1,4-Bis(fluoro­meth­yl)benzene

The title compound, C₈H₈F₂, lies across a crystallographic inversion centre. The structure features short C...F [2.8515 (18) Å] and F...F [2.490 (4) Å] contacts, which are significantly shorter than the sum of the van der Waals radii of these atoms. The F atom and methyl­ene H atoms are disordered over two positions with a site-occupancy ratio of 0.633 (3):0.367 (3). In the crystal structure, inter­molecular C—H...F inter­actions link neighboring mol­ecules into infinite chains along the b axis. In addition, C—H...π inter­actions link these mol­ecules along [10], forming a two-dimensional network parallel to (101).

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](C-C) = 0.002 Å
• Disorder in main residue
• R factor = 0.074
• wR factor = 0.251
• Data-to-parameter ratio = 24.9

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT431_ALERT_2_B Short Inter HL..A Contact  F1B    ..  F1B     ..       2.49 Ang.
PLAT432_ALERT_2_B Short Inter X...Y Contact  F1A    ..  C4      ..       2.85 Ang.

Alert level C
            Value of measurement temperature given =   100.000
            Value of melting point given =     0.000
CHEMW01_ALERT_1_C  The difference between the given and expected weight for
            compound is greater 1 mass unit. Check that all hydrogen
            atoms have been taken into account.
RFACR01_ALERT_3_C  The value of the weighted R factor is > 0.25
            Weighted R factor given   0.251
PLAT301_ALERT_3_C Main Residue  Disorder .........................      17.00 Perc.
PLAT351_ALERT_3_C Long    C-H Bond (0.96A)   C1     -   H1     ...       1.13 Ang.
PLAT066_ALERT_1_C Predicted and Reported Transmissions Identical .          ?
PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) .       1.17 Ratio

   0 ALERT level A = In general: serious problem
   2 ALERT level B = Potentially serious problem
   6 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   2 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

As part of an ongoing investigation into compounds with non-linear optical properties (Chantrapromma et al., 2006; Fun et al., 2008; Patil et al., 2007), the crystal structure of the title compound is presented here.

The title compound, (I), lies across a crystallographic inversion centre (Fig. 1). The interesting features of the crystal structure are the short C4A···F1Aⁱ [2.8515 (18)Å; (i) 3/2-x, 1/2+y, 3/2-z] and F1B···F1Bⁱⁱ [2.490 (4)Å; (ii) 1-x, 1-y, 1-z] contacts which are significantly shorter than the sum of the van der Waals radii of these atoms. The fluorine atom and methylene hydrogens are disordered over two positions with a site-occupancy ratio of 0.633 (3):0.367 (3). In the crystal structure, intermolecular C—H···F interactions link neighboring molecules into one-dimensional infinite chains along the b axis (Table 1 and Fig. 2). In addition, C—H···π interactions [C4—H4B···Cg1ⁱⁱⁱ; (iii) x, 1+y, z and C4—H4C···Cg1ⁱⁱⁱ; Cg1 is the centroid of the C1–C3/C1A–C3A benzene ring] link these molecules along the [101] direction, thus forming a two-dimensional network which is parallel to the (101) plane.

Related literature

For the structures of compounds with non-linear properties, see, for example: Chantrapromma et al. (2006); Fun et al. (2008); Patil et al. (2007). Cg1 is the centroid of the C1–C3/C1A–C3A benzene ring.

S2. Experimental

Commercially available 1,4-bis(difluoromethyl) benzene was further purified by repeated recrystallization from acetone. Single crystals suitable for X-ray analysis were grown by slow evaporation of an acetone solution at room temperature.

S3. Refinement

The hydrogen atoms bound to C1 and C3 were located from the difference Fourier map and refined freely. Hydrogen atoms of the methylene groups were positioned geometrically and constrained to refine with a riding model approximation with C—H = 0.96–0.97 Å and U_iso(H) = 1.2 U_eq(C).

Computing details

Data collection: APEX2 (Bruker, 2005); cell refinement: APEX2 (Bruker, 2005); data reduction: SAINT (Bruker, 2005); 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) and PLATON (Spek, 2003).

Figures

	Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atomic numbering. Open bonds indicate the minor disordered component.
	Fig. 2. The crystal packing of the major component of (I), viewed down the a-axis, showing a one-dimensional infinite chain of molecules along the b-axis. Intramolecular and intermolecular interactions are drawn as dashed lines.

1,4-Bis(fluoromethyl)benzene

Crystal data

C8H8F2	F(000) = 148
Mr = 143.15	Dx = 1.458 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 3653 reflections
a = 6.1886 (2) Å	θ = 2.5–34.7°
b = 5.0152 (2) Å	µ = 0.12 mm^−1
c = 10.4750 (4) Å	T = 100 K
β = 95.107 (2)°	Needle, colourless
V = 323.82 (2) Å^3	0.55 × 0.24 × 0.14 mm
Z = 2

Data collection

Bruker APEXII CCD area-detector diffractometer	1591 independent reflections
Radiation source: fine-focus sealed tube	1343 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.029
ϕ and ω scans	θmax = 36.6°, θmin = 3.7°
Absorption correction: multi-scan (SADABS; Bruker, 2005)	h = −10→10
Tmin = 0.935, Tmax = 0.982	k = −7→8
11592 measured reflections	l = −17→17

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)] = 0.074	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.251	H atoms treated by a mixture of independent and constrained refinement
S = 1.18	w = 1/[σ^2(Fo^2) + (0.1441P)^2 + 0.1329P] where P = (Fo^2 + 2Fc^2)/3
1591 reflections	(Δ/σ)max < 0.001
64 parameters	Δρmax = 0.67 e Å^−3
0 restraints	Δρmin = −0.59 e Å^−3

Special details

Experimental. The low-temperature data was collected with the Oxford Cyrosystem Cobra low-temperature attachment.

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	Occ. (<1)
F1A	0.9163 (2)	0.5267 (3)	0.72717 (12)	0.0219 (3)	0.633 (3)
F1B	0.6221 (4)	0.4849 (5)	0.6008 (3)	0.0260 (6)	0.367 (3)
C4	0.8122 (2)	0.4155 (2)	0.63866 (12)	0.0204 (3)
H4C	0.7640	0.5505	0.5776	0.025*	0.633 (3)
H4D	0.6847	0.3437	0.6718	0.025*	0.633 (3)
H4A	0.8129	0.3600	0.7274	0.025*	0.367 (3)
H4B	0.9052	0.5709	0.6369	0.025*	0.367 (3)
C1	0.7876 (2)	0.0844 (3)	0.46363 (13)	0.0222 (3)
C2	0.9095 (2)	0.1998 (2)	0.56704 (11)	0.0194 (3)
C3	1.1209 (2)	0.1184 (3)	0.60446 (12)	0.0217 (3)
H1	0.620 (4)	0.159 (6)	0.431 (2)	0.037 (6)*
H3	1.207 (4)	0.205 (5)	0.682 (2)	0.026 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
F1A	0.0227 (6)	0.0216 (6)	0.0215 (6)	0.0012 (4)	0.0030 (4)	−0.0057 (4)
F1B	0.0216 (10)	0.0244 (11)	0.0324 (12)	0.0115 (8)	0.0045 (8)	−0.0018 (8)
C4	0.0224 (5)	0.0170 (5)	0.0227 (5)	0.0024 (4)	0.0064 (4)	0.0013 (4)
C1	0.0204 (5)	0.0220 (5)	0.0243 (5)	0.0030 (4)	0.0023 (4)	0.0001 (4)
C2	0.0208 (5)	0.0176 (5)	0.0204 (5)	0.0020 (3)	0.0048 (4)	0.0013 (4)
C3	0.0207 (5)	0.0217 (6)	0.0226 (5)	0.0016 (4)	0.0007 (4)	−0.0006 (4)

Geometric parameters (Å, º)

F1A—C4	1.2162 (18)	C4—H4A	0.9699
F1A—H4A	1.0529	C4—H4B	0.9700
F1A—H4B	0.9681	C1—C2	1.3900 (18)
F1B—C4	1.257 (3)	C1—C3^i	1.3916 (19)
F1B—H4C	0.9881	C1—H1	1.13 (3)
F1B—H4D	1.0739	C2—C3	1.3927 (18)
C4—C2	1.4754 (17)	C3—C1^i	1.3916 (19)
C4—H4C	0.9600	C3—H3	1.02 (2)
C4—H4D	0.9600
C4—F1A—H4A	50.0	C2—C4—H4A	108.0
C4—F1A—H4B	51.2	H4C—C4—H4A	144.6
H4A—F1A—H4B	101.2	H4D—C4—H4A	58.7
C4—F1B—H4C	48.9	F1A—C4—H4B	51.1
C4—F1B—H4D	47.9	F1B—C4—H4B	108.2
H4C—F1B—H4D	96.7	C2—C4—H4B	108.0
F1A—C4—F1B	122.09 (16)	H4C—C4—H4B	64.6
F1A—C4—C2	120.74 (12)	H4D—C4—H4B	144.8
F1B—C4—C2	117.11 (16)	H4A—C4—H4B	107.3
F1A—C4—H4C	107.2	C2—C1—C3^i	119.09 (12)
F1B—C4—H4C	50.8	C2—C1—H1	121.3 (14)
C2—C4—H4C	107.2	C3^i—C1—H1	119.6 (14)
F1A—C4—H4D	107.0	C1—C2—C3	121.91 (12)
F1B—C4—H4D	56.0	C1—C2—C4	118.92 (11)
C2—C4—H4D	107.1	C3—C2—C4	119.17 (12)
H4C—C4—H4D	106.8	C1^i—C3—C2	119.00 (12)
F1A—C4—H4A	56.2	C1^i—C3—H3	120.6 (14)
F1B—C4—H4A	107.9	C2—C3—H3	120.4 (14)
C3^i—C1—C2—C3	0.1 (2)	F1A—C4—C2—C3	1.96 (19)
C3^i—C1—C2—C4	179.75 (11)	F1B—C4—C2—C3	179.18 (17)
F1A—C4—C2—C1	−177.73 (13)	C1—C2—C3—C1^i	−0.1 (2)
F1B—C4—C2—C1	−0.5 (2)	C4—C2—C3—C1^i	−179.75 (11)

Symmetry code: (i) −x+2, −y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C4—H4D···F1A^ii	0.96	2.04	2.8515 (18)	141
C4—H4B···Cg1^iii	0.97	2.84	3.5148 (12)	128
C4—H4C···Cg1^iii	0.96	2.64	3.5148 (12)	144

Symmetry codes: (ii) −x+3/2, y−1/2, −z+3/2; (iii) x, y+1, z.