Azelaic acid

The crystal structure of heptane-1,7-di­carboxyl­ic acid (azelaic acid), C₉H₁₆O₄, has been redetermined at 180 K. The molecular units have twofold symmetry and are linked via the ubiquitous syn-syn carboxyl­ic acid dimer to form infinite chains running approximately along the [01] vector.

Key indicators

• Single-crystal X-ray study
• T = 180 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.037
• wR factor = 0.096
• Data-to-parameter ratio = 17.0

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

Two polymorphs of azelaic acid, (I), have been reported previously: the α form crystallizes in P2₁/c (Caspari, 1928; Housty & Hospital, 1967) and the β form crystallizes in C2/c (Housty & Hospital, 1967). For both polymorphs, the structures present in the CSD (AZELAC10 and AZELAC01; Allen & Kennard, 1993) are derived from room-temperature data with R factors ca 10% and ambiguities in the treatment of H atoms. We have, therefore, re-examined azelaic acid and report here the structure of the β form measured at 180 K to significantly greater precision.

S2. Experimental

Azelaic acid was obtained from Aldrich and recrystallized from ethanol.

S3. Refinement

The H atom of the carboxylic acid group was located in a difference Fourier map and refined without restraint. All other H atoms were placed geometrically and allowed to ride during subsequent refinement with an isotropic displacement parameter fixed at 1.2 times that for the C atom to which they are attached.

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Sheldrick, 1993) and CAMERON (Watkin et al., 1996); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The molecular unit of the title compound showing displacement ellipsoids at the 50% probability level.
	Fig. 2. Projection onto (010) showing hydrogen-bonded chains running approximately along the [401] vector.

heptane-1,7-dicarboxylic acid

Crystal data

C9H16O4	Dx = 1.287 Mg m^−3
Mr = 188.22	Melting point = 382–384 K
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 22.622 (2) Å	Cell parameters from 2161 reflections
b = 4.7348 (2) Å	θ = 1.0–27.5°
c = 9.6864 (7) Å	µ = 0.10 mm^−1
β = 110.559 (3)°	T = 180 K
V = 971.5 (1) Å^3	Plate, colourless
Z = 4	0.25 × 0.12 × 0.06 mm
F(000) = 408

Data collection

Nonius KappaCCD diffractometer	1085 independent reflections
Radiation source: fine-focus sealed tube	913 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.039
Thin–slice ω and ϕ scans	θmax = 27.4°, θmin = 3.9°
Absorption correction: multi-scan (SORTAV; Blessing, 1995)	h = 0→28
Tmin = 0.907, Tmax = 0.994	k = −6→6
3154 measured reflections	l = −12→11

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)] = 0.037	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.096	H atoms treated by a mixture of independent and constrained refinement
S = 1.09	w = 1/[σ^2(Fo^2) + (0.0328P)^2 + 0.515P] where P = (Fo^2 + 2Fc^2)/3
1085 reflections	(Δ/σ)max = 0.010
64 parameters	Δρmax = 0.25 e Å^−3
0 restraints	Δρmin = −0.19 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
O1	0.18109 (4)	0.17201 (19)	0.01920 (10)	0.0312 (3)
O2	0.24341 (4)	0.54364 (19)	0.11100 (10)	0.0314 (3)
H1	0.2682 (9)	0.465 (4)	0.057 (2)	0.079 (6)*
C1	0.19218 (5)	0.3923 (3)	0.09015 (12)	0.0244 (3)
C2	0.14794 (6)	0.5227 (3)	0.15576 (14)	0.0307 (3)
H2A	0.1264	0.6833	0.0927	0.037*
H2B	0.1732	0.6004	0.2536	0.037*
C3	0.09798 (5)	0.3284 (3)	0.17462 (14)	0.0282 (3)
H3A	0.1183	0.1874	0.2523	0.034*
H3B	0.0767	0.2257	0.0813	0.034*
C4	0.04919 (5)	0.4949 (3)	0.21683 (13)	0.0270 (3)
H4A	0.0715	0.6108	0.3048	0.032*
H4B	0.0272	0.6258	0.1353	0.032*
C5	0.0000	0.3150 (4)	0.2500	0.0294 (4)
H5A	−0.0213	0.1920	0.1643	0.035*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0272 (5)	0.0337 (5)	0.0397 (5)	−0.0021 (4)	0.0205 (4)	−0.0071 (4)
O2	0.0262 (5)	0.0340 (5)	0.0429 (5)	−0.0043 (4)	0.0235 (4)	−0.0055 (4)
C1	0.0213 (6)	0.0289 (6)	0.0267 (6)	0.0018 (5)	0.0132 (4)	0.0030 (5)
C2	0.0269 (6)	0.0322 (7)	0.0424 (7)	−0.0027 (5)	0.0240 (6)	−0.0064 (5)
C3	0.0244 (6)	0.0299 (7)	0.0373 (7)	0.0008 (5)	0.0196 (5)	−0.0003 (5)
C4	0.0222 (6)	0.0300 (7)	0.0348 (7)	0.0002 (5)	0.0175 (5)	−0.0012 (5)
C5	0.0251 (9)	0.0317 (9)	0.0389 (9)	0.000	0.0206 (7)	0.000

Geometric parameters (Å, º)

O1—C1	1.2255 (15)	C3—H3A	0.9900
O2—C1	1.3166 (14)	C3—H3B	0.9900
O2—H1	0.96 (2)	C4—C5	1.5224 (14)
C1—C2	1.4944 (16)	C4—H4A	0.9900
C2—C3	1.5172 (16)	C4—H4B	0.9900
C2—H2A	0.9900	C5—C4^i	1.5224 (14)
C2—H2B	0.9900	C5—H5A	0.9899
C3—C4	1.5244 (15)
C1—O2—H1	110.9 (12)	C2—C3—H3B	109.4
O1—C1—O2	123.02 (10)	C4—C3—H3B	109.4
O1—C1—C2	123.67 (10)	H3A—C3—H3B	108.0
O2—C1—C2	113.25 (10)	C5—C4—C3	114.78 (11)
C1—C2—C3	116.05 (10)	C5—C4—H4A	108.6
C1—C2—H2A	108.3	C3—C4—H4A	108.6
C3—C2—H2A	108.3	C5—C4—H4B	108.6
C1—C2—H2B	108.3	C3—C4—H4B	108.6
C3—C2—H2B	108.3	H4A—C4—H4B	107.5
H2A—C2—H2B	107.4	C4^i—C5—C4	111.97 (14)
C2—C3—C4	111.04 (10)	C4^i—C5—H5A	109.2
C2—C3—H3A	109.4	C4—C5—H5A	109.2
C4—C3—H3A	109.4
O1—C1—C2—C3	19.17 (18)	C2—C3—C4—C5	−175.40 (9)
O2—C1—C2—C3	−163.41 (10)	C3—C4—C5—C4^i	−176.92 (11)
C1—C2—C3—C4	−170.14 (11)

Symmetry code: (i) −x, y, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H1···O1^ii	0.96 (2)	1.70 (2)	2.6576 (12)	173.5 (17)

Symmetry code: (ii) −x+1/2, −y+1/2, −z.