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The packing of the title compound, C2HBr3O2, involves regions of hydrogen-bonded carboxyl­ic acid dimers, in turn linked by two contacts of the type Br...Br and one Br...O.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536803007268/bt6261sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536803007268/bt6261Isup2.hkl
Contains datablock I

CCDC reference: 214602

Key indicators

  • Single-crystal X-ray study
  • T = 133 K
  • Mean [sigma](C-C) = 0.003 Å
  • R factor = 0.022
  • wR factor = 0.053
  • Data-to-parameter ratio = 26.8

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


Red Alert Alert Level A:
ABSTM_02 Alert A The ratio of expected to reported Tmax/Tmin(RR) is > 2.00 Tmin and Tmax reported: 0.268 0.564 Tmin and Tmax expected: 0.070 0.463 RR = 3.153 Please check that your absorption correction is appropriate.
Author response: The redundancy of 3.6 was not as high as would be wished for effective use of SADABS, but was unfortunately limited by the longer exposure times for a very small crystal. Nevertheless, the reduction of R(int) from 0.151 to 0.034, and the low residual electron density, would usually be considered as signs of a successful correction.
General Notes

ABSTM_02 When printed, the submitted absorption T values will be replaced by the scaled T values. Since the ratio of scaled T's is identical to the ratio of reported T values, the scaling does not imply a change to the absorption corrections used in the study. Ratio of Tmax expected/reported 0.821 Tmax scaled 0.463 Tmin scaled 0.220
1 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
0 Alert Level C = Please check

Comment top

We have begun to investigate the structures of tribromoacetates and therefore decided to determine the structure of the parent acid, tribromoacetic acid. The structure of trichloracetic acid has recently been reported by Rajagopal et al. (2003).

The molecular structure of tribromoacetic acid, (I), is presented in Fig. 1. Bond lengths and angles may be regarded as normal, in particular the C—O bond lengths, which show no signs of the disorder sometimes observed in carboxylic acids (for a detailed discussion, see Wilson, 2002). Atom Br2 is approximately synperiplanar to O1.

More interesting features are observed in the packing. Apart from the classical `carboxylic acid dimer' formed by hydrogen bonding, there are three significant contacts involving atom Br1; 3.6284 (5) Å to Br2(x − 1/2, y − 1/2, z), 3.6193 (5) Å to Br3(-x − 1/2, y + 1/2, −z + 1/2), and 3.009 (2) Å to the carbonyl atom O2(x − 1/2, y + 1/2, z).

The Br···Br contacts are established as `type II' in the classification of Pedireddi et al. (1994) by the angles at bromine; 101.25 (7)/167.92 (7)° for the first and 93.77 (7)/167.05 (7)° for the second. Such contacts are thought to be associated with a positive region of charge in the extension of the C—Br vector beyond Br, which can interact with the negative region perpendicular to the C—Br bond at the other bromine. The somewhat longer Br3···Br3 interaction of 3.8020 (5) Å (code: −x − 1/2, y − 1/2, −z + 1/2), however, has equal angles at bromine [142.57 (7)°, equal by symmetry] and such `type I' contacts are regarded as less energetically favourable.

Contacts of the type Br···O may be regarded as one form of `halogen bond' (Metrangolo & Resnati, 2001). Although the distance observed here is significantly shorter than the sum of the van der Waals radii (Br = 1.85 Å and O = 1.52 Å; Bondi, 1964), much shorter values have been observed (down to ca 2.7 Å, as quoted in the above-mentioned article). Lommerse et al. (1996), in a review of contacts between halogens and oxygen or nitrogen, pointed out that these also tend to be approximately linear at the halogen [here 157.24 (8)°], but show little preferred directionality to the O-atom lone pairs [here the bromine lies 1.964 (5) Å out of the C1/C2/O1/O2 plane]. Again, electrostatic forces are thought to play an important role.

The net effect of the contacts can be seen in the packing diagrams. Carboxylic acid dimers occupy the regions z 0, 1/2, 1, etc. Fig. 2 shows the region at z 1/2, with dimer formation supported by Br1···Br2 and Br1···O2; Br1···Br3 links the CBr3 moieties of successive dimer regions to form double layers of molecules between e.g. z 1/2 and 1 (Fig. 3).

Experimental top

The title material was purchased from Aldrich. Single crystals grew from a solution in dichloromethane/petrol ether (ca 1/5 v/v) on cooling to 255 K.

Computing details top

Data collection: SMART (Bruker, 1998); 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, 1997); molecular graphics: XP (Siemens, 1994); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. The molecule of the title compound in the crystal. Ellipsoids represent 50% probability levels. H-atom radii are arbitrary.
[Figure 2] Fig. 2. Packing diagram of the title compound viewed perpendicular to the xy plane. Secondary interactions are indicated by dashed lines.
[Figure 3] Fig. 3. Packing diagram of the title compound viewed perpendicular to the yz plane. Secondary interactions are indicated by dashed lines.
Tribromoacetic acid top
Crystal data top
C2HBr3O2F(000) = 1072
Mr = 296.76Dx = 3.155 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
a = 11.1679 (12) ÅCell parameters from 4624 reflections
b = 5.7966 (6) Åθ = 3.8–30.5°
c = 19.821 (2) ŵ = 19.26 mm1
β = 103.132 (4)°T = 133 K
V = 1249.6 (2) Å3Tablet, colourless
Z = 80.15 × 0.13 × 0.04 mm
Data collection top
Bruker SMART 1000 CCD
diffractometer
1823 independent reflections
Radiation source: fine-focus sealed tube1577 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.037
Detector resolution: 8.192 pixels mm-1θmax = 30.0°, θmin = 2.1°
ω and ϕ scansh = 1515
Absorption correction: multi-scan
(SADABS; Bruker, 1998)
k = 88
Tmin = 0.268, Tmax = 0.564l = 2727
9331 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.022Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.053All H-atom parameters refined
S = 1.00 w = 1/[σ2(Fo2) + (0.031P)2]
where P = (Fo2 + 2Fc2)/3
1823 reflections(Δ/σ)max = 0.001
68 parametersΔρmax = 0.61 e Å3
0 restraintsΔρmin = 0.80 e Å3
Crystal data top
C2HBr3O2V = 1249.6 (2) Å3
Mr = 296.76Z = 8
Monoclinic, C2/cMo Kα radiation
a = 11.1679 (12) ŵ = 19.26 mm1
b = 5.7966 (6) ÅT = 133 K
c = 19.821 (2) Å0.15 × 0.13 × 0.04 mm
β = 103.132 (4)°
Data collection top
Bruker SMART 1000 CCD
diffractometer
1823 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 1998)
1577 reflections with I > 2σ(I)
Tmin = 0.268, Tmax = 0.564Rint = 0.037
9331 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0220 restraints
wR(F2) = 0.053All H-atom parameters refined
S = 1.00Δρmax = 0.61 e Å3
1823 reflectionsΔρmin = 0.80 e Å3
68 parameters
Special details top

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.

Non-bonded contacts:

Distances

3.6284 (0.0005) Br1 - Br2_$2 3.6193 (0.0005) Br1 - Br3_$3 3.8020 (0.0005) Br3 - Br3_$4 3.0091 (0.0020) Br1 - O2_$5 3.4620 (0.0022) Br1 - O1_$6

Angles

101.25 (0.07) C1 - Br1 - Br2_$2 167.92 (0.07) Br1 - Br2_$2 - C1_$2 93.77 (0.07) C1 - Br1 - Br3_$3 161.05 (0.07) Br1 - Br3_$3 - C1_$3 142.57 (0.07) C1 - Br3 - Br3_$4 157.24 (0.08) C1 - Br1 - O2_$5 129.94 (0.17) Br1 - O2_$5 - C2_$5 108.12 (0.08) C1 - Br1 - O1_$6 124.07 (0.16) Br1 - O1_$6 - C2_$6

Operators for generating equivalent atoms:

$2 x − 1/2, y − 1/2, z $3 − x − 1/2, y + 1/2, −z + 1/2 $4 − x − 1/2, y − 1/2, −z + 1/2 $5 x − 1/2, y + 1/2, z $6 x, y + 1, z

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) top
xyzUiso*/Ueq
Br10.24614 (2)0.57970 (4)0.389915 (13)0.01850 (7)
Br20.02550 (3)0.62438 (5)0.369499 (15)0.02254 (8)
Br30.14928 (3)0.22989 (5)0.291161 (13)0.02456 (8)
O10.14986 (18)0.1241 (4)0.45092 (11)0.0219 (4)
H010.134 (4)0.014 (7)0.472 (2)0.046 (13)*
O20.04944 (17)0.2079 (3)0.45893 (10)0.0213 (4)
C10.1044 (2)0.4116 (4)0.37556 (12)0.0148 (5)
C20.0599 (2)0.2358 (4)0.43403 (12)0.0155 (5)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Br10.01605 (13)0.01810 (13)0.02177 (13)0.00315 (9)0.00519 (10)0.00137 (9)
Br20.01902 (15)0.02053 (14)0.02938 (15)0.00299 (9)0.00825 (11)0.00536 (10)
Br30.03220 (17)0.02463 (15)0.01537 (13)0.00207 (11)0.00232 (11)0.00475 (10)
O10.0154 (10)0.0233 (11)0.0261 (10)0.0013 (8)0.0029 (8)0.0101 (8)
O20.0155 (10)0.0257 (10)0.0226 (9)0.0015 (8)0.0042 (8)0.0081 (8)
C10.0143 (12)0.0155 (12)0.0146 (11)0.0000 (9)0.0033 (9)0.0010 (9)
C20.0185 (13)0.0161 (12)0.0123 (11)0.0000 (9)0.0041 (9)0.0010 (9)
Geometric parameters (Å, º) top
Br1—C11.934 (2)O2—C21.219 (3)
Br2—C11.929 (3)C1—C21.539 (3)
Br3—C11.944 (2)O1—H010.76 (4)
O1—C21.302 (3)
C2—C1—Br2110.56 (17)Br1—C1—Br3109.90 (12)
C2—C1—Br1111.01 (17)O2—C2—O1126.2 (2)
Br2—C1—Br1109.85 (12)O2—C2—C1121.0 (2)
C2—C1—Br3105.38 (16)O1—C2—C1112.7 (2)
Br2—C1—Br3110.08 (12)C2—O1—H01118 (3)
Br2—C1—C2—O216.4 (3)Br2—C1—C2—O1165.00 (18)
Br1—C1—C2—O2138.6 (2)Br1—C1—C2—O142.8 (3)
Br3—C1—C2—O2102.5 (2)Br3—C1—C2—O176.1 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H01···O2i0.76 (4)1.95 (4)2.691 (3)162 (4)
Symmetry code: (i) x, y, z+1.

Experimental details

Crystal data
Chemical formulaC2HBr3O2
Mr296.76
Crystal system, space groupMonoclinic, C2/c
Temperature (K)133
a, b, c (Å)11.1679 (12), 5.7966 (6), 19.821 (2)
β (°) 103.132 (4)
V3)1249.6 (2)
Z8
Radiation typeMo Kα
µ (mm1)19.26
Crystal size (mm)0.15 × 0.13 × 0.04
Data collection
DiffractometerBruker SMART 1000 CCD
diffractometer
Absorption correctionMulti-scan
(SADABS; Bruker, 1998)
Tmin, Tmax0.268, 0.564
No. of measured, independent and
observed [I > 2σ(I)] reflections
9331, 1823, 1577
Rint0.037
(sin θ/λ)max1)0.704
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.022, 0.053, 1.00
No. of reflections1823
No. of parameters68
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.61, 0.80

Computer programs: SMART (Bruker, 1998), SAINT (Bruker, 1998), SAINT, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), XP (Siemens, 1994), SHELXL97.

Selected geometric parameters (Å, º) top
Br1—C11.934 (2)O1—C21.302 (3)
Br2—C11.929 (3)O2—C21.219 (3)
Br3—C11.944 (2)C1—C21.539 (3)
C2—C1—Br2110.56 (17)Br1—C1—Br3109.90 (12)
C2—C1—Br1111.01 (17)O2—C2—O1126.2 (2)
Br2—C1—Br1109.85 (12)O2—C2—C1121.0 (2)
C2—C1—Br3105.38 (16)O1—C2—C1112.7 (2)
Br2—C1—Br3110.08 (12)
Br2—C1—C2—O216.4 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H01···O2i0.76 (4)1.95 (4)2.691 (3)162 (4)
Symmetry code: (i) x, y, z+1.
 

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