Bis­(melaminium) sulfate dihydrate

The crystals of a new melaminium salt, bis(2,4,6-tri­amino-1,3,5-triazin-1-ium) sulfate dihydrate, 2C₃H₇N₆⁺·SO₄^2-·2H₂O, are built up from monoprotonated melaminium(1+) residues, sulfate(2-) anions and water mol­ecules. The SO₄^2- ion has a slightly distorted tetrahedral geometry. The melaminium residues are interconnected by N-H...N hydrogen bonds, forming chains. The chains of melaminium residues develop a three-dimensional network through multiple donor-acceptor hydrogen-bond interactions with sulfate anions and water mol­ecules.

S1. Comment

The present study is a continuation of our investigation on the characterization of the hydrogen bonds formed by melamine molecule in solid state (Janczak & Perpétuo, 2001a,b,c). The melamine molecule and its derivatives, as well as its organic and inorganic complexes or salts, can develop supramolecular structures via a multiple hydrogen-bonding system by self-assembly of components which contain complementary arrays of hydrogen-bonding sites (MacDonald & Whitesides, 1994; Row, 1999; Krische & Lehn, 2000; Sherrington & Taskinen, 2001). To expand the understanding of the solid-state physical–organic chemistry of compounds containing multiple and different hydrogen-bonding systems, we present here solid-state structure of the protonated bis(melaminium) sulfate dihydrate, (I).

The asymmetric unit of the title compound consists of two melaminium residues protonated at one ring N atom, a sulfate anion and two water molecules (Fig. 1). The protonated melaminium residues do not differ significantly. The six-membered aromatic rings of the melaminium residues are similar and exhibit significant distortions from ideal hexagonal form. The internal C—N—C angle at the protonated N atom is significantly greater than the other two C—N—C angles within the rings. This is a result of the steric effect of a lone-pair of electrons and is fully consistent with the valence-shell electron-pair repulsion (VSEPR) theory (Gillespie, 1963). The correlation between the internal C—N—C angles within the melaminium ring is quite similar to that reported for barbituric acid with melamine (Zerkowski et al., 1994), melaminium phthalate (Janczak & Perpétuo, 2001a) and melaminium chloride hemihydrate (Janczak & Perpétuo, 2001c), the three single-protonated melaminium salts that have been structurally characterized previously. As a result of the protonation of the melamine ring at the N atom, the internal N—C—N angle containing only non-protonated N atoms is significantly greater than both N—C—N angles containing protonated and non-protonated N atoms.

The melaminium residue M1 (C1—C3/N1—N6) in the crystal is involved into nine hydrogen bonds, i.e. four N—H···N bonds with two neighbouring melaminium residues (M1 and M2) and five N—H···O bonds with with four neighbouring SO₄^2- anions. One of the SO₄^2- anions is an acceptor of two hydrogen bonds, while the other three are acceptors of one hydrogen bond each. The second melaminium residue, M2 (C21—C23/N21—N26), similar to M1, forms four N—H···N hydrogen bonds with two neighbouring melaminium residues and five N—H···O hydrogen bonds with two different SO₄^2- anions and three distinct water molecules. The H atom at the protonated N atom of melaminium residue M1 is involved in a slightly bent [168 (2)°] N—H···O hydrogen bond with the O1 atom of the SO₄^2- ion, while the H atom at the protonated N atom of melaminium residue M2 is involved in an almost linear [177 (2)°] N—H···O hydrogen bond with the water O5 atom.

The sulfate anion has an expected but slightly distorted tetrahedral geometry, with the S—O bond lengths ranging from 1.450 (1) to 1.483 (1) Å and the O—S—O bond angles ranging from 108.43 (7) to 110.90 (8)°. The differences between the S—O bonds of the SO₄^2- ion correlate well with the number and strength of the hydrogen bonds formed by the O atoms. The O2 atom, which has the longest S—O bond, is involved in the shortest hydrogen bond. The SO₄^2- ion is involved as acceptor in nine hydrogen bonds. These bonds involve from five melaminium residues (three M1 and two M2) and three water molecules. The O2 atom is the most interesting as it accepts three hydrogen bonds, two from water molecules and one from the amine group of melaminium residue M2. The other three O atoms of the SO₄^2- ion are involved in two hydrogen bonds. The O3 atom is involved as acceptor in two hydrogen bonds with two M1 melaminium residues, while O4 forms two hydrogen bonds with two different melaminium residues (M1 and M2) via the H atoms of the melamine groups. The O1 atom form hydrogen bonds with the H1 atom at the protonated N atom of the M1 melaminium residue and with the water H1O5 atom.

The water molecules form a hydrogen-bonded dimeric structure (O6—H2O6···O5) which joins three SO₄^2- ions and three M2 melaminium residues and do not form any hydrogen bonds with M1 melaminium residues. The O5 water molecule as donor forms two O—H···O hydrogen bonds with two SO₄^2- ions and as acceptor one hydrogen bond with M2 melaminium residues via the H atom at the protonated ring N atom, while the O6 water molecule is involved as acceptor with two melaminium M2 residues via the H atoms of the amine groups and as donor forms a hydrogen bond with O2 of the SO₄^2- ion. Details of the hydrogen-bonding geometry are given in Table 2. The most noticable feature of the structure is that the interaction between the water molecules and sulfate ions in the crystal leads to the formation of {SO₄^2-(H₂O)₂}_n chains that are almost parrallel to the OX axis (~13.5°).

In the crystal, the melaminium residues are interconnected by four almost linear N—H···N hydrogen bonds [N—H···N angles range from 171 (2) to 178 (2)°] that form (M1M1M2M2)_n chains which are inclined by ~23, \sim 27 and ~53° to the OX, OY and OZ axes, respectively. These chains are separated by ~3.5 Å, slightly longer than the distance (~3.4 Å) between π-aromatic rings (Pauling, 1960), indicating a weaker interaction between the melaminium rings of neighbouring chains. The chains of melaminium cations are exrensively interconnected by multiple hydrogen bonds with water molecules and sulfate anions that develop a three-dimensional supramolecular structure (Fig. 2).

Related literature

For related literature, see: Gillespie (1963); Janczak & Perpétuo (2001a, 2001b, 2001c); Krische & Lehn (2000); MacDonald & Whitesides (1994); Pauling (1960); Row (1999); Sherrington & Taskinen (2001); Zerkowski et al. (1994).

S2. Experimental

Melanine was dissolved in a 20% solution of H₂SO₄ and the resulting solution was evaporated slowly. After several days, colourless crystals of the title salt appeared.

S3. Refinement

The position of the H atoms of the melamine residues were refined [U_iso = 1.2U_eq(N); see Table 2 for distances], but the water H atoms were located from a difference Fourier map and were constrained [U_iso = 1.5U_eq(O)].

Computing details

Data collection: KM-4 CCD Software (Kuma, 1999); cell refinement: KM-4 CCD Software; data reduction: KM-4 CCD Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 1990); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The molecular structure of (I) showing 50% probability displacement ellipsoids. H atoms are shown as spheres of arbitrary radii.
	Fig. 2. The molecular arrangement in the unit cell showing the hydrogen-bonding interactions (dashed lines).

Bis(2,4,6-triamino-1,3,5-triazine-1-ium) sulfate dihydrate

Crystal data

2C3N6H7^+·O4S^2^−·2H2O	F(000) = 404
Mr = 386.38	Dx = 1.645 Mg m^−3 Dm = 1.64 Mg m^−3 Dm measured by flotation in a mixture of chloroform/bromoform
Triclinic, P1	Melting point: dehydratated K
a = 6.446 (1) Å	Mo Kα radiation, λ = 0.71073 Å
b = 10.457 (2) Å	Cell parameters from 1890 reflections
c = 12.363 (2) Å	θ = 3–28°
α = 104.28 (3)°	µ = 0.27 mm^−1
β = 92.16 (3)°	T = 293 K
γ = 103.81 (3)°	Parallelepiped, colourless
V = 780.1 (2) Å^3	0.32 × 0.27 × 0.23 mm
Z = 2

Data collection

Kuma KM-4 with CCD area-detector diffractometer	3659 independent reflections
Radiation source: fine-focus sealed tube	1890 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.016
Detector resolution: 1024x1024 with blocks 2x2 pixels mm^-1	θmax = 28.2°, θmin = 3.3°
ω scans	h = −8→8
Absorption correction: analytical face-indexed (SHELXTL; Sheldrick, 1990)	k = −13→13
Tmin = 0.919, Tmax = 0.941	l = −16→14
7091 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.034	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.038	w = 1/[σ^2(Fo^2) + (0.006P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.99	(Δ/σ)max = 0.001
3659 reflections	Δρmax = 0.26 e Å^−3
281 parameters	Δρmin = −0.42 e Å^−3
1 restraint	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0149 (5)

Special details

Experimental. crystal density was measured by flotation in a mixture of chloroform/bromoform

The measurements have been performed on a KUMA KM-4 diffractometer equipped with a two-dimension area CCD detector. The ω–scan technique was used with Δω=0.75° for one image. The 960 images taken for six different runs covered aver 95% of the Ewald sphere. The lattice parameters were calculated using 256 reflections obtained from 30 images for 10 runs with different orientations in reciprocal space and after data collection were refined on 1890 reflections.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
S1	0.21170 (7)	0.38725 (4)	0.69248 (4)	0.03255 (13)
O1	0.44704 (16)	0.44153 (10)	0.69965 (9)	0.0403 (3)
O2	0.12374 (17)	0.48260 (10)	0.77657 (10)	0.0476 (3)
O3	0.12008 (18)	0.37855 (12)	0.58061 (9)	0.0548 (4)
O4	0.16017 (18)	0.25437 (10)	0.71531 (11)	0.0593 (4)
O5	0.7175 (2)	0.35411 (12)	0.82402 (11)	0.0451 (4)
H1O5	0.629 (3)	0.3757 (18)	0.7850 (15)	0.068*
H2O5	0.866 (3)	0.3857 (16)	0.8021 (14)	0.068*
O6	0.7714 (3)	0.59270 (12)	1.01020 (12)	0.0599 (4)
H1O6	0.773 (4)	0.5791 (19)	1.0734 (16)	0.090*
H2O6	0.749 (3)	0.514 (2)	0.9599 (15)	0.090*
N1	0.5995 (2)	0.66880 (13)	0.62096 (12)	0.0322 (4)
H1	0.549 (2)	0.5906 (14)	0.6361 (12)	0.039*
N2	0.5267 (2)	0.83638 (12)	0.54054 (11)	0.0317 (3)
N3	0.8652 (2)	0.87297 (12)	0.64766 (11)	0.0326 (3)
N4	0.2755 (2)	0.63248 (15)	0.52194 (13)	0.0414 (4)
H4A	0.189 (3)	0.6592 (15)	0.4838 (14)	0.050*
H4B	0.243 (3)	0.5570 (15)	0.5388 (13)	0.050*
N5	0.7832 (2)	1.03726 (14)	0.57482 (13)	0.0404 (4)
H5A	0.699 (3)	1.0672 (15)	0.5384 (13)	0.049*
H5B	0.906 (3)	1.0910 (16)	0.6066 (14)	0.049*
N6	0.9257 (2)	0.70024 (15)	0.71840 (14)	0.0424 (4)
H6A	1.050 (3)	0.7490 (16)	0.7464 (14)	0.051*
H6B	0.885 (3)	0.6208 (15)	0.7249 (13)	0.051*
C1	0.4663 (3)	0.71463 (15)	0.55992 (13)	0.0293 (4)
C2	0.7231 (3)	0.91238 (15)	0.58727 (13)	0.0310 (4)
C3	0.7994 (3)	0.74802 (15)	0.66126 (14)	0.0303 (4)
N21	0.6162 (2)	0.09033 (12)	0.84907 (12)	0.0332 (4)
H21	0.651 (2)	0.1740 (14)	0.8389 (12)	0.040*
N22	0.7150 (2)	−0.07001 (12)	0.92907 (11)	0.0308 (3)
N23	0.3810 (2)	−0.12836 (11)	0.81335 (11)	0.0316 (3)
N24	0.9379 (2)	0.14420 (14)	0.95689 (14)	0.0467 (5)
H24A	1.030 (3)	0.1197 (16)	0.9962 (14)	0.056*
H24B	0.967 (3)	0.2240 (17)	0.9475 (14)	0.056*
N25	0.4806 (2)	−0.27988 (13)	0.89529 (13)	0.0392 (4)
H25A	0.364 (3)	−0.3409 (15)	0.8603 (13)	0.047*
H25B	0.572 (3)	−0.2999 (15)	0.9357 (14)	0.047*
N26	0.2964 (2)	0.03710 (15)	0.74129 (14)	0.0459 (5)
H26A	0.168 (3)	−0.0188 (16)	0.7152 (14)	0.055*
H26B	0.324 (3)	0.1217 (16)	0.7365 (13)	0.055*
C21	0.7580 (3)	0.05396 (15)	0.91172 (14)	0.0318 (4)
C22	0.5273 (3)	−0.15634 (15)	0.87787 (13)	0.0276 (4)
C23	0.4282 (3)	−0.00133 (15)	0.80160 (14)	0.0308 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0289 (3)	0.0277 (2)	0.0413 (3)	0.00417 (19)	−0.0010 (2)	0.0131 (2)
O1	0.0244 (7)	0.0419 (7)	0.0571 (8)	0.0036 (5)	0.0003 (6)	0.0226 (6)
O2	0.0404 (8)	0.0362 (6)	0.0590 (8)	0.0106 (6)	0.0136 (7)	−0.0023 (6)
O3	0.0442 (8)	0.0775 (9)	0.0375 (8)	0.0030 (7)	−0.0112 (7)	0.0202 (7)
O4	0.0463 (8)	0.0350 (7)	0.1060 (11)	0.0061 (6)	0.0023 (8)	0.0406 (7)
O5	0.0316 (8)	0.0473 (7)	0.0645 (10)	0.0093 (6)	0.0051 (7)	0.0304 (7)
O6	0.0806 (10)	0.0453 (8)	0.0490 (9)	0.0049 (8)	−0.0047 (9)	0.0165 (7)
N1	0.0290 (9)	0.0273 (8)	0.0420 (9)	0.0049 (7)	0.0018 (7)	0.0147 (7)
N2	0.0275 (8)	0.0272 (7)	0.0391 (9)	0.0040 (6)	−0.0034 (7)	0.0103 (7)
N3	0.0298 (8)	0.0263 (7)	0.0427 (9)	0.0062 (6)	−0.0005 (7)	0.0125 (7)
N4	0.0317 (10)	0.0381 (9)	0.0545 (11)	0.0013 (8)	−0.0057 (8)	0.0212 (8)
N5	0.0310 (10)	0.0306 (9)	0.0605 (12)	0.0031 (7)	−0.0108 (8)	0.0203 (8)
N6	0.0347 (10)	0.0369 (9)	0.0602 (12)	0.0068 (8)	−0.0053 (9)	0.0248 (9)
C1	0.0255 (10)	0.0292 (9)	0.0322 (11)	0.0047 (8)	0.0029 (8)	0.0088 (8)
C2	0.0302 (11)	0.0312 (10)	0.0335 (11)	0.0076 (8)	0.0066 (9)	0.0118 (8)
C3	0.0268 (10)	0.0311 (9)	0.0350 (11)	0.0078 (8)	0.0057 (9)	0.0114 (8)
N21	0.0316 (9)	0.0229 (7)	0.0444 (10)	0.0036 (7)	−0.0031 (7)	0.0121 (7)
N22	0.0298 (8)	0.0229 (7)	0.0383 (9)	0.0039 (6)	−0.0039 (7)	0.0092 (6)
N23	0.0305 (8)	0.0243 (7)	0.0395 (9)	0.0055 (6)	−0.0045 (7)	0.0099 (7)
N24	0.0362 (10)	0.0321 (9)	0.0677 (12)	−0.0033 (8)	−0.0168 (9)	0.0205 (9)
N25	0.0369 (10)	0.0269 (9)	0.0498 (12)	0.0016 (7)	−0.0112 (8)	0.0118 (8)
N26	0.0361 (10)	0.0301 (9)	0.0702 (12)	0.0035 (7)	−0.0155 (9)	0.0185 (9)
C21	0.0284 (10)	0.0282 (9)	0.0378 (11)	0.0060 (8)	0.0019 (9)	0.0086 (8)
C22	0.0291 (10)	0.0237 (9)	0.0290 (10)	0.0071 (8)	0.0050 (8)	0.0046 (8)
C23	0.0286 (10)	0.0292 (9)	0.0347 (11)	0.0081 (8)	0.0015 (9)	0.0081 (8)

Geometric parameters (Å, º)

S1—O4	1.450 (1)	N5—H5B	0.869 (16)
S1—O3	1.456 (1)	N6—C3	1.318 (2)
S1—O1	1.478 (1)	N6—H6A	0.849 (16)
S1—O2	1.483 (1)	N6—H6B	0.834 (15)
O5—H1O5	0.839 (18)	N21—C21	1.356 (2)
O5—H2O5	1.006 (18)	N21—C23	1.359 (2)
O6—H1O6	0.828 (19)	N21—H21	0.891 (13)
O6—H2O6	0.878 (19)	N22—C21	1.332 (2)
N1—C3	1.354 (2)	N22—C22	1.348 (2)
N1—C1	1.365 (2)	N23—C23	1.336 (2)
N1—H1	0.873 (14)	N23—C22	1.342 (2)
N2—C1	1.323 (2)	N24—C21	1.310 (2)
N2—C2	1.344 (2)	N24—H24A	0.878 (17)
N3—C3	1.328 (2)	N24—H24B	0.848 (16)
N3—C2	1.359 (2)	N25—C22	1.328 (2)
N4—C1	1.313 (2)	N25—H25A	0.879 (15)
N4—H4A	0.856 (16)	N25—H25B	0.853 (16)
N4—H4B	0.846 (15)	N26—C23	1.305 (2)
N5—C2	1.320 (2)	N26—H26A	0.885 (17)
N5—H5A	0.855 (16)	N26—H26B	0.877 (16)
O4—S1—O3	110.80 (8)	N2—C2—N3	125.9 (2)
O4—S1—O1	110.30 (7)	N6—C3—N3	120.33 (15)
O3—S1—O1	108.43 (7)	N6—C3—N1	118.36 (14)
O4—S1—O2	109.19 (7)	N3—C3—N1	121.3 (2)
O3—S1—O2	109.15 (8)	C21—N21—C23	119.8 (2)
O1—S1—O2	108.93 (7)	C21—N21—H21	118.5 (10)
H1O5—O5—H2O5	109.5 (16)	C23—N21—H21	121.7 (10)
H1O6—O6—H2O6	108.6 (16)	C21—N22—C22	115.9 (2)
C3—N1—C1	119.7 (2)	C23—N23—C22	115.5 (2)
C3—N1—H1	122.2 (10)	C21—N24—H24A	118.4 (11)
C1—N1—H1	118.0 (10)	C21—N24—H24B	121.6 (12)
C1—N2—C2	115.9 (2)	H24A—N24—H24B	120.0 (16)
C3—N3—C2	115.7 (2)	C22—N25—H25A	119.7 (10)
C1—N4—H4A	118.6 (11)	C22—N25—H25B	118.4 (11)
C1—N4—H4B	118.1 (11)	H25A—N25—H25B	121.7 (15)
H4A—N4—H4B	123.3 (16)	C23—N26—H26A	118.9 (11)
C2—N5—H5A	120.2 (11)	C23—N26—H26B	120.8 (11)
C2—N5—H5B	120.1 (10)	H26A—N26—H26B	119.5 (15)
H5A—N5—H5B	119.5 (14)	N24—C21—N22	120.25 (15)
C3—N6—H6A	120.2 (11)	N24—C21—N21	118.66 (14)
C3—N6—H6B	119.9 (12)	N22—C21—N21	121.1 (2)
H6A—N6—H6B	119.9 (16)	N25—C22—N23	116.92 (15)
N4—C1—N2	121.74 (15)	N25—C22—N22	116.74 (15)
N4—C1—N1	116.83 (14)	N23—C22—N22	126.3 (2)
N2—C1—N1	121.4 (2)	N26—C23—N23	120.56 (15)
N5—C2—N2	117.34 (15)	N26—C23—N21	118.03 (14)
N5—C2—N3	116.74 (15)	N23—C23—N21	121.4 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1	0.87 (2)	1.91 (2)	2.767 (2)	169 (2)
N4—H4A···O3^i	0.86 (2)	2.03 (2)	2.769 (2)	145 (2)
N4—H4B···O3	0.85 (2)	2.04 (2)	2.884 (2)	172 (2)
N5—H5A···N2^ii	0.86 (2)	2.27 (2)	3.122 (2)	174 (2)
N5—H5B···O4^iii	0.87 (2)	2.18 (2)	3.030 (2)	164 (2)
N6—H6A···N23^iii	0.85 (2)	2.22 (2)	3.065 (2)	178 (2)
N6—H6B···O2^iv	0.84 (2)	2.51 (2)	3.074 (2)	126 (2)
N21—H21···O5	0.89 (2)	1.89 (2)	2.776 (2)	177 (2)
N24—H24A···N22^v	0.88 (2)	2.09 (2)	2.954 (2)	171 (2)
N24—H24B···O6^vi	0.85 (2)	2.16 (2)	2.859 (2)	139 (2)
N25—H25A···O2^vii	0.88 (2)	2.11 (2)	2.972 (2)	168 (2)
N25—H25B···O6^vii	0.85 (2)	2.21 (2)	3.039 (2)	165 (2)
N26—H26A···N3^viii	0.89 (2)	2.04 (2)	2.917 (2)	172 (2)
N26—H26B···O4	0.88 (2)	1.99 (2)	2.707 (2)	138 (2)
O5—H1O5···O1	0.84 (2)	1.90 (2)	2.737 (2)	175 (2)
O5—H2O5···O2^iv	1.01 (2)	1.81 (2)	2.798 (2)	166 (2)
O6—H1O6···O2^ix	0.83 (2)	2.24 (2)	3.028 (2)	160 (2)
O6—H2O6···O5	0.88 (2)	2.02 (2)	2.887 (2)	169 (2)

Symmetry codes: (i) −x, −y+1, −z+1; (ii) −x+1, −y+2, −z+1; (iii) x+1, y+1, z; (iv) x+1, y, z; (v) −x+2, −y, −z+2; (vi) −x+2, −y+1, −z+2; (vii) x, y−1, z; (viii) x−1, y−1, z; (ix) −x+1, −y+1, −z+2.