Selective crystallization of indigo B by a modified sublimation method and its redetermined structure.

Good-quality single crystals of the title compound, indigo B [systematic name: 2-(3-oxoindolin-2-yl-idene)indolin-3-one], C(16)H(10)N(2)O(2), have been prepared with high selectivity by a sublimation process. The previous structure of indigo B [Süsse & Wolf (1980 ▶). Naturwissenschaften, 67, 453], which showed that the complete mol-ecule is generated by crystallographic inversion symmetry has been confirmed, but the present study reports more realistic geometrical parameters and modern standards of precision (e.g. σ for C-C bonds = 0.002-0.003 Å). Each mol-ecule features two intra-molecular N-H⋯O hydrogen bonds. In the crystal, mol-ecules are linked by strong face-to-face π-π stacking inter-actions involving both the six- and five-membered rings [centroid-centroid separations = 3.6290 (14) and 3.6506 (14) Å] and inter-molecular N-H⋯O hydrogen bonds.

Related literature

For background to the history and uses of indigo, see: Berger & Sicker (2009 ▶); Johnson-Buck et al. (2009 ▶). For previous studies of the polymorphism of indigo, see: von Eller (1955 ▶); von Eller-Pandraud (1958 ▶); Süsse & Wolf (1980 ▶); Süsse et al. (1988 ▶). For aromatic stacking, see: Meyer et al. (2003 ▶).

Experimental

Crystal data

C16H10N2O2

M = 262.26

Monoclinic,

a = 9.799 (2) Å

b = 5.9064 (10) Å

c = 10.755 (3) Å

β = 106.781 (18)°

V = 596.0 (2) Å3

Z = 2

Mo Kα radiation

μ = 0.10 mm−1

T = 213 K

1.00 × 0.50 × 0.30 mm

Data collection

Stoe IPDS 1 diffractometer

4479 measured reflections

1115 independent reflections

896 reflections with I > 2σ(I)

R int = 0.033

Refinement

R[F 2 > 2σ(F 2)] = 0.036

wR(F 2) = 0.096

S = 1.03

1115 reflections

91 parameters

H-atom parameters constrained

Δρmax = 0.20 e Å−3

Δρmin = −0.16 e Å−3

Data collection: X-AREA (Stoe & Cie, 2005 ▶); cell refinement: X-AREA; data reduction: X-AREA; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg, 2004 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶).

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536811040220/hb6323sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536811040220/hb6323Isup2.hkl

Supplementary material file. DOI: 10.1107/S1600536811040220/hb6323Isup3.cml

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

C16H10N2O2	F(000) = 272
Mr = 262.26	Dx = 1.461 Mg m−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 3816 reflections
a = 9.799 (2) Å	θ = 1.9–26.0°
b = 5.9064 (10) Å	µ = 0.10 mm−1
c = 10.755 (3) Å	T = 213 K
β = 106.781 (18)°	Fragment of long platelet, dark blue
V = 596.0 (2) Å3	1.00 × 0.50 × 0.30 mm
Z = 2

Stoe IPDS 1 diffractometer	896 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.033
graphite	θmax = 26.0°, θmin = 1.9°
ω scans	h = −12→11
4479 measured reflections	k = −6→6
1115 independent reflections	l = −13→13

Refinement on F2	0 restraints
Least-squares matrix: full	H-atom parameters constrained
R[F2 > 2σ(F2)] = 0.036	w = 1/[σ2(Fo2) + (0.0607P)2] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.096	(Δ/σ)max < 0.001
S = 1.03	Δρmax = 0.20 e Å−3
1115 reflections	Δρmin = −0.16 e Å−3
91 parameters

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.

	x	y	z	Uiso*/Ueq
N1	0.51536 (12)	0.2222 (2)	0.62685 (11)	0.0300 (3)
H1	0.5926	0.1963	0.6897	0.036*
C2	0.46722 (14)	0.0924 (3)	0.51583 (13)	0.0275 (4)
C3	0.32960 (14)	0.1920 (3)	0.43595 (13)	0.0291 (4)
C3a	0.30488 (14)	0.3864 (3)	0.50987 (14)	0.0306 (4)
C4	0.19548 (16)	0.5474 (3)	0.48631 (16)	0.0386 (4)
H4	0.1176	0.5391	0.4111	0.046*
C5	0.20430 (18)	0.7188 (3)	0.57588 (17)	0.0419 (4)
H5	0.1310	0.8269	0.5622	0.050*
C6	0.32189 (17)	0.7325 (3)	0.68710 (16)	0.0387 (4)
H6	0.3261	0.8513	0.7463	0.046*
C7	0.43206 (16)	0.5759 (3)	0.71239 (15)	0.0342 (4)
H7	0.5108	0.5872	0.7868	0.041*
C7a	0.42120 (14)	0.4009 (3)	0.62272 (14)	0.0284 (4)
O	0.25789 (11)	0.1165 (2)	0.32944 (10)	0.0380 (3)

	U11	U22	U33	U12	U13	U23
N1	0.0249 (6)	0.0319 (8)	0.0282 (6)	0.0016 (5)	−0.0003 (4)	−0.0006 (5)
C2	0.0234 (6)	0.0297 (10)	0.0270 (7)	−0.0025 (5)	0.0034 (5)	0.0038 (6)
C3	0.0241 (7)	0.0322 (10)	0.0280 (7)	−0.0018 (6)	0.0028 (5)	0.0053 (6)
C3a	0.0279 (7)	0.0317 (10)	0.0311 (8)	0.0006 (6)	0.0068 (6)	0.0041 (6)
C4	0.0327 (7)	0.0423 (11)	0.0382 (8)	0.0080 (7)	0.0064 (6)	0.0058 (7)
C5	0.0413 (9)	0.0378 (12)	0.0489 (10)	0.0121 (7)	0.0164 (7)	0.0053 (7)
C6	0.0440 (9)	0.0322 (11)	0.0447 (9)	−0.0008 (7)	0.0202 (7)	−0.0045 (7)
C7	0.0339 (7)	0.0351 (11)	0.0334 (8)	−0.0048 (6)	0.0091 (6)	−0.0021 (6)
C7a	0.0267 (6)	0.0294 (10)	0.0289 (7)	−0.0014 (6)	0.0079 (5)	0.0044 (6)
O	0.0321 (5)	0.0408 (8)	0.0320 (6)	0.0019 (5)	−0.0051 (4)	−0.0010 (5)

N1—C2	1.3821 (19)	C4—C5	1.383 (3)
N1—C7a	1.394 (2)	C4—H4	0.9400
N1—H1	0.8700	C5—C6	1.403 (3)
C2—C2i	1.359 (3)	C5—H5	0.9400
C2—C3	1.4944 (19)	C6—C7	1.387 (2)
C3—O	1.2409 (18)	C6—H6	0.9400
C3—C3a	1.456 (2)	C7—C7a	1.397 (2)
C3a—C4	1.400 (2)	C7—H7	0.9400
C3a—C7a	1.407 (2)
C2—N1—C7a	109.55 (12)	C3a—C4—H4	120.6
C2—N1—H1	125.2	C4—C5—C6	120.45 (15)
C7a—N1—H1	125.2	C4—C5—H5	119.8
C2i—C2—N1	126.43 (16)	C6—C5—H5	119.8
C2i—C2—C3	125.83 (16)	C7—C6—C5	121.99 (15)
N1—C2—C3	107.74 (13)	C7—C6—H6	119.0
O—C3—C3a	130.39 (13)	C5—C6—H6	119.0
O—C3—C2	124.47 (15)	C6—C7—C7a	117.26 (14)
C3a—C3—C2	105.14 (12)	C6—C7—H7	121.4
C4—C3a—C7a	120.14 (15)	C7a—C7—H7	121.4
C4—C3a—C3	132.53 (14)	N1—C7a—C7	128.36 (13)
C7a—C3a—C3	107.31 (12)	N1—C7a—C3a	110.21 (13)
C5—C4—C3aA	118.71 (14)	C7—C7a—C3a	121.43 (14)
C5—C4—H4	120.6

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···Oi	0.87	2.40	2.9254 (17)	119
N1—H1···Oii	0.87	2.17	2.8832 (17)	139

	Indigo Aa	Indigo Bb	Indigo Bc	Indigo Bd
a	9.24 (3)	9.799 (2)	10.84 (1)	9.85 (1)
b	5.77 (2)	5.906 (1)	5.887 (6)	5.887 (6)
c	12.22 (3)	10.755 (3)	12.28 (1)	10.84 (1)
β	117.0	106.78 (2)	130.02 (5)	107.38 (5)
a	580	596.0	600	600
space group	P 21/c	P 21/n	P 21/c	P 21/n

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1⋯Oi	0.87	2.40	2.9254 (17)	119
N1—H1⋯Oii	0.87	2.17	2.8832 (17)	139

Symmetry codes: (i) ; (ii) .