Indole-3-carboxyl­ic acid

The crystal structure of indole-3-carboxyl­ic acid, C₉H₇NO₂, shows the presence of centrosymmetric hydrogen-bonded cyclic carboxyl­ic acid dimers [O...O = 2.649 (2) Å]. These dimers are linked into a sheet structure through peripheral intermolecular hydrogen bonds between the carboxyl­ic acid groups and the hetero-amine group of the n-glide-related indole ring [O...N = 3.013 (2) Å].

Key indicators

• Single-crystal X-ray study
• T = 295 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.043
• wR factor = 0.152
• Data-to-parameter ratio = 14.6

checkCIF/PLATON results

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Computing details

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1999); cell refinement: TEXSAN for Windows (Molecular Structure Corporation, 1999); data reduction: TEXSAN for Windows; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON for Windows (Spek, 1999); software used to prepare material for publication: PLATON for Windows.

1H-indole-3-carboxylic acid

Crystal data

C9H7NO2	F(000) = 336
Mr = 161.16	Dx = 1.415 Mg m^−3
Monoclinic, P21/n	Melting point = 483–484 K
Hall symbol: -P 2yn	Mo Kα radiation, λ = 0.71069 Å
a = 16.048 (3) Å	Cell parameters from 25 reflections
b = 10.611 (3) Å	θ = 12.5–17.4°
c = 4.4588 (16) Å	µ = 0.10 mm^−1
β = 94.95 (2)°	T = 295 K
V = 756.5 (4) Å^3	Block, colourless
Z = 4	0.40 × 0.35 × 0.15 mm

Data collection

Rigaku AFC-7R diffractometer	Rint = 0.054
Radiation source: Rigaku rotating anode	θmax = 27.5°, θmin = 2.6°
Graphite monochromator	h = −20→20
ω–2θ scans	k = 0→13
2023 measured reflections	l = −5→2
1723 independent reflections	3 standard reflections every 150 reflections
1148 reflections with I > 2σ(I)	intensity decay: 1.0%

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)] = 0.043	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.152	H atoms treated by a mixture of independent and constrained refinement
S = 0.93	w = 1/[σ^2(Fo^2) + (0.1P)^2 + 0.2856P] where P = (Fo^2 + 2Fc^2)/3
1723 reflections	(Δ/σ)max = 0.004
118 parameters	Δρmax = 0.20 e Å^−3
0 restraints	Δρmin = −0.26 e Å^−3

Special details

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All e.s.d.'s are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

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
O31	0.95392 (8)	0.63915 (14)	−0.1747 (4)	0.0617 (6)
O32	0.90078 (8)	0.47819 (13)	0.0703 (3)	0.0494 (5)
N1	0.71411 (11)	0.77920 (16)	−0.2844 (4)	0.0440 (5)
C2	0.79524 (12)	0.74662 (18)	−0.2885 (4)	0.0420 (6)
C3	0.81204 (11)	0.64470 (16)	−0.1034 (4)	0.0369 (5)
C4	0.71154 (12)	0.52017 (17)	0.2253 (4)	0.0418 (6)
C5	0.62999 (14)	0.5186 (2)	0.2969 (5)	0.0513 (7)
C6	0.57115 (13)	0.6065 (2)	0.1756 (5)	0.0538 (7)
C7	0.59325 (12)	0.6977 (2)	−0.0201 (5)	0.0496 (7)
C8	0.67524 (12)	0.69927 (17)	−0.0952 (4)	0.0389 (6)
C9	0.73551 (11)	0.61164 (16)	0.0239 (4)	0.0355 (5)
C31	0.89139 (11)	0.58096 (18)	−0.0611 (4)	0.0390 (5)
H1	0.6893 (14)	0.842 (2)	−0.386 (5)	0.054 (6)*
H2	0.835100	0.788000	−0.403700	0.0480*
H4	0.750800	0.459600	0.310700	0.0470*
H5	0.612900	0.456400	0.433900	0.0600*
H6	0.514600	0.601500	0.229900	0.0620*
H7	0.553900	0.760500	−0.100700	0.0570*
H31	1.0030 (14)	0.586 (2)	−0.137 (5)	0.0380*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O31	0.0321 (7)	0.0524 (9)	0.1008 (13)	0.0004 (6)	0.0067 (8)	0.0273 (8)
O32	0.0304 (7)	0.0400 (8)	0.0766 (10)	0.0011 (5)	−0.0022 (6)	0.0133 (7)
N1	0.0427 (9)	0.0381 (9)	0.0501 (9)	0.0092 (7)	−0.0030 (7)	0.0022 (7)
C2	0.0391 (10)	0.0363 (10)	0.0499 (11)	0.0001 (8)	−0.0002 (8)	0.0011 (8)
C3	0.0319 (9)	0.0335 (9)	0.0441 (9)	−0.0010 (7)	−0.0034 (7)	−0.0032 (7)
C4	0.0420 (10)	0.0397 (10)	0.0431 (10)	0.0007 (8)	0.0006 (8)	−0.0037 (8)
C5	0.0507 (12)	0.0534 (13)	0.0512 (11)	−0.0038 (9)	0.0133 (10)	−0.0030 (10)
C6	0.0369 (10)	0.0674 (14)	0.0581 (12)	0.0007 (9)	0.0096 (9)	−0.0116 (11)
C7	0.0372 (10)	0.0586 (13)	0.0518 (11)	0.0135 (9)	−0.0022 (9)	−0.0126 (10)
C8	0.0382 (10)	0.0384 (10)	0.0390 (9)	0.0067 (7)	−0.0034 (7)	−0.0085 (8)
C9	0.0324 (9)	0.0347 (9)	0.0384 (9)	0.0007 (7)	−0.0033 (7)	−0.0080 (7)
C31	0.0288 (8)	0.0360 (9)	0.0509 (10)	−0.0042 (7)	−0.0033 (7)	−0.0008 (8)

Geometric parameters (Å, º)

O31—C31	1.316 (2)	C4—C5	1.374 (3)
O32—C31	1.241 (2)	C5—C6	1.402 (3)
O31—H31	0.97 (2)	C6—C7	1.370 (3)
N1—C2	1.349 (3)	C7—C8	1.386 (3)
N1—C8	1.382 (3)	C8—C9	1.412 (3)
N1—H1	0.88 (2)	C2—H2	0.9605
C2—C3	1.373 (3)	C4—H4	0.9558
C3—C9	1.440 (3)	C5—H5	0.9554
C3—C31	1.440 (3)	C6—H6	0.9607
C4—C9	1.399 (3)	C7—H7	0.9658
C31—O31—H31	107.1 (13)	C3—C9—C4	135.50 (17)
C2—N1—C8	109.75 (16)	C3—C9—C8	105.73 (15)
C2—N1—H1	125.5 (15)	O31—C31—O32	121.90 (17)
C8—N1—H1	124.7 (15)	O31—C31—C3	115.10 (16)
N1—C2—C3	109.48 (17)	O32—C31—C3	123.00 (16)
C2—C3—C9	107.39 (16)	N1—C2—H2	125.33
C9—C3—C31	127.49 (16)	C3—C2—H2	125.19
C2—C3—C31	125.05 (17)	C5—C4—H4	120.51
C5—C4—C9	118.55 (18)	C9—C4—H4	120.93
C4—C5—C6	121.7 (2)	C4—C5—H5	119.26
C5—C6—C7	120.9 (2)	C6—C5—H5	119.03
C6—C7—C8	117.76 (19)	C5—C6—H6	119.04
N1—C8—C7	130.00 (18)	C7—C6—H6	120.11
N1—C8—C9	107.64 (16)	C6—C7—H7	121.83
C7—C8—C9	122.36 (17)	C8—C7—H7	120.39
C4—C9—C8	118.76 (17)
C2—N1—C8—C7	179.4 (2)	C9—C3—C31—O32	8.2 (3)
C8—N1—C2—C3	0.1 (2)	C5—C4—C9—C8	0.6 (3)
C2—N1—C8—C9	−0.3 (2)	C9—C4—C5—C6	−0.6 (3)
N1—C2—C3—C9	0.17 (19)	C5—C4—C9—C3	179.5 (2)
N1—C2—C3—C31	177.40 (17)	C4—C5—C6—C7	0.0 (3)
C2—C3—C9—C4	−179.4 (2)	C5—C6—C7—C8	0.5 (3)
C2—C3—C9—C8	−0.3 (2)	C6—C7—C8—N1	179.9 (2)
C31—C3—C9—C4	3.5 (3)	C6—C7—C8—C9	−0.4 (3)
C31—C3—C9—C8	−177.49 (18)	N1—C8—C9—C3	0.4 (2)
C9—C3—C31—O31	−172.38 (18)	N1—C8—C9—C4	179.61 (16)
C2—C3—C31—O31	11.0 (3)	C7—C8—C9—C3	−179.34 (18)
C2—C3—C31—O32	−168.49 (18)	C7—C8—C9—C4	−0.1 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O32^i	0.88 (2)	2.16 (2)	3.013 (2)	164 (2)
O31—H31···O32^ii	0.97 (2)	1.69 (2)	2.649 (2)	168 (2)

Symmetry codes: (i) −x+3/2, y+1/2, −z−1/2; (ii) −x+2, −y+1, −z.