2,3-Difluoro­benzoic acid

Abstract

2,3-Difluoro­benzoic acid, C₇H₄F₂O₂, forms dimers that are stabilized by hydrogen bonds. The dimers are stacked and the stacks are held together by weak C—H⋯F and C—H⋯O inter­actions.

Related literature

For related literature, see: Juhler & Mortensen (2002 ▶); Malone et al. (2006 ▶); Potrzebowski & Chruszcz (2007 ▶).

Experimental

Crystal data

• C₇H₄F₂O₂

• M _r = 158.10

• Monoclinic,

• a = 3.761 (1) Å

• b = 6.520 (1) Å

• c = 26.521 (2) Å

• β = 92.27 (1)°

• V = 649.8 (2) ų

• Z = 4

• Mo Kα radiation

• μ = 0.15 mm⁻¹

• T = 293 (2) K

• 0.15 × 0.15 × 0.02 mm

Data collection

• Rigaku R-AXIS RAPID diffractometer

• Absorption correction: multi-scan (Otwinowski et al., 2003 ▶) T _min = 0.98, T _max = 1.00 (expected range = 0.977–0.997)

• 25713 measured reflections

• 1881 independent reflections

• 1371 reflections with I > 2σ(I)

• R _int = 0.031

Refinement

• R[F ² > 2σ(F ²)] = 0.043

• wR(F ²) = 0.133

• S = 1.06

• 1881 reflections

• 116 parameters

• All H-atom parameters refined

• Δρ_max = 0.28 e Å⁻³

• Δρ_min = −0.13 e Å⁻³

Data collection: HKL-2000 (Otwinowski & Minor, 1997 ▶); cell refinement: HKL-2000; data reduction: HKL-2000; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶) and HKL-3000SM (Minor et al., 2006 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶) and HKL-3000SM; molecular graphics: HKL-3000SM, Mercury (Macrae et al., 2006 ▶), ORTEPIII (Burnett & Johnson, 1996 ▶) and ORTEP-3 (Farrugia, 1997 ▶); software used to prepare material for publication: HKL-3000SM.

Supplementary Material

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C5—H5⋯O1i	0.94 (2)	2.65 (2)	3.509 (2)	153 (2)
O2—H2⋯O1ii	1.03 (3)	1.60 (3)	2.625 (2)	173 (3)
C6—H6⋯O2iii	0.95 (2)	2.67 (2)	3.498 (2)	146 (1)
C4—H4⋯F2iv	0.95 (2)	2.65 (2)	3.513 (2)	151 (2)

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) .

supplementary crystallographic information

Comment

2,3-Difluorobenzoic acid (I) (Fig. 1) is used as a tracer for determining the extent of recovery of materials injected into oil wells (Malone et al., 2006) or for observing water movment in soil (Juhler & Mortensen, 2002). 2,3-Difluorobenzoic acid crystallized, like 3,5-difluorobenzoic acid (Potrzebowski & Chruszcz, 2007), in the space group P2₁/c with one molecule per asymmetric unit. Both (I) and 3,5-difluorobenzoic acid form dimers in the crystal lattice (Fig. 2), but the dimers of the two compounds pack differently. The molecules of (I) pack more tightly in the crystal, as the crystal density is 8% higher than in case of 3,5-difluorobenzoic acid. The dimers of (I) are stabilized by hydrogen bonds (Table 1). The dimers are arranged in stacks that are held together by weak C—H···F and C—H···O interactions (Fig. 2).

Experimental

2,3-Difluorobenzoic acid (98%) was purchased from Aldrich, and dissolved in 1-propanol. Single crystals suitable for X-ray diffraction study were obtained by slow evaporation at 293 K.

Refinement

All hydrogen atoms were localized using the difference density Fourier map. Their positions and isotropic displacement parameters were refined.

Figures

Fig. 1.

An asymmetric unit of 2,3-difluorobenzoic acid. Displacement ellipsoids are drawn at the 50% probability level, while hydrogen atoms are drawn as spheres of an arbitrary radius.

Fig. 2.

The packing of 2,3-difluorobenzoic acid shown along [010]. Hydrogen bonds are marked with blue, dashed lines. Weak C—H···F and C—H···O interactions are shown as light-blue, dashed lines.

Crystal data

C7H4F2O2	F000 = 320
Mr = 158.10	Dx = 1.616 Mg m−3
Monoclinic, P21/c	Mo Kα radiation λ = 0.71074 Å
Hall symbol: -P 2ybc	Cell parameters from 25713 reflections
a = 3.761 (1) Å	θ = 3.1–30.0º
b = 6.520 (1) Å	µ = 0.15 mm−1
c = 26.521 (2) Å	T = 293 (2) K
β = 92.27 (1)º	Plate, colorless
V = 649.8 (2) Å3	0.15 × 0.15 × 0.02 mm
Z = 4

Data collection

Rigaku R-AXIS RAPID diffractometer	1881 independent reflections
Radiation source: fine-focus sealed tube	1371 reflections with I > 2σ(I)
Monochromator: graphite	Rint = 0.031
Detector resolution: 10 pixels mm-1	θmax = 30.0º
T = 293(2) K	θmin = 3.1º
ω scans with χ offset	h = −5→5
Absorption correction: multi-scan(Otwinowski et al., 2003)	k = −9→9
Tmin = 0.98, Tmax = 1.00	l = −37→37
25713 measured reflections

Refinement

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.044	All H-atom parameters refined
wR(F2) = 0.133	w = 1/[σ2(Fo2) + (0.0665P)2 + 0.0891P] where P = (Fo2 + 2Fc2)/3
S = 1.06	(Δ/σ)max < 0.001
1881 reflections	Δρmax = 0.29 e Å−3
116 parameters	Δρmin = −0.13 e Å−3
Primary atom site location: structure-invariant direct methods	Extinction correction: none

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
C1	0.3028 (3)	0.18896 (18)	0.09787 (4)	0.0453 (3)
C2	0.3710 (3)	0.2435 (2)	0.14793 (5)	0.0507 (3)
C3	0.2895 (4)	0.1088 (2)	0.18600 (5)	0.0580 (3)
C4	0.1428 (4)	−0.0797 (2)	0.17592 (6)	0.0607 (4)
C5	0.0737 (4)	−0.1357 (2)	0.12626 (6)	0.0587 (3)
C6	0.1521 (3)	−0.0033 (2)	0.08785 (5)	0.0517 (3)
C7	0.3892 (3)	0.32666 (19)	0.05550 (5)	0.0485 (3)
F1	0.5159 (3)	0.42443 (14)	0.16134 (3)	0.0748 (3)
F2	0.3611 (3)	0.16829 (19)	0.23412 (3)	0.0893 (4)
O1	0.5592 (3)	0.48801 (16)	0.06313 (4)	0.0673 (3)
O2	0.2818 (3)	0.26822 (19)	0.01143 (4)	0.0742 (4)
H2	0.330 (8)	0.372 (4)	−0.0169 (13)	0.158 (11)*
H4	0.090 (5)	−0.174 (3)	0.2020 (8)	0.087 (6)*
H5	−0.026 (5)	−0.264 (3)	0.1183 (7)	0.079 (5)*
H6	0.104 (4)	−0.037 (3)	0.0534 (6)	0.057 (4)*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
C1	0.0441 (6)	0.0446 (6)	0.0472 (6)	0.0012 (5)	0.0014 (4)	−0.0005 (5)
C2	0.0550 (7)	0.0465 (6)	0.0503 (6)	0.0009 (5)	0.0003 (5)	−0.0037 (5)
C3	0.0635 (8)	0.0653 (8)	0.0451 (6)	0.0066 (6)	0.0024 (5)	0.0018 (6)
C4	0.0593 (7)	0.0625 (8)	0.0607 (8)	0.0018 (6)	0.0074 (6)	0.0151 (6)
C5	0.0565 (7)	0.0494 (7)	0.0699 (9)	−0.0047 (6)	0.0003 (6)	0.0058 (6)
C6	0.0524 (7)	0.0495 (7)	0.0529 (7)	−0.0036 (5)	−0.0017 (5)	−0.0021 (5)
C7	0.0503 (6)	0.0481 (6)	0.0471 (6)	−0.0027 (5)	0.0001 (5)	−0.0024 (5)
F1	0.1091 (7)	0.0572 (5)	0.0576 (5)	−0.0162 (5)	−0.0039 (5)	−0.0095 (4)
F2	0.1270 (9)	0.0956 (8)	0.0449 (5)	−0.0067 (7)	0.0015 (5)	−0.0011 (5)
O1	0.0901 (7)	0.0569 (6)	0.0544 (5)	−0.0240 (5)	−0.0021 (5)	0.0016 (4)
O2	0.1028 (9)	0.0728 (7)	0.0461 (5)	−0.0317 (6)	−0.0058 (5)	0.0013 (5)

Geometric parameters (Å, °)

C1—C2	1.3885 (17)	C4—H4	0.95 (2)
C1—C6	1.3968 (17)	C5—C6	1.376 (2)
C1—C7	1.4842 (17)	C5—H5	0.94 (2)
C2—F1	1.3415 (16)	C6—H6	0.950 (16)
C2—C3	1.3819 (19)	C7—O1	1.2435 (16)
C3—F2	1.3508 (16)	C7—O2	1.2796 (15)
C3—C4	1.369 (2)	O2—H2	1.03 (3)
C4—C5	1.381 (2)
C2—C1—C6	118.03 (12)	C5—C4—H4	119.0 (12)
C2—C1—C7	122.09 (11)	C6—C5—C4	120.17 (14)
C6—C1—C7	119.88 (11)	C6—C5—H5	119.2 (12)
F1—C2—C3	117.71 (12)	C4—C5—H5	120.6 (11)
F1—C2—C1	122.43 (12)	C5—C6—C1	121.28 (13)
C3—C2—C1	119.86 (12)	C5—C6—H6	122.0 (10)
F2—C3—C4	120.41 (13)	C1—C6—H6	116.8 (10)
F2—C3—C2	117.76 (14)	O1—C7—O2	122.84 (12)
C4—C3—C2	121.82 (13)	O1—C7—C1	121.00 (11)
C3—C4—C5	118.84 (13)	O2—C7—C1	116.15 (11)
C3—C4—H4	122.2 (12)	C7—O2—H2	114.3 (16)
C6—C1—C2—F1	179.84 (11)	C2—C3—C4—C5	−0.2 (2)
C7—C1—C2—F1	0.6 (2)	C3—C4—C5—C6	0.0 (2)
C6—C1—C2—C3	−0.03 (19)	C4—C5—C6—C1	0.2 (2)
C7—C1—C2—C3	−179.23 (12)	C2—C1—C6—C5	−0.17 (19)
F1—C2—C3—F2	0.0 (2)	C7—C1—C6—C5	179.05 (12)
C1—C2—C3—F2	179.88 (12)	C2—C1—C7—O1	7.3 (2)
F1—C2—C3—C4	−179.64 (13)	C6—C1—C7—O1	−171.85 (12)
C1—C2—C3—C4	0.2 (2)	C2—C1—C7—O2	−173.28 (12)
F2—C3—C4—C5	−179.87 (13)	C6—C1—C7—O2	7.53 (18)

Hydrogen-bond geometry (Å, °)

D—H···A	D—H	H···A	D···A	D—H···A
C5—H5···O1i	0.94 (2)	2.65 (2)	3.509 (2)	153 (2)
O2—H2···O1ii	1.03 (3)	1.60 (3)	2.625 (2)	173 (3)
C6—H6···O2iii	0.95 (2)	2.67 (2)	3.498 (2)	146 (1)
C4—H4···F2iv	0.95 (2)	2.65 (2)	3.513 (2)	151 (2)

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