Triclinic polymorph of sulfasalazine

In this modification of the title compound, 5-{4-[(2-pyridyl­amino)­sulfonyl]­phenyl­diazenyl}salicylic acid, C₁₈H₁₄N₄O₅S, the mol­ecule is present in the amide tautomeric form. Two azo-bridged phenyl rings render the bulk of the mol­ecule planar, with the carboxyl­ic acid group at one terminal and the pyridyl­amino residue at the other. The repeating unit in the crystal is a centrosymmetric dimer containing two identical R(8) hydrogen-bonded ring systems, each involving the carboxyl­ic acid and pyridyl­amino moieties. Additional stabilization is due to an intramolecular hydrogen bond between the 2-hydroxyl group and the carbonyl O atom of the carboxyl­ic acid group, as well as intermolecular π–π stacking.

Computing details

Data collection: COLLECT (2000); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ZORTEP (Zsolnai & Pritzkow, 1994); software used to prepare material for publication: SHELXL97.

2-hydroxy-5-[[4-[(2-pyridinylamino)sulfonyl]phenyl]azo]benzoic acid

Crystal data

C18H14N4O5S	F(000) = 412
Mr = 398.39	Dx = 1.497 Mg m^−3 Dm = 1.48 Mg m^−3 Dm measured by flotation in aqueous KI
Triclinic, P1	Melting point: 249°C K
a = 7.017 (1) Å	Mo Kα radiation, λ = 0.71073 Å
b = 7.307 (1) Å	Cell parameters from 7652 reflections
c = 18.091 (1) Å	θ = 2.3–27.8°
α = 94.673 (3)°	µ = 0.22 mm^−1
β = 92.059 (3)°	T = 298 K
γ = 106.633 (3)°	Prism, orange
V = 884.11 (18) Å^3	0.35 × 0.20 × 0.14 mm
Z = 2

Data collection

Nonius Kappa CCD diffractometer	3021 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.018
Graphite monochromator	θmax = 27.8°, θmin = 2.3°
1.2° φ scans and ω scans	h = −9→9
7652 measured reflections	k = −8→9
4046 independent reflections	l = −23→22

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) = 0.113	H atoms treated by a mixture of independent and constrained refinement
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0484P)^2 + 0.1794P] where P = (Fo^2 + 2Fc^2)/3
4046 reflections	(Δ/σ)max < 0.001
262 parameters	Δρmax = 0.30 e Å^−3
1 restraint	Δρmin = −0.32 e Å^−3

Special details

Experimental. Complete sphere of data collected using COLLECT strategy (Nonius, 2000). Crystal to detector distance = 40 mm; combination of φ and ω scans of 1.2°, 120 s per °, 2 iterations.

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
N1	0.5765 (2)	0.0880 (2)	0.36408 (8)	0.0478 (4)
C2	0.6969 (3)	0.2346 (2)	0.40835 (10)	0.0416 (4)
C3	0.6353 (3)	0.3103 (3)	0.47195 (10)	0.0507 (5)
H3	0.7232	0.4090	0.5027	0.061*
C4	0.4397 (3)	0.2362 (3)	0.48920 (13)	0.0613 (6)
H4	0.3934	0.2869	0.5313	0.074*
C5	0.3141 (3)	0.0877 (3)	0.44401 (14)	0.0637 (6)
H5	0.1817	0.0367	0.4546	0.076*
C6	0.3888 (3)	0.0163 (3)	0.38280 (12)	0.0583 (5)
H6	0.3051	−0.0869	0.3528	0.070*
N7	0.8950 (2)	0.3061 (2)	0.38584 (8)	0.0442 (4)
H7	0.934 (3)	0.211 (2)	0.3519 (9)	0.053*
S8	0.95555 (6)	0.51649 (6)	0.35133 (2)	0.04352 (15)
O9	1.15455 (17)	0.5453 (2)	0.32961 (8)	0.0589 (4)
O10	0.91068 (18)	0.65118 (17)	0.40438 (7)	0.0527 (3)
C11	0.7931 (2)	0.4841 (2)	0.27155 (9)	0.0388 (4)
C12	0.6077 (3)	0.5101 (3)	0.27960 (10)	0.0516 (5)
H12	0.5745	0.5567	0.3252	0.062*
C13	0.4720 (3)	0.4661 (3)	0.21897 (11)	0.0566 (5)
H13	0.3474	0.4852	0.2236	0.068*
C14	0.5195 (3)	0.3938 (3)	0.15145 (10)	0.0426 (4)
C15	0.7069 (3)	0.3706 (3)	0.14339 (10)	0.0452 (4)
H15	0.7400	0.3247	0.0976	0.054*
C16	0.8442 (3)	0.4157 (3)	0.20326 (10)	0.0448 (4)
H16	0.9703	0.4005	0.1981	0.054*
N17	0.3630 (2)	0.3489 (2)	0.09440 (9)	0.0502 (4)
N18	0.4046 (2)	0.2833 (2)	0.03312 (8)	0.0457 (4)
C19	0.2435 (2)	0.2371 (2)	−0.02202 (10)	0.0438 (4)
C20	0.0560 (3)	0.2614 (3)	−0.00902 (12)	0.0568 (5)
H20	0.0334	0.3136	0.0373	0.068*
C21	−0.0932 (3)	0.2092 (3)	−0.06368 (12)	0.0631 (6)
H21	−0.2167	0.2267	−0.0545	0.076*
C22	−0.0621 (3)	0.1296 (3)	−0.13317 (11)	0.0530 (5)
C23	0.1253 (3)	0.1086 (2)	−0.14790 (10)	0.0432 (4)
C24	0.2761 (3)	0.1624 (2)	−0.09094 (10)	0.0434 (4)
H24	0.4007	0.1473	−0.0999	0.052*
C25	0.1626 (3)	0.0347 (2)	−0.22239 (10)	0.0469 (4)
O26	0.34599 (19)	0.04106 (19)	−0.23240 (8)	0.0555 (4)
H26	0.365 (3)	−0.011 (3)	−0.2839 (13)	0.067*
O27	0.0270 (2)	−0.0293 (2)	−0.27170 (8)	0.0625 (4)
O28	−0.2159 (2)	0.0791 (3)	−0.18453 (10)	0.0776 (5)
H28	−0.164 (4)	0.031 (4)	−0.2244 (16)	0.093*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0487 (9)	0.0494 (8)	0.0399 (9)	0.0066 (7)	−0.0006 (7)	0.0024 (7)
C2	0.0432 (9)	0.0484 (9)	0.0338 (9)	0.0140 (7)	−0.0009 (7)	0.0060 (7)
C3	0.0612 (12)	0.0518 (10)	0.0392 (10)	0.0165 (9)	0.0070 (9)	0.0026 (8)
C4	0.0727 (14)	0.0639 (12)	0.0567 (13)	0.0294 (11)	0.0262 (11)	0.0158 (10)
C5	0.0526 (12)	0.0693 (13)	0.0724 (15)	0.0165 (10)	0.0170 (11)	0.0247 (11)
C6	0.0517 (11)	0.0571 (11)	0.0585 (13)	0.0023 (9)	−0.0009 (10)	0.0118 (10)
N7	0.0417 (8)	0.0544 (9)	0.0351 (8)	0.0143 (7)	−0.0014 (6)	−0.0038 (6)
S8	0.0355 (2)	0.0513 (3)	0.0352 (2)	0.00235 (18)	0.00055 (17)	−0.00737 (18)
O9	0.0344 (7)	0.0802 (9)	0.0493 (8)	0.0007 (6)	0.0033 (6)	−0.0097 (7)
O10	0.0529 (7)	0.0522 (7)	0.0426 (7)	0.0035 (6)	0.0027 (6)	−0.0132 (6)
C11	0.0378 (9)	0.0416 (8)	0.0321 (9)	0.0046 (7)	0.0033 (7)	−0.0007 (7)
C12	0.0473 (10)	0.0736 (12)	0.0333 (10)	0.0197 (9)	0.0057 (8)	−0.0083 (9)
C13	0.0436 (10)	0.0862 (14)	0.0421 (11)	0.0249 (10)	0.0045 (8)	−0.0055 (10)
C14	0.0391 (9)	0.0520 (10)	0.0345 (9)	0.0112 (7)	0.0017 (7)	0.0004 (7)
C15	0.0470 (10)	0.0565 (10)	0.0310 (9)	0.0149 (8)	0.0047 (7)	−0.0036 (7)
C16	0.0363 (9)	0.0583 (10)	0.0379 (10)	0.0125 (8)	0.0042 (7)	−0.0025 (8)
N17	0.0450 (8)	0.0668 (10)	0.0371 (9)	0.0159 (7)	−0.0001 (7)	−0.0027 (7)
N18	0.0419 (8)	0.0557 (9)	0.0359 (8)	0.0107 (7)	−0.0014 (6)	−0.0023 (7)
C19	0.0380 (9)	0.0503 (10)	0.0402 (10)	0.0092 (7)	−0.0007 (7)	0.0021 (8)
C20	0.0477 (11)	0.0780 (14)	0.0445 (11)	0.0204 (10)	0.0028 (9)	−0.0040 (10)
C21	0.0395 (10)	0.0903 (16)	0.0612 (14)	0.0250 (10)	0.0003 (9)	−0.0040 (12)
C22	0.0401 (10)	0.0627 (12)	0.0534 (12)	0.0138 (8)	−0.0102 (9)	−0.0002 (9)
C23	0.0433 (9)	0.0418 (9)	0.0425 (10)	0.0115 (7)	−0.0039 (8)	−0.0005 (7)
C24	0.0373 (9)	0.0490 (9)	0.0429 (10)	0.0127 (7)	−0.0035 (7)	−0.0001 (8)
C25	0.0497 (11)	0.0449 (9)	0.0439 (11)	0.0135 (8)	−0.0088 (8)	−0.0034 (8)
O26	0.0488 (8)	0.0697 (9)	0.0438 (8)	0.0162 (6)	−0.0039 (6)	−0.0123 (6)
O27	0.0586 (8)	0.0767 (9)	0.0502 (9)	0.0254 (7)	−0.0180 (7)	−0.0173 (7)
O28	0.0480 (9)	0.1143 (13)	0.0684 (11)	0.0295 (8)	−0.0207 (8)	−0.0148 (10)

Geometric parameters (Å, º)

N1—C6	1.338 (2)	C14—C15	1.384 (2)
N1—C2	1.340 (2)	C14—N17	1.427 (2)
C2—C3	1.373 (2)	C15—C16	1.377 (2)
C2—N7	1.425 (2)	C15—H15	0.9300
C3—C4	1.381 (3)	C16—H16	0.9300
C3—H3	0.9300	N17—N18	1.249 (2)
C4—C5	1.371 (3)	N18—C19	1.426 (2)
C4—H4	0.9300	C19—C24	1.374 (2)
C5—C6	1.370 (3)	C19—C20	1.402 (3)
C5—H5	0.9300	C20—C21	1.362 (3)
C6—H6	0.9300	C20—H20	0.9300
N7—S8	1.6539 (16)	C21—C22	1.392 (3)
N7—H7	0.990 (5)	C21—H21	0.9300
S8—O9	1.4258 (13)	C22—O28	1.344 (2)
S8—O10	1.4262 (13)	C22—C23	1.399 (3)
S8—C11	1.7637 (17)	C23—C24	1.398 (2)
C11—C12	1.379 (2)	C23—C25	1.471 (3)
C11—C16	1.392 (2)	C24—H24	0.9300
C12—C13	1.380 (3)	C25—O27	1.239 (2)
C12—H12	0.9300	C25—O26	1.294 (2)
C13—C14	1.381 (2)	O26—H26	1.00 (2)
C13—H13	0.9300	O28—H28	0.91 (3)
C6—N1—C2	117.91 (17)	C13—C14—C15	120.05 (16)
N1—C2—C3	122.51 (17)	C13—C14—N17	114.60 (16)
N1—C2—N7	115.71 (15)	C15—C14—N17	125.35 (15)
C3—C2—N7	121.78 (15)	C16—C15—C14	119.85 (16)
C2—C3—C4	118.39 (18)	C16—C15—H15	120.1
C2—C3—H3	120.8	C14—C15—H15	120.1
C4—C3—H3	120.8	C15—C16—C11	119.61 (16)
C5—C4—C3	119.78 (19)	C15—C16—H16	120.2
C5—C4—H4	120.1	C11—C16—H16	120.2
C3—C4—H4	120.1	N18—N17—C14	115.06 (15)
C6—C5—C4	118.21 (19)	N17—N18—C19	113.37 (15)
C6—C5—H5	120.9	C24—C19—C20	119.26 (16)
C4—C5—H5	120.9	C24—C19—N18	117.12 (15)
N1—C6—C5	123.15 (19)	C20—C19—N18	123.61 (16)
N1—C6—H6	118.4	C21—C20—C19	120.55 (18)
C5—C6—H6	118.4	C21—C20—H20	119.7
C2—N7—S8	117.45 (12)	C19—C20—H20	119.7
C2—N7—H7	112.4 (11)	C20—C21—C22	120.41 (18)
S8—N7—H7	109.4 (11)	C20—C21—H21	119.8
O9—S8—O10	120.15 (7)	C22—C21—H21	119.8
O9—S8—N7	105.22 (8)	O28—C22—C21	117.60 (18)
O10—S8—N7	107.45 (8)	O28—C22—C23	122.43 (18)
O9—S8—C11	109.47 (8)	C21—C22—C23	119.95 (17)
O10—S8—C11	108.59 (8)	C24—C23—C22	118.68 (17)
N7—S8—C11	104.87 (7)	C24—C23—C25	121.01 (16)
C12—C11—C16	120.76 (16)	C22—C23—C25	120.30 (16)
C12—C11—S8	118.65 (13)	C19—C24—C23	121.11 (16)
C16—C11—S8	120.30 (13)	C19—C24—H24	119.4
C11—C12—C13	119.04 (16)	C23—C24—H24	119.4
C11—C12—H12	120.5	O27—C25—O26	122.76 (17)
C13—C12—H12	120.5	O27—C25—C23	121.98 (17)
C12—C13—C14	120.65 (17)	O26—C25—C23	115.26 (15)
C12—C13—H13	119.7	C25—O26—H26	112.8 (12)
C14—C13—H13	119.7	C22—O28—H28	103.1 (17)
C6—N1—C2—C3	1.1 (3)	C14—C15—C16—C11	0.1 (3)
C6—N1—C2—N7	−179.82 (16)	C12—C11—C16—C15	−1.0 (3)
N1—C2—C3—C4	−2.4 (3)	S8—C11—C16—C15	172.71 (14)
N7—C2—C3—C4	178.59 (17)	C13—C14—N17—N18	−179.93 (17)
C2—C3—C4—C5	1.5 (3)	C15—C14—N17—N18	0.2 (3)
C3—C4—C5—C6	0.5 (3)	C14—N17—N18—C19	178.99 (14)
C2—N1—C6—C5	1.1 (3)	N17—N18—C19—C24	−179.44 (16)
C4—C5—C6—N1	−1.8 (3)	N17—N18—C19—C20	−0.4 (3)
N1—C2—N7—S8	107.13 (16)	C24—C19—C20—C21	0.9 (3)
C3—C2—N7—S8	−73.8 (2)	N18—C19—C20—C21	−178.10 (19)
C2—N7—S8—O9	−176.44 (12)	C19—C20—C21—C22	0.4 (3)
C2—N7—S8—O10	54.42 (14)	C20—C21—C22—O28	179.3 (2)
C2—N7—S8—C11	−61.00 (13)	C20—C21—C22—C23	−2.0 (3)
O9—S8—C11—C12	−161.16 (15)	O28—C22—C23—C24	−179.13 (18)
O10—S8—C11—C12	−28.25 (17)	C21—C22—C23—C24	2.3 (3)
N7—S8—C11—C12	86.38 (16)	O28—C22—C23—C25	2.0 (3)
O9—S8—C11—C16	24.96 (17)	C21—C22—C23—C25	−176.61 (18)
O10—S8—C11—C16	157.88 (14)	C20—C19—C24—C23	−0.6 (3)
N7—S8—C11—C16	−87.49 (15)	N18—C19—C24—C23	178.43 (15)
C16—C11—C12—C13	0.4 (3)	C22—C23—C24—C19	−0.9 (3)
S8—C11—C12—C13	−173.40 (15)	C25—C23—C24—C19	177.92 (16)
C11—C12—C13—C14	1.1 (3)	C24—C23—C25—O27	173.58 (17)
C12—C13—C14—C15	−2.1 (3)	C22—C23—C25—O27	−7.6 (3)
C12—C13—C14—N17	178.04 (18)	C24—C23—C25—O26	−6.3 (3)
C13—C14—C15—C16	1.5 (3)	C22—C23—C25—O26	172.58 (17)
N17—C14—C15—C16	−178.65 (17)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N7—H7···O27^i	0.99 (1)	1.97 (1)	2.9473 (19)	170 (2)
O26—H26···N1^i	1.00 (2)	1.62 (2)	2.623 (2)	173.3 (18)
O28—H28···O27	0.91 (3)	1.76 (3)	2.604 (2)	154 (3)

Symmetry code: (i) −x+1, −y, −z.