2,3,4-Trihy­droxy­benzoic acid 0.25-hydrate

Li, J.-H.; Dong, F.-Y.; Cai, F.; Yuan, X.-F.; Jiang, R.-W.

doi:10.1107/S160053681200709X

organic compounds

CRYSTALLOGRAPHIC
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ISSN: 2056-9890

Volume 68| Part 3| March 2012| Pages o825-o826

doi:10.1107/S160053681200709X

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2,3,4-Trihydroxybenzoic acid 0.25-hydrate

Jin-Hang Li,^a Fu-Yue Dong,^a Fang Cai,^a Xiao-Feng Yuan ^a and Ren-Wang Jiang ^a ^*

^aGuangdong Province Key Laboratory of Pharmacodynamic Constituents of, Traditional Chinese Medicine and New Drugs Research, Institute of Traditional Chinese Medicine and Natural Products, Jinan University, Guangzhou 510632, People's Republic of China
^*Correspondence e-mail: trwjiang@jnu.edu.cn

(Received 4 February 2012; accepted 16 February 2012; online 24 February 2012)

The asymmetric unit of the title compound, C₇H₆O₅·0.25H₂O, contains two molecules of 2,3,4-trihydroxybenzoic acid, with similar conformations, and one water molecule which lies on a twofold rotation axis. Both acid molecules are essentially planar [maximum r.m.s deviations = 0.0324 (2) and 0.0542 (3) Å for the two acid molecules]. The molecular conformations are stabilized by intramolecular O(phenol)—H⋯O(carboxyl/phenol) interactions. A cyclic intermolecular association is formed between the two acid and one water molecule [graph set R₃³(12)] involving O—H⋯O hydrogen bonds. The two acid molecules are further linked through a cyclic R₂²(8) carboxylic acid hydrogen-bonding association, which together with intermolecular O—H⋯O hydrogen-bonding interactions involving the phenol groups and the water molecule, and weak π–π interactions [minimum ring centroid separation = 3.731 (3) Å], give a three-dimensional network.

Related literature

For the natural distribution of 2,3,4-trihydroxybenzoic acid, see: Zhai et al. (2010 ); Xu & Chang (2010 ). For its antioxidant and antibacterial activities, see: Kodama et al. (2007 ); Friedman et al. (2003 ). For the inhibition of xanthine oxidase, see: Chang et al. (1995 ). For the crystal structure of the dihydrate pseudopolymorph, see: Prior & Sharp (2010 ). For π–π interactions in gallic acid pyridine monosolvate and in natural flavonoids, see: Dong et al. (2011 ); Jiang et al. (2009 , 2002 ). For graph-set analysis, see: Etter et al. (1990 ); Bernstein et al. (1995 ).

Experimental

Crystal data

C₇H₆O₅·0.25H₂O
M_r = 174.62
Orthorhombic, P 2₁ 2₁ 2
a = 11.8364 (12) Å
b = 32.598 (3) Å
c = 3.7306 (4) Å
V = 1439.4 (3) Å³
Z = 8
Mo Kα radiation
μ = 0.14 mm⁻¹
T = 291 K
0.42 × 0.28 × 0.20 mm

Data collection

Bruker SMART 1000 CCD diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2004 ) T_min = 0.874, T_max = 1.000
7863 measured reflections
2552 independent reflections
2010 reflections with I > 2σ(I)
R_int = 0.060

Refinement

R[F² > 2σ(F²)] = 0.036
wR(F²) = 0.090
S = 0.97
2552 reflections
222 parameters
H-atom parameters constrained
Δρ_max = 0.17 e Å⁻³
Δρ_min = −0.15 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1W—H1WA⋯O2	0.82	2.19	2.963 (2)	156
O1—H1A⋯O4	0.82	1.88	2.587 (3)	143
O2—H2A⋯O2′ⁱ	0.82	2.05	2.839 (4)	161
O3—H3A⋯O3′ⁱⁱ	0.82	2.06	2.828 (3)	155
O5—H5B⋯O4′ⁱⁱⁱ	0.82	1.88	2.679 (4)	165
O1′—H1′A⋯O4′	0.82	1.87	2.588 (3)	145
O2′—H2′A⋯O1	0.82	1.95	2.729 (4)	159
O3′—H3′A⋯O1W	0.82	2.06	2.841 (3)	158
O5′—H5′B⋯O4^iv	0.82	1.85	2.659 (4)	171
Symmetry codes: (i) x, y, z+1; (ii) -x+1, -y, z+1; (iii) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z-1]$ ; (iv) $[x-{\script{1\over 2}}, -y+{\script{1\over 2}}, -z-1]$ .

Data collection: SMART (Bruker, 1998 ); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP (Siemens, 1998 ); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S160053681200709X/zs2181sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S160053681200709X/zs2181Isup2.hkl

Supporting information file. DOI: 10.1107/S160053681200709X/zs2181Isup3.cml

checkCIF report

Comment top

2,3,4-Trihydroxybenzoic acid is a polyphenolic acid which has been isolated from Pachysandra terminalis (Zhai et al., 2010) and the lentil (Xu & Chang, 2010). It has been found to show antioxidant (Kodama et al., 2007) and antibacterial activities (Friedman et al., 2003) and also to inhibit the xanthine oxidase enzyme (Chang et al., 1995). This compound contains two of the most common functional groups in natural products: the carboxylic acid and the phenolic groups. The dihydrate pseudopolymorph of the acid with a space group P-1 has previusly been reported (Prior & Sharp, 2010). In this study, we report the structure of the second pseudopolymorph, the partial hydrate C₇H₆O₅ . 0.25H₂O.

The asymmetric unit of the title compound contains two molecules of 2,3,4-trihydroxybenzoic acid [(1) and (2)] with similar conformations, and one water molecule of solvation which lies on a crystallographic twofold rotation axis (Fig. 1). Both acid molecules are essentially planar [maximum r.m.s deviation 0.0324 (2) and 0.0542 (3) Å for the two acid molecules], with a dihedral angle of 49.4 (3)° between the planes. The molecular conformation of the acid molecules is stabilized by a number of intramolecular phenolic O—H···O interactions (Table 1).

The water molecule and the acid molecules are linked through O—H···O hydrogen bonds (Table 1) with both acting as donors and acceptors, giving a cyclic association [graph set R³₃(12) (Etter et al., 1990; Bernstein et al., 1995)]. The 2,3,4-trihydroxybenzoic acid molecules form head-to-head pairs through intermolecular hydrogen bonds [graph set R²₂(8). The molecular pairs are further extended into chains through hydrogen bond O2–H···O2'ⁱ , while adjacent chains are connected via hydrogen bond O3–H···O3'ⁱⁱ into a three-dimensional network (Fig. 2) [for symmetry codes (i) and (ii), see Table 1]. It is noteworthy that aromatic π–π associations also play an important role in the molecular packing. Adjacent 2,3,4-trihydroxybenzoic acid molecules form stacks which extend down the c-axis giving weak π–π interactions [minimum ring centroid separation, 3.731 (3) Å], which is larger than that in the dihydrate form of the acid (Prior & Sharp, 2010) and in gallic acid pyridine monosolvate (Dong et al., 2011), but comparable with those in natural flavonoids (Jiang et al., 2002, 2009).

Related literature top

For the natural distribution of 2,3,4-trihydroxybenzoic acid, see: Zhai et al. (2010); Xu & Chang (2010). For the antioxidant and antibacterial activities, see: Kodama et al. (2007); Friedman et al. (2003). For the inhibition of xanthine oxidase, see: Chang et al. (1995). For the crystal structure of the dihydrate pseudopolymorph, see: Prior & Sharp (2010). For the π–π interactions in gallic acid pyridine monosolvate and in natural flavonoids, see: Dong et al. (2011); Jiang et al. (2009, 2002). For graph-set analysis, see: Etter et al. (1990); Bernstein et al. (1995).

Experimental top

2,3,4-Trihydroxybenzoic acid (purity >98%) was purchased from the Sigma-Aldrich Company. Sample of 34 mg (0.2 mmol) was dissolved in methanol (1.5 ml) in a tube (4 ml) and sealed by parafilm. Light brown crystals were formed after three days at room temperature.

Computing details top

Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT (Bruker, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP (Siemens, 1998); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top

	Fig. 1. An ORTEP plot of the asymmetric unit of the title compound with atoms shown as 30% probability ellipsoids. The water molecule lies on a crystallographic twofold rotation axis and hydrogen bonds are shown as dashed lines.
	Fig. 2. Packing diagram viewed down the c-axis showing hydrogen bonds as dashed lines.

2,3,4-Trihydroxybenzoic acid 0.25-hydrate top

Crystal data top

C₇H₆O₅·0.25H₂O	F(000) = 724
M_r = 174.62	D_x = 1.612 Mg m⁻³
Orthorhombic, P2₁2₁2	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 2552 reflections
a = 11.8364 (12) Å	θ = 2.1–50.0°
b = 32.598 (3) Å	µ = 0.14 mm⁻¹
c = 3.7306 (4) Å	T = 291 K
V = 1439.4 (3) Å³	Prism, light brown
Z = 8	0.42 × 0.28 × 0.20 mm

Data collection top

Bruker SMART 1000 CCD diffractometer	2552 independent reflections
Radiation source: fine-focus sealed tube	2010 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.060
ω scan	θ_max = 25.0°, θ_min = 2.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 2004)	h = −13→14
T_min = 0.874, T_max = 1.000	k = −38→34
7863 measured reflections	l = −4→4

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.036	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.090	H-atom parameters constrained
S = 0.97	w = 1/[σ²(F_o²) + (0.0443P)²] where P = (F_o² + 2F_c²)/3
2552 reflections	(Δ/σ)_max < 0.001
222 parameters	Δρ_max = 0.17 e Å⁻³
0 restraints	Δρ_min = −0.15 e Å⁻³

Crystal data top

C₇H₆O₅·0.25H₂O	V = 1439.4 (3) Å³
M_r = 174.62	Z = 8
Orthorhombic, P2₁2₁2	Mo Kα radiation
a = 11.8364 (12) Å	µ = 0.14 mm⁻¹
b = 32.598 (3) Å	T = 291 K
c = 3.7306 (4) Å	0.42 × 0.28 × 0.20 mm

Data collection top

Bruker SMART 1000 CCD diffractometer	2552 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 2004)	2010 reflections with I > 2σ(I)
T_min = 0.874, T_max = 1.000	R_int = 0.060
7863 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.036	0 restraints
wR(F²) = 0.090	H-atom parameters constrained
S = 0.97	Δρ_max = 0.17 e Å⁻³
2552 reflections	Δρ_min = −0.15 e Å⁻³
222 parameters

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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 (Å²) top

	x	y	z	U_iso*/U_eq
O1W	0.5000	0.0000	−0.1102 (7)	0.0395 (6)
H1WA	0.5263	0.0173	0.0258	0.059*
O1	0.65345 (12)	0.12870 (4)	0.2193 (5)	0.0334 (4)
H1A	0.6637	0.1534	0.1900	0.040*
O2	0.65656 (13)	0.04688 (4)	0.3549 (4)	0.0323 (4)
H2A	0.6145	0.0640	0.4444	0.039*
O3	0.84576 (14)	0.00203 (5)	0.2010 (5)	0.0445 (5)
H3A	0.7859	−0.0048	0.2940	0.053*
O4	0.75826 (14)	0.19200 (4)	−0.0346 (6)	0.0429 (5)
O5	0.93058 (15)	0.18491 (4)	−0.2704 (6)	0.0481 (5)
H5B	0.9243	0.2098	−0.2919	0.058*
C1	0.84467 (19)	0.12653 (6)	−0.0250 (7)	0.0273 (5)
C2	0.74982 (19)	0.10787 (6)	0.1337 (6)	0.0245 (5)
C3	0.74932 (18)	0.06626 (6)	0.2074 (6)	0.0254 (5)
C4	0.84311 (19)	0.04271 (6)	0.1272 (7)	0.0295 (5)
C5	0.9374 (2)	0.06046 (7)	−0.0324 (7)	0.0330 (6)
H5A	0.9998	0.0444	−0.0891	0.040*
C6	0.9383 (2)	0.10180 (7)	−0.1064 (7)	0.0313 (6)
H6A	1.0018	0.1135	−0.2117	0.038*
C7	0.8406 (2)	0.17017 (7)	−0.1079 (7)	0.0310 (6)
O1'	0.49399 (13)	0.17376 (4)	−0.2824 (5)	0.0359 (4)
H1'A	0.4856	0.1982	−0.3270	0.043*
O2'	0.49999 (12)	0.09083 (4)	−0.2151 (5)	0.0308 (4)
H2'A	0.5380	0.1075	−0.1033	0.037*
O3'	0.32290 (14)	0.04439 (4)	−0.4474 (5)	0.0397 (5)
H3'A	0.3817	0.0378	−0.3464	0.048*
O4'	0.39072 (15)	0.23703 (5)	−0.5434 (6)	0.0446 (5)
O5'	0.22055 (15)	0.23003 (5)	−0.7935 (6)	0.0506 (5)
H5'B	0.2294	0.2547	−0.8259	0.061*
C1'	0.3088 (2)	0.17066 (7)	−0.5659 (7)	0.0293 (6)
C2'	0.40325 (19)	0.15242 (6)	−0.4052 (6)	0.0271 (6)
C3'	0.40863 (19)	0.11019 (6)	−0.3646 (6)	0.0267 (5)
C4'	0.31874 (19)	0.08593 (6)	−0.4795 (7)	0.0281 (6)
C5'	0.22322 (19)	0.10389 (7)	−0.6322 (7)	0.0328 (6)
H5'A	0.1630	0.0876	−0.7056	0.039*
C6'	0.2185 (2)	0.14569 (7)	−0.6737 (7)	0.0336 (6)
H6'A	0.1546	0.1576	−0.7746	0.040*
C7'	0.3098 (2)	0.21492 (7)	−0.6310 (7)	0.0349 (6)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1W	0.0469 (15)	0.0229 (11)	0.0486 (16)	−0.0056 (10)	0.000	0.000
O1	0.0299 (9)	0.0177 (7)	0.0527 (11)	0.0023 (6)	0.0057 (9)	0.0020 (8)
O2	0.0280 (9)	0.0212 (8)	0.0475 (11)	0.0003 (6)	0.0064 (8)	0.0020 (8)
O3	0.0386 (10)	0.0215 (8)	0.0734 (13)	0.0038 (7)	0.0121 (10)	0.0077 (10)
O4	0.0398 (11)	0.0244 (8)	0.0644 (13)	−0.0006 (8)	0.0084 (10)	0.0075 (9)
O5	0.0463 (11)	0.0268 (9)	0.0713 (14)	−0.0031 (8)	0.0157 (11)	0.0094 (10)
C1	0.0298 (13)	0.0244 (11)	0.0278 (13)	−0.0029 (10)	−0.0040 (11)	0.0009 (11)
C2	0.0265 (12)	0.0208 (11)	0.0261 (13)	0.0014 (9)	−0.0058 (11)	−0.0024 (10)
C3	0.0285 (13)	0.0211 (11)	0.0268 (12)	−0.0056 (9)	−0.0017 (11)	0.0004 (10)
C4	0.0334 (14)	0.0193 (11)	0.0359 (14)	0.0014 (10)	−0.0033 (12)	0.0009 (11)
C5	0.0278 (14)	0.0303 (13)	0.0409 (15)	0.0041 (10)	0.0006 (12)	−0.0034 (12)
C6	0.0257 (13)	0.0324 (13)	0.0360 (15)	−0.0042 (10)	−0.0001 (12)	0.0006 (11)
C7	0.0315 (14)	0.0255 (12)	0.0361 (14)	−0.0068 (11)	−0.0040 (12)	0.0019 (11)
O1'	0.0346 (9)	0.0185 (7)	0.0546 (11)	−0.0032 (6)	−0.0058 (10)	0.0011 (8)
O2'	0.0294 (9)	0.0191 (7)	0.0440 (10)	0.0016 (6)	−0.0038 (9)	0.0011 (7)
O3'	0.0408 (11)	0.0207 (8)	0.0575 (12)	−0.0029 (7)	−0.0115 (9)	−0.0004 (9)
O4'	0.0476 (12)	0.0208 (8)	0.0655 (14)	0.0004 (8)	−0.0142 (10)	0.0057 (9)
O5'	0.0482 (11)	0.0279 (9)	0.0758 (14)	0.0047 (8)	−0.0172 (12)	0.0138 (10)
C1'	0.0340 (14)	0.0227 (12)	0.0312 (13)	0.0031 (10)	0.0040 (11)	−0.0003 (11)
C2'	0.0295 (13)	0.0221 (12)	0.0297 (14)	−0.0024 (10)	0.0035 (12)	−0.0021 (10)
C3'	0.0280 (13)	0.0231 (11)	0.0290 (13)	0.0037 (10)	0.0045 (11)	0.0009 (10)
C4'	0.0334 (14)	0.0199 (11)	0.0311 (14)	0.0005 (10)	0.0052 (11)	−0.0007 (11)
C5'	0.0297 (14)	0.0299 (12)	0.0388 (15)	−0.0033 (10)	−0.0005 (12)	−0.0019 (12)
C6'	0.0342 (14)	0.0326 (12)	0.0339 (15)	0.0051 (10)	−0.0039 (12)	0.0022 (12)
C7'	0.0399 (16)	0.0271 (13)	0.0376 (15)	0.0071 (11)	0.0020 (12)	0.0021 (12)

Geometric parameters (Å, º) top

O1W—H1WA	0.8200	O1'—C2'	1.359 (3)
O1—C2	1.365 (3)	O1'—H1'A	0.8200
O1—H1A	0.8200	O2'—C3'	1.371 (3)
O2—C3	1.381 (3)	O2'—H2'A	0.8200
O2—H2A	0.8200	O3'—C4'	1.360 (2)
O3—C4	1.355 (2)	O3'—H3'A	0.8200
O3—H3A	0.8200	O4'—C7'	1.243 (3)
O4—C7	1.237 (3)	O5'—C7'	1.314 (3)
O5—C7	1.317 (3)	O5'—H5'B	0.8200
O5—H5B	0.8200	C1'—C2'	1.401 (3)
C1—C6	1.404 (3)	C1'—C6'	1.403 (3)
C1—C2	1.407 (3)	C1'—C7'	1.463 (3)
C1—C7	1.457 (3)	C2'—C3'	1.386 (3)
C2—C3	1.384 (3)	C3'—C4'	1.393 (3)
C3—C4	1.382 (3)	C4'—C5'	1.395 (3)
C4—C5	1.391 (3)	C5'—C6'	1.373 (3)
C5—C6	1.376 (3)	C5'—H5'A	0.9300
C5—H5A	0.9300	C6'—H6'A	0.9300
C6—H6A	0.9300

C2—O1—H1A	109.5	C2'—O1'—H1'A	109.5
C3—O2—H2A	109.5	C3'—O2'—H2'A	109.5
C4—O3—H3A	109.5	C4'—O3'—H3'A	109.5
C7—O5—H5B	109.5	C7'—O5'—H5'B	109.5
C6—C1—C2	118.2 (2)	C2'—C1'—C6'	119.0 (2)
C6—C1—C7	122.8 (2)	C2'—C1'—C7'	118.9 (2)
C2—C1—C7	119.0 (2)	C6'—C1'—C7'	122.1 (2)
O1—C2—C3	115.9 (2)	O1'—C2'—C3'	115.8 (2)
O1—C2—C1	123.35 (18)	O1'—C2'—C1'	123.89 (18)
C3—C2—C1	120.7 (2)	C3'—C2'—C1'	120.3 (2)
O2—C3—C4	118.08 (17)	O2'—C3'—C2'	122.5 (2)
O2—C3—C2	122.06 (19)	O2'—C3'—C4'	117.79 (18)
C4—C3—C2	119.9 (2)	C2'—C3'—C4'	119.7 (2)
O3—C4—C3	121.2 (2)	O3'—C4'—C3'	120.7 (2)
O3—C4—C5	118.4 (2)	O3'—C4'—C5'	118.9 (2)
C3—C4—C5	120.4 (2)	C3'—C4'—C5'	120.4 (2)
C6—C5—C4	119.9 (2)	C6'—C5'—C4'	119.7 (2)
C6—C5—H5A	120.0	C6'—C5'—H5'A	120.1
C4—C5—H5A	120.0	C4'—C5'—H5'A	120.1
C5—C6—C1	120.9 (2)	C5'—C6'—C1'	120.8 (2)
C5—C6—H6A	119.6	C5'—C6'—H6'A	119.6
C1—C6—H6A	119.6	C1'—C6'—H6'A	119.6
O4—C7—O5	122.0 (2)	O4'—C7'—O5'	121.6 (2)
O4—C7—C1	122.7 (2)	O4'—C7'—C1'	122.3 (2)
O5—C7—C1	115.3 (2)	O5'—C7'—C1'	116.1 (2)

C6—C1—C2—O1	−178.9 (2)	C6'—C1'—C2'—O1'	−178.2 (2)
C7—C1—C2—O1	−0.8 (3)	C7'—C1'—C2'—O1'	4.6 (4)
C6—C1—C2—C3	0.1 (3)	C6'—C1'—C2'—C3'	2.1 (4)
C7—C1—C2—C3	178.2 (2)	C7'—C1'—C2'—C3'	−175.1 (2)
O1—C2—C3—O2	0.7 (3)	O1'—C2'—C3'—O2'	−0.9 (3)
C1—C2—C3—O2	−178.4 (2)	C1'—C2'—C3'—O2'	178.8 (2)
O1—C2—C3—C4	179.6 (2)	O1'—C2'—C3'—C4'	179.3 (2)
C1—C2—C3—C4	0.5 (3)	C1'—C2'—C3'—C4'	−1.0 (4)
O2—C3—C4—O3	−2.0 (3)	O2'—C3'—C4'—O3'	−0.8 (3)
C2—C3—C4—O3	179.0 (2)	C2'—C3'—C4'—O3'	179.0 (2)
O2—C3—C4—C5	177.9 (2)	O2'—C3'—C4'—C5'	179.7 (2)
C2—C3—C4—C5	−1.0 (4)	C2'—C3'—C4'—C5'	−0.5 (4)
O3—C4—C5—C6	−179.1 (2)	O3'—C4'—C5'—C6'	−178.6 (2)
C3—C4—C5—C6	1.0 (4)	C3'—C4'—C5'—C6'	0.9 (4)
C4—C5—C6—C1	−0.4 (4)	C4'—C5'—C6'—C1'	0.3 (4)
C2—C1—C6—C5	−0.1 (4)	C2'—C1'—C6'—C5'	−1.8 (4)
C7—C1—C6—C5	−178.2 (2)	C7'—C1'—C6'—C5'	175.3 (2)
C6—C1—C7—O4	−179.6 (2)	C2'—C1'—C7'—O4'	−1.2 (4)
C2—C1—C7—O4	2.3 (4)	C6'—C1'—C7'—O4'	−178.3 (2)
C6—C1—C7—O5	1.0 (3)	C2'—C1'—C7'—O5'	177.7 (2)
C2—C1—C7—O5	−177.1 (2)	C6'—C1'—C7'—O5'	0.6 (4)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1WA···O2	0.82	2.19	2.963 (2)	156
O1W—H1WA···O2′	0.82	2.58	2.987 (3)	112
O1—H1A···O4	0.82	1.88	2.587 (3)	143
O2—H2A···O2′ⁱ	0.82	2.05	2.839 (4)	161
O2—H2A···O1	0.82	2.32	2.715 (2)	111
O3—H3A···O3′ⁱⁱ	0.82	2.06	2.828 (3)	155
O3—H3A···O2	0.82	2.29	2.735 (3)	115
O5—H5B···O4′ⁱⁱⁱ	0.82	1.88	2.679 (4)	165
O1′—H1′A···O4′	0.82	1.87	2.588 (3)	145
O2′—H2′A···O1	0.82	1.95	2.729 (4)	159
O2′—H2′A···O1′	0.82	2.32	2.716 (2)	110
O3′—H3′A···O1W	0.82	2.06	2.841 (3)	158
O3′—H3′A···O2′	0.82	2.28	2.727 (4)	115
O5′—H5′B···O4^iv	0.82	1.85	2.659 (4)	171

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

Experimental details

Crystal data
Chemical formula	C₇H₆O₅·0.25H₂O
M_r	174.62
Crystal system, space group	Orthorhombic, P2₁2₁2
Temperature (K)	291
a, b, c (Å)	11.8364 (12), 32.598 (3), 3.7306 (4)
V (Å³)	1439.4 (3)
Z	8
Radiation type	Mo Kα
µ (mm⁻¹)	0.14
Crystal size (mm)	0.42 × 0.28 × 0.20

Data collection
Diffractometer	Bruker SMART 1000 CCD diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 2004)
T_min, T_max	0.874, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	7863, 2552, 2010
R_int	0.060
(sin θ/λ)_max (Å⁻¹)	0.595

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.036, 0.090, 0.97
No. of reflections	2552
No. of parameters	222
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.17, −0.15

Computer programs: SMART (Bruker, 1998), SAINT (Bruker, 1998), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), XP (Siemens, 1998), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1WA···O2	0.82	2.19	2.963 (2)	156
O1—H1A···O4	0.82	1.88	2.587 (3)	143
O2—H2A···O2'ⁱ	0.82	2.05	2.839 (4)	161
O3—H3A···O3'ⁱⁱ	0.82	2.06	2.828 (3)	155
O5—H5B···O4'ⁱⁱⁱ	0.82	1.88	2.679 (4)	165
O1'—H1'A···O4'	0.82	1.87	2.588 (3)	145
O2'—H2'A···O1	0.82	1.95	2.729 (4)	159
O3'—H3'A···O1W	0.82	2.06	2.841 (3)	158
O5'—H5'B···O4^iv	0.82	1.85	2.659 (4)	171

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

Acknowledgements

This work was supported by a grant from the New Century Excellent Talents Scheme of the Ministry of Education (grant No. NCET-08–0612), the Guangdong High Level Talent Scheme (RWJ) and the Fundamental Research Funds for the Central Universities (grant No. 21609202).

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