4-(Trifluoromethyl)benzonitrile

4-(Tri­fluoro­methyl)­benzo­nitrile, C₈H₄F₃N, at 123 K contains mol­ecules linked together through one C—H...F bond and two C—H...N hydrogen bonds into sheets that are further crosslinked to form a dense two-dimensional network without π...π ring interactions. The aromatic ring is slightly deformed due to the two para-related electronegative groups.

S1. Comment

Most aromatic compounds which contain a trifluoromethyl group are known to have higher melting points, in some cases significantly higher, than the corresponding methyl-substituted compounds. The latter, however, despite their lower molecular weight, generally have higher boiling points. Apparently, forces exist in the crystalline state between molecules containing a CF₃ group which are stronger than in the corresponding methyl-substituted compounds, but which are absent in the liquid state. Intermolecular C—H···F—C contacts are known to be rather weak and are only infrequently reported. However, the structures of several fluoro-substituted aromatic compounds have been published by Thalladi et al. (1998). Furthermore, the presence of such contacts has repeatedly been suggested to be the cause of the preferential gauche conformation of 2-fluoroethanol and related compounds (Huang & Hedberg, 1989; Dixon & Smart, 1991). A contradicting view, however, has been forwarded by Bakke et al. (1994) and the ability of 2,4-difluorotoluene to act as both a hydrogen-bond donor and acceptor has been the subject of some controversy (Evans & Seddon, 1997). Detailed discussions on F···H interactions have recently been published (Shimoni et al., 1994, 1995; Howard et al., 1996; Plenio, 1997; Desiraju & Steiner, 1999; Hiyama, 2000). The present work on the title compound, (I), provides evidence in support of the presence of such contacts. \sch

The molecular structure of (I) is shown in Fig. 1, and the bond lengths and angles are listed in Table 1. The two ipso bond angles at C1 and C4 are, as expected, larger than 120° but are also equal, reflecting the rather similar Hammett σ_p-values of the two polar substituents, -0.66 (CN) and -0.54 (CF₃) (Hine, 1962). The C1—C2 and C1—C6 bonds are only slightly longer than the remaining four C—C bonds. The C2—C3 and C5—C6 bonds are not significantly shortened, as anticipated for a compound containing two electronegative substituents para to each other (Colapietro et al., 1984). The C7—C1—C2 and C7—C1—C6 bond angles are equal, but the cyano group is bent out of the plane of the aromatic ring, atoms C7 and N deviating by -0.0165 (17) and -0.033 (2) Å, respectively. The trifluoromethyl carbon C8 does not distort from the ring plane but is slightly tilted towards atom C3. The C4—C8—F and C—F—C bond angles, as well as the C—F bond lengths, are essentially equal and as expected (Schultz et al., 1981).

Atoms F1 and F3 are located gauche to the plane of the phenyl ring, with C3—C4—C8—F torsion angles of 67.91 (12) and -51.71 (13)°, respectively, whereas atom F2 lies close to the phenyl ring plane at a distance of -0.1812 (18) Å, with an F2—C8—C4—C3 torsion angle of -171.86 (9)°. As a result, the intramolecular F2···H5 distance is fairly small (2.40 Å), but the C4—C8—F2 bond angle and the geometry around atom C5 do not suggest any interaction (Sheppard, 1965).

The aromatic ring itself is essentially planar, but a slight tendency towards a boat conformation can be detected as atoms C1 and C4 depart from the plane by -0.0055 (7) and -0.0051 (7) Å, respectively.

An approximate view of the molecular interactions down [110] is given in Fig. 2, and the intermolecular bond distances and angles are summarized in Table 2. The intermolecular bonds connect the molecules into sheets alternating between directions [210] and [210] along [001]. Within the sheets, there are two types of centrosymmetric ten-membered rings, the first created through N···H2 and H2···N intermolecular bonds, the second through F2···H5 and H5···F2 intermolecular bonds. The N atom becomes bifurcated, as a second hydrogen bond crosslinks the sheets along [001] via alternating N···H3 and H3···N bonds. The N atom deviates by -0.046 (1) Å from the plane of C7, H2(3 - x, 2 - y, 1 - z) and H3(1/2 + x, 3/2 - y, 1/2 + z). The angle to the aromatic ring plane is 17.86 (5)°.

There are two types of stacking arrangements within the sheets involving three ring layers, A (x, y, z), B (2 - x, 1 - y, 1 - z) and C (3 - x, 1 - y, 1 - z). In the first type, the antiparallel rings in A and B are shifted in relation to one another by about one ring radius normal to the C7···C8 vector. The ring centroid-to-centroid distance, Cg_A···Cg_B, is 4.00 (3) Å. Whereas the smallest distance between ring atoms is 3.618 (2) Å for C6_A···C4_B, the overall shortest stacking distance in the structure occurs between these layers for F2_A···C7_B, at 3.427 (2) Å.

The second arrangement relates the antiparallel rings in layers B and C, which are shifted by about one ring diameter parallel to the C7···C8 vector. Consequently, the Cg_B···Cg_C distance is longer, at 4.84 (3) Å. The shortest distances between rings in layers B and C are 3.521 (3) and 3.581 (2) Å for C1_B···C1_C and C4_B···N_C, respectively. Hence, there is no π···π stacking overlap between the aromatic rings in the structure of (I).

Due to the numerous contacts which are slightly but significantly smaller than the sum of the van der Waals radii (2.67 and 2.75 Å for F···H and N···H, respectively; reference?), the molecules are closely packed, resulting in a crystal density of 1.5497 (2) Mg m^-3, higher than for e.g. 1,4-dicyanobenzene (1.285 Mg m^-3; Colapietro et al., 1984). The latter structure also exhibits a bifurcated N atom but with longer N···H distances, of 2.61 and 2.72 Å. Instead, the molecules are linked through antiparallel contacts between neighbouring cyano groups, with a shortest N···N distance of 3.65 Å. No such short interactions appear in the packing structure of (I), the shortest N···N(3 - x, 2 - y, 1 - z) contact being 3.887 (2) Å.

S2. Experimental

4-(Trifluoromethyl)benzonitrile (Aldrich, 99%, m.p. 312–314 K) was dissolved in a minimum amount of cyclohexane at room temperature. After filtration, a similar volume of hexane was added and the solution was left at 275 K overnight, yielding crystals of (I) suitable for X-ray analysis.

S3. Refinement

H atoms were refined as riding, with C—H 0.95 Å and U_iso(H) = 1.2U_eq(C). The maximum residual peak is located on the C4—C5 bond, 0.68 Å from C4.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997b); molecular graphics: SHELXTL/PC (Sheldrick, 1997a); software used to prepare material for publication: SHELXTL/PC.

Figures

Fig. 1. A view of the molecular structure of (I). Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.

Fig. 2. The packing structure of (I) with a ten-membered hydrogen-bonded ring of a [210] sheet centred around the inversion centre at (1/2 0 1/2) (all 1 indicated with small circles) and crosslinked along [001] with two [210] sheets. H atoms not participating in the hydrogen bonding have been omitted. Atoms labelled with the suffix A lie at positions (1 - x, -y, 1 - z), B at (-x, -2 - y, 1 - z), C at (1 + x, 2 + y, z), D at (x + 1/2, -y - 1/2, z + 1/2), E at (1/2 - x, y + 1/2, 1/2 - z), F at (3/2 - x, y + 1/2, 3/2 - z), G at (x - 1/2, -y - 1/2, z - 1/2), H at (x + 1/2, 1/2 - y, z + 1/2) and J at (1/2 - x, y - 1/2, 1/2 - z).

4-(trifluoromethyl)benzonitrile

Crystal data

C8H4F3N	F(000) = 344
Mr = 171.12	Dx = 1.550 Mg m^−3
Monoclinic, P21/n	Melting point = 312–314 K
Hall symbol: -P2yn	Mo Kα radiation, λ = 0.71073 Å
a = 8.2189 (6) Å	Cell parameters from 4972 reflections
b = 6.0621 (3) Å	θ = 2.6–31.5°
c = 15.0977 (10) Å	µ = 0.15 mm^−1
β = 102.835 (3)°	T = 123 K
V = 733.43 (8) Å^3	Block, colourless
Z = 4	0.45 × 0.33 × 0.25 mm

Data collection

Bruker SMART 2K CCD diffractometer	2417 independent reflections
Radiation source: normal-focus sealed tube	1835 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.029
ω scans	θmax = 31.5°, θmin = 2.6°
Absorption correction: numerical (SHELXTL/PC; Sheldrick 1997a)	h = −12→12
Tmin = 0.947, Tmax = 0.988	k = −8→8
12772 measured reflections	l = −22→22

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)] = 0.039	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.115	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.0674P)^2 + 0.0443P] where P = (Fo^2 + 2Fc^2)/3
2417 reflections	(Δ/σ)max < 0.001
109 parameters	Δρmax = 0.30 e Å^−3
0 restraints	Δρmin = −0.40 e Å^−3

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
F1	1.05225 (10)	0.11424 (14)	0.25672 (5)	0.0457 (2)
F2	0.91875 (10)	0.03120 (12)	0.35907 (5)	0.0419 (2)
F3	0.84468 (9)	0.31119 (13)	0.27290 (5)	0.0426 (2)
N	1.50418 (13)	0.87351 (17)	0.61878 (6)	0.0346 (2)
C1	1.30643 (12)	0.61636 (17)	0.50577 (6)	0.0225 (2)
C2	1.25432 (13)	0.67997 (17)	0.41489 (7)	0.0256 (2)
H2	1.2922	0.8148	0.3945	0.031*
C3	1.14659 (13)	0.54429 (17)	0.35452 (6)	0.0252 (2)
H3	1.1096	0.5861	0.2927	0.030*
C4	1.09343 (12)	0.34637 (16)	0.38561 (6)	0.02092 (19)
C5	1.14720 (13)	0.28124 (17)	0.47580 (7)	0.0246 (2)
H5	1.1110	0.1448	0.4957	0.030*
C6	1.25416 (13)	0.41693 (17)	0.53667 (6)	0.0253 (2)
H6	1.2912	0.3746	0.5985	0.030*
C7	1.41723 (13)	0.75943 (18)	0.56882 (7)	0.0266 (2)
C8	0.97776 (13)	0.20115 (17)	0.31900 (6)	0.0253 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
F1	0.0448 (4)	0.0590 (5)	0.0351 (4)	−0.0105 (4)	0.0125 (3)	−0.0244 (4)
F2	0.0506 (4)	0.0407 (4)	0.0291 (3)	−0.0221 (3)	−0.0025 (3)	0.0041 (3)
F3	0.0349 (4)	0.0414 (4)	0.0404 (4)	0.0020 (3)	−0.0158 (3)	−0.0002 (3)
N	0.0373 (5)	0.0390 (5)	0.0260 (5)	−0.0081 (4)	0.0040 (4)	−0.0042 (4)
C1	0.0209 (4)	0.0265 (5)	0.0194 (4)	−0.0005 (3)	0.0032 (3)	−0.0030 (3)
C2	0.0287 (5)	0.0259 (5)	0.0216 (4)	−0.0034 (4)	0.0042 (4)	0.0025 (4)
C3	0.0287 (5)	0.0275 (5)	0.0178 (4)	−0.0010 (4)	0.0019 (3)	0.0029 (3)
C4	0.0201 (4)	0.0251 (5)	0.0167 (4)	0.0003 (3)	0.0022 (3)	−0.0003 (3)
C5	0.0279 (5)	0.0260 (5)	0.0190 (4)	−0.0033 (4)	0.0032 (4)	0.0032 (3)
C6	0.0275 (5)	0.0302 (5)	0.0165 (4)	−0.0020 (4)	0.0013 (3)	0.0015 (3)
C7	0.0267 (5)	0.0305 (5)	0.0225 (5)	−0.0022 (4)	0.0053 (4)	−0.0017 (4)
C8	0.0272 (5)	0.0272 (5)	0.0199 (4)	−0.0022 (4)	0.0021 (4)	0.0001 (4)

Geometric parameters (Å, º)

C1—C2	1.3978 (13)	C7—N	1.1482 (14)
C1—C6	1.3975 (14)	C8—F1	1.3388 (13)
C1—C7	1.4500 (13)	C8—F2	1.3390 (12)
C2—C3	1.3902 (14)	C8—F3	1.3370 (12)
C3—C4	1.3935 (14)	C2—H2	0.9500
C4—C5	1.3922 (13)	C3—H3	0.9500
C4—C8	1.5050 (13)	C5—H5	0.9500
C5—C6	1.3911 (14)	C6—H6	0.9500
C2—C1—C6	121.10 (9)	F2—C8—F3	106.41 (9)
C2—C1—C7	119.35 (9)	F1—C8—C4	112.33 (9)
C6—C1—C7	119.54 (9)	F2—C8—C4	112.74 (8)
C1—C2—C3	119.47 (9)	F3—C8—C4	112.22 (8)
C2—C3—C4	119.36 (9)	C1—C2—H2	120.3
C3—C4—C4	121.23 (9)	C3—C2—H2	120.3
C3—C4—C8	118.52 (8)	C2—C3—H3	120.3
C5—C4—C8	120.25 (9)	C4—C3—H3	120.3
C4—C5—C6	119.69 (9)	C4—C5—H5	120.2
C1—C6—C5	119.14 (9)	C6—C5—H5	120.2
N—C7—C1	179.59 (12)	C1—C6—H6	120.4
F1—C8—F2	106.41 (9)	C5—C6—H6	120.4
F1—C8—F3	106.23 (8)
C6—C1—C2—C3	1.03 (15)	C2—C1—C6—C5	−0.63 (15)
C7—C1—C2—C3	−179.28 (10)	C7—C1—C6—C5	179.68 (9)
C1—C2—C3—C4	−0.46 (15)	C5—C4—C8—F3	129.20 (10)
C2—C3—C4—C5	−0.50 (15)	C3—C4—C8—F3	−51.71 (13)
C2—C3—C4—C8	−179.58 (9)	C5—C4—C8—F1	−111.18 (11)
C3—C4—C5—C6	0.90 (15)	C3—C4—C8—F1	67.91 (12)
C8—C4—C5—C6	179.97 (10)	C5—C4—C8—F2	9.05 (14)
C4—C5—C6—C1	−0.34 (15)	C3—C4—C8—F2	−171.86 (9)