Gallic acid monohydrate

In the crystal structure of the title compound, 3,4,5-tri­hydroxy­benzoic acid monohydrate, C₇H₆O₅·H₂O, the gallic acid mol­ecule has an intramolecular hydrogen bond involving a pair of hydroxyl groups, and it is also linked to a water mol­ecule by a three-centre (bifurcated) OW—H...O hydrogen bond. The packing of the mol­ecules is stabilized by intermolecular O—H...O and C—H...O hydrogen bonds.

S1. Comment

Tannins are widely distributed in many edible and medicinal plants, and some with strong pharmacological activities have been used as haemostatic and astringent agents. There are two kinds of tannins in nature: one is condensation tannin and the other is hydrolysable tannin. The basic units of hydrolysable tannins are ellagic acid, (I), and gallic acid. The crystal structure of the former was published over three decades ago (Mathieson & Poppleton, 1968). In the present paper, we report the crystal structure of gallic acid monohydrate, (II), which has been shown to exhibit antibacterial and antiviral activities (Jiang & Xiao, 1986). \scheme

The molecule of (II) is essentially planar. The mean deviation of the benzene ring is 0.0028 Å and its dihedral angle with the plane of the carboxyl group is 2.9°. The bond distances are all normal.

Within the asymmetric unit, there is an intramolecular hydrogen bond between O1 and O2. The water molecule is linked to the gallic acid by a three-centre (bifurcated) donor hydrogen bond to two acceptor hydroxyl groups, as represented by OW-HOWB···O2 and OW-HOWB···O3 (Fig. 1). These hydrogen bonds form two five-membered hydrogen-bonded rings. The intermolecular hydrogen bonds O3—H···OW, O2—H···OW and OW-HOWA···O2 link the asymmetric unit at the junction where the water molecules are spirally distributed, to form a channel running parallel to the a axis. The intermolecular hydrogen bond O4—H···O5 links the two adjacent channels and results in extended `wavy' sheets parallel to the (200) plane. Adjacent sheets are linked by hydrogen bond O1—H···O5 and a weak C—H···O hydrogen bond between C6 and O1 to form a supramolecular assembly. Details of the hydrogen bonds are displayed in Table 2. The crystal packing is shown in Fig. 2 in a projection along the short b axis.

S2. Experimental

A sample of compound (II) was extracted from the whole plant of Geum japonicum. The dried plant material (3 kg) was chopped into small pieces and extracted with 95% ethanol at room temperature. The extracted liquid was evaporated in vacuo to yield an ethanol extract (80 g), which was then suspended in distilled water and successively extracted with hexane, ethyl acetate and n-butanol. The n-butanol extract was subjected to Sephadex LH-20 column chromatography and eluted with EtOH-H2O (4:1). The eluted liquid was condensed and allowed to stand at room temperature and yellow prismatic crystals of (II) (50 mg) were obtained.

S3. Refinement

H(—C) atoms were generated geometrically and treated with a riding model. H(—O) were located from difference maps and refined with isotropic displacement parameters.

Computing details

Data collection: Rigaku/AFC Diffractometer Control Software (Rigaku, 1998); cell refinement: Rigaku/AFC Diffractometer Control Software (Rigaku, 1998); data reduction: TEXSAN (Molecular Structure Corporation, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Siemens, 1998).

Figures

	Fig. 1. The molecular structure of (II) showing 50% probability displacement ellipsoids and the atom-numbering scheme; the hydrogen bonds in the asymmetric unit are indicated by dashed lines.
	Fig. 2. Packing diagram for (II) viewed down the b axis.

3,4,5-trihydroxybenzoic acid monohydrate

Crystal data

C7H6O5·H2O	F(000) = 392
Mr = 188.13	Dx = 1.599 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 5.794 (4) Å	Cell parameters from 25 reflections
b = 4.719 (5) Å	θ = 7.5–12.5°
c = 28.688 (5) Å	µ = 0.14 mm^−1
β = 95.08 (3)°	T = 293 K
V = 781.4 (3) Å^3	Prism, yellow
Z = 4	0.5 × 0.2 × 0.1 mm

Data collection

Rigaku AFC-7R diffractometer	907 reflections with F > 4σ(F^2)
Radiation source: fine-focus sealed tube	Rint = 0.032
Graphite monochromator	θmax = 25.0°, θmin = 2.9°
ω/2θ scan	h = −1→6
Absorption correction: ψ-scan (Rigaku, 1998)	k = −1→5
Tmin = 0.945, Tmax = 1.000	l = −34→33
1514 measured reflections	3 standard reflections every 197 reflections
1369 independent reflections	intensity decay: none

Refinement

Refinement on F^2	H atoms treated by a mixture of independent and constrained refinement
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0746P)^2] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.042	(Δ/σ)max = 0.016
wR(F^2) = 0.127	Δρmax = 0.17 e Å^−3
S = 1.01	Δρmin = −0.25 e Å^−3
1369 reflections	Extinction correction: SHELXL97 (Sheldrick, 1997)
122 parameters	Extinction coefficient: 0.000
0 restraints

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.

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

	x	y	z	Uiso*/Ueq
OW	0.7751 (3)	0.5779 (4)	0.28320 (5)	0.0469 (5)
HOWA	0.8645	0.7584	0.2911	0.050*
HOWB	0.7931	0.5493	0.2503	0.050*
O1	0.9971 (3)	0.9452 (4)	0.11455 (6)	0.0483 (5)
HO1	0.9772	1.0534	0.0922	0.074 (11)*
O2	0.9880 (3)	0.6028 (4)	0.18947 (5)	0.0409 (5)
HO2	1.0507	0.7586	0.1898	0.079 (12)*
O3	0.6535 (3)	0.2416 (4)	0.19812 (5)	0.0475 (5)
HO3	0.5315	0.1563	0.2002	0.067 (10)*
O4	0.2646 (3)	0.7063 (4)	0.01282 (6)	0.0504 (5)
HO4	0.1471	0.6871	−0.0050	0.078 (11)*
O5	0.1029 (3)	0.3531 (4)	0.04903 (5)	0.0439 (5)
C1	0.4555 (4)	0.5521 (5)	0.08415 (7)	0.0318 (5)
C2	0.6327 (4)	0.7460 (5)	0.07956 (8)	0.0355 (6)
H2A	0.6308	0.8615	0.0533	0.043*
C3	0.8119 (4)	0.7646 (5)	0.11470 (8)	0.0336 (6)
C4	0.8137 (4)	0.5936 (5)	0.15374 (7)	0.0324 (5)
C5	0.6362 (4)	0.4022 (5)	0.15812 (7)	0.0332 (6)
C6	0.4571 (4)	0.3782 (5)	0.12326 (8)	0.0361 (6)
H6A	0.3390	0.2473	0.1259	0.043*
C7	0.2599 (4)	0.5274 (5)	0.04787 (7)	0.0347 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
OW	0.0467 (10)	0.0597 (12)	0.0334 (9)	−0.0059 (8)	−0.0020 (7)	0.0097 (9)
O1	0.0410 (10)	0.0580 (11)	0.0435 (10)	0.0169 (9)	−0.0103 (8)	−0.0190 (9)
O2	0.0372 (9)	0.0475 (11)	0.0353 (10)	0.0047 (7)	−0.0125 (7)	−0.0100 (8)
O3	0.0449 (11)	0.0610 (12)	0.0343 (9)	0.0145 (8)	−0.0102 (8)	−0.0191 (10)
O4	0.0487 (11)	0.0606 (13)	0.0383 (10)	0.0173 (9)	−0.0168 (8)	−0.0174 (9)
O5	0.0395 (10)	0.0539 (11)	0.0357 (10)	0.0086 (8)	−0.0119 (7)	−0.0139 (9)
C1	0.0314 (12)	0.0378 (13)	0.0253 (11)	−0.0026 (10)	−0.0025 (9)	−0.0021 (11)
C2	0.0355 (12)	0.0415 (14)	0.0287 (12)	0.0037 (10)	−0.0017 (9)	−0.0034 (11)
C3	0.0286 (12)	0.0379 (13)	0.0336 (12)	0.0015 (10)	−0.0015 (9)	−0.0054 (11)
C4	0.0300 (11)	0.0404 (13)	0.0259 (12)	−0.0011 (10)	−0.0030 (9)	−0.0004 (11)
C5	0.0349 (12)	0.0391 (13)	0.0245 (11)	0.0033 (10)	−0.0029 (9)	−0.0013 (11)
C6	0.0297 (11)	0.0430 (14)	0.0347 (13)	0.0016 (11)	−0.0016 (9)	−0.0085 (11)
C7	0.0330 (12)	0.0405 (13)	0.0296 (12)	0.0007 (11)	−0.0017 (9)	−0.0040 (12)

Geometric parameters (Å, º)

O1—C3	1.371 (3)	C1—C6	1.390 (3)
O2—C4	1.375 (3)	C1—C7	1.474 (3)
O3—C5	1.371 (3)	C2—C3	1.385 (3)
O4—C7	1.315 (3)	C3—C4	1.380 (3)
O5—C7	1.229 (3)	C4—C5	1.383 (3)
C1—C2	1.390 (3)	C5—C6	1.381 (3)
C2—C1—C6	120.9 (2)	C3—C4—C5	120.2 (1)
C2—C1—C7	120.9 (2)	O3—C5—C6	123.7 (2)
C6—C1—C7	118.2 (2)	O3—C5—C4	115.9 (1)
C3—C2—C1	119.0 (2)	C6—C5—C4	120.3 (2)
O1—C3—C4	114.6 (2)	C5—C6—C1	119.2 (2)
O1—C3—C2	125.0 (2)	O5—C7—O4	121.1 (2)
C4—C3—C2	120.3 (2)	O5—C7—C1	123.9 (2)
O2—C4—C3	122.6 (2)	O4—C7—C1	115.0 (2)
O2—C4—C5	117.1 (1)
C6—C1—C2—C3	−0.1 (3)	O2—C4—C5—C6	−179.0 (2)
C7—C1—C2—C3	179.3 (2)	C3—C4—C5—C6	0.7 (4)
C1—C2—C3—O1	179.8 (2)	O3—C5—C6—C1	179.8 (2)
C1—C2—C3—C4	−0.2 (3)	C4—C5—C6—C1	−1.1 (4)
O1—C3—C4—O2	−0.3 (3)	C2—C1—C6—C5	0.8 (4)
C2—C3—C4—O2	179.7 (2)	C7—C1—C6—C5	−178.6 (2)
O1—C3—C4—C5	179.9 (2)	C2—C1—C7—O5	177.1 (2)
C2—C3—C4—C5	0.0 (4)	C6—C1—C7—O5	−3.5 (4)
O2—C4—C5—O3	0.2 (3)	C2—C1—C7—O4	−2.2 (3)
C3—C4—C5—O3	179.9 (2)	C6—C1—C7—O4	177.3 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
OW—HOWA···O2^i	1.01	1.90	2.906 (4)	174
OW—HOWB···O2	0.97	2.18	3.058 (4)	151
OW—HOWB···O3	0.97	2.19	2.944 (4)	134
O1—HO1···O5^ii	0.82	2.06	2.796 (4)	150
O2—HO2···O1	0.82	2.33	2.693 (4)	108
O2—HO2···OW^i	0.82	1.94	2.708 (4)	157
O3—HO3···OW^iii	0.82	1.92	2.699 (4)	160
O4—HO4···O5^iv	0.82	1.85	2.663 (4)	175
C6—H6···O1^v	0.93	2.44	3.350 (5)	166

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