11—C10—C9120.63 (10)
C5—C3—H3118.0 (8)C12—C10—C9120.53 (10)
C2—C3—H3120.6 (8)C12i—C11—C10120.62 (10)
C6—C4—C2121.23 (10)C12i—C11—H11119.8 (7)
C6—C4—H4119.2 (7)C10—C11—H11119.6 (7)
C2—C4—H4119.5 (7)C11i—C12—C10120.54 (10)
C3—C5—C7120.52 (10)C11i—C12—H12119.0 (7)
C3—C5—H5119.2 (7)C10—C12—H12120.5 (7)
C7—C5—H5120.3 (7)
C4—C2—C3—C50.41 (17)C3—C5—C7—C8179.00 (10)
C1—C2—C3—C5179.25 (10)C4—C6—C7—C50.37 (17)
C3—C2—C4—C60.58 (17)C4—C6—C7—C8179.16 (10)
C1—C2—C4—C6179.41 (10)C12—C10—C11—C12i0.07 (18)
C2—C3—C5—C70.15 (18)C9—C10—C11—C12i179.96 (9)
C2—C4—C6—C70.19 (17)C11—C10—C12—C11i0.07 (18)
C3—C5—C7—C60.54 (17)C9—C10—C12—C11i179.96 (9)
Symmetry code: (i) x+2, y, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C1—H1A···Cg1ii1.000 (18)2.605 (19)3.578 (2)164 (2)
Symmetry code: (ii) x, y1, z.

Experimental details

Crystal data
Chemical formulaC24H18
Mr306.38
Crystal system, space groupMonoclinic, P21/c
Temperature (K)173
a, b, c (Å)14.5478 (11), 4.9229 (4), 11.3006 (9)
β (°) 100.711 (1)
V3)795.22 (11)
Z2
Radiation typeMo Kα
µ (mm1)0.07
Crystal size (mm)0.27 × 0.12 × 0.04
Data collection
DiffractometerBruker SMART APEX CCD area-detector
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
6512, 1863, 1358
Rint0.034
(sin θ/λ)max1)0.666
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.045, 0.144, 1.02
No. of reflections1863
No. of parameters145
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.28, 0.22

Computer programs: SMART (Bruker, 1999), SMART, SAINT (Bruker, 1999), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEP-3 for Windows (Farrugia, 1997) and SHELXTL (Bruker, 1997), SHELXTL.

Selected geometric parameters (Å, º) top
C1—C21.5054 (15)C8—C91.1992 (15)
C7—C81.4378 (14)C9—C101.4372 (14)
C7—C8—C9179.10 (12)C8—C9—C10179.76 (14)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C1—H1A···Cg1i1.000 (18)2.605 (19)3.578 (2)164 (2)
Symmetry code: (i) x, y1, z.
 

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