2,6-Dihydroxy­anthraquinone: an isomer of the well known alizarin dye

The structure of anthraflavic acid (2,6-dihydroxy­anthra­quinone), C₁₄H₈O₄, an isomer of the alizarin dye, adopts a planar conformation, with crystallographic mm symmetry. Its crystal packing, which can be described as superimposed sheets of mol­ecules (like a graphite structure), is very different from that of alizarin, which contains a herringbone stacking of mol­ecules.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.003 Å
• Disorder in main residue
• R factor = 0.057
• wR factor = 0.188
• Data-to-parameter ratio = 10.7

checkCIF/PLATON results

No syntax errors found



Alert level A
PLAT726_ALERT_1_A H...A   Calc     5.69000, Rep     1.86000 Dev...       3.83 Ang.
              H4   -O1      1.555   1.555
PLAT727_ALERT_1_A D...A   Calc    4.906(4), Rep     2.68000 Dev...       2.23 Ang.
              O4   -O1      1.555   1.555
PLAT728_ALERT_1_A D-H..A  Calc       17.00, Rep      178.00 Dev...     161.00 Deg.
              O4   -H4   -O1      1.555   1.555   1.555

Alert level B
PLAT601_ALERT_2_B Structure Contains Solvent Accessible VOIDS of .     107.00 A   3 

Alert level C
PLAT076_ALERT_1_C Occupancy       0.50 less than 1.0 for Sp.pos  .         O4
PLAT076_ALERT_1_C Occupancy       0.50 less than 1.0 for Sp.pos  .         H4
PLAT076_ALERT_1_C Occupancy       0.50 less than 1.0 for Sp.pos  .        H4'
PLAT094_ALERT_2_C Ratio of Maximum / Minimum Residual Density ....       2.19
PLAT301_ALERT_3_C Main Residue  Disorder .........................      10.00 Perc.
PLAT313_ALERT_2_C Oxygen with three covalent bonds (rare) ........         O4
PLAT366_ALERT_2_C Short? C(sp?)-C(sp?) Bond  C3     -   C4     ...       1.38 Ang.

Alert level G
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature .        293 K

   3 ALERT level A = In general: serious problem
   1 ALERT level B = Potentially serious problem
   7 ALERT level C = Check and explain
   2 ALERT level G = General alerts; check

   8 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   4 ALERT type 2 Indicator that the structure model may be wrong or deficient
   1 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

---

Computing details

Data collection: CAD-4/MACH3 (Nonius, 2000); cell refinement: CAD-4/MACH3; data reduction: HELENA (Spek, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: PLATON.

2,6-dihydroxyanthraquinone

Crystal data

C14H8O4	Dx = 1.284 Mg m^−3
Mr = 240.20	Cu Kα radiation, λ = 1.54178 Å
Tetragonal, I4/mcm	Cell parameters from 18 reflections
Hall symbol: -I 4 2c	θ = 19.7–33.9°
a = 13.640 (4) Å	µ = 0.80 mm^−1
c = 6.678 (3) Å	T = 293 K
V = 1242.4 (8) Å^3	Thin needles, yellow
Z = 4	0.50 × 0.19 × 0.15 mm
F(000) = 496

Data collection

Nonius diffractometer	346 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.022
Graphite monochromator	θmax = 75.0°, θmin = 4.6°
ω/2θ scans	h = 0→17
Absorption correction: analytical (Alcock, 1970)	k = −17→0
Tmin = 0.691, Tmax = 0.890	l = −8→0
702 measured reflections	3 standard reflections every 60 min
375 independent reflections	intensity decay: 11.0%

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)] = 0.057	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.188	H atoms treated by a mixture of independent and constrained refinement
S = 1.20	w = 1/[σ^2(Fo^2) + (0.1314P)^2 + 0.1721P] where P = (Fo^2 + 2Fc^2)/3
375 reflections	(Δ/σ)max < 0.001
35 parameters	Δρmax = 0.41 e Å^−3
41 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. Structure was refined using the option Squeeze (van der Sluis, 1990) in PLATON suite. Void is present in the centre of the tetrameric assembly. This cavity potentialy hosts a cation or water molecules. Attempts to refine this electron density were niot successful. The δρ_max was carefully analysed and is present on the partial double bond between C2 and C2e. This is due to the electronic resonance.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
O1	0.36072 (9)	−0.13928 (9)	0.0000	0.0518 (7)
C1	0.42437 (12)	−0.07563 (12)	0.0000	0.0368 (7)
C2	0.39765 (11)	0.02914 (11)	0.0000	0.0363 (7)
C3	0.29948 (14)	0.05674 (13)	0.0000	0.0452 (7)
H3	0.2510	0.0088	0.0000	0.054*
C4	0.27310 (13)	0.15455 (14)	0.0000	0.0491 (7)
O4	0.1729 (2)	0.1675 (2)	0.0000	0.0692 (10)	0.50
H4	0.1603	0.2263	0.0000	0.104*	0.50
H4'	0.2068 (6)	0.170 (2)	0.0000	0.083*	0.50

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0387 (9)	0.0387 (9)	0.0781 (14)	−0.0073 (6)	0.000	0.000
C1	0.0341 (9)	0.0341 (9)	0.0420 (12)	−0.0023 (8)	0.000	0.000
C2	0.0321 (10)	0.0337 (10)	0.0430 (10)	0.0001 (7)	0.000	0.000
C3	0.0333 (10)	0.0437 (10)	0.0585 (12)	0.0008 (6)	0.000	0.000
C4	0.0372 (10)	0.0464 (11)	0.0638 (13)	0.0093 (7)	0.000	0.000
O4	0.0399 (16)	0.0483 (17)	0.119 (2)	0.0096 (11)	0.000	0.000

Geometric parameters (Å, º)

O1—C1	1.228 (3)	C3—H3	0.9300
C1—C2^i	1.475 (2)	C4—O4	1.377 (4)
C1—C2	1.475 (2)	C4—C4^ii	1.396 (4)
C2—C3	1.391 (2)	C4—H4'	0.9300 (10)
C2—C2^ii	1.412 (3)	O4—H4	0.8200
C3—C4	1.382 (2)
O1—C1—C2^i	120.69 (11)	C2—C3—H3	119.6
O1—C1—C2	120.69 (11)	O4—C4—C3	112.5 (2)
C2^i—C1—C2	118.6 (2)	O4—C4—C4^ii	127.64 (15)
C3—C2—C2^ii	119.29 (10)	C3—C4—C4^ii	119.91 (11)
C3—C2—C1	120.02 (17)	C3—C4—H4'	118.6 (19)
C2^ii—C2—C1	120.69 (11)	C4^ii—C4—H4'	121.5 (19)
C4—C3—C2	120.80 (17)	C4—O4—H4	109.5
C4—C3—H3	119.6

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O4—H4···O1	0.82	1.86	2.68	178