Melaminium hydrogen malonate

Barbara Froschauer; Matthias Weil

doi:10.1107/S1600536812033016

. 2012 Jul 25;68(Pt 8):o2553–o2554. doi: 10.1107/S1600536812033016

Melaminium hydrogen malonate

Barbara Froschauer ^a, Matthias Weil ^b,^*

PMCID: PMC3414997 PMID: 22904984

Abstract

The melaminium (2,4,6-triamino-1,3,5-triazin-1-ium) cation in the title compound, C₃H₇N₆ ⁺·C₃H₃O₄ ⁻, is essentially planar, with a r.m.s. deviation of the non-H atoms of 0.0085 Å. Extensive hydrogen bonding of the types N—H⋯N and N—H⋯O between cations and cations and between cations and hydrogen malonate (2-carboxyethanoate) anions leads to the formation of supramolecular layers parallel to (1-2-1). An intramolecular O—H⋯O hydrogen bond in the single deprotonated malonate anion also occurs.

Related literature

For the use of melaminium salts in polymer science, see: Weinstabl et al. (2001 ▶). For structural studies of melaminium salts of purely organic carboxylic acids, see: Choi et al. (2004 ▶); Janczak & Perpétuo (2001 ▶, 2002 ▶, 2003 ▶, 2004 ▶); Karle et al. (2003 ▶); Marchewka et al. (2003 ▶); Perpétuo & Janczak (2002 ▶, 2005 ▶); Perpétuo et al. (2005 ▶); Prior et al. (2009 ▶); Su et al. (2009 ▶); Udaya Lakshmi et al. (2006 ▶); Froschauer & Weil (2012 ▶); Zhang et al. (2004 ▶, 2005 ▶).

Experimental

Crystal data

C₃H₇N₆ ⁺·C₃H₃O₄ ⁻
M _r = 230.20
Triclinic,
a = 5.1996 (15) Å
b = 7.499 (2) Å
c = 13.119 (4) Å
α = 100.206 (5)°
β = 98.014 (5)°
γ = 106.534 (5)°
V = 472.7 (2) Å³
Z = 2
Mo Kα radiation
μ = 0.14 mm⁻¹
T = 293 K
0.23 × 0.18 × 0.12 mm

Data collection

Siemens SMART CCD diffractometer
4807 measured reflections
2354 independent reflections
1190 reflections with I > 2σ(I)
R _int = 0.078

Refinement

R[F ² > 2σ(F ²)] = 0.042
wR(F ²) = 0.105
S = 0.89
2354 reflections
150 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.23 e Å⁻³
Δρ_min = −0.23 e Å⁻³

Data collection: SMART (Siemens, 1996 ▶); cell refinement: SAINT (Siemens, 1996 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: Mercury (Macrae et al., 2006 ▶) and ATOMS (Dowty, 2006 ▶); software used to prepare material for publication: publCIF (Westrip, 2010 ▶).

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536812033016/cv5323sup1.cif

e-68-o2553-sup1.cif^{(19.2KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536812033016/cv5323Isup2.hkl

e-68-o2553-Isup2.hkl^{(115.7KB, hkl)}

Supplementary material file. DOI: 10.1107/S1600536812033016/cv5323Isup3.cml

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
N1—H1⋯O4ⁱ	0.86	1.82	2.6785 (19)	176
N4—H2⋯O2ⁱⁱ	0.86	2.17	2.8350 (19)	134
N4—H3⋯N2ⁱⁱ	0.86	2.14	2.994 (2)	171
N5—H4⋯O2	0.86	2.14	2.998 (2)	172
N5—H5⋯N3ⁱⁱⁱ	0.86	2.23	3.091 (2)	178
N6—H6⋯O1ⁱⁱⁱ	0.86	2.15	2.8592 (19)	140
N6—H7⋯O3ⁱ	0.86	2.02	2.880 (2)	173
O1—H10⋯O3	1.00 (2)	1.47 (2)	2.450 (2)	165 (2)

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) .

Acknowledgments

The X-ray centre of the Vienna University of Technology is acknowledged for financial support and for providing access to the single-crystal diffractometer.

supplementary crystallographic information

Comment

Melamine is a weak base with three different pK_a values which decline with decreasing protonation status. The first (pK_a = 5.10) is slightly above the pK_a of acetic acid (4.75), the second and third (0.20 and -2.10, respectively) are significantly below the most organic carboxylic acids. Since the difference between the pK_a values during an acid-base reaction corresponds to the free energy of reaction, stable products can only be expected for acids with a pK_a value significantly below 5.10, whereas organic acids with acidities in the range of 5.10 or above can be expected to yield mixtures of unreacted melamine, free acid and melaminium salts. Depending on the acid valency and strengths, mono and disalts can be formed by simply heating the components or their respective solutions.

In the past, organic melamine salts were tested as potential melamine substitutes for melamine urea formaldehyde (MUF) resins (Weinstabl et al., 2001). Up to now, the following melaminium salts of purely organic carboxylic acids, viz only those with C, H and N contents, have been crystallographically characterized: melaminium acetate acetic acid solvate monohydrate (Perpétuo & Janczak, 2002), melaminium 2,4,6-trihydroxybenzoate dihydrate (Prior et al.., 2009), melaminium benzoate dihydrate (Perpétuo & Janczak, 2005), melaminium formate (Perpétuo et al., 2005), melaminium glutarate monohydrate (Janczak & Perpétuo, 2002), melaminium levulinate monohydrate (Choi et al., 2004), melaminium maleate monohydrate (Janczak & Perpétuo, 2004), bis(melaminium) DL-malate tetrahydrate (Janczak & Perpétuo, 2003), melamin(1,3)ium dihydrogenmellitate dihydrate (Karle et al.., 2003), melaminium bis(hydrogen oxalate) (Zhang et al., 2005), melaminium hydrogenphtalate (Janczak & Perpétuo, 2001), bis(melaminium) succinate succinic acid solvate dihydrate (Froschauer & Weil, 2012), melamin(1,3)ium tartrate monohydrate (Marchewka et al., 2003), bis(melaminium) tartrate 2.5-hydrate (Udaya Lakshmi et al., 2006), bis(melaminium) tartrate dihydrate (Su et al., 2009), and bis(melaminium) terephtalate dihydrate (Zhang et al., 2004).

The pK_a values of 2.82 and 5.69 for the first and second deprotonation step of malonic acid led to a single deprotonated anion in the title compound, melaminium hydrogen malonate, C₃H₇N₆^+.C₃H₃O₄^-. The protonation of melamine takes place at one of the triazine N ring atoms (Fig. 1) as observed for all other single protonated melaminium salts listed above.

Both the melaminium cation and the hydrogenmalonate anions are essentially planar with r.m.s. deviations of 0.0085 Å (cation) and 0.061 Å (anion) for the non-H atoms. The angle between the two least-squares planes is 6.61 (8) °, making it possible to set up supramolecular layers held together by strong to medium hydrogen bonds of the type N—H···O and N—H···.N between cations and cations and cations and anions (Fig. 2; Table 1). The motif for the hydrogen-bonded assembly of two melaminium cations is observed in many other melamine or melaminium structures as reported previously by Prior et al. (2009). In the crystal, the supramolecular layers are arranged parallel to (121) (Fig. 3) with an interplanar distance of approximately 2.96 Å.

Experimental

39.6 mmol melamine was dissolved under refluxing conditions in 150 ml distilled water. The stoichiometric quantity (1:1) of malonic acid was added within five minutes. The mixture was then refluxed for 30 minutes and then cooled to room temperature. The precipitate formed on cooling was separeted by filtration and washed with cold methanol. The crystalline product was then dried in vacuo at 303–313 K. Single crystal growth was accomplished by dissolution of 1 g of the crystalline product under refluxing conditions in an aqueous methanol solution (2:1 v/v) to get a saturated solution. Then the solution was slowly cooled down to room temperature. Suitable crystals were obtained by slow evaporation of the solvents during five days. The crystals were washed with methanol and dried in vacuo at room temperature giving analytical pure samples. CHN analysis (found/calc.): C (31.19/31.30), H (4.01/4.37), N (36.26/36.50). NMR: (solution, DMSO) chemical shift [p.p.m.]: ¹H 11.04 (s, 2H), 6.97 (s, 6H), 3.01 (s, 2H); ¹³C 170.45, 163.38, 40.95.