Melaminium 2,4,6-trihydroxy­benzoate dihydrate

Timothy J Prior; Osman Goch; Rebecca L Kift

doi:10.1107/S1600536809031055

. 2009 Aug 12;65(Pt 9):o2133. doi: 10.1107/S1600536809031055

Melaminium 2,4,6-trihydroxybenzoate dihydrate

Timothy J Prior ^a,^*, Osman Goch ^a, Rebecca L Kift ^a

PMCID: PMC2969927 PMID: 21577544

Abstract

In the title compound, C₃H₇N₆ ⁺·C₇H₅O₅ ⁻·2H₂O, 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 molecules 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 Inline graphic (8) motif, see: Bouvet et al. (2007 ▶).

Experimental

Crystal data

C₃H₇N₆ ⁺·C₇H₅O₅ ⁻·2H₂O
M _r = 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
Δρ_max = 0.46 e Å⁻³
Δρ_min = −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.

Supplementary Material

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

e-65-o2133-sup1.cif^{(18.8KB, cif)}

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

e-65-o2133-Isup2.hkl^{(288.1KB, hkl)}

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

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⋯O2W^iv	0.902 (15)	2.145 (17)	2.8319 (15)	132.2 (15)
N5—H5B⋯N2^v	0.917 (15)	2.017 (15)	2.9339 (15)	179.0 (17)
N6—H6A⋯O3^vi	0.902 (15)	2.334 (16)	3.1215 (14)	145.9 (16)
N6—H6B⋯O2W^vii	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⋯O1W^viii	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⋯O4^ix	0.975 (17)	2.582 (17)	3.5529 (15)	173.9 (15)

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

Acknowledgments

RLK thanks the University of Hull for the award of a studentship.

supplementary crystallographic information

Comment

Melamine (2,4,6-triamino-s-triazine, C₃H₆N₆) has been widely studied for its potential in the formation of extended hydrogen-bonded solids. For example, crystals of melamine with the following aromatic acids have been reported: benzoic acid (Perpétuo & Janczak, 2005); phthalic acid (Janczak & Perpétuo, 2001); terephthalic acid (Zhang et al., 2004, and Zhang & Chen, 2005); mellitic acid (Karle et al., 2003). The structure of 2,4,6-trihydroxybenzoic acid and those of some co-crystals of this acid have been reported previously by Jankowski et al. (2007). Here we report a co-crystal of melamine and 2,4,6-trihydroxybenzoic acid obtained from aqueous solution.

The title compound crystallizes in the centrosymmetric space group P2₁/n with four formula units in the unit cell. The 2,4,6-trihydroxybenzoic acid molecule is deprotonated at the carboxylic acid function. One of the nitrogen atoms of the triazine ring of melamine is protonated. This acid-base pair forms a complementary C₂²(8) embrace illustrated in Figure 1. Details of the hydrogen bonding within this structure are given in Table 1. A second acid-base pair is generated by the inversion centre. This forms a pair of strong hydrogen bonds to the first through the two melaminium ions. This melamine-melamine C₂²(8) embrace is observed in many other compounds involving melamine. This four molecule unit (illustrated in Figure 2) can be thought of as the repeat unit in an infinite chain. These links are held together by weaker, non-classical C—H···O hydrogen bonds between the C6-(H6) and the hydroxyl group (O4) of another acid unit. This is illustrated in Figure 3. The C···O distance here is 3.5529 (15) Å and the H···O distance is 2.5812 (17) Å. A brief review of about 350 structures with a similar C—H···O (aromatic hydroxyl) homomeric C₂²(8) embrace in the Cambridge Structural Database (Allen, 2002) reveals that the distances and geometry displayed here are in good agreement with those previously reported. One similar example is reported by Bouvet et al. (2007).

Infinite chains formed from this repeat unit are arranged in stacks. The vertical separation between chains is 3.3496 (5) Å. These stacks of chains are arranged along the c axis. The chains within adjacent stacks are alternately parallel to the [120] and [120] directions. The angle between chains parallel to [120] and [120] is 33.242 (8) °. A view of part of the structure down the crystallographic c axis is shown in Figure 4. Between these stacks a large number of classical hydrogen bonds are formed. These are reinforced by the presence of the two water molecules. Full details are given in Table 1.

Experimental

A solution of melamine and 2,4,6-trihydroxybenzoic acid (0.012 mol dm^-3 in each component) was prepared in deionized water. 5 mL portions of this solution were allowed to evaporate at room temperature in air from suitably sized vials. After a period of approximately two weeks, good sized colourless crystals were obtained.