metal-organic compounds
Hexaaquazinc(II) 4,4′-(1,2-dihydroxyethane-1,2-diyl)dibenzoate monohydrate
aDepartment of Chemistry and Chemical Engineering, Henan University of Urban Construction, Pingdingshan, Henan 467044, People's Republic of China, bZhongzhou University, Zhongzhou 450044, People's Republic of China, and cCollege of Chemistry and Chemical Engineering, Pingdingshan University, Pingdingshan 467000, People's Republic of China
*Correspondence e-mail: tiandamin2009@163.com
The title compound, [Zn(H2O)6](C16H12O6)·H2O, consists of one 4,4′-(1,2-dihydroxyethane-1,2-diyl)dibenzoate anion lying on an inversion centre, one [Zn(H2O)6]2+ dication lying on a mirror plane and one solvent water molecule located on a mirror plane. The octahedral [Zn(H2O)6]2+ cations, solvent water molecules and anions interact via O—H⋯O hydrogen bonds, forming a three-dimensional network.
Related literature
For the architectures and potential application of polymeric coordination networks, see: Carlucci et al. (2003); Rosi et al. (2003). For the isostructural Mn complex, see: Hao & Cao (2010).
Experimental
Crystal data
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Refinement
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Data collection: SMART (Bruker, 2007); cell SAINT (Bruker, 2007); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.
Supporting information
https://doi.org/10.1107/S1600536810027972/jh2181sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536810027972/jh2181Isup2.hkl
A mixture of Zn(NO3)2 (0.1 mmol, 0.02 g) and 1,2-diol-1,2-bis(4-Carboxyphenyl) (0.1 mmol, 0.03 g) and 10 ml of H2O was loaded in a 20 ml Telflon-lined stainless steel vessel and heated at 303k for 2 days. Colorless crystals were obtained when the solution was cooled to room temperature slowly.
Carbon and nitrogen bound H atoms were placed at calculated positions and were treated as riding on the parent C or N atoms with C—H = 0.93 Å, N—H = 0.86 Å, and with Uiso(H) = 1.2 Ueq(C, N). H atoms of water molecule were located in a difference Fourier map and refined as riding, with Uiso(H) = 1.2Ueq(O)
Current interest in polymeric coordination networks is rapidly expanding for their intriguing architectures (Carlucci et al., 2003) and potential applications (Rosi et al., 2003). thus, we have reacted the ligand with Zn(NO3)2 under hydrothermal conditions to obtain new metal-organic complexes and the structure will be reported here.
As illustrated in figure 1, the title compound (C16H12O6)[Zn6H2O]. H2O is isostructural to a Mn complex based on the same ligand (Hao et al., 2010), containing one 4,4'-(1,2-dihydroxyethane-1,2-diyl)dibenzoate anions ligand, one [Zn6H2O]2+ dicationic complex and a solvent water molecule, The carboxyl group lies in the plane of the benzene ring as indicated by the O1—C1—C2—C3 and O2—C1—C2—C7 torsion angles of -0.2 (10) ° and 176.8 (6) °, and the two benzene rings are parallel to each other. In the crystal packing, a three-dimensional network was stabilized by a wide range of O—H···O hydrogen bonds involving the [Mn6H2O]2+ cations, 4,4'-(1,2-dihydroxyethane-1,2-diyl)dibenzoate anions and solvent water molecules.
For the architectures and potential application of polymeric coordination networks, see: Carlucci et al. (2003); Rosi et al. (2003). For the isostructural Mn complex, see: Hao et al. (2010).
Data collection: SMART (Bruker, 2007); cell
SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).Fig. 1. The structure of the title compound, showing the atomic numbering scheme. Non-H atoms are shown with 30% probability displacement ellipsoids (H atoms are omitted for clarity). [Symmetry codes: (i) 1-x, 1-y, 1-z; (ii) x, 1.5-y, z.] | |
Fig. 2. View of the three-dimensional network constructed by O—H···O hydrogen bonding interactions(the H atoms is not shown in the picture for clarity) |
[Zn(H2O)6](C16H12O6)·H2O | F(000) = 512 |
Mr = 491.76 | Dx = 1.577 Mg m−3 |
Monoclinic, P21/m | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2yb | Cell parameters from 2215 reflections |
a = 6.0356 (9) Å | θ = 2.5–24.0° |
b = 20.508 (2) Å | µ = 1.25 mm−1 |
c = 8.626 (1) Å | T = 298 K |
β = 104.141 (1)° | Block, colourless |
V = 1035.4 (2) Å3 | 0.37 × 0.27 × 0.22 mm |
Z = 2 |
Bruker SMART 1000 CCD area-detector diffractometer | 1877 independent reflections |
Radiation source: fine-focus sealed tube | 1608 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.035 |
φ and ω scans | θmax = 25.0°, θmin = 2.0° |
Absorption correction: multi-scan (SADABS; Bruker, 2007) | h = −7→7 |
Tmin = 0.673, Tmax = 0.759 | k = −22→24 |
5208 measured reflections | l = −9→10 |
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)] = 0.068 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.160 | H-atom parameters constrained |
S = 1.26 | w = 1/[σ2(Fo2) + (0.P)2 + 7.6103P] where P = (Fo2 + 2Fc2)/3 |
1865 reflections | (Δ/σ)max < 0.001 |
142 parameters | Δρmax = 0.65 e Å−3 |
11 restraints | Δρmin = −0.45 e Å−3 |
[Zn(H2O)6](C16H12O6)·H2O | V = 1035.4 (2) Å3 |
Mr = 491.76 | Z = 2 |
Monoclinic, P21/m | Mo Kα radiation |
a = 6.0356 (9) Å | µ = 1.25 mm−1 |
b = 20.508 (2) Å | T = 298 K |
c = 8.626 (1) Å | 0.37 × 0.27 × 0.22 mm |
β = 104.141 (1)° |
Bruker SMART 1000 CCD area-detector diffractometer | 1877 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 2007) | 1608 reflections with I > 2σ(I) |
Tmin = 0.673, Tmax = 0.759 | Rint = 0.035 |
5208 measured reflections |
R[F2 > 2σ(F2)] = 0.068 | 11 restraints |
wR(F2) = 0.160 | H-atom parameters constrained |
S = 1.26 | Δρmax = 0.65 e Å−3 |
1865 reflections | Δρmin = −0.45 e Å−3 |
142 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
Zn1 | 0.64994 (18) | 0.7500 | 0.45837 (12) | 0.0273 (3) | |
O1 | 1.0813 (8) | 0.6420 (2) | 1.2091 (6) | 0.0434 (13) | |
O2 | 1.3273 (9) | 0.6522 (3) | 1.0577 (6) | 0.0551 (15) | |
O3 | 0.6711 (9) | 0.4276 (2) | 0.5239 (6) | 0.0513 (15) | |
H3 | 0.7356 | 0.4058 | 0.6016 | 0.077* | |
C1 | 1.1427 (12) | 0.6326 (3) | 1.0801 (9) | 0.0390 (18) | |
C2 | 0.9861 (11) | 0.5948 (3) | 0.9467 (8) | 0.0323 (16) | |
C3 | 1.0476 (12) | 0.5830 (3) | 0.8047 (9) | 0.0401 (18) | |
H3A | 1.1838 | 0.6000 | 0.7900 | 0.048* | |
C4 | 0.9090 (12) | 0.5462 (3) | 0.6841 (9) | 0.0424 (18) | |
H4 | 0.9515 | 0.5390 | 0.5890 | 0.051* | |
C5 | 0.7052 (11) | 0.5202 (3) | 0.7064 (8) | 0.0355 (17) | |
C6 | 0.6432 (12) | 0.5318 (3) | 0.8475 (8) | 0.0384 (17) | |
H6 | 0.5071 | 0.5147 | 0.8624 | 0.046* | |
C7 | 0.7824 (12) | 0.5687 (3) | 0.9672 (8) | 0.0379 (17) | |
H7 | 0.7392 | 0.5761 | 1.0621 | 0.046* | |
C8 | 0.5501 (12) | 0.4796 (3) | 0.5750 (8) | 0.0382 (17) | |
H8 | 0.4248 | 0.4616 | 0.6155 | 0.046* | |
O1W | 0.9972 (11) | 0.7500 | 0.5576 (8) | 0.051 (2) | |
H2W | 1.0963 | 0.7500 | 0.5043 | 0.076* | |
H1W | 1.0565 | 0.7500 | 0.6564 | 0.076* | |
O2W | 0.6821 (8) | 0.6753 (3) | 0.3037 (6) | 0.0552 (16) | |
H3W | 0.7949 | 0.6545 | 0.2879 | 0.083* | |
H4W | 0.5702 | 0.6735 | 0.2233 | 0.083* | |
O3W | 0.2891 (10) | 0.7500 | 0.3548 (7) | 0.0258 (13) | |
H5W | 0.2368 | 0.7168 | 0.3015 | 0.039* | |
O4W | 0.5898 (9) | 0.8184 (2) | 0.6248 (6) | 0.0453 (13) | |
H7W | 0.5008 | 0.8129 | 0.6846 | 0.068* | |
H8W | 0.5569 | 0.8518 | 0.5677 | 0.068* | |
O5W | 0.3294 (15) | 0.7500 | 0.8358 (10) | 0.090 (4) | |
H9W | 0.3342 | 0.7207 | 0.9046 | 0.135* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Zn1 | 0.0228 (6) | 0.0323 (6) | 0.0253 (6) | 0.000 | 0.0031 (4) | 0.000 |
O1 | 0.033 (3) | 0.043 (3) | 0.046 (3) | −0.001 (2) | −0.007 (2) | −0.011 (2) |
O2 | 0.030 (3) | 0.066 (4) | 0.061 (4) | −0.012 (3) | −0.004 (2) | −0.025 (3) |
O3 | 0.053 (3) | 0.032 (3) | 0.056 (3) | 0.003 (2) | −0.010 (3) | −0.006 (2) |
C1 | 0.030 (4) | 0.030 (4) | 0.045 (4) | 0.007 (3) | −0.013 (3) | −0.011 (3) |
C2 | 0.026 (4) | 0.026 (3) | 0.036 (4) | 0.005 (3) | −0.010 (3) | −0.007 (3) |
C3 | 0.024 (4) | 0.038 (4) | 0.050 (5) | 0.000 (3) | −0.006 (3) | −0.010 (3) |
C4 | 0.039 (4) | 0.039 (4) | 0.042 (4) | 0.005 (3) | −0.005 (3) | −0.011 (3) |
C5 | 0.028 (4) | 0.020 (3) | 0.045 (4) | 0.002 (3) | −0.016 (3) | −0.004 (3) |
C6 | 0.035 (4) | 0.029 (4) | 0.042 (4) | −0.009 (3) | −0.007 (3) | −0.001 (3) |
C7 | 0.035 (4) | 0.033 (4) | 0.038 (4) | 0.000 (3) | −0.006 (3) | −0.007 (3) |
C8 | 0.037 (4) | 0.029 (4) | 0.036 (4) | 0.001 (3) | −0.016 (3) | −0.007 (3) |
O1W | 0.019 (4) | 0.104 (7) | 0.025 (4) | 0.000 | −0.003 (3) | 0.000 |
O2W | 0.023 (3) | 0.075 (4) | 0.059 (3) | 0.011 (3) | −0.005 (2) | −0.036 (3) |
O3W | 0.022 (3) | 0.025 (3) | 0.029 (3) | 0.000 | 0.002 (3) | 0.000 |
O4W | 0.051 (3) | 0.043 (3) | 0.040 (3) | −0.001 (2) | 0.008 (2) | −0.012 (2) |
O5W | 0.054 (6) | 0.180 (12) | 0.036 (5) | 0.000 | 0.011 (4) | 0.000 |
Zn1—O1W | 2.061 (6) | C4—H4 | 0.9300 |
Zn1—O2W | 2.071 (5) | C5—C6 | 1.379 (10) |
Zn1—O2Wi | 2.071 (5) | C5—C8 | 1.528 (8) |
Zn1—O4Wi | 2.101 (5) | C6—C7 | 1.386 (9) |
Zn1—O4W | 2.101 (5) | C6—H6 | 0.9300 |
Zn1—O3W | 2.142 (6) | C7—H7 | 0.9300 |
O1—C1 | 1.270 (9) | C8—C8ii | 1.535 (13) |
O2—C1 | 1.243 (9) | C8—H8 | 0.9800 |
O3—C8 | 1.422 (8) | O1W—H2W | 0.8387 |
O3—H3 | 0.8200 | O1W—H1W | 0.8393 |
C1—C2 | 1.512 (9) | O2W—H3W | 0.8423 |
C2—C3 | 1.384 (10) | O2W—H4W | 0.8423 |
C2—C7 | 1.392 (10) | O3W—H5W | 0.8393 |
C3—C4 | 1.388 (9) | O4W—H7W | 0.8385 |
C3—H3A | 0.9300 | O4W—H8W | 0.8383 |
C4—C5 | 1.396 (10) | O5W—H9W | 0.8396 |
O1W—Zn1—O2W | 91.25 (19) | C5—C4—H4 | 120.2 |
O1W—Zn1—O2Wi | 91.25 (19) | C6—C5—C4 | 119.6 (6) |
O2W—Zn1—O2Wi | 95.3 (3) | C6—C5—C8 | 120.0 (7) |
O1W—Zn1—O4Wi | 92.5 (2) | C4—C5—C8 | 120.5 (7) |
O2W—Zn1—O4Wi | 90.3 (2) | C5—C6—C7 | 120.4 (7) |
O2Wi—Zn1—O4Wi | 173.1 (2) | C5—C6—H6 | 119.8 |
O1W—Zn1—O4W | 92.5 (2) | C7—C6—H6 | 119.8 |
O2W—Zn1—O4W | 173.1 (2) | C6—C7—C2 | 120.6 (7) |
O2Wi—Zn1—O4W | 90.3 (2) | C6—C7—H7 | 119.7 |
O4Wi—Zn1—O4W | 83.8 (3) | C2—C7—H7 | 119.7 |
O1W—Zn1—O3W | 179.9 (3) | O3—C8—C5 | 111.7 (6) |
O2W—Zn1—O3W | 88.69 (17) | O3—C8—C8ii | 105.9 (7) |
O2Wi—Zn1—O3W | 88.69 (17) | C5—C8—C8ii | 111.8 (7) |
O4Wi—Zn1—O3W | 87.55 (18) | O3—C8—H8 | 109.1 |
O4W—Zn1—O3W | 87.55 (18) | C5—C8—H8 | 109.1 |
C8—O3—H3 | 109.5 | C8ii—C8—H8 | 109.1 |
O2—C1—O1 | 123.4 (6) | Zn1—O1W—H2W | 124.1 |
O2—C1—C2 | 117.7 (7) | Zn1—O1W—H1W | 124.0 |
O1—C1—C2 | 118.9 (7) | H2W—O1W—H1W | 111.9 |
C3—C2—C7 | 118.8 (6) | Zn1—O2W—H3W | 133.3 |
C3—C2—C1 | 120.7 (7) | Zn1—O2W—H4W | 112.4 |
C7—C2—C1 | 120.5 (6) | H3W—O2W—H4W | 111.2 |
C2—C3—C4 | 121.0 (7) | Zn1—O3W—H5W | 115.9 |
C2—C3—H3A | 119.5 | Zn1—O4W—H7W | 125.1 |
C4—C3—H3A | 119.5 | Zn1—O4W—H8W | 101.5 |
C3—C4—C5 | 119.7 (7) | H7W—O4W—H8W | 112.0 |
C3—C4—H4 | 120.2 | ||
O2—C1—C2—C3 | −0.2 (10) | C4—C5—C6—C7 | −0.4 (10) |
O1—C1—C2—C3 | −179.5 (6) | C8—C5—C6—C7 | −179.8 (6) |
O2—C1—C2—C7 | 176.8 (6) | C5—C6—C7—C2 | 0.3 (10) |
O1—C1—C2—C7 | −2.5 (10) | C3—C2—C7—C6 | −0.3 (10) |
C7—C2—C3—C4 | 0.4 (10) | C1—C2—C7—C6 | −177.3 (6) |
C1—C2—C3—C4 | 177.4 (6) | C6—C5—C8—O3 | −127.4 (7) |
C2—C3—C4—C5 | −0.5 (11) | C4—C5—C8—O3 | 53.2 (8) |
C3—C4—C5—C6 | 0.6 (10) | C6—C5—C8—C8ii | 114.1 (9) |
C3—C4—C5—C8 | 179.9 (6) | C4—C5—C8—C8ii | −65.3 (10) |
Symmetry codes: (i) x, −y+3/2, z; (ii) −x+1, −y+1, −z+1. |
D—H···A | D—H | H···A | D···A | D—H···A |
O5W—H9W···O2iii | 0.84 | 1.94 | 2.774 (8) | 177 |
O4W—H8W···O3iv | 0.84 | 2.10 | 2.856 (7) | 150 |
O4W—H7W···O5W | 0.84 | 2.26 | 3.025 (9) | 152 |
O3W—H5W···O2v | 0.84 | 2.65 | 3.306 (7) | 136 |
O3—H3···O1vi | 0.82 | 1.99 | 2.810 (7) | 175 |
O1W—H2W···O3Wvii | 0.84 | 1.94 | 2.770 (9) | 172 |
O1W—H1W···O5Wvii | 0.84 | 1.97 | 2.725 (10) | 150 |
O2W—H3W···O1viii | 0.84 | 2.02 | 2.810 (7) | 155 |
O2W—H4W···O2v | 0.84 | 1.83 | 2.663 (7) | 169 |
O3W—H5W···O1v | 0.84 | 1.87 | 2.699 (6) | 169 |
Symmetry codes: (iii) x−1, y, z; (iv) −x+1, y+1/2, −z+1; (v) x−1, y, z−1; (vi) −x+2, −y+1, −z+2; (vii) x+1, y, z; (viii) x, y, z−1. |
Experimental details
Crystal data | |
Chemical formula | [Zn(H2O)6](C16H12O6)·H2O |
Mr | 491.76 |
Crystal system, space group | Monoclinic, P21/m |
Temperature (K) | 298 |
a, b, c (Å) | 6.0356 (9), 20.508 (2), 8.626 (1) |
β (°) | 104.141 (1) |
V (Å3) | 1035.4 (2) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 1.25 |
Crystal size (mm) | 0.37 × 0.27 × 0.22 |
Data collection | |
Diffractometer | Bruker SMART 1000 CCD area-detector |
Absorption correction | Multi-scan (SADABS; Bruker, 2007) |
Tmin, Tmax | 0.673, 0.759 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 5208, 1877, 1608 |
Rint | 0.035 |
(sin θ/λ)max (Å−1) | 0.595 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.068, 0.160, 1.26 |
No. of reflections | 1865 |
No. of parameters | 142 |
No. of restraints | 11 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.65, −0.45 |
Computer programs: SMART (Bruker, 2007), SAINT (Bruker, 2007), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).
D—H···A | D—H | H···A | D···A | D—H···A |
O5W—H9W···O2i | 0.84 | 1.94 | 2.774 (8) | 176.8 |
O4W—H8W···O3ii | 0.84 | 2.10 | 2.856 (7) | 150.0 |
O4W—H7W···O5W | 0.84 | 2.26 | 3.025 (9) | 152.2 |
O3W—H5W···O2iii | 0.84 | 2.65 | 3.306 (7) | 135.8 |
O3—H3···O1iv | 0.82 | 1.99 | 2.810 (7) | 174.6 |
O1W—H2W···O3Wv | 0.84 | 1.94 | 2.770 (9) | 171.9 |
O1W—H1W···O5Wv | 0.84 | 1.97 | 2.725 (10) | 150.0 |
O2W—H3W···O1vi | 0.84 | 2.02 | 2.810 (7) | 155.3 |
O2W—H4W···O2iii | 0.84 | 1.83 | 2.663 (7) | 168.7 |
O3W—H5W···O1iii | 0.84 | 1.87 | 2.699 (6) | 168.8 |
Symmetry codes: (i) x−1, y, z; (ii) −x+1, y+1/2, −z+1; (iii) x−1, y, z−1; (iv) −x+2, −y+1, −z+2; (v) x+1, y, z; (vi) x, y, z−1. |
Acknowledgements
The authors acknowledge Henan University of Urban Construction for supporting this work.
References
Bruker (2007). SMART, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Carlucci, L., Ciani, G. & Proserpio, D. M. (2003). Coord. Chem. Rev. 246, 247–289. Web of Science CrossRef CAS Google Scholar
Hao, C.-J. & Cao, Y.-L. (2010). Acta Cryst. E66, m809. Web of Science CSD CrossRef IUCr Journals Google Scholar
Rosi, N. L., Eckert, J., Eddaoudi, M., Vodak, D. T., Kim, J., O'Keeffe, M. & Yaghi, O. M. (2003). Science, 300, 1127–1129. Web of Science CSD CrossRef PubMed CAS Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
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Current interest in polymeric coordination networks is rapidly expanding for their intriguing architectures (Carlucci et al., 2003) and potential applications (Rosi et al., 2003). thus, we have reacted the ligand with Zn(NO3)2 under hydrothermal conditions to obtain new metal-organic complexes and the structure will be reported here.
As illustrated in figure 1, the title compound (C16H12O6)[Zn6H2O]. H2O is isostructural to a Mn complex based on the same ligand (Hao et al., 2010), containing one 4,4'-(1,2-dihydroxyethane-1,2-diyl)dibenzoate anions ligand, one [Zn6H2O]2+ dicationic complex and a solvent water molecule, The carboxyl group lies in the plane of the benzene ring as indicated by the O1—C1—C2—C3 and O2—C1—C2—C7 torsion angles of -0.2 (10) ° and 176.8 (6) °, and the two benzene rings are parallel to each other. In the crystal packing, a three-dimensional network was stabilized by a wide range of O—H···O hydrogen bonds involving the [Mn6H2O]2+ cations, 4,4'-(1,2-dihydroxyethane-1,2-diyl)dibenzoate anions and solvent water molecules.