organic compounds
Triethylammonium 3,4-dihydroxybenzoate monohydrate
aSchool of Chemistry and Environment, South China Normal University, Guangzhou 510631, People's Republic of China
*Correspondence e-mail: licaizhu1977@yahoo.com.cn
In the structure of the title compound, C6H16N+·C7H5O4−·H2O, O—H⋯O and N—H⋯O hydrogen bonds link the components into a three-dimensional array. The 3,4-dihydroxybenzoate anion is approximately planar, with a maximum deviation of 0.083 (2) Å.
Related literature
For protocatechuic acid (3,4-dihydroxybenzoic acid) and its pharmacological activity, see: An et al. (2006); Guan et al. (2006); Lin et al. (2009); Tseng et al. (1998); Yip et al. (2006).
Experimental
Crystal data
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Data collection
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Refinement
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Data collection: APEX2 (Bruker, 2004); cell SAINT (Bruker, 2004); 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: SHELXL97.
Supporting information
https://doi.org/10.1107/S1600536810046441/zl2325sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536810046441/zl2325Isup2.hkl
A solution of triethylamine (2 mmol in 0.5 ml water) was added dropwise to a solution of protocatechuic acid (2 mmol) in acetonitrile (15 ml), and the mixture was stirred for 30 min at room temperature. After several days colourless block-like crystals, suitable for X-ray
were obtained by slow evaporation of the solution.H14 atom of the triethylammonium cation and H atoms of the water molecule were found from difference Fourier maps and refined isotropically with a restraint of N—H = 0.89 (2) Å, O—H = 0.86 (2) Å and Uiso(H) = 1.5 Ueq(N, O). All other H atoms were positioned geometrically and refined as riding, with O—H = 0.82 Å and C—H = 0.93, 0.96 or 0.97 Å, and with Uiso(H) = 1.2 or 1.5 Ueq(C, O).
Protocatechuic acid (3,4-dihydroxybenzoic acid) is one of the main
in the plant kingdom (Guan et al., 2006). Significantly, it has been found that protocatechuic acid and its derivatives possess diverse pharmacological activities such as antioxidant, antiapoptosis, anticarcinogen, anticoagulatory and antiinflammatory (An et al., 2006; Lin et al., 2009; Tseng et al., 1998; Yip et al., 2006). The molecular and of the title compound, a triethylammonium of protocatechuic acid, is presented in this article.In the
of the title compound, illustrated in Fig. 1, there are a triethylammonium cation, one singly deprotonated 3,4-dihydroxybenzoate anion and one water molecule. The 3,4-dihydroxybenzoate anion is approximately planar, with a maximum deviation of any non-H atom from its plane of 0.083 (2) Å for atom O1. The orientations of the three ethyl groups of the triethylammonium cation are different. Two of the ethyl substituents are rougly in plane with the nitrogen atom and the methylene carbon atoms. The torsion angles of these two groups against the N—H bond are -53.1 for C10—C11, and -61.8 for C12—C13. The third ethyl group, C8—C9, is rotated out of this plane and is pointing downward with respect to the N—H bond with a torsion angle of 175.4°. The water molecule forms two O—H···O hydrogen bonds with two 3,4-dihydroxybenzoate anions involving O1w—H1w···O3ii and O1w—H2w···O2i (see Table 1 for symmetry operators and bonding geometries). The hydroxy groups of the 3,4-dihydroxybenzoate anion form O—H···O hydrogen bonds to the carboxylate groups of two adjacent anions. The N1—H14···O2i hydrogen bond between the triethylammonium cation and the 3,4-dihydroxybenzoate anion is the main force influencing the orientation of the triethylammonium cation. These hydrogen bonds link the triethylammonium cations, 3,4-dihydroxybenzoate anions and water molecules into a three-dimensional array (Fig. 2).For protocatechuic acid (3,4-dihydroxybenzoic acid) and its pharmacological activity, see: An et al. (2006); Guan et al. (2006); Lin et al. (2009); Tseng et al. (1998); Yip et al. (2006).
Data collection: APEX2 (Bruker, 2004); cell
SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); 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: SHELXL97 (Sheldrick, 2008).C6H16N+·C7H5O4−·H2O | F(000) = 592 |
Mr = 273.32 | Dx = 1.241 Mg m−3 |
Orthorhombic, P212121 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2ac 2ab | Cell parameters from 1465 reflections |
a = 10.7163 (16) Å | θ = 2.5–21.3° |
b = 11.5973 (17) Å | µ = 0.10 mm−1 |
c = 11.7690 (17) Å | T = 296 K |
V = 1462.7 (4) Å3 | Block, colourless |
Z = 4 | 0.30 × 0.28 × 0.28 mm |
Bruker APEXII area-detector diffractometer | 1211 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.043 |
Graphite monochromator | θmax = 25.2°, θmin = 2.5° |
φ and ω scans | h = −12→6 |
7531 measured reflections | k = −13→13 |
1519 independent reflections | l = −14→14 |
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)] = 0.038 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.093 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.04 | w = 1/[σ2(Fo2) + (0.0404P)2 + 0.2897P] where P = (Fo2 + 2Fc2)/3 |
1519 reflections | (Δ/σ)max < 0.001 |
186 parameters | Δρmax = 0.20 e Å−3 |
3 restraints | Δρmin = −0.14 e Å−3 |
C6H16N+·C7H5O4−·H2O | V = 1462.7 (4) Å3 |
Mr = 273.32 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 10.7163 (16) Å | µ = 0.10 mm−1 |
b = 11.5973 (17) Å | T = 296 K |
c = 11.7690 (17) Å | 0.30 × 0.28 × 0.28 mm |
Bruker APEXII area-detector diffractometer | 1211 reflections with I > 2σ(I) |
7531 measured reflections | Rint = 0.043 |
1519 independent reflections |
R[F2 > 2σ(F2)] = 0.038 | 3 restraints |
wR(F2) = 0.093 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.04 | Δρmax = 0.20 e Å−3 |
1519 reflections | Δρmin = −0.14 e Å−3 |
186 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. |
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. |
x | y | z | Uiso*/Ueq | ||
C1 | 0.9308 (3) | 0.5565 (2) | 0.8260 (2) | 0.0342 (6) | |
H1 | 0.9565 | 0.5065 | 0.7688 | 0.041* | |
C6 | 0.9902 (3) | 0.6627 (2) | 0.8383 (2) | 0.0325 (6) | |
C3 | 0.7962 (3) | 0.5995 (2) | 0.9826 (2) | 0.0368 (7) | |
C2 | 0.8350 (3) | 0.5241 (2) | 0.8967 (2) | 0.0344 (6) | |
C5 | 0.9503 (3) | 0.7362 (2) | 0.9238 (2) | 0.0414 (7) | |
H5 | 0.9891 | 0.8073 | 0.9334 | 0.050* | |
C4 | 0.8538 (3) | 0.7050 (2) | 0.9948 (2) | 0.0422 (7) | |
H4 | 0.8273 | 0.7555 | 1.0513 | 0.051* | |
C7 | 1.0953 (3) | 0.6967 (2) | 0.7614 (2) | 0.0359 (7) | |
O1 | 1.1524 (2) | 0.79093 (17) | 0.78093 (16) | 0.0458 (5) | |
O2 | 1.12389 (19) | 0.6316 (2) | 0.68029 (18) | 0.0531 (6) | |
O4 | 0.7734 (2) | 0.42081 (17) | 0.89033 (19) | 0.0537 (6) | |
H4A | 0.8011 | 0.3831 | 0.8370 | 0.081* | |
O3 | 0.7002 (2) | 0.56347 (19) | 1.05036 (17) | 0.0491 (6) | |
H3 | 0.6853 | 0.6129 | 1.0983 | 0.074* | |
N1 | 0.3697 (2) | 0.6142 (2) | 0.6203 (2) | 0.0417 (6) | |
C10 | 0.4121 (3) | 0.6946 (3) | 0.5286 (3) | 0.0608 (9) | |
H10A | 0.4949 | 0.6720 | 0.5039 | 0.073* | |
H10B | 0.4178 | 0.7720 | 0.5595 | 0.073* | |
C12 | 0.3732 (4) | 0.4905 (3) | 0.5826 (3) | 0.0574 (9) | |
H12A | 0.3205 | 0.4817 | 0.5162 | 0.069* | |
H12B | 0.4578 | 0.4710 | 0.5608 | 0.069* | |
C11 | 0.3266 (4) | 0.6960 (4) | 0.4277 (3) | 0.0885 (14) | |
H11A | 0.3283 | 0.6220 | 0.3912 | 0.133* | |
H11B | 0.3536 | 0.7541 | 0.3751 | 0.133* | |
H11C | 0.2431 | 0.7128 | 0.4523 | 0.133* | |
C13 | 0.3304 (5) | 0.4082 (3) | 0.6726 (4) | 0.0840 (13) | |
H13A | 0.3883 | 0.4094 | 0.7348 | 0.126* | |
H13B | 0.3264 | 0.3318 | 0.6415 | 0.126* | |
H13C | 0.2493 | 0.4307 | 0.6990 | 0.126* | |
C8 | 0.4404 (3) | 0.6357 (3) | 0.7284 (3) | 0.0577 (9) | |
H8A | 0.4001 | 0.5934 | 0.7894 | 0.069* | |
H8B | 0.4349 | 0.7171 | 0.7466 | 0.069* | |
C9 | 0.5759 (3) | 0.6018 (4) | 0.7247 (4) | 0.0822 (13) | |
H9A | 0.5825 | 0.5197 | 0.7161 | 0.123* | |
H9B | 0.6159 | 0.6249 | 0.7941 | 0.123* | |
H9C | 0.6157 | 0.6392 | 0.6616 | 0.123* | |
H14 | 0.288 (2) | 0.633 (4) | 0.637 (4) | 0.123* | |
O1W | 0.0402 (3) | 0.5325 (3) | 0.4727 (2) | 0.0719 (8) | |
H1W | −0.035 (2) | 0.514 (4) | 0.482 (4) | 0.108* | |
H2W | 0.066 (4) | 0.568 (3) | 0.533 (3) | 0.108* |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0341 (15) | 0.0357 (15) | 0.0328 (14) | 0.0014 (13) | 0.0032 (13) | −0.0061 (12) |
C6 | 0.0319 (15) | 0.0328 (15) | 0.0329 (14) | 0.0021 (12) | −0.0029 (12) | 0.0010 (12) |
C3 | 0.0340 (16) | 0.0435 (17) | 0.0327 (15) | 0.0026 (14) | 0.0009 (13) | −0.0001 (13) |
C2 | 0.0343 (16) | 0.0341 (14) | 0.0347 (14) | −0.0005 (12) | −0.0006 (13) | −0.0044 (13) |
C5 | 0.0458 (19) | 0.0339 (15) | 0.0446 (16) | −0.0034 (14) | −0.0005 (15) | −0.0077 (14) |
C4 | 0.0415 (17) | 0.0403 (18) | 0.0448 (17) | 0.0033 (15) | 0.0063 (15) | −0.0131 (14) |
C7 | 0.0336 (16) | 0.0405 (17) | 0.0335 (15) | −0.0009 (14) | −0.0043 (12) | −0.0001 (13) |
O1 | 0.0550 (13) | 0.0438 (12) | 0.0387 (11) | −0.0165 (11) | 0.0005 (10) | 0.0018 (9) |
O2 | 0.0471 (14) | 0.0624 (14) | 0.0497 (12) | −0.0131 (11) | 0.0134 (11) | −0.0191 (11) |
O4 | 0.0581 (15) | 0.0441 (13) | 0.0590 (15) | −0.0146 (11) | 0.0204 (12) | −0.0139 (11) |
O3 | 0.0463 (14) | 0.0550 (13) | 0.0459 (12) | −0.0037 (11) | 0.0149 (10) | −0.0132 (10) |
N1 | 0.0393 (15) | 0.0445 (14) | 0.0413 (14) | −0.0017 (12) | 0.0058 (12) | −0.0020 (11) |
C10 | 0.055 (2) | 0.061 (2) | 0.067 (2) | −0.0040 (19) | 0.0120 (18) | 0.0178 (18) |
C12 | 0.065 (2) | 0.0475 (19) | 0.060 (2) | 0.0024 (17) | 0.0031 (19) | −0.0145 (17) |
C11 | 0.081 (3) | 0.117 (4) | 0.068 (3) | 0.002 (3) | −0.003 (2) | 0.039 (3) |
C13 | 0.098 (3) | 0.055 (2) | 0.099 (3) | −0.013 (2) | −0.013 (3) | 0.013 (2) |
C8 | 0.060 (2) | 0.060 (2) | 0.0527 (19) | −0.0054 (19) | −0.0044 (18) | −0.0096 (17) |
C9 | 0.055 (2) | 0.099 (3) | 0.094 (3) | −0.003 (2) | −0.018 (2) | 0.003 (3) |
O1W | 0.0682 (19) | 0.0815 (19) | 0.0658 (16) | −0.0147 (16) | 0.0034 (15) | −0.0133 (14) |
C1—C2 | 1.374 (4) | C10—C11 | 1.500 (5) |
C1—C6 | 1.395 (4) | C10—H10A | 0.9700 |
C1—H1 | 0.9300 | C10—H10B | 0.9700 |
C6—C5 | 1.387 (4) | C12—C13 | 1.497 (5) |
C6—C7 | 1.498 (4) | C12—H12A | 0.9700 |
C3—O3 | 1.368 (3) | C12—H12B | 0.9700 |
C3—C4 | 1.378 (4) | C11—H11A | 0.9600 |
C3—C2 | 1.400 (4) | C11—H11B | 0.9600 |
C2—O4 | 1.370 (3) | C11—H11C | 0.9600 |
C5—C4 | 1.379 (4) | C13—H13A | 0.9600 |
C5—H5 | 0.9300 | C13—H13B | 0.9600 |
C4—H4 | 0.9300 | C13—H13C | 0.9600 |
C7—O2 | 1.255 (3) | C8—C9 | 1.505 (5) |
C7—O1 | 1.273 (3) | C8—H8A | 0.9700 |
O4—H4A | 0.8200 | C8—H8B | 0.9700 |
O3—H3 | 0.8200 | C9—H9A | 0.9600 |
N1—C10 | 1.497 (4) | C9—H9B | 0.9600 |
N1—C12 | 1.501 (4) | C9—H9C | 0.9600 |
N1—C8 | 1.502 (4) | O1W—H1W | 0.841 (19) |
N1—H14 | 0.92 (2) | O1W—H2W | 0.87 (4) |
C2—C1—C6 | 121.3 (3) | C11—C10—H10B | 109.0 |
C2—C1—H1 | 119.3 | H10A—C10—H10B | 107.8 |
C6—C1—H1 | 119.3 | C13—C12—N1 | 113.1 (3) |
C5—C6—C1 | 118.6 (3) | C13—C12—H12A | 108.9 |
C5—C6—C7 | 120.6 (2) | N1—C12—H12A | 108.9 |
C1—C6—C7 | 120.9 (2) | C13—C12—H12B | 108.9 |
O3—C3—C4 | 123.2 (3) | N1—C12—H12B | 108.9 |
O3—C3—C2 | 117.0 (3) | H12A—C12—H12B | 107.8 |
C4—C3—C2 | 119.8 (3) | C10—C11—H11A | 109.5 |
O4—C2—C1 | 124.5 (2) | C10—C11—H11B | 109.5 |
O4—C2—C3 | 116.3 (2) | H11A—C11—H11B | 109.5 |
C1—C2—C3 | 119.3 (3) | C10—C11—H11C | 109.5 |
C4—C5—C6 | 120.7 (3) | H11A—C11—H11C | 109.5 |
C4—C5—H5 | 119.7 | H11B—C11—H11C | 109.5 |
C6—C5—H5 | 119.7 | C12—C13—H13A | 109.5 |
C3—C4—C5 | 120.4 (3) | C12—C13—H13B | 109.5 |
C3—C4—H4 | 119.8 | H13A—C13—H13B | 109.5 |
C5—C4—H4 | 119.8 | C12—C13—H13C | 109.5 |
O2—C7—O1 | 122.5 (3) | H13A—C13—H13C | 109.5 |
O2—C7—C6 | 119.0 (2) | H13B—C13—H13C | 109.5 |
O1—C7—C6 | 118.6 (2) | N1—C8—C9 | 114.8 (3) |
C2—O4—H4A | 109.5 | N1—C8—H8A | 108.6 |
C3—O3—H3 | 109.5 | C9—C8—H8A | 108.6 |
C10—N1—C12 | 112.0 (2) | N1—C8—H8B | 108.6 |
C10—N1—C8 | 110.7 (3) | C9—C8—H8B | 108.6 |
C12—N1—C8 | 113.3 (3) | H8A—C8—H8B | 107.6 |
C10—N1—H14 | 107 (3) | C8—C9—H9A | 109.5 |
C12—N1—H14 | 108 (3) | C8—C9—H9B | 109.5 |
C8—N1—H14 | 105 (3) | H9A—C9—H9B | 109.5 |
N1—C10—C11 | 113.0 (3) | C8—C9—H9C | 109.5 |
N1—C10—H10A | 109.0 | H9A—C9—H9C | 109.5 |
C11—C10—H10A | 109.0 | H9B—C9—H9C | 109.5 |
N1—C10—H10B | 109.0 | H1W—O1W—H2W | 108 (4) |
D—H···A | D—H | H···A | D···A | D—H···A |
O1W—H2W···O2i | 0.87 (4) | 1.98 (2) | 2.845 (3) | 173 (4) |
O1W—H1W···O3ii | 0.84 (2) | 2.14 (2) | 2.951 (3) | 162 (4) |
N1—H14···O2i | 0.92 (2) | 1.83 (2) | 2.734 (3) | 166 (5) |
O3—H3···O1iii | 0.82 | 1.84 | 2.656 (3) | 173 |
O4—H4A···O1iv | 0.82 | 1.82 | 2.639 (3) | 174 |
Symmetry codes: (i) x−1, y, z; (ii) −x+1/2, −y+1, z−1/2; (iii) x−1/2, −y+3/2, −z+2; (iv) −x+2, y−1/2, −z+3/2. |
Experimental details
Crystal data | |
Chemical formula | C6H16N+·C7H5O4−·H2O |
Mr | 273.32 |
Crystal system, space group | Orthorhombic, P212121 |
Temperature (K) | 296 |
a, b, c (Å) | 10.7163 (16), 11.5973 (17), 11.7690 (17) |
V (Å3) | 1462.7 (4) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.10 |
Crystal size (mm) | 0.30 × 0.28 × 0.28 |
Data collection | |
Diffractometer | Bruker APEXII area-detector |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 7531, 1519, 1211 |
Rint | 0.043 |
(sin θ/λ)max (Å−1) | 0.599 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.038, 0.093, 1.04 |
No. of reflections | 1519 |
No. of parameters | 186 |
No. of restraints | 3 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.20, −0.14 |
Computer programs: APEX2 (Bruker, 2004), SAINT (Bruker, 2004), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).
D—H···A | D—H | H···A | D···A | D—H···A |
O1W—H2W···O2i | 0.87 (4) | 1.98 (2) | 2.845 (3) | 173 (4) |
O1W—H1W···O3ii | 0.841 (19) | 2.14 (2) | 2.951 (3) | 162 (4) |
N1—H14···O2i | 0.92 (2) | 1.83 (2) | 2.734 (3) | 166 (5) |
O3—H3···O1iii | 0.82 | 1.84 | 2.656 (3) | 172.8 |
O4—H4A···O1iv | 0.82 | 1.82 | 2.639 (3) | 174.1 |
Symmetry codes: (i) x−1, y, z; (ii) −x+1/2, −y+1, z−1/2; (iii) x−1/2, −y+3/2, −z+2; (iv) −x+2, y−1/2, −z+3/2. |
Acknowledgements
The author acknowledges South China Normal University for supporting this work.
References
An, L. J., Guan, S., Shi, G. F., Bao, Y. M., Duan, Y. L. & Jiang, B. (2006). Food Chem. Toxicol. 44, 436–443. Web of Science CrossRef PubMed CAS Google Scholar
Bruker (2004). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Guan, S., Bao, Y. M., Jiang, B. & An, L. J. (2006). Eur. J. Pharmacol. 538, 73–79. PubMed CAS Google Scholar
Lin, C. Y., Huang, C. S., Huang, C. Y. & Yin, M. C. (2009). J. Agric. Food Chem. 57, 6661–6667. Web of Science CrossRef PubMed CAS Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Tseng, T. H., Hsu, J. D., Lo, M. H., Chu, C. Y., Chou, F. P., Huang, C. L. & Wang, C. J. (1998). Cancer Lett. 126, 199–207. Web of Science CrossRef CAS PubMed Google Scholar
Yip, E. C. H., Chan, A. S. L., Pang, H., Tam, Y. K. & Wong, Y. H. (2006). Cell Biol. Toxicol. 22, 293–302. Web of Science CrossRef PubMed CAS Google Scholar
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Protocatechuic acid (3,4-dihydroxybenzoic acid) is one of the main secondary metabolites in the plant kingdom (Guan et al., 2006). Significantly, it has been found that protocatechuic acid and its derivatives possess diverse pharmacological activities such as antioxidant, antiapoptosis, anticarcinogen, anticoagulatory and antiinflammatory (An et al., 2006; Lin et al., 2009; Tseng et al., 1998; Yip et al., 2006). The molecular and crystal structure of the title compound, a triethylammonium of protocatechuic acid, is presented in this article.
In the asymmetric unit of the title compound, illustrated in Fig. 1, there are a triethylammonium cation, one singly deprotonated 3,4-dihydroxybenzoate anion and one water molecule. The 3,4-dihydroxybenzoate anion is approximately planar, with a maximum deviation of any non-H atom from its plane of 0.083 (2) Å for atom O1. The orientations of the three ethyl groups of the triethylammonium cation are different. Two of the ethyl substituents are rougly in plane with the nitrogen atom and the methylene carbon atoms. The torsion angles of these two groups against the N—H bond are -53.1 for C10—C11, and -61.8 for C12—C13. The third ethyl group, C8—C9, is rotated out of this plane and is pointing downward with respect to the N—H bond with a torsion angle of 175.4°. The water molecule forms two O—H···O hydrogen bonds with two 3,4-dihydroxybenzoate anions involving O1w—H1w···O3ii and O1w—H2w···O2i (see Table 1 for symmetry operators and bonding geometries). The hydroxy groups of the 3,4-dihydroxybenzoate anion form O—H···O hydrogen bonds to the carboxylate groups of two adjacent anions. The N1—H14···O2i hydrogen bond between the triethylammonium cation and the 3,4-dihydroxybenzoate anion is the main force influencing the orientation of the triethylammonium cation. These hydrogen bonds link the triethylammonium cations, 3,4-dihydroxybenzoate anions and water molecules into a three-dimensional array (Fig. 2).