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Acta Crystallogr Sect E Struct Rep Online. 2009 January 1; 65(Pt 1): o44–o45.
Published online 2008 December 10. doi:  10.1107/S1600536808040646
PMCID: PMC2967960

2,4-Difluoro­phenyl­boronic acid

Abstract

The mol­ecular structure of the title compound, C6H5BF2O2, is essentially planar (mean deviation = 0.019 Å), indicating electronic delocalization between the dihydroxy­boryl group and the aromatic ring. In the crystal structure, inversion dimers linked by two O—H(...)O hydrogen bonds arise. An intra­molecular O—H(...)F hydrogen bond reinforces the conformation and the same H atom is also involved in an inter­molecular O—H(...)F link, leading to mol­ecular sheets in the crystal.

Related literature

For general backround to boronic acids, see: Hall (2005 [triangle]); Höpfl (2002 [triangle]); Fujita et al. (2008 [triangle]); Soloway et al. (1998 [triangle]). For hydrogen-bond motifs, see: Bernstein et al. (1995 [triangle]); Desiraju (2002 [triangle]). For related structures, see: Wu et al. (2006 [triangle]); Bradley et al. (1996 [triangle]); Horton et al. (2004 [triangle]). For crystal engineering, see: Fournier et al. (2003 [triangle]); Rodríguez-Cuamatzi et al. (2004 [triangle], 2005 [triangle]).

An external file that holds a picture, illustration, etc.
Object name is e-65-00o44-scheme1.jpg

Experimental

Crystal data

  • C6H5BF2O2
  • M r = 157.91
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is e-65-00o44-efi1.jpg
  • a = 3.7617 (11) Å
  • b = 12.347 (4) Å
  • c = 14.620 (4) Å
  • β = 95.450 (5)°
  • V = 676.0 (3) Å3
  • Z = 4
  • Mo Kα radiation
  • μ = 0.15 mm−1
  • T = 293 (2) K
  • 0.37 × 0.35 × 0.22 mm

Data collection

  • Bruker SMART APEX CCD area-detector diffractometer
  • Absorption correction: multi-scan (SADABS; Sheldrick, 1996 [triangle]) T min = 0.947, T max = 0.968
  • 3196 measured reflections
  • 1190 independent reflections
  • 1012 reflections with I > 2σ(I)
  • R int = 0.028

Refinement

  • R[F 2 > 2σ(F 2)] = 0.056
  • wR(F 2) = 0.127
  • S = 1.15
  • 1190 reflections
  • 106 parameters
  • 2 restraints
  • H atoms treated by a mixture of independent and constrained refinement
  • Δρmax = 0.14 e Å−3
  • Δρmin = −0.18 e Å−3

Data collection: SMART (Bruker, 2000 [triangle]); cell refinement: SAINT-Plus-NT (Bruker, 2001 [triangle]); data reduction: SAINT-Plus-NT; program(s) used to solve structure: SHELXTL-NT (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXTL-NT; molecular graphics: CAMERON (Watkin et al., 1996 [triangle]); software used to prepare material for publication: PLATON (Spek, 2003 [triangle]) and publCIF (Westrip, 2009 [triangle]).

Table 1
Hydrogen-bond geometry (Å, °)

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808040646/hb2865sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808040646/hb2865Isup2.hkl

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

Acknowledgments

This work was supported by Consejo Nacional de Ciencia y Tecnología (CIAM-59213 for HH).

supplementary crystallographic information

Comment

Boronic acids, RB(OH)2 with R = alkyl and aryl, have applications in organic synthesis (Hall, 2005), host–guest chemistry (Höpfl, 2002), the molecular recognition of biochemically active molecules (Fujita et al., 2008) and in medicine as antibiotics, inhibitors and for the treatment of tumors (Soloway et al., 1998). Similar to carboxylic acids they are capable to form hydrogen-bonded dimeric units and, therefore, boronic acids have been used recently as new building blocks in crystal engineering (Fournier et al., 2003; Rodríguez-Cuamatzi et al., 2004; Rodríguez-Cuamatzi et al., 2005). Previously, the structures of 3-fluorophenylboronic acid (Wu et al., 2006), 2,6-difluoroboronic acid (Bradley et al., 1996) and pentafluoroboronic acid (Horton et al., 2004) had been reported. We now present the crystal structure of (I).

The molecular structure is essentially planar, O1—B1—C1—C2 = 4.4 (4)°, indicating that there is a π···π interaction between the dihydroxyboryl group and the aromatic ring, to which it is attached (Fig. 1). This interaction is also evidenced by the B—C bond length of 1.566 (3) Å, which is significantly shorter than that observed in boronates containing tetra-coordinate boron atoms (Höpfl, 2002). The crystal structure is stabilized by strong O2—H2···O1 hydrogen-bonding interactions, forming R22(8) motifs (Bernstein et al., 1995), as well as, O1—H1···F1 and O1—H1···F2 bifurcated hydrogen bonds (Fig. 2; Table 1) (Desiraju, 2002). Due to these interactions each boronic acid homodimer is linked to two neighboring homodimeric units, thus creating a two-dimensional hydrogen-bonded network, in which fluorine is therefore an essential structural component.

Experimental

2,4-Difluorophenylboronic acid was purchased from Aldrich and crystallized from water to yield colourless blocks of (I).

Refinement

The aromatic H atoms were positioned geometrically (C—H = 0.93Å) and refined as riding with Uiso(H) = 1.2Ueq(C). The O—H hydrogen atoms were localized in a difference map and their coordinates were refined with O—H = 0.84+/0.01Å and Uiso(H) = 1.5 Ueq(O).

Figures

Fig. 1.
The molecular structure of (I) with displacement ellipsoids drawn at the 30% probability level and H atoms shown as small spheres of arbitrary radius.
Fig. 2.
View of the packing arrangement of the two-dimensional network of (I)(I).

Crystal data

C6H5BF2O2F(000) = 320
Mr = 157.91Dx = 1.552 Mg m3
Monoclinic, P21/nMelting point = 521–522 K
Hall symbol: -P 2ynMo Kα radiation, λ = 0.71073 Å
a = 3.7617 (11) ÅCell parameters from 1052 reflections
b = 12.347 (4) Åθ = 2.3–26.2°
c = 14.620 (4) ŵ = 0.15 mm1
β = 95.450 (5)°T = 293 K
V = 676.0 (3) Å3Block, colorless
Z = 40.37 × 0.35 × 0.22 mm

Data collection

Bruker SMART APEX CCD area-detector diffractometer1190 independent reflections
Radiation source: fine-focus sealed tube1012 reflections with I > 2σ(I)
graphiteRint = 0.028
Detector resolution: 8.3 pixels mm-1θmax = 25.0°, θmin = 2.2°
[var phi] and ω scansh = −3→4
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)k = −14→12
Tmin = 0.947, Tmax = 0.968l = −17→17
3196 measured reflections

Refinement

Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.056Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.127H atoms treated by a mixture of independent and constrained refinement
S = 1.15w = 1/[σ2(Fo2) + (0.0442P)2 + 0.2673P] where P = (Fo2 + 2Fc2)/3
1190 reflections(Δ/σ)max < 0.001
106 parametersΔρmax = 0.14 e Å3
2 restraintsΔρmin = −0.18 e Å3

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 (Å2)

xyzUiso*/Ueq
B10.7704 (8)0.4548 (2)0.62567 (18)0.0452 (7)
O10.6825 (6)0.38623 (15)0.55419 (13)0.0695 (6)
H10.748 (9)0.3215 (9)0.562 (2)0.104*
O20.6880 (6)0.55977 (14)0.61557 (12)0.0630 (6)
H20.593 (8)0.577 (3)0.5632 (10)0.094*
F11.0385 (5)0.23728 (11)0.67473 (11)0.0768 (6)
F21.4329 (5)0.33016 (14)0.97634 (10)0.0822 (6)
C10.9591 (6)0.41789 (18)0.72069 (15)0.0424 (6)
C21.0796 (7)0.31430 (18)0.74175 (16)0.0470 (6)
C31.2380 (7)0.2819 (2)0.82553 (17)0.0539 (7)
H31.31380.21090.83630.065*
C41.2785 (7)0.3593 (2)0.89223 (17)0.0547 (7)
C51.1696 (8)0.4640 (2)0.87828 (17)0.0586 (7)
H51.20130.51500.92510.070*
C61.0119 (7)0.49169 (19)0.79282 (16)0.0498 (6)
H60.93710.56280.78270.060*

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
B10.0451 (16)0.0425 (15)0.0471 (16)−0.0009 (12)−0.0005 (12)0.0033 (12)
O10.1000 (17)0.0484 (11)0.0540 (11)0.0158 (10)−0.0241 (10)−0.0009 (9)
O20.0850 (15)0.0441 (10)0.0552 (11)0.0087 (9)−0.0172 (10)0.0048 (8)
F10.1192 (15)0.0456 (9)0.0602 (10)0.0151 (9)−0.0187 (9)−0.0046 (7)
F20.1070 (14)0.0804 (12)0.0527 (10)−0.0120 (10)−0.0262 (9)0.0181 (8)
C10.0383 (13)0.0412 (13)0.0473 (13)−0.0039 (10)0.0019 (10)0.0048 (10)
C20.0523 (16)0.0410 (13)0.0467 (13)−0.0017 (11)0.0001 (11)0.0008 (10)
C30.0584 (17)0.0449 (14)0.0564 (15)0.0002 (12)−0.0053 (13)0.0124 (12)
C40.0579 (17)0.0613 (17)0.0426 (13)−0.0099 (13)−0.0075 (12)0.0135 (12)
C50.0696 (19)0.0552 (16)0.0489 (14)−0.0109 (13)−0.0058 (13)−0.0020 (12)
C60.0559 (16)0.0399 (13)0.0522 (14)−0.0011 (11)−0.0011 (12)0.0029 (11)

Geometric parameters (Å, °)

B1—O21.338 (3)C1—C61.394 (3)
B1—O11.361 (3)C2—C31.370 (3)
B1—C11.566 (3)C3—C41.363 (4)
O1—H10.841 (15)C3—H30.93
O2—H20.841 (15)C4—C51.366 (4)
F1—C21.364 (3)C5—C61.374 (3)
F2—C41.358 (3)C5—H50.93
C1—C21.382 (3)C6—H60.93
O2—B1—O1118.7 (2)C4—C3—H3121.8
O2—B1—C1117.4 (2)C2—C3—H3121.8
O1—B1—C1123.8 (2)F2—C4—C3118.1 (2)
B1—O1—H1116 (2)F2—C4—C5118.8 (2)
B1—O2—H2115 (2)C3—C4—C5123.0 (2)
C2—C1—C6114.6 (2)C4—C5—C6117.9 (2)
C2—C1—B1125.3 (2)C4—C5—H5121.0
C6—C1—B1120.1 (2)C6—C5—H5121.0
F1—C2—C3116.7 (2)C5—C6—C1122.9 (2)
F1—C2—C1118.2 (2)C5—C6—H6118.5
C3—C2—C1125.1 (2)C1—C6—H6118.5
C4—C3—C2116.4 (2)
O2—B1—C1—C2−176.5 (2)C1—C2—C3—C4−0.3 (4)
O1—B1—C1—C24.5 (4)C2—C3—C4—F2179.7 (2)
O2—B1—C1—C64.6 (4)C2—C3—C4—C50.0 (4)
O1—B1—C1—C6−174.5 (2)F2—C4—C5—C6−179.6 (2)
C6—C1—C2—F1−179.9 (2)C3—C4—C5—C60.1 (4)
B1—C1—C2—F11.1 (4)C4—C5—C6—C10.0 (4)
C6—C1—C2—C30.4 (4)C2—C1—C6—C5−0.3 (4)
B1—C1—C2—C3−178.6 (2)B1—C1—C6—C5178.8 (2)
F1—C2—C3—C4180.0 (2)

Hydrogen-bond geometry (Å, °)

D—H···AD—HH···AD···AD—H···A
O1—H1···F10.84 (2)2.16 (3)2.799 (3)133 (2)
O1—H1···F2i0.84 (2)2.39 (2)3.086 (3)140 (3)
O2—H2···O1ii0.84 (2)1.97 (2)2.809 (3)174 (3)

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

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HB2865).

References

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