organic compounds
Bis(melaminium) succinate succinic acid monosolvate dihydrate
aInstitute for Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9/163, A-1060 Vienna, Austria, and bInstitute for Chemical Technologies and Analytics, Division of Structural Chemistry, Vienna University of Technology, Getreidemarkt 9/164-SC, A-1060 Vienna, Austria
*Correspondence e-mail: mweil@mail.zserv.tuwien.ac.at
The 3H7N6+·C4H4O42−·C4H6O4·2H2O, contains one essentially planar melaminium (2,4,6-triamino-1,3,5-triazin-1-ium) cation (r.m.s. deviation of the non-H atoms = 0.0097 Å), one-half of a succinate anion, one-half of a succinic acid solvent molecule and one water molecule of crystallization; full molecules are generated by inversion symmetry. Supramolecular layers parallel to (12-1) are formed through extensive intermolecular hydrogen bonding of the types O—H⋯O, N—H⋯N and N—H⋯O between the components.
of the solvated title salt, 2CRelated literature
For the use of melaminium salts in polymer science, see: Weinstabl et al. (2001). For a list of structurally determined melaminium salts of purely organic carboxylic acids, see: Froschauer & Weil (2012).
Experimental
Crystal data
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Data collection
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Refinement
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Data collection: SMART (Siemens, 1996); cell 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).
Supporting information
https://doi.org/10.1107/S1600536812033387/cv5324sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536812033387/cv5324Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S1600536812033387/cv5324Isup3.cml
79.3 mmol melamine was dissolved under refluxing conditions in 200 ml distilled water. The stoichiometric quantity (1:1) of succinic 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
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 (32.13/32.10), H (5.50/5.38), N (31.93/32.05). NMR: (solution, DMSO) [p.p.m.]: 1H 10.37 (s, 2H), 6.22 (s, 6H), 2.39 (s, 4H); 13C 174.32, 166.43, 29.29.The proton at the triazine ring of the melaminium cation was clearly discernible from a difference Fourier map (like all other H atoms). For
the H atoms attached to C or N atoms were set in calculated positions and treated as riding on their parent atoms with C—H = 0.97 Å and N—H = 0.86 Å and with Uiso(H) = 1.2Ueq(C,N). The proton of the carboxy group of the succinic acid solvent molecule was refined with a distance restraint O—H = 1.00 (2) Å; H atoms of the water molecule were likewise refined with a distance restraint of O—H = 0.88 (2) Å.The potential substitution of melamine through organic melaminium salts for production of melamine urea formaldehyde (MUF) resins (Weinstabl et al., 2001) render the structural investigation of these compounds interesting. A list of already determined structures of purely organic melaminium salts has been compiled recently by Froschauer & Weil (2012).
The pKa values of 4.21 and 5.72 for the first and second deprotonation step of succinic acid (the pKa of the first deprotonation step of melamine is 5.10) led to a doubly deprotonated anion in the title compound, bis-melaminium succinate succinic acid solvate dihydrate, 2(C3H7N6)+.C4H4O4-.C4H6O4.2(H2O). However, besides lattice water, there is also one succinic acid solvent molecule present in the
The succinic acid molecule and the succinate anion are located with their central C—C bond on inversion centres. As observed for all single protonated melaminium cations, the protonation of melamine takes place at one of the triazine N ring atoms (Fig. 1).The melaminium cation is essentially planar with a r.m.s. deviation of 0.0097 Å. Likewise, the anion (r.m.s. deviation 0.039 Å) and the succinic acid molecule (r.m.s. deviation 0.060 Å) can be considered as planar. The angles between the least-squares planes of 6.59 (9) ° and 5.76 (12) ° between the anion and the cation and the succinic acid molecule, respectively, lead to the formation of supramolecular layers where cations are arranged in rows alternating with rows of anions, succinic acid solvent and lattice water molecules (Fig. 2). Extensive intermolecular hydrogen bonding of the types O—H···O, N—H···N and N—H···O between the molecular components is present. Details are reported in Table 1. The motif for the hydrogen-bonded assembly of two melaminium cations in such a layer is the same as in the hydrogenmalonate salt and other melaminium salts (Froschauer & Weil, 2012). In the crystal, the supramolecular layers are arranged parallel to (121) (Fig. 3) with an interplanar distance of approximately 3.15 Å.
For the use of melaminium salts in polymer science, see: Weinstabl et al. (2001). For a list of structurally determined melaminium salts of purely organic
see: Froschauer & Weil (2012).Data collection: SMART (Siemens, 1996); cell
SAINT (Siemens, 1996); data reduction: SAINT (Siemens, 1996); 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).Fig. 1. The molecular components of the title compound drawn with atomic displacement factors at the 90% probability level. H atoms are displayed as spheres with an arbirtary radius. For the centrosymmetric succinate anion and the succinic acid solvent molecule the symmetry-equivalent atoms are not labelled. | |
Fig. 2. Supramolecular layer built up through hydrogen bonding interactions (dashed lines) between the molecular components. | |
Fig. 3. The assembly of supramolecular layers in the crystal parallel to (121). |
2C3H7N6+·C4H4O42−·C4H6O4·2H2O | Z = 1 |
Mr = 524.48 | F(000) = 276 |
Triclinic, P1 | Dx = 1.576 Mg m−3 |
Hall symbol: -P 1 | Mo Kα radiation, λ = 0.71073 Å |
a = 7.1193 (7) Å | Cell parameters from 1570 reflections |
b = 8.1650 (8) Å | θ = 2.5–28.8° |
c = 9.5595 (9) Å | µ = 0.13 mm−1 |
α = 88.013 (2)° | T = 293 K |
β = 84.647 (2)° | Parallelepiped, colourless |
γ = 88.093 (2)° | 0.23 × 0.18 × 0.12 mm |
V = 552.68 (9) Å3 |
Siemens SMART CCD diffractometer | 1545 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.028 |
Graphite monochromator | θmax = 28.3°, θmin = 2.1° |
ω scans | h = −9→9 |
5533 measured reflections | k = −10→10 |
2719 independent reflections | l = −12→12 |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.047 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.142 | w = 1/[σ2(Fo2) + (0.0791P)2] where P = (Fo2 + 2Fc2)/3 |
S = 0.97 | (Δ/σ)max < 0.001 |
2719 reflections | Δρmax = 0.30 e Å−3 |
173 parameters | Δρmin = −0.26 e Å−3 |
3 restraints | Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.010 (4) |
2C3H7N6+·C4H4O42−·C4H6O4·2H2O | γ = 88.093 (2)° |
Mr = 524.48 | V = 552.68 (9) Å3 |
Triclinic, P1 | Z = 1 |
a = 7.1193 (7) Å | Mo Kα radiation |
b = 8.1650 (8) Å | µ = 0.13 mm−1 |
c = 9.5595 (9) Å | T = 293 K |
α = 88.013 (2)° | 0.23 × 0.18 × 0.12 mm |
β = 84.647 (2)° |
Siemens SMART CCD diffractometer | 1545 reflections with I > 2σ(I) |
5533 measured reflections | Rint = 0.028 |
2719 independent reflections |
R[F2 > 2σ(F2)] = 0.047 | 3 restraints |
wR(F2) = 0.142 | H atoms treated by a mixture of independent and constrained refinement |
S = 0.97 | Δρmax = 0.30 e Å−3 |
2719 reflections | Δρmin = −0.26 e Å−3 |
173 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 | ||
N3 | 0.3081 (2) | 1.0330 (2) | 0.36672 (15) | 0.0308 (4) | |
N1 | 0.4064 (2) | 0.8895 (2) | 0.16163 (15) | 0.0323 (4) | |
H1 | 0.4894 | 0.8279 | 0.1160 | 0.039* | |
O1 | 0.62741 (19) | 0.68205 (18) | −0.02657 (14) | 0.0385 (4) | |
O3 | 0.6682 (2) | 0.2996 (2) | 0.25900 (15) | 0.0456 (4) | |
O2 | 0.8071 (2) | 0.6984 (2) | 0.14806 (15) | 0.0480 (5) | |
O4 | 0.3997 (2) | 0.44613 (19) | 0.26505 (14) | 0.0431 (4) | |
C7 | 0.5535 (3) | 0.3930 (3) | 0.3191 (2) | 0.0309 (5) | |
C1 | 0.2450 (3) | 0.9365 (2) | 0.10469 (19) | 0.0284 (4) | |
N2 | 0.1121 (2) | 1.0287 (2) | 0.17327 (15) | 0.0305 (4) | |
C2 | 0.1488 (3) | 1.0729 (2) | 0.30373 (18) | 0.0281 (4) | |
C6 | 0.5839 (3) | 0.4567 (3) | 0.46117 (19) | 0.0339 (5) | |
H6A | 0.6871 | 0.5321 | 0.4491 | 0.041* | |
H6B | 0.6233 | 0.3651 | 0.5200 | 0.041* | |
N4 | 0.2251 (2) | 0.8874 (2) | −0.02317 (16) | 0.0370 (4) | |
H3 | 0.1250 | 0.9151 | −0.0632 | 0.044* | |
H2 | 0.3123 | 0.8277 | −0.0664 | 0.044* | |
N6 | 0.5975 (2) | 0.8950 (2) | 0.34112 (18) | 0.0402 (5) | |
H6 | 0.6226 | 0.9242 | 0.4228 | 0.048* | |
H7 | 0.6778 | 0.8356 | 0.2909 | 0.048* | |
C3 | 0.4365 (3) | 0.9412 (2) | 0.29314 (19) | 0.0301 (5) | |
C4 | 0.7771 (3) | 0.6435 (2) | 0.0324 (2) | 0.0308 (5) | |
N5 | 0.0177 (2) | 1.1639 (2) | 0.37353 (17) | 0.0396 (5) | |
H5 | 0.0347 | 1.1959 | 0.4561 | 0.048* | |
H4 | −0.0848 | 1.1912 | 0.3365 | 0.048* | |
O1W | 0.0343 (3) | 0.6661 (3) | 0.36216 (18) | 0.0637 (6) | |
H1W | 0.126 (4) | 0.591 (3) | 0.353 (3) | 0.097* | |
H2W | −0.024 (4) | 0.667 (4) | 0.288 (2) | 0.097* | |
H12 | 0.385 (4) | 0.393 (3) | 0.171 (2) | 0.097* | |
C5 | 0.9192 (3) | 0.5292 (3) | −0.04228 (19) | 0.0306 (5) | |
H5A | 0.9717 | 0.5841 | −0.1280 | 0.037* | |
H5B | 0.8543 | 0.4341 | −0.0690 | 0.037* |
U11 | U22 | U33 | U12 | U13 | U23 | |
N3 | 0.0277 (9) | 0.0441 (10) | 0.0218 (8) | 0.0109 (8) | −0.0092 (7) | −0.0101 (7) |
N1 | 0.0283 (9) | 0.0444 (10) | 0.0248 (8) | 0.0147 (8) | −0.0070 (7) | −0.0131 (7) |
O1 | 0.0295 (8) | 0.0537 (10) | 0.0344 (8) | 0.0173 (7) | −0.0150 (6) | −0.0151 (7) |
O3 | 0.0392 (9) | 0.0659 (11) | 0.0337 (8) | 0.0230 (8) | −0.0151 (7) | −0.0236 (7) |
O2 | 0.0455 (9) | 0.0664 (11) | 0.0351 (8) | 0.0258 (8) | −0.0193 (7) | −0.0285 (8) |
O4 | 0.0381 (9) | 0.0635 (11) | 0.0303 (8) | 0.0209 (7) | −0.0178 (6) | −0.0191 (7) |
C7 | 0.0278 (10) | 0.0395 (12) | 0.0261 (9) | 0.0081 (9) | −0.0067 (8) | −0.0069 (8) |
C1 | 0.0269 (10) | 0.0366 (11) | 0.0222 (9) | 0.0051 (8) | −0.0061 (8) | −0.0061 (8) |
N2 | 0.0281 (9) | 0.0428 (10) | 0.0217 (8) | 0.0076 (7) | −0.0085 (7) | −0.0097 (7) |
C2 | 0.0250 (10) | 0.0386 (11) | 0.0215 (9) | 0.0063 (8) | −0.0062 (8) | −0.0067 (8) |
C6 | 0.0296 (11) | 0.0479 (13) | 0.0257 (10) | 0.0076 (9) | −0.0106 (8) | −0.0085 (9) |
N4 | 0.0332 (9) | 0.0548 (12) | 0.0245 (8) | 0.0131 (8) | −0.0107 (7) | −0.0169 (8) |
N6 | 0.0330 (10) | 0.0596 (12) | 0.0295 (9) | 0.0231 (9) | −0.0130 (7) | −0.0173 (8) |
C3 | 0.0301 (10) | 0.0372 (12) | 0.0243 (9) | 0.0055 (9) | −0.0095 (8) | −0.0070 (8) |
C4 | 0.0282 (10) | 0.0357 (11) | 0.0294 (10) | 0.0105 (9) | −0.0083 (8) | −0.0083 (8) |
N5 | 0.0322 (9) | 0.0630 (13) | 0.0255 (8) | 0.0174 (9) | −0.0127 (7) | −0.0182 (8) |
O1W | 0.0646 (12) | 0.0902 (15) | 0.0408 (9) | 0.0294 (10) | −0.0287 (8) | −0.0315 (9) |
C5 | 0.0299 (10) | 0.0388 (12) | 0.0243 (9) | 0.0108 (9) | −0.0087 (8) | −0.0104 (8) |
N3—C3 | 1.328 (2) | C6—H6A | 0.9700 |
N3—C2 | 1.358 (2) | C6—H6B | 0.9700 |
N1—C1 | 1.356 (2) | N4—H3 | 0.8600 |
N1—C3 | 1.378 (2) | N4—H2 | 0.8600 |
N1—H1 | 0.8600 | N6—C3 | 1.313 (2) |
O1—C4 | 1.277 (2) | N6—H6 | 0.8600 |
O3—C7 | 1.217 (2) | N6—H7 | 0.8600 |
O2—C4 | 1.246 (2) | C4—C5 | 1.500 (3) |
O4—C7 | 1.309 (2) | N5—H5 | 0.8600 |
O4—H12 | 1.023 (17) | N5—H4 | 0.8600 |
C7—C6 | 1.507 (3) | O1W—H1W | 0.882 (17) |
C1—N4 | 1.321 (2) | O1W—H2W | 0.856 (18) |
C1—N2 | 1.328 (2) | C5—C5ii | 1.522 (3) |
N2—C2 | 1.361 (2) | C5—H5A | 0.9700 |
C2—N5 | 1.319 (2) | C5—H5B | 0.9700 |
C6—C6i | 1.514 (4) | ||
C3—N3—C2 | 115.93 (15) | C1—N4—H2 | 120.0 |
C1—N1—C3 | 119.48 (16) | H3—N4—H2 | 120.0 |
C1—N1—H1 | 120.3 | C3—N6—H6 | 120.0 |
C3—N1—H1 | 120.3 | C3—N6—H7 | 120.0 |
C7—O4—H12 | 111.6 (17) | H6—N6—H7 | 120.0 |
O3—C7—O4 | 122.87 (17) | N6—C3—N3 | 122.22 (17) |
O3—C7—C6 | 121.05 (18) | N6—C3—N1 | 116.61 (17) |
O4—C7—C6 | 116.07 (17) | N3—C3—N1 | 121.17 (17) |
N4—C1—N2 | 120.96 (17) | O2—C4—O1 | 121.88 (17) |
N4—C1—N1 | 117.14 (17) | O2—C4—C5 | 120.22 (17) |
N2—C1—N1 | 121.90 (16) | O1—C4—C5 | 117.90 (16) |
C1—N2—C2 | 115.70 (16) | C2—N5—H5 | 120.0 |
N5—C2—N3 | 117.76 (16) | C2—N5—H4 | 120.0 |
N5—C2—N2 | 116.44 (16) | H5—N5—H4 | 120.0 |
N3—C2—N2 | 125.80 (17) | H1W—O1W—H2W | 107 (3) |
C7—C6—C6i | 116.3 (2) | C4—C5—C5ii | 115.00 (19) |
C7—C6—H6A | 108.2 | C4—C5—H5A | 108.5 |
C6i—C6—H6A | 108.2 | C5ii—C5—H5A | 108.5 |
C7—C6—H6B | 108.2 | C4—C5—H5B | 108.5 |
C6i—C6—H6B | 108.2 | C5ii—C5—H5B | 108.5 |
H6A—C6—H6B | 107.4 | H5A—C5—H5B | 107.5 |
C1—N4—H3 | 120.0 |
Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+2, −y+1, −z. |
D—H···A | D—H | H···A | D···A | D—H···A |
N4—H3···N2iii | 0.86 | 2.10 | 2.959 (2) | 176 |
N1—H1···O1 | 0.86 | 2.01 | 2.844 (2) | 164 |
N5—H4···O3iv | 0.86 | 2.13 | 2.976 (2) | 170 |
N6—H6···N3v | 0.86 | 2.16 | 3.015 (2) | 173 |
N1—H1···O2 | 0.86 | 2.50 | 3.199 (2) | 138 |
N4—H2···O3vi | 0.86 | 2.14 | 2.799 (2) | 134 |
N4—H2···O1 | 0.86 | 2.56 | 3.268 (2) | 141 |
N6—H7···O2 | 0.86 | 1.94 | 2.782 (2) | 166 |
N5—H5···O1Wvii | 0.86 | 2.11 | 2.912 (2) | 154 |
O1W—H1W···O4 | 0.88 (2) | 2.35 (2) | 3.195 (2) | 162 (3) |
O1W—H2W···O2viii | 0.86 (2) | 1.89 (2) | 2.726 (2) | 167 (3) |
O4—H12···O1vi | 1.02 (2) | 1.55 (2) | 2.5673 (19) | 177 (3) |
Symmetry codes: (iii) −x, −y+2, −z; (iv) x−1, y+1, z; (v) −x+1, −y+2, −z+1; (vi) −x+1, −y+1, −z; (vii) −x, −y+2, −z+1; (viii) x−1, y, z. |
Experimental details
Crystal data | |
Chemical formula | 2C3H7N6+·C4H4O42−·C4H6O4·2H2O |
Mr | 524.48 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 293 |
a, b, c (Å) | 7.1193 (7), 8.1650 (8), 9.5595 (9) |
α, β, γ (°) | 88.013 (2), 84.647 (2), 88.093 (2) |
V (Å3) | 552.68 (9) |
Z | 1 |
Radiation type | Mo Kα |
µ (mm−1) | 0.13 |
Crystal size (mm) | 0.23 × 0.18 × 0.12 |
Data collection | |
Diffractometer | Siemens SMART CCD |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 5533, 2719, 1545 |
Rint | 0.028 |
(sin θ/λ)max (Å−1) | 0.667 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.047, 0.142, 0.97 |
No. of reflections | 2719 |
No. of parameters | 173 |
No. of restraints | 3 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.30, −0.26 |
Computer programs: SMART (Siemens, 1996), SAINT (Siemens, 1996), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), Mercury (Macrae et al., 2006) and ATOMS (Dowty, 2006), publCIF (Westrip, 2010).
D—H···A | D—H | H···A | D···A | D—H···A |
N4—H3···N2i | 0.86 | 2.10 | 2.959 (2) | 175.7 |
N1—H1···O1 | 0.86 | 2.01 | 2.844 (2) | 164.2 |
N5—H4···O3ii | 0.86 | 2.13 | 2.976 (2) | 170.0 |
N6—H6···N3iii | 0.86 | 2.16 | 3.015 (2) | 173.2 |
N1—H1···O2 | 0.86 | 2.50 | 3.199 (2) | 138.4 |
N4—H2···O3iv | 0.86 | 2.14 | 2.799 (2) | 133.5 |
N4—H2···O1 | 0.86 | 2.56 | 3.268 (2) | 140.6 |
N6—H7···O2 | 0.86 | 1.94 | 2.782 (2) | 165.6 |
N5—H5···O1Wv | 0.86 | 2.11 | 2.912 (2) | 154.1 |
O1W—H1W···O4 | 0.882 (17) | 2.35 (2) | 3.195 (2) | 162 (3) |
O1W—H2W···O2vi | 0.856 (18) | 1.886 (19) | 2.726 (2) | 167 (3) |
O4—H12···O1iv | 1.023 (17) | 1.545 (18) | 2.5673 (19) | 177 (3) |
Symmetry codes: (i) −x, −y+2, −z; (ii) x−1, y+1, z; (iii) −x+1, −y+2, −z+1; (iv) −x+1, −y+1, −z; (v) −x, −y+2, −z+1; (vi) x−1, y, z. |
Acknowledgements
The X-ray centre of the Vienna University of Technology is acknowledged for financial support and for providing access to the single-crystal diffractometer.
References
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The potential substitution of melamine through organic melaminium salts for production of melamine urea formaldehyde (MUF) resins (Weinstabl et al., 2001) render the structural investigation of these compounds interesting. A list of already determined structures of purely organic melaminium salts has been compiled recently by Froschauer & Weil (2012).
The pKa values of 4.21 and 5.72 for the first and second deprotonation step of succinic acid (the pKa of the first deprotonation step of melamine is 5.10) led to a doubly deprotonated anion in the title compound, bis-melaminium succinate succinic acid solvate dihydrate, 2(C3H7N6)+.C4H4O4-.C4H6O4.2(H2O). However, besides lattice water, there is also one succinic acid solvent molecule present in the unit cell. The succinic acid molecule and the succinate anion are located with their central C—C bond on inversion centres. As observed for all single protonated melaminium cations, the protonation of melamine takes place at one of the triazine N ring atoms (Fig. 1).
The melaminium cation is essentially planar with a r.m.s. deviation of 0.0097 Å. Likewise, the anion (r.m.s. deviation 0.039 Å) and the succinic acid molecule (r.m.s. deviation 0.060 Å) can be considered as planar. The angles between the least-squares planes of 6.59 (9) ° and 5.76 (12) ° between the anion and the cation and the succinic acid molecule, respectively, lead to the formation of supramolecular layers where cations are arranged in rows alternating with rows of anions, succinic acid solvent and lattice water molecules (Fig. 2). Extensive intermolecular hydrogen bonding of the types O—H···O, N—H···N and N—H···O between the molecular components is present. Details are reported in Table 1. The motif for the hydrogen-bonded assembly of two melaminium cations in such a layer is the same as in the hydrogenmalonate salt and other melaminium salts (Froschauer & Weil, 2012). In the crystal, the supramolecular layers are arranged parallel to (121) (Fig. 3) with an interplanar distance of approximately 3.15 Å.