Melaminium 2,4,6-trihydroxy-benzoate dihydrate.

In the title compound, C(3)H(7)N(6) (+)·C(7)H(5)O(5) (-)·2H(2)O, the melaminium and benzoate ions are approximately planar (r.m.s. deviation of the non-hydrogen atoms is 0.093 Å) and there is a strong C(2) (2)(8) hydrogen-bonding embrace between them. The centre of symmetry generates a second acid-base pair which is bound to the first by a C(2) (2)(8) (N-H⋯N) embrace common between melamine mol-ecules in similar compounds. Further extensive hydrogen bonding assembles the components into a three-dimensional hydrogen-bonded network.

Related literature

For 2,4,6-trihydroxy­benzoic acid and some of its compounds, see: Jankowski et al. (2007 ▶). For compounds of melamine with aromatic acids, see: Zhang & Chen (2005 ▶); Perpétuo & Janczak (2005 ▶); Zhang et al. (2004 ▶); Karle et al. (2003 ▶); Janczak & Perpétuo (2001 ▶). For a description of the Cambridge Crystallographic Database, see: Allen (2002 ▶). For a structure related to the title compound with C—H⋯O inter­actions with a homomeric (8) motif, see: Bouvet et al. (2007 ▶).

Experimental

Crystal data

C3H7N6 +·C7H5O5 −·2H2O

M = 332.29

Monoclinic,

a = 6.9914 (6) Å

b = 11.7105 (14) Å

c = 17.1784 (14) Å

β = 93.247 (7)°

V = 1404.2 (2) Å3

Z = 4

Mo Kα radiation

μ = 0.13 mm−1

T = 150 K

0.55 × 0.30 × 0.24 mm

Data collection

Stoe IPDS2 diffractometer

Absorption correction: analytical (X-RED; Stoe & Cie, 2002 ▶) T min = 0.945, T max = 0.973

17706 measured reflections

6005 independent reflections

3332 reflections with I > 2σ(I)

R int = 0.047

Refinement

R[F 2 > 2σ(F 2)] = 0.042

wR(F 2) = 0.127

S = 0.85

6005 reflections

272 parameters

31 restraints

All H-atom parameters refined

Δρmax = 0.46 e Å−3

Δρmin = −0.36 e Å−3

Data collection: X-AREA (Stoe & Cie, 2002 ▶); cell refinement: X-AREA; data reduction: X-RED (Stoe & Cie, 2002 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶); software used to prepare material for publication: SHELXL97.

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809031055/zl2230sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809031055/zl2230Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

C3H7N6+·C7H5O5−·2H2O	F(000) = 696
Mr = 332.29	Dx = 1.572 Mg m−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 10461 reflections
a = 6.9914 (6) Å	θ = 3.0–34.7°
b = 11.7105 (14) Å	µ = 0.13 mm−1
c = 17.1784 (14) Å	T = 150 K
β = 93.247 (7)°	Block, colourless
V = 1404.2 (2) Å3	0.55 × 0.30 × 0.24 mm
Z = 4

Stoe IPDS2 diffractometer	6005 independent reflections
Radiation source: fine-focus sealed tube	3332 reflections with I > 2σ(I)
graphite	Rint = 0.047
Detector resolution: 6.67 pixels mm-1	θmax = 34.8°, θmin = 2.9°
ω scans	h = −11→9
Absorption correction: analytical (X-RED; Stoe & Cie, 2002)	k = −18→16
Tmin = 0.945, Tmax = 0.973	l = −27→27
17706 measured reflections

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)] = 0.042	Hydrogen site location: difference Fourier map
wR(F2) = 0.127	All H-atom parameters refined
S = 0.85	w = 1/[σ2(Fo2) + (0.0793P)2] where P = (Fo2 + 2Fc2)/3
6005 reflections	(Δ/σ)max < 0.001
272 parameters	Δρmax = 0.46 e Å−3
31 restraints	Δρmin = −0.36 e Å−3

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	0.73313 (18)	0.52661 (10)	0.05113 (6)	0.0196 (2)
C2	0.68970 (18)	0.63258 (9)	0.00699 (6)	0.0183 (2)
C3	0.69836 (18)	0.63594 (10)	−0.07492 (6)	0.0194 (2)
H3	0.776 (3)	0.4883 (18)	−0.0746 (12)	0.056 (6)*
C4	0.65003 (19)	0.73346 (10)	−0.11738 (6)	0.0211 (2)
H4	0.660 (2)	0.7325 (14)	−0.1742 (9)	0.023 (4)*
C5	0.59022 (19)	0.83049 (10)	−0.07820 (6)	0.0210 (2)
C6	0.5819 (2)	0.83144 (10)	0.00264 (6)	0.0216 (2)
H6	0.542 (3)	0.8992 (15)	0.0306 (10)	0.034 (5)*
C7	0.63057 (18)	0.73331 (10)	0.04389 (6)	0.0194 (2)
O1	0.78156 (15)	0.43781 (8)	0.01487 (5)	0.02431 (19)
O2	0.71931 (15)	0.52808 (8)	0.12494 (5)	0.0244 (2)
O3	0.75288 (15)	0.54163 (8)	−0.11399 (5)	0.0253 (2)
O4	0.53417 (16)	0.92717 (8)	−0.11604 (5)	0.0277 (2)
H4C	0.545 (3)	0.9184 (17)	−0.1665 (10)	0.043 (5)*
O5	0.61673 (15)	0.73672 (8)	0.12263 (5)	0.0243 (2)
H5	0.643 (3)	0.6637 (17)	0.1401 (13)	0.057 (6)*
N1	0.85916 (16)	0.24155 (9)	0.10129 (5)	0.01968 (19)
H1	0.826 (3)	0.3064 (15)	0.0749 (11)	0.039 (5)*
C8	0.91589 (18)	0.14661 (10)	0.06277 (6)	0.0194 (2)
N2	0.97775 (16)	0.05353 (8)	0.10108 (5)	0.0199 (2)
C9	0.98111 (18)	0.06016 (10)	0.17934 (6)	0.0191 (2)
N3	0.92138 (17)	0.14924 (9)	0.22141 (5)	0.0222 (2)
C10	0.86211 (19)	0.23957 (10)	0.18066 (6)	0.0205 (2)
N4	0.8030 (2)	0.33205 (10)	0.21642 (6)	0.0274 (2)
H4A	0.766 (3)	0.3971 (16)	0.1869 (11)	0.047 (6)*
H4B	0.801 (3)	0.3291 (15)	0.2681 (9)	0.028 (4)*
N5	0.90875 (19)	0.14847 (10)	−0.01381 (6)	0.0254 (2)
H5A	0.855 (3)	0.2084 (14)	−0.0399 (10)	0.033 (5)*
H5B	0.944 (3)	0.0848 (14)	−0.0407 (10)	0.032 (5)*
N6	1.04817 (18)	−0.02974 (9)	0.21995 (6)	0.0235 (2)
H6A	1.055 (3)	−0.0259 (16)	0.2725 (9)	0.033 (5)*
H6B	1.102 (3)	−0.0896 (15)	0.1960 (10)	0.033 (5)*
O1W	1.03866 (16)	0.57703 (9)	0.22527 (5)	0.0268 (2)
H1A	1.108 (3)	0.5212 (19)	0.2061 (13)	0.059 (7)*
H1B	0.925 (3)	0.573 (2)	0.2010 (14)	0.066 (7)*
O2W	0.22325 (17)	0.76457 (9)	0.16102 (6)	0.0294 (2)
H2A	0.171 (3)	0.7042 (18)	0.1850 (13)	0.059 (7)*
H2B	0.349 (3)	0.753 (2)	0.1578 (14)	0.062 (7)*

	U11	U22	U33	U12	U13	U23
C1	0.0214 (6)	0.0183 (5)	0.0188 (4)	0.0010 (4)	−0.0005 (4)	0.0010 (4)
C2	0.0225 (6)	0.0170 (5)	0.0155 (4)	0.0011 (4)	0.0011 (4)	0.0009 (3)
C3	0.0220 (6)	0.0197 (5)	0.0164 (4)	0.0010 (4)	0.0010 (4)	−0.0020 (3)
C4	0.0257 (6)	0.0221 (5)	0.0154 (4)	0.0015 (4)	0.0011 (4)	0.0008 (4)
C5	0.0239 (6)	0.0192 (5)	0.0197 (5)	0.0016 (4)	0.0004 (4)	0.0022 (4)
C6	0.0281 (7)	0.0185 (5)	0.0183 (5)	0.0042 (4)	0.0019 (4)	0.0002 (4)
C7	0.0223 (6)	0.0197 (5)	0.0163 (4)	0.0015 (4)	0.0011 (4)	0.0007 (3)
O1	0.0338 (5)	0.0176 (4)	0.0215 (4)	0.0046 (3)	0.0016 (3)	0.0002 (3)
O2	0.0352 (6)	0.0205 (4)	0.0175 (4)	0.0044 (4)	0.0011 (3)	0.0024 (3)
O3	0.0389 (6)	0.0204 (4)	0.0168 (3)	0.0066 (4)	0.0026 (3)	−0.0019 (3)
O4	0.0423 (6)	0.0218 (4)	0.0193 (4)	0.0088 (4)	0.0020 (4)	0.0050 (3)
O5	0.0386 (6)	0.0197 (4)	0.0147 (3)	0.0064 (4)	0.0027 (3)	0.0006 (3)
N1	0.0254 (5)	0.0174 (4)	0.0163 (4)	0.0029 (4)	0.0014 (3)	0.0018 (3)
C8	0.0213 (6)	0.0197 (5)	0.0172 (4)	0.0006 (4)	0.0013 (4)	0.0007 (3)
N2	0.0251 (6)	0.0185 (4)	0.0161 (4)	0.0024 (4)	0.0012 (3)	0.0006 (3)
C9	0.0218 (6)	0.0179 (5)	0.0176 (4)	−0.0009 (4)	0.0004 (4)	0.0009 (3)
N3	0.0316 (6)	0.0189 (4)	0.0160 (4)	0.0038 (4)	0.0011 (4)	0.0003 (3)
C10	0.0242 (6)	0.0193 (5)	0.0179 (4)	−0.0001 (4)	0.0015 (4)	−0.0005 (4)
N4	0.0430 (7)	0.0214 (5)	0.0179 (4)	0.0079 (5)	0.0024 (4)	0.0000 (3)
N5	0.0363 (7)	0.0228 (5)	0.0170 (4)	0.0078 (4)	0.0014 (4)	0.0012 (3)
N6	0.0340 (7)	0.0186 (4)	0.0179 (4)	0.0042 (4)	0.0007 (4)	0.0024 (3)
O1W	0.0306 (6)	0.0269 (5)	0.0227 (4)	0.0023 (4)	0.0000 (4)	−0.0043 (3)
O2W	0.0324 (6)	0.0274 (5)	0.0286 (4)	0.0063 (4)	0.0024 (4)	0.0053 (4)

C1—O1	1.2680 (14)	N1—H1	0.908 (16)
C1—O2	1.2772 (13)	C8—N5	1.3139 (15)
C1—C2	1.4768 (16)	C8—N2	1.3327 (15)
C2—C7	1.4120 (16)	N2—C9	1.3455 (14)
C2—C3	1.4124 (15)	C9—N6	1.3333 (15)
C3—O3	1.3580 (14)	C9—N3	1.3487 (15)
C3—C4	1.3865 (16)	N3—C10	1.3221 (15)
C4—C5	1.3967 (17)	C10—N4	1.3226 (16)
C4—H4	0.983 (15)	N4—H4A	0.942 (17)
C5—O4	1.3524 (14)	N4—H4B	0.890 (14)
C5—C6	1.3932 (16)	N5—H5A	0.902 (15)
C6—C7	1.3825 (16)	N5—H5B	0.917 (15)
C6—H6	0.975 (17)	N6—H6A	0.902 (15)
C7—O5	1.3622 (13)	N6—H6B	0.905 (15)
O3—H3	0.928 (19)	O1W—H1A	0.887 (19)
O4—H4C	0.880 (18)	O1W—H1B	0.88 (2)
O5—H5	0.921 (19)	O2W—H2A	0.906 (19)
N1—C10	1.3625 (14)	O2W—H2B	0.897 (19)
N1—C8	1.3642 (15)
O1—C1—O2	122.41 (11)	C10—N1—H1	120.3 (12)
O1—C1—C2	119.33 (10)	C8—N1—H1	120.8 (12)
O2—C1—C2	118.26 (10)	N5—C8—N2	120.06 (11)
C7—C2—C3	117.01 (10)	N5—C8—N1	118.46 (11)
C7—C2—C1	121.90 (9)	N2—C8—N1	121.48 (10)
C3—C2—C1	121.05 (10)	C8—N2—C9	115.66 (10)
O3—C3—C4	118.48 (10)	N6—C9—N2	117.57 (11)
O3—C3—C2	119.91 (10)	N6—C9—N3	116.15 (10)
C4—C3—C2	121.60 (10)	N2—C9—N3	126.27 (11)
C3—C4—C5	119.17 (10)	C10—N3—C9	115.62 (9)
C3—C4—H4	119.0 (10)	N3—C10—N4	120.39 (10)
C5—C4—H4	121.8 (10)	N3—C10—N1	122.00 (11)
O4—C5—C6	116.43 (11)	N4—C10—N1	117.60 (11)
O4—C5—C4	122.40 (10)	C10—N4—H4A	119.7 (13)
C6—C5—C4	121.15 (11)	C10—N4—H4B	117.1 (12)
C7—C6—C5	118.77 (11)	H4A—N4—H4B	123.3 (17)
C7—C6—H6	119.4 (11)	C8—N5—H5A	120.1 (12)
C5—C6—H6	121.8 (11)	C8—N5—H5B	119.6 (11)
O5—C7—C6	117.08 (10)	H5A—N5—H5B	119.8 (16)
O5—C7—C2	120.62 (10)	C9—N6—H6A	118.7 (12)
C6—C7—C2	122.29 (10)	C9—N6—H6B	121.1 (12)
C3—O3—H3	103.2 (14)	H6A—N6—H6B	119.5 (17)
C5—O4—H4C	109.7 (13)	H1A—O1W—H1B	106 (2)
C7—O5—H5	105.9 (14)	H2A—O2W—H2B	109 (2)
C10—N1—C8	118.89 (10)
O1—C1—C2—C7	178.44 (12)	C3—C2—C7—O5	179.37 (12)
O2—C1—C2—C7	−1.23 (19)	C1—C2—C7—O5	1.85 (19)
O1—C1—C2—C3	1.01 (19)	C3—C2—C7—C6	0.30 (19)
O2—C1—C2—C3	−178.65 (12)	C1—C2—C7—C6	−177.22 (12)
C7—C2—C3—O3	−179.54 (12)	C10—N1—C8—N5	178.60 (13)
C1—C2—C3—O3	−2.00 (19)	C10—N1—C8—N2	−1.51 (18)
C7—C2—C3—C4	−0.34 (19)	N5—C8—N2—C9	179.55 (12)
C1—C2—C3—C4	177.20 (12)	N1—C8—N2—C9	−0.35 (18)
O3—C3—C4—C5	178.81 (12)	C8—N2—C9—N6	−177.79 (12)
C2—C3—C4—C5	−0.4 (2)	C8—N2—C9—N3	2.79 (19)
C3—C4—C5—O4	−177.51 (13)	N6—C9—N3—C10	177.49 (12)
C3—C4—C5—C6	1.2 (2)	N2—C9—N3—C10	−3.09 (19)
O4—C5—C6—C7	177.54 (12)	C9—N3—C10—N4	−179.08 (13)
C4—C5—C6—C7	−1.3 (2)	C9—N3—C10—N1	0.93 (19)
C5—C6—C7—O5	−178.62 (12)	C8—N1—C10—N3	1.20 (19)
C5—C6—C7—C2	0.5 (2)	C8—N1—C10—N4	−178.79 (12)

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1B···O2	0.88 (2)	1.96 (2)	2.8015 (15)	160 (2)
O1W—H1A···O3i	0.89 (2)	2.04 (2)	2.8329 (13)	148 (2)
O2W—H2B···O5	0.90 (2)	2.01 (2)	2.8835 (16)	166 (2)
O2W—H2A···O1Wii	0.91 (2)	1.90 (2)	2.8050 (15)	173 (2)
N1—H1···O1	0.91 (2)	1.87 (2)	2.7729 (13)	174 (2)
N4—H4A···O2	0.94 (2)	1.89 (2)	2.8245 (14)	174 (2)
N4—H4B···O5iii	0.89 (1)	2.21 (2)	3.0049 (14)	148 (2)
N5—H5A···O2Wiv	0.90 (2)	2.15 (2)	2.8319 (15)	132 (2)
N5—H5B···N2v	0.92 (2)	2.02 (2)	2.9339 (15)	179 (2)
N6—H6A···O3vi	0.90 (2)	2.33 (2)	3.1215 (14)	146 (2)
N6—H6B···O2Wvii	0.91 (2)	2.01 (2)	2.9096 (15)	170 (2)
O3—H3···O1	0.93 (2)	1.64 (2)	2.5235 (12)	156 (2)
O4—H4C···O1Wviii	0.88 (2)	1.86 (2)	2.7284 (13)	170 (2)
O5—H5···O2	0.92 (2)	1.70 (2)	2.5461 (13)	151 (2)
C6—H6···O4ix	0.98 (2)	2.58 (2)	3.5529 (15)	174 (2)

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1W—H1B⋯O2	0.88 (2)	1.96 (2)	2.8015 (15)	160 (2)
O1W—H1A⋯O3i	0.887 (19)	2.04 (2)	2.8329 (13)	148 (2)
O2W—H2B⋯O5	0.897 (19)	2.01 (2)	2.8835 (16)	166 (2)
O2W—H2A⋯O1Wii	0.906 (19)	1.903 (19)	2.8050 (15)	173 (2)
N1—H1⋯O1	0.908 (16)	1.869 (16)	2.7729 (13)	173.9 (19)
N4—H4A⋯O2	0.942 (17)	1.886 (17)	2.8245 (14)	174 (2)
N4—H4B⋯O5iii	0.890 (14)	2.214 (16)	3.0049 (14)	147.9 (16)
N5—H5A⋯O2Wiv	0.902 (15)	2.145 (17)	2.8319 (15)	132.2 (15)
N5—H5B⋯N2v	0.917 (15)	2.017 (15)	2.9339 (15)	179.0 (17)
N6—H6A⋯O3vi	0.902 (15)	2.334 (16)	3.1215 (14)	145.9 (16)
N6—H6B⋯O2Wvii	0.905 (15)	2.013 (16)	2.9096 (15)	170.2 (17)
O3—H3⋯O1	0.928 (19)	1.64 (2)	2.5235 (12)	156 (2)
O4—H4C⋯O1Wviii	0.880 (18)	1.858 (18)	2.7284 (13)	170 (2)
O5—H5⋯O2	0.921 (19)	1.70 (2)	2.5461 (13)	151 (2)
C6—H6⋯O4ix	0.975 (17)	2.582 (17)	3.5529 (15)	173.9 (15)

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) ; (vi) ; (vii) ; (viii) ; (ix) .