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The title compound, C7H2F3N, contains three crystallographically independent mol­ecules in the crystal structure; two of these mol­ecules have symmetry m and the third has symmetry mm. Each independent mol­ecule forms a planar or approximately planar layer with its own kind. There are three different types of inter­layer contacts, two of which are similar to each other, while the third is distinctly different. The packing within the layers is similar to that found in 2,5- and 3,6-difluoro­benzonitrile, with weak C—H...N inter­actions holding the mol­ecules in the layers. The remarkable feature of this structure is the presence of more than one type of inter­layer inter­action.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270108031739/fn3002sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270108031739/fn3002Isup2.hkl
Contains datablock I

CCDC reference: 710749

Comment top

3,5-Difluorobenzonitrile (hereafter 35D; Britton, 2002) and 2,6-difluorobenzonitrile (hereafter 26D; Britton, 2004) both pack in slightly puckered molecular sheets held together by weak C—H···N and very weak C—H···F hydrogen bonds. The structure determination of the title compound (hereafter 246T) was undertaken to see the effect of replacing one more H atom with F, with the expectation that the C—H···N interactions would be slightly stronger (shorter).

There are two half-molecules and one quarter-molecule in the asymmetric unit (Z' = 5/4). Molecules 1 and 2 are normal to a mirror plane, and molecule 3 is on the intersection of two mirror planes. The Z value can be described, in the notation of Zorky (1996), as Z = 20(m2mm1). The atom labelling and anisotropic displacement parameters for all three moleclules are shown in Fig. 1. The bond lengths and angles are all normal. The ring angles at atoms C11 and C13 and analogous atoms are less than 120°, and those at atoms C12 and C14 and analogous atoms are greater, in reasonable agreement with the substituent effects described by Domenicano (1992).

The molecules are arranged in layers normal to c. Each of the three types of molecules form layers with their own kind. The stacking of these layers is shown in Fig. 2; the unique layers are indicated by the labelling of the N atoms. Layer 3 is exactly planar. Molecules in layer 2 are tilted 2.9 (1)° away from parallel to layer 3. The N28 atoms are 2.862 (3) Å away from the plane of layer 3, and the F24 atoms 3.181 (2) Å away. A molecule in layer 1 is tilted 8.7 (1)° away from the plane of layer 3, and 11.6° away from the mean plane of a molecule in layer 2.

The molecules in the layers form C—H···N hydrogen bonds. The metric data for these bonds are given in Table 1, where they are compared with similar bonds in 35D and 26D. The H···N distances in molecules 2 and 3 are shorter than those in 35D and 26D, but the H···N distance in molecule 1 is not. This would appear to be a consequence of the deviation from planarity in the layer.

The stacking of the layers is shown in Fig. 3. The overlaps between layers 1 and 2 and between 2 and 3 are about the same, with no overlap between the rings and F atoms in one ring above the ring in the next layer. When layer 1 overlaps with layer 1', the rings do overlap, and the CN group in one molecule lies above the ring in the next layer. The two intralayer packing modes must have about the same energy; otherwise a structure with one of these modes exclusively ought to be favored.

Given the two distinctly different packing modes in the same structure, it seems likely that polymorphs might exist. Crystals were grown from acetone, benzene, CH2Cl2, CHCl3, CCl4 and acetonitrile. However, the crystals were all poor; in the two cases where a unit cell could be determined, it was the known cell.

Related literature top

For related literature, see: Britton (2002, 2004); Domenicano (1992); Zorky (1996).

Experimental top

The compound was obtained from Lancaster Synthesis Inc. Attempts were made to recrystallize the compound from a number of solvents but none gave acceptable crystals. Crystals from the original sample were used for the data collection.

Refinement top

The crystals had a strong tendency to twin. When a single crystal was eventually found, the solution and refinement were straightforward. The H-atom positions and isotropic displacement parameters were refined [C—H = 0.970 (18) and 0.91 (3) Å].

Structure description top

3,5-Difluorobenzonitrile (hereafter 35D; Britton, 2002) and 2,6-difluorobenzonitrile (hereafter 26D; Britton, 2004) both pack in slightly puckered molecular sheets held together by weak C—H···N and very weak C—H···F hydrogen bonds. The structure determination of the title compound (hereafter 246T) was undertaken to see the effect of replacing one more H atom with F, with the expectation that the C—H···N interactions would be slightly stronger (shorter).

There are two half-molecules and one quarter-molecule in the asymmetric unit (Z' = 5/4). Molecules 1 and 2 are normal to a mirror plane, and molecule 3 is on the intersection of two mirror planes. The Z value can be described, in the notation of Zorky (1996), as Z = 20(m2mm1). The atom labelling and anisotropic displacement parameters for all three moleclules are shown in Fig. 1. The bond lengths and angles are all normal. The ring angles at atoms C11 and C13 and analogous atoms are less than 120°, and those at atoms C12 and C14 and analogous atoms are greater, in reasonable agreement with the substituent effects described by Domenicano (1992).

The molecules are arranged in layers normal to c. Each of the three types of molecules form layers with their own kind. The stacking of these layers is shown in Fig. 2; the unique layers are indicated by the labelling of the N atoms. Layer 3 is exactly planar. Molecules in layer 2 are tilted 2.9 (1)° away from parallel to layer 3. The N28 atoms are 2.862 (3) Å away from the plane of layer 3, and the F24 atoms 3.181 (2) Å away. A molecule in layer 1 is tilted 8.7 (1)° away from the plane of layer 3, and 11.6° away from the mean plane of a molecule in layer 2.

The molecules in the layers form C—H···N hydrogen bonds. The metric data for these bonds are given in Table 1, where they are compared with similar bonds in 35D and 26D. The H···N distances in molecules 2 and 3 are shorter than those in 35D and 26D, but the H···N distance in molecule 1 is not. This would appear to be a consequence of the deviation from planarity in the layer.

The stacking of the layers is shown in Fig. 3. The overlaps between layers 1 and 2 and between 2 and 3 are about the same, with no overlap between the rings and F atoms in one ring above the ring in the next layer. When layer 1 overlaps with layer 1', the rings do overlap, and the CN group in one molecule lies above the ring in the next layer. The two intralayer packing modes must have about the same energy; otherwise a structure with one of these modes exclusively ought to be favored.

Given the two distinctly different packing modes in the same structure, it seems likely that polymorphs might exist. Crystals were grown from acetone, benzene, CH2Cl2, CHCl3, CCl4 and acetonitrile. However, the crystals were all poor; in the two cases where a unit cell could be determined, it was the known cell.

For related literature, see: Britton (2002, 2004); Domenicano (1992); Zorky (1996).

Computing details top

Data collection: SMART (Bruker, 2003); cell refinement: SAINT (Bruker, 2003); data reduction: SAINT (Bruker, 2003); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title compound. All of the molecules contain a mirror plane perpendicular to the plane of the molecule; only the crystallographically independent atoms are labelled. Displacement ellipsoids are drawn at the 50% probability level; H atoms are shown with arbitrary radius.
[Figure 2] Fig. 2. The crystal packing viewed along the a axis. One atom in each of the three independent layers is labeled.
[Figure 3] Fig. 3. The layers and their interactions with adjacent layers. In every case the C—H···N interactions are shown with dashed lines. Top: Layer 1, shown with solid bands, and layer 1', shown with dashed bonds, related to layer 1 by an inversion center at (1/2, 1/2, 0). Center: Layer 2, shown with solid bonds, and layer 1, shown with dashed bonds. Bottom: Layer 3, shown with solid bonds, and layer 2, shown with dashed bonds. Note that the overlap 1–1' is distinctly different from that of 2–1 and 3–2, which are similar to each other.
2,4,6-trifluorobenzonitrile top
Crystal data top
C7H2F3NF(000) = 1560
Mr = 157.10Dx = 1.631 Mg m3
Orthorhombic, CmcmMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2c 2Cell parameters from 2977 reflections
a = 7.5228 (10) Åθ = 2.9–27.4°
b = 13.8222 (18) ŵ = 0.16 mm1
c = 30.755 (4) ÅT = 173 K
V = 3198.0 (7) Å3Prism, colorless
Z = 200.5 × 0.5 × 0.4 mm
Data collection top
Bruker SMART 1K CCD area-detector
diffractometer
2004 independent reflections
Radiation source: fine-focus sealed tube1721 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.028
ω scansθmax = 27.5°, θmin = 1.3°
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003; Blessing, 1995)
h = 99
Tmin = 0.93, Tmax = 0.94k = 1717
18050 measured reflectionsl = 3939
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.040All H-atom parameters refined
wR(F2) = 0.127 w = 1/[σ2(Fo2) + (0.064P)2 + 1.81P]
where P = (Fo2 + 2Fc2)/3
S = 1.12(Δ/σ)max = 0.001
2004 reflectionsΔρmax = 0.35 e Å3
165 parametersΔρmin = 0.27 e Å3
0 restraintsExtinction correction: SHELXTL (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0016 (3)
Crystal data top
C7H2F3NV = 3198.0 (7) Å3
Mr = 157.10Z = 20
Orthorhombic, CmcmMo Kα radiation
a = 7.5228 (10) ŵ = 0.16 mm1
b = 13.8222 (18) ÅT = 173 K
c = 30.755 (4) Å0.5 × 0.5 × 0.4 mm
Data collection top
Bruker SMART 1K CCD area-detector
diffractometer
2004 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003; Blessing, 1995)
1721 reflections with I > 2σ(I)
Tmin = 0.93, Tmax = 0.94Rint = 0.028
18050 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0400 restraints
wR(F2) = 0.127All H-atom parameters refined
S = 1.12Δρmax = 0.35 e Å3
2004 reflectionsΔρmin = 0.27 e Å3
165 parameters
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
C110.50000.01950 (12)0.05738 (5)0.0287 (4)
F120.19046 (11)0.01670 (7)0.05722 (3)0.0514 (3)
C120.34258 (17)0.03226 (10)0.05363 (4)0.0341 (3)
C130.3385 (2)0.13039 (11)0.04635 (5)0.0433 (4)
H130.233 (3)0.1608 (13)0.0436 (6)0.053 (5)*
F140.50000.27250 (9)0.03568 (5)0.0714 (5)
C140.50000.17609 (15)0.04288 (6)0.0449 (5)
C170.50000.12236 (14)0.06366 (6)0.0326 (4)
N180.50000.20423 (13)0.06765 (6)0.0437 (4)
C210.50000.42065 (12)0.15322 (5)0.0256 (4)
F220.18998 (10)0.41825 (7)0.15336 (3)0.0402 (3)
C220.34242 (16)0.36836 (10)0.15196 (4)0.0279 (3)
C230.33765 (19)0.26903 (10)0.14946 (4)0.0323 (3)
H230.225 (2)0.2352 (12)0.1486 (5)0.038 (4)*
F240.50000.12533 (8)0.14657 (4)0.0462 (4)
C240.50000.22265 (13)0.14846 (5)0.0316 (4)
C270.50000.52423 (13)0.15530 (6)0.0317 (4)
N280.50000.60661 (13)0.15692 (7)0.0489 (5)
C310.50000.01780 (17)0.25000.0259 (5)
F320.18994 (14)0.01524 (9)0.25000.0409 (3)
C320.3421 (2)0.03461 (13)0.25000.0280 (4)
C330.3377 (3)0.13438 (13)0.25000.0323 (4)
H330.232 (4)0.1666 (19)0.25000.052 (7)*
F340.50000.27807 (11)0.25000.0453 (5)
C340.50000.18077 (18)0.25000.0327 (6)
C370.50000.12155 (19)0.25000.0324 (5)
N380.50000.20380 (18)0.25000.0496 (7)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C110.0299 (9)0.0305 (9)0.0257 (8)0.0000.0000.0000 (6)
F120.0272 (4)0.0619 (6)0.0650 (6)0.0003 (4)0.0024 (4)0.0032 (5)
C120.0302 (7)0.0405 (7)0.0316 (6)0.0029 (5)0.0024 (5)0.0014 (5)
C130.0511 (9)0.0408 (8)0.0381 (7)0.0166 (7)0.0008 (6)0.0011 (6)
F140.1211 (15)0.0285 (7)0.0645 (9)0.0000.0000.0033 (6)
C140.0726 (15)0.0286 (10)0.0337 (10)0.0000.0000.0001 (7)
C170.0311 (9)0.0359 (10)0.0306 (9)0.0000.0000.0006 (7)
N180.0498 (10)0.0328 (9)0.0487 (10)0.0000.0000.0006 (7)
C210.0253 (8)0.0236 (8)0.0280 (8)0.0000.0000.0018 (6)
F220.0210 (4)0.0431 (5)0.0566 (5)0.0032 (3)0.0018 (3)0.0015 (4)
C220.0234 (6)0.0310 (7)0.0294 (6)0.0005 (5)0.0012 (4)0.0011 (4)
C230.0351 (7)0.0312 (7)0.0306 (6)0.0086 (5)0.0018 (5)0.0002 (5)
F240.0747 (10)0.0225 (6)0.0413 (6)0.0000.0000.0016 (4)
C240.0491 (11)0.0218 (8)0.0238 (8)0.0000.0000.0004 (6)
C270.0248 (8)0.0270 (9)0.0434 (10)0.0000.0000.0023 (7)
N280.0398 (10)0.0283 (9)0.0787 (14)0.0000.0000.0016 (8)
C310.0240 (11)0.0251 (12)0.0285 (11)0.0000.0000.000
F320.0217 (5)0.0427 (7)0.0584 (7)0.0028 (4)0.0000.000
C320.0224 (8)0.0315 (9)0.0302 (8)0.0010 (6)0.0000.000
C330.0340 (10)0.0316 (9)0.0313 (9)0.0107 (7)0.0000.000
F340.0754 (13)0.0212 (7)0.0392 (9)0.0000.0000.000
C340.0495 (16)0.0220 (11)0.0264 (11)0.0000.0000.000
C370.0246 (12)0.0276 (13)0.0448 (14)0.0000.0000.000
N380.0385 (13)0.0281 (12)0.082 (2)0.0000.0000.000
Geometric parameters (Å, º) top
C11—C171.435 (2)C23—C241.3797 (16)
C11—C121.3884 (16)C23—H230.970 (18)
F12—C121.3341 (16)F24—C241.346 (2)
C12—C131.375 (2)C27—N281.140 (3)
C13—C141.3733 (19)C31—C321.391 (2)
C13—H130.905 (19)C31—C371.434 (3)
F14—C141.351 (2)F32—C321.336 (2)
C17—N181.138 (3)C32—C331.379 (3)
C21—C221.3890 (15)C33—C341.379 (2)
C21—C271.433 (2)C33—H330.91 (3)
F22—C221.3387 (14)F34—C341.345 (3)
C22—C231.3756 (19)C37—N381.137 (4)
C17—C11—C12121.45 (8)C22—C23—H23120.3 (10)
C12—C11—C12i117.07 (17)C24—C23—H23123.5 (10)
F12—C12—C13119.66 (13)F24—C24—C23117.72 (8)
F12—C12—C11117.60 (12)C23—C24—C23i124.56 (17)
C13—C12—C11122.74 (14)N28—C27—C21179.9 (2)
C12—C13—C14116.54 (15)C32—C31—C32ii117.3 (2)
C12—C13—H13119.6 (12)C32—C31—C37121.37 (11)
C14—C13—H13123.9 (12)F32—C32—C33119.69 (16)
F14—C14—C13117.81 (9)F32—C32—C31117.58 (15)
C13i—C14—C13124.39 (18)C33—C32—C31122.73 (17)
N18—C17—C11178.5 (2)C32—C33—C34116.35 (17)
C22—C21—C22i117.18 (15)C32—C33—H33120.7 (17)
C22—C21—C27121.41 (8)C34—C33—H33123.0 (17)
F22—C22—C23119.57 (12)F34—C34—C33117.71 (11)
F22—C22—C21117.53 (11)C33—C34—C33ii124.6 (2)
C23—C22—C21122.90 (12)N38—C37—C31180.0
C22—C23—C24116.23 (13)
C17—C11—C12—F121.7 (2)F22—C22—C23—C24179.54 (12)
C12i—C11—C12—F12179.95 (9)C21—C22—C23—C240.33 (19)
C17—C11—C12—C13178.07 (15)C22—C23—C24—F24179.19 (12)
C12i—C11—C12—C130.3 (3)C22—C23—C24—C23i0.5 (2)
F12—C12—C13—C14179.82 (14)C32ii—C31—C32—F32180.0
C11—C12—C13—C140.0 (2)C37—C31—C32—F320.0
C12—C13—C14—F14179.94 (15)C32ii—C31—C32—C330.0
C12—C13—C14—C13i0.2 (3)C37—C31—C32—C33180.0
C22i—C21—C22—F22179.71 (9)F32—C32—C33—C34180.0
C27—C21—C22—F220.9 (2)C31—C32—C33—C340.0
C22i—C21—C22—C230.2 (2)C32—C33—C34—F34180.0
C27—C21—C22—C23179.24 (14)C32—C33—C34—C33ii0.0
Symmetry codes: (i) x+1, y, z; (ii) x+1, y, z+1/2.

Experimental details

Crystal data
Chemical formulaC7H2F3N
Mr157.10
Crystal system, space groupOrthorhombic, Cmcm
Temperature (K)173
a, b, c (Å)7.5228 (10), 13.8222 (18), 30.755 (4)
V3)3198.0 (7)
Z20
Radiation typeMo Kα
µ (mm1)0.16
Crystal size (mm)0.5 × 0.5 × 0.4
Data collection
DiffractometerBruker SMART 1K CCD area-detector
Absorption correctionMulti-scan
(SADABS; Sheldrick, 2003; Blessing, 1995)
Tmin, Tmax0.93, 0.94
No. of measured, independent and
observed [I > 2σ(I)] reflections
18050, 2004, 1721
Rint0.028
(sin θ/λ)max1)0.650
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.040, 0.127, 1.12
No. of reflections2004
No. of parameters165
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.35, 0.27

Computer programs: SMART (Bruker, 2003), SAINT (Bruker, 2003), SHELXTL (Sheldrick, 2008).

Distances and angles (Å, °) in C—H···NC interactions top
compoundHNC-HC-H···NH···NH···NCC···N
35DH2N10.97 (2)151 (1)2.65 (2)134 (1)3.523 (2)
26DH3N10.95 (2)160 (1)2.63 (2)99 (1)3.537 (2)
26DH4N10.97 (2)124 (1)2.75 (2)124 (1)3.393 (2)
26DH5N10.97 (2)125 (1)2.71 (2)175 (1)3.352 (2)
246TH13N18i0.91 (2)151 (1)2.66 (2)132 (1)3.484 (2)
246TH23N28ii0.97 (2)161 (1)2.47 (2)136 (1)3.398 (2)
246TH33N38i0.91 (3)164 (1)2.50 (3)136 (1)3.385 (2)
Symmetry codes: (i) x-1/2, y+1/2, z; (ii) x-1/2, y-1/2, z.
 

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