Melaminium chloride hemihydrate

The crystals of a new melaminium salt, 2,4,6-tri­amino-1,3,5-triazin-1-ium chloride hemihydrate, C₃H₇N₆⁺·Cl⁻·0.5H₂O, are built up from single-protonated melaminium residues, chloride anions and water mol­ecules. The protonated melaminium cations lie on a twofold axis, while the chloride anions and water mol­ecule lie on the m plane. The melaminium residues are interconnected by N—H...N hydrogen bonds, forming chains parallel to the (001) plane. The chains of melaminium residues form a three-dimensional network through hydrogen-bond interactions with chloride anions and water mol­ecules.

S1. Comment

This study is a continuation of our investigation on the characterization of hydrogen bonds formed by the melamine molecule in the solid state (Janczak & Perpétuo, 2001a,b). The melamine molecule and 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). Solid-state properties, such as electrical conductivity, solid-state reactivity or non-linear optical properties, are influenced by the solid-state structure, i.e. the molecular structure and the orientation of the molecules with respect to each other in the crystal. Knowledge of the molecular architecture can provide a better understanding of the observed macroscopic properties of the crystals.

To expand the understanding of the solid-state physical-organic chemistry of compounds containing multiple and different hydrogen-bonding systems, we studyied the solid-state structure of protonated melaminium chloride hemihydrate, (I). To our knowledge, this is the third stucturally characterized melaminium salt which is protonated at only one ring N atom. Earlier structurally characterized compounds were the cocrystal of barbituric acid with melamine (Zerkowski et al., 1994) and melaminium phthalate (Janczak & Perpétuo, 2001a). In addition to these single-protonated melaminium salts, double-protonated melaminium salts have also been structurally characterized (Wang et al., 1990; Martin & Pinkerton, 1995; Janczak & Perpétuo, 2001b).

The asymmetric unit of the title compound consists of two halves of melaminium residues, two halves of chloride anions and half a water molecule. The protonated melaminium cations lie on the twofold axis, while the chloride anions and water molecule lie on the m plane. The two melaminium residues (Fig. 1) do not differ significantly from one another. The six-membered aromatic ring of both melaminium residues are similar and exhibit significant distortions from the ideal hexagonal form. The internal C—N—C angle at the protonated N atom is greater than the other two C—N—C angles of the ring. These differences are due to the steric effect of a lone pair of electrons and are fully consistent with the valence-shell electron-pair repulsion theory (VSEPR; Gillespie, 1963, 1992). A similar correlation between the internal C—N—C angles of the melaminium ring is observed in the crystal structure of the cocrystal of barbituric acid with melamine (Zerkowski et al., 1994) and melaminium phthalate (Janczak & Perpétuo, 2001a). As a result of the protonation of the melamine ring at the N atom, the internal N—C—N angles containing the non-protonated ring N atoms are significantly greater than those containing protonated and non-protonated N atoms.

The melaminium residues are interconnected by four N—H···N hydrogen bonds, forming chains parallel to the (001) plane (Fig. 2). The chains are ~3.2 Å apart; this distance is shorter than the distance (~3.4 Å) between π-aromatic rings (Pauling, 1960) and indicates nteraction between the melaminium rings of neighbouring chains. The chains of melaminium residues are interconnected by N—H···Cl and N—H···O hydrogen bonds, developing a three-dimensional supramolecular structure (Fig. 2). Each melaminium residue in the crystal is involved in 12 hydrogen bonds; four N—H···N bonds with two neighbouring melaminium residues, two N—H···O bonds with two distinct water molecules and six N—H···Cl bonds. Each H atom of the amine group para with respect to the protonated ring N atom is involved in one hydrogen bond with water. The H atom of the protonated ring N atom is involved in two hydrogen bonds with two chloride ions (Cl2 and its symmetrical equivalent). One of the amine H atoms of the group ortho with respect to the protonated ring N atom is involved in two N—H···Cl hydrogen bonds, while the other forms one N—H···N bond with a neighbouring melamine residue (Fig. 2).

The Cl1 ion acts as an acceptor in four hydrogen bonds with four neighbouring melaminium residues, forming N—H···Cl bonds. Additionally, it interacts with one water H atom. The second chloride ion (Cl2) interacts with two neighbouring melaminium residues through the H atom of the protonated ring N atom and with two other melaminium residues through the H atom of the protonated ring N atom, as well as through the one of the H atoms of melamine group.

The water molecule is involved as an acceptor in two hydrogen bonds with the amine groups (para with respect to the protonated ring N atom) of two different melaminium residues and as a donor in hydrogen bonds with both chloride ions (Cl1 and Cl2). Details of the hydrogen-bonding geometry are given in Table 2.

S2. Experimental

A 10% solution of HCl was added slowly to a solution of melanine in hot water. After several days, colourless crystals of the title salt appeared.

S3. Refinement

The position of H atoms of the melamine residues were refined (U_iso = 1.2U_eq of the N atom joined the H atoms), but the H atoms of water molecules were located from a difference Fourier map and were not refined (U_iso = 1.5U_eq of the O atom).

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, 1990); 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 the title compound showing 50% probability displacement ellipsoids. H atoms are shown as spheres of arbitrary radii. [Symmetry code: (i) -x, y, 1 - z.]
	Fig. 2. The molecular arrangement in the unit cell showing the hydrogen-bonding interactions (dashed lines).

2,4,6-triamino-1,3,5-triazine-1-ium chloride hemihydrate

Crystal data

C3H7N6Cl·0.5H2O	Dx = 1.603 Mg m^−3 Dm = 1.60 Mg m^−3 Dm measured by flotation
Mr = 343.21	Melting point: dehydratated K
Monoclinic, C2/m	Mo Kα radiation, λ = 0.71073 Å
a = 12.441 (2) Å	Cell parameters from 1143 reflections
b = 17.667 (4) Å	θ = 3–29°
c = 7.137 (1) Å	µ = 0.48 mm^−1
β = 114.99 (3)°	T = 293 K
V = 1421.8 (4) Å^3	Parallelepiped, colourless
Z = 4	0.33 × 0.22 × 0.16 mm
F(000) = 712

Data collection

Kuma KM-4 with two-dimensional CCD area-detector diffractometer	1870 independent reflections
Radiation source: fine-focus sealed tube	1143 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.012
Detector resolution: 1024x1024 with blocks 2x2 pixels mm^-1	θmax = 29.1°, θmin = 3.6°
ω scans	h = −16→16
Absorption correction: analytical face-indexed (SHELXTL; Sheldrick, 1990)	k = −23→23
Tmin = 0.858, Tmax = 0.927	l = −8→9
6439 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.029	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.054	H atoms treated by a mixture of independent and constrained refinement
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0227P)^2] where P = (Fo^2 + 2Fc^2)/3
1870 reflections	(Δ/σ)max < 0.001
123 parameters	Δρmax = 0.38 e Å^−3
0 restraints	Δρmin = −0.31 e Å^−3

Special details

Experimental. 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 about 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 1143 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
Cl1	0.20661 (4)	0.5000	0.07661 (9)	0.05976 (18)
Cl2	0.44321 (5)	0.5000	0.71423 (7)	0.04848 (15)
O1	0.16045 (13)	0.5000	0.4898 (3)	0.0788 (5)
H1O	0.2318	0.5000	0.5800	0.118*
H2O	0.1823	0.5000	0.3855	0.118*
N1	0.0000	0.37551 (7)	0.0000	0.0405 (4)
H1	0.0642 (11)	0.4030 (7)	0.0099 (18)	0.049*
C1	0.0000	0.30112 (8)	0.0000	0.0238 (3)
N2	0.09884 (7)	0.26610 (5)	0.00637 (14)	0.0256 (2)
C2	0.09649 (9)	0.19118 (6)	0.00636 (17)	0.0254 (2)
N3	0.18781 (10)	0.15190 (6)	0.01165 (18)	0.0385 (3)
H31	0.1790 (11)	0.1054 (8)	−0.0051 (18)	0.046*
H32	0.2491 (12)	0.1763 (7)	0.0059 (19)	0.046*
N4	0.0000	0.15252 (7)	0.0000	0.0325 (3)
H4	0.0000	0.1089 (10)	0.0000	0.039*
N21	0.0000	0.37950 (8)	0.5000	0.0439 (4)
H211	0.0612 (11)	0.4057 (7)	0.5006 (19)	0.053*
C21	0.0000	0.30541 (8)	0.5000	0.0241 (3)
N22	0.09884 (7)	0.27012 (5)	0.50657 (14)	0.0267 (2)
C22	0.09706 (9)	0.19542 (6)	0.50899 (17)	0.0254 (2)
N24	0.0000	0.15671 (7)	0.5000	0.0329 (3)
H24	0.0000	0.1107 (10)	0.5000	0.039*
N23	0.18930 (9)	0.15563 (6)	0.52066 (18)	0.0392 (3)
H231	0.1787 (11)	0.1054 (8)	0.4991 (17)	0.047*
H232	0.2515 (12)	0.1764 (7)	0.5189 (19)	0.047*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.0514 (3)	0.0239 (2)	0.1255 (5)	0.000	0.0583 (3)	0.000
Cl2	0.0585 (3)	0.0252 (2)	0.0525 (3)	0.000	0.0144 (2)	0.000
O1	0.0535 (9)	0.0419 (8)	0.1552 (15)	0.000	0.0580 (10)	0.000
N1	0.0331 (8)	0.0194 (7)	0.0791 (11)	0.000	0.0335 (9)	0.000
C1	0.0214 (8)	0.0214 (7)	0.0307 (9)	0.000	0.0129 (7)	0.000
N2	0.0225 (5)	0.0213 (5)	0.0377 (5)	0.0000 (4)	0.0172 (4)	−0.0013 (4)
C2	0.0245 (6)	0.0238 (6)	0.0296 (6)	0.0022 (4)	0.0128 (5)	−0.0005 (5)
N3	0.0325 (6)	0.0241 (5)	0.0671 (8)	0.0038 (4)	0.0291 (6)	−0.0027 (5)
N4	0.0296 (7)	0.0165 (6)	0.0567 (10)	0.000	0.0234 (7)	0.000
N21	0.0392 (9)	0.0192 (7)	0.0868 (12)	0.000	0.0399 (9)	0.000
C21	0.0245 (8)	0.0226 (8)	0.0282 (9)	0.000	0.0141 (7)	0.000
N22	0.0227 (5)	0.0243 (5)	0.0373 (5)	0.0006 (4)	0.0169 (4)	0.0003 (4)
C22	0.0247 (6)	0.0227 (6)	0.0302 (6)	0.0003 (4)	0.0131 (5)	−0.0017 (5)
N24	0.0256 (7)	0.0175 (6)	0.0596 (10)	0.000	0.0218 (7)	0.000
N23	0.0270 (6)	0.0236 (5)	0.0726 (8)	0.0004 (4)	0.0264 (6)	−0.0057 (5)

Geometric parameters (Å, º)

O1—H1O	0.8485	N4—H4	0.771 (17)
O1—H2O	0.8933	N21—C21	1.309 (2)
N1—C1	1.314 (2)	N21—H211	0.890 (12)
N1—H1	0.911 (11)	C21—N22	1.362 (1)
C1—N2^i	1.360 (1)	C21—N22^ii	1.362 (1)
C1—N2	1.360 (1)	N22—C22	1.320 (1)
N2—C2	1.324 (1)	C22—N23	1.318 (2)
C2—N3	1.318 (2)	C22—N24	1.365 (1)
C2—N4	1.365 (1)	N24—C22^ii	1.365 (1)
N3—H31	0.831 (13)	N24—H24	0.812 (17)
N3—H32	0.892 (13)	N23—H231	0.900 (13)
N4—C2^i	1.365 (1)	N23—H232	0.861 (14)
H1O—O1—H2O	92.5	C21—N21—H211	121.4 (8)
C1—N1—H1	122.2 (8)	N21—C21—N22	117.3 (1)
N1—C1—N2^i	117.1 (1)	N21—C21—N22^ii	117.3 (1)
N1—C1—N2	117.1 (1)	N22—C21—N22^ii	125.5 (1)
N2^i—C1—N2	125.9 (1)	C22—N22—C21	116.0 (1)
C2—N2—C1	115.8 (1)	N23—C22—N22	121.0 (1)
N3—C2—N2	120.5 (1)	N23—C22—N24	117.7 (1)
N3—C2—N4	118.2 (1)	N22—C22—N24	121.3 (1)
N2—C2—N4	121.3 (1)	C22—N24—C22^ii	119.9 (1)
C2—N3—H31	117.2 (9)	C22—N24—H24	120.06 (6)
C2—N3—H32	119.1 (8)	C22^ii—N24—H24	120.1 (1)
H31—N3—H32	122.4 (12)	C22—N23—H231	117.0 (8)
C2^i—N4—C2	120.0 (1)	C22—N23—H232	122.4 (9)
C2^i—N4—H4	120.02 (6)	H231—N23—H232	119.0 (12)
C2—N4—H4	120.02 (6)

Symmetry codes: (i) −x, y, −z; (ii) −x, y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···Cl1	0.91 (1)	2.36 (1)	3.249 (1)	164 (1)
N3—H31···Cl1^iii	0.83 (2)	2.52 (1)	3.166 (1)	135 (1)
N3—H32···N2^iii	0.89 (2)	2.18 (1)	3.074 (1)	179 (1)
N4—H4···Cl2^iv	0.77 (2)	2.67 (1)	3.271 (1)	136 (1)
N21—H211···O1	0.89 (1)	2.09 (1)	2.940 (1)	159 (1)
N24—H24···Cl2^v	0.81 (2)	2.75 (1)	3.379 (1)	135 (1)
N23—H231···Cl2^v	0.90 (2)	2.48 (1)	3.279 (1)	149 (1)
N23—H232···N22^v	0.86 (2)	2.16 (1)	3.023 (1)	176 (1)
O1—H1O···Cl2	0.85	2.39	3.191 (2)	157
O1—H2O···Cl1	0.90	2.35	3.233 (2)	170

Symmetry codes: (iii) −x+1/2, −y+1/2, −z; (iv) x−1/2, y−1/2, z−1; (v) −x+1/2, −y+1/2, −z+1.