Tri­chloro­acetic acid at 105 K

In the crystal structure of the title compound, Cl₃CCOOH or C₂HCl₃O₂, mol­ecules form centrosymmetric pairs leading to centrosymmetric dimers through strong O—H...O hydrogen bonds. In the absence of other strong intermolecular interactions, the Cl...O [3.029 (1) Å] and Cl...Cl [3.612 (1) Å] interactions presumably play an important role in the stabilization of the crystal structure.

Key indicators

• Single-crystal X-ray study
• T = 105 K
• Mean [sigma](C-C) = 0.001 Å
• R factor = 0.031
• wR factor = 0.081
• Data-to-parameter ratio = 43.7

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1999); software used to prepare material for publication: SHELXL97.

Trichloroacetic acid

Crystal data

C2HCl3O2	F(000) = 320
Mr = 163.38	Dx = 1.886 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 1024 reflections
a = 6.126 (1) Å	θ = 1.7–27.5°
b = 9.573 (1) Å	µ = 1.48 mm^−1
c = 11.243 (1) Å	T = 105 K
β = 119.23 (2)°	Needle, colorless
V = 575.35 (16) Å^3	0.32 × 0.16 × 0.12 mm
Z = 4

Data collection

BRUKER SMART diffractometer	2969 independent reflections
Radiation source: fine-focus sealed tube	2569 reflections with I > 2s(I)
Graphite monochromator	Rint = 0.022
Detector resolution: 8 pixels mm^-1	θmax = 37.5°, θmin = 3.0°
ω scans	h = −10→9
Absorption correction: multi-scan (SADABS; BRUKER, 1998)	k = −16→16
Tmin = 0.743, Tmax = 0.843	l = −19→19
10831 measured reflections

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)] = 0.031	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.081	All H-atom parameters refined
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0393P)^2 + 0.2185P] where P = (Fo^2 + 2Fc^2)/3
2969 reflections	(Δ/σ)max < 0.001
68 parameters	Δρmax = 0.63 e Å^−3
0 restraints	Δρmin = −0.67 e Å^−3

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
Cl1	0.67530 (5)	0.20777 (3)	0.33409 (3)	0.03381 (8)
Cl2	0.15067 (5)	0.27781 (3)	0.20562 (3)	0.03215 (7)
Cl3	0.33109 (8)	0.08824 (3)	0.07213 (4)	0.03863 (9)
O1	0.23841 (13)	0.39734 (8)	−0.00685 (7)	0.02190 (13)
O2	0.65320 (13)	0.40803 (8)	0.13902 (8)	0.02216 (13)
C1	0.44580 (16)	0.35958 (9)	0.10041 (9)	0.01676 (13)
C2	0.40326 (17)	0.23771 (10)	0.17783 (9)	0.01953 (15)
H1	0.276 (4)	0.450 (2)	−0.046 (2)	0.049 (6)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.02229 (11)	0.03563 (14)	0.03089 (13)	−0.00022 (9)	0.00314 (9)	0.01801 (10)
Cl2	0.02767 (12)	0.04369 (16)	0.03347 (13)	0.00858 (10)	0.02147 (10)	0.01320 (11)
Cl3	0.0617 (2)	0.01853 (11)	0.03852 (16)	−0.00496 (11)	0.02673 (15)	−0.00376 (9)
O1	0.0179 (3)	0.0234 (3)	0.0195 (3)	−0.0012 (2)	0.0052 (2)	0.0055 (2)
O2	0.0161 (3)	0.0253 (3)	0.0235 (3)	0.0009 (2)	0.0084 (2)	0.0065 (2)
C1	0.0168 (3)	0.0166 (3)	0.0167 (3)	0.0022 (2)	0.0081 (2)	0.0015 (2)
C2	0.0188 (3)	0.0191 (3)	0.0201 (3)	0.0013 (3)	0.0091 (3)	0.0034 (3)

Geometric parameters (Å, º)

Cl1—C2	1.7568 (10)	O1—H1	0.77 (2)
Cl2—C2	1.7640 (10)	O2—C1	1.2162 (11)
Cl3—C2	1.7725 (10)	C1—C2	1.5518 (12)
O1—C1	1.3049 (11)
C1—O1—H1	106.3 (17)	C1—C2—Cl2	109.74 (6)
O2—C1—O1	126.88 (8)	Cl1—C2—Cl2	110.13 (5)
O2—C1—C2	121.25 (8)	C1—C2—Cl3	106.63 (6)
O1—C1—C2	111.86 (8)	Cl1—C2—Cl3	110.06 (5)
C1—C2—Cl1	110.27 (6)	Cl2—C2—Cl3	109.95 (5)
O2—C1—C2—Cl1	9.94 (11)	O1—C1—C2—Cl2	−49.73 (9)
O1—C1—C2—Cl1	−171.22 (7)	O2—C1—C2—Cl3	−109.52 (9)
O2—C1—C2—Cl2	131.43 (8)	O1—C1—C2—Cl3	69.32 (9)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O2^i	0.77 (2)	1.89 (2)	2.6615 (10)	175 (2)

Symmetry code: (i) −x+1, −y+1, −z.