Bis­(melaminium) hydrogen phosphite tetrahydrate

The title compound, 2C₃H₇N₆⁺·HPO₃²⁻·4H₂O, crystallizes as a layered structure. The intermolecular packing appears to be controlled by hydrogen bonds and π–π stacking.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](P-O) = 0.001 Å
• R factor = 0.037
• wR factor = 0.102
• Data-to-parameter ratio = 15.6

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



PLAT_420  Alert C D-H Without Acceptor       P(1)   -   H(1)              ?


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

---

S1. Comment

The title compound, bis(melaminium) hydrogen phosphite tetrahydrate, (I) (Fig. 1), arose as an unexpected by-product during our synthetic investigations of organically templated zinc hydrogen phosphites (Rodgers & Harrison, 2000; Harrison, 2001).

There are two distinct melaminium (2,4,6-triamino-1,3,5-triazine-1-ium) cations, both of which are singly protonated at a ring N atom. Their average ring and terminal C—N bond lengths are 1.348 (2) and 1.318 (2) Å, respectively. The C—N—C bond angles at the protonated ring N atoms (N2 and N7) are somewhat larger than the equivalent angles for the non-protonated ring N atoms, as seen for similar materials (Janczak & Perpétuo, 2001). Both melaminium cations are essentially planar (non-H atom r.m.s. deviations from the best least-squares planes are 0.011 and 0.012 Å for the C1- and C4-containing molecules, respectively). For the hydrogen phosphite anion, the average P—O separation of 1.516 (2) Å and the average O—P—O bond angle of 112.2 (2)° compare well to those seen (1.516 Å and 111.2°, respectively) in [{H₂N(CH₂)₂NH₂}_0.5Zn]HPO₃ [please check] (Rodgers & Harrison, 2000).

The packing in this phase (Figs. 2 and 3) is dominated by a combination of hydrogen bonding (Table 2) and π–π-stacking effects, resulting in a structure with strongly layered character. In any (100) sheet, adjacent melaminium cations are linked into zigzag chains in the c direction, by way of side-by-side pairs of N—H···N links (Fig. 2). This `synthon' bonding motif has also been seen in melaminium chloride hemihydrate (Janczak & Perpétuo, 2001) and melaminium acetate acetic acid solvate monohydrate (Perpétuo & Janczak, 2002). The melaminium chains are crosslinked in the b direction by the hydrogen phosphite moieties, by way of N—H···O bonds. As expected, the phosphite (P—H) H atom is not involved in hydrogen bonding (Harrison, 2001). The four water molecules each form two H bonds (as O—H···N or O—H···O) and also act as acceptors for hydrogen bonds from melaminium cations or other water molecules. Overall, each melaminium cation makes seven hydrogen bonds and acts as an acceptor for two more, assuming a maximum H···N or H···O contact of 2.5 Å.

Intersheet bonding in the [100] direction involves probable π–π-stacking interactions of the melaminium species [shortest intersheet C···N separation = 3.375 (2) Å for C3···N3ⁱ;symmetry code: (i) −x, −y, −z]. Even stronger melaminium-melaminium π–π-stacking interactions have been observed in related compounds (Perpétuo & Janczak, 2002). In addition, there are intersheet O—H···O hydrogen bonds involving atoms H41, H51, H61, and H72 (Table 2). The acceptor species for these interactions are three phosphite O atoms and one water molecule O atom.

S2. Experimental

A mixture of 0.407 g (5 mmol) ZnO, 0.820 g (10 mmol) H₃PO₃, 0.631 g (5 mmol) melamine, and 20 ml H₂O was sealed in a plastic bottle and heated to 353 K for 5 d. After cooling to room temperature, transparent, plate-shaped crystals of the title compound were recovered by vacuum filtration and washing with water and acetone.

S3. Refinement

The melaminium N—H and phosphite P—H H atoms were refined as riding [U_iso(H) = 1.2U_eq of the attached atom]. The positions of the water molecule H atoms were refined freely, with U_iso(H) fixed at 1.5U_eq of the attached O atom.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SMART; data reduction: SMART; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The asymmetric unit of (I) (50% displacement ellipsoids and arbitrary spheres for the H atoms), with hydrogen bonds indicated by dashed lines.
	Fig. 2. Hydrogen-bonding scheme (dashed lines) for part of a (100) sheet in (I) (50% displacement ellipsoids and arbitrary spheres for the H atoms).
	Fig. 3. Packing diagram for (I), viewed approximately down [001] (50% displacement ellipsoids, atom colours as in Fig. 1, and H atoms omitted for clarity).

(I)

Crystal data

2C3H7N6^+·HPO3^2^−·4H2O	Dx = 1.524 Mg m^−3
Mr = 406.33	Melting point: not measured K
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 6.7702 (3) Å	Cell parameters from 4112 reflections
b = 21.4106 (11) Å	θ = 3.2–27.5°
c = 12.3411 (6) Å	µ = 0.22 mm^−1
β = 98.108 (10)°	T = 293 K
V = 1771.01 (15) Å^3	Plate, colourless
Z = 4	0.43 × 0.26 × 0.01 mm
F(000) = 856

Data collection

Bruker SMART1000 CCD diffractometer	4053 independent reflections
Radiation source: fine-focus sealed tube	2841 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.024
ω scans	θmax = 27.5°, θmin = 1.9°
Absorption correction: multi-scan (SADABS; Bruker, 1999)	h = −8→8
Tmin = 0.913, Tmax = 0.998	k = −27→27
13097 measured reflections	l = −11→16

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)] = 0.037	Hydrogen site location: difmap and geom
wR(F^2) = 0.102	H atoms treated by a mixture of independent and constrained refinement
S = 0.96	w = 1/[σ^2(Fo^2) + (0.061P)^2] where P = (Fo^2 + 2Fc^2)/3
4053 reflections	(Δ/σ)max = 0.001
259 parameters	Δρmax = 0.21 e Å^−3
0 restraints	Δρmin = −0.32 e Å^−3

Special details

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
N1	0.2370 (2)	0.52099 (6)	0.65042 (11)	0.0326 (3)
N2	0.2407 (2)	0.42733 (6)	0.55177 (11)	0.0322 (3)
H3	0.2522	0.3844	0.5549	0.039*
N3	0.25635 (19)	0.52219 (6)	0.45694 (10)	0.0314 (3)
N4	0.2481 (2)	0.61198 (6)	0.55561 (12)	0.0415 (4)
H4A	0.2532	0.6325	0.4962	0.050*
H4B	0.2430	0.6316	0.6159	0.050*
N5	0.2206 (2)	0.42640 (6)	0.73572 (12)	0.0414 (4)
H5A	0.2150	0.4453	0.7967	0.050*
H5B	0.2181	0.3863	0.7331	0.050*
N6	0.2539 (2)	0.42789 (6)	0.36748 (11)	0.0397 (3)
H6A	0.2592	0.4470	0.3067	0.048*
H6B	0.2504	0.3878	0.3690	0.048*
C1	0.2481 (2)	0.55011 (7)	0.55430 (13)	0.0297 (3)
C2	0.2331 (2)	0.45890 (7)	0.64636 (13)	0.0311 (3)
C3	0.2510 (2)	0.45986 (7)	0.45766 (13)	0.0298 (3)
N7	0.2395 (2)	0.58514 (6)	0.05030 (11)	0.0343 (3)
H7	0.2212	0.6293	0.0514	0.041*
N8	0.2790 (2)	0.49104 (6)	0.14883 (11)	0.0317 (3)
N9	0.2400 (2)	0.49152 (6)	−0.04861 (10)	0.0323 (3)
N10	0.2679 (2)	0.58477 (6)	0.23773 (12)	0.0417 (4)
H10A	0.2825	0.5656	0.2996	0.050*
H10B	0.2569	0.6248	0.2357	0.050*
N11	0.2858 (2)	0.40122 (6)	0.04947 (11)	0.0389 (3)
H11A	0.3037	0.3807	0.1100	0.047*
H11B	0.2794	0.3817	−0.0118	0.047*
N12	0.2000 (2)	0.58588 (6)	−0.13740 (12)	0.0422 (4)
H12A	0.1915	0.5670	−0.1994	0.051*
H12B	0.1912	0.6259	−0.1353	0.051*
C4	0.2622 (2)	0.55284 (7)	0.14606 (13)	0.0316 (3)
C5	0.2680 (2)	0.46257 (7)	0.05065 (13)	0.0295 (3)
C6	0.2265 (2)	0.55340 (7)	−0.04541 (13)	0.0311 (3)
P1	0.19791 (7)	0.261583 (19)	0.47846 (4)	0.03450 (13)
H1	0.0215	0.2413	0.4968	0.041*
O1	0.27983 (19)	0.30165 (5)	0.57668 (10)	0.0436 (3)
O2	0.16261 (19)	0.29984 (5)	0.37421 (10)	0.0424 (3)
O3	0.3247 (2)	0.20447 (5)	0.46897 (12)	0.0539 (4)
O4	0.1998 (2)	0.19275 (6)	0.12411 (13)	0.0507 (4)
H41	0.088 (4)	0.1992 (11)	0.111 (2)	0.076*
H42	0.261 (4)	0.2264 (12)	0.143 (2)	0.076*
O5	0.1525 (2)	0.31715 (6)	0.86714 (13)	0.0557 (4)
H51	0.058 (4)	0.3056 (11)	0.900 (2)	0.084*
H52	0.212 (4)	0.2837 (12)	0.845 (2)	0.084*
O6	0.3866 (2)	0.30563 (6)	0.21085 (12)	0.0480 (3)
H61	0.501 (4)	0.3025 (11)	0.229 (2)	0.072*
H62	0.332 (4)	0.3035 (10)	0.272 (2)	0.072*
O7	0.3097 (2)	0.21543 (7)	0.74931 (12)	0.0491 (3)
H71	0.312 (4)	0.2463 (10)	0.699 (2)	0.074*
H72	0.427 (4)	0.2110 (11)	0.783 (2)	0.074*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0426 (8)	0.0275 (6)	0.0281 (7)	−0.0021 (6)	0.0065 (6)	−0.0006 (5)
N2	0.0421 (8)	0.0230 (6)	0.0315 (7)	0.0018 (5)	0.0055 (6)	0.0001 (5)
N3	0.0394 (8)	0.0265 (6)	0.0286 (7)	0.0014 (5)	0.0052 (6)	0.0006 (5)
N4	0.0677 (10)	0.0248 (6)	0.0326 (7)	−0.0009 (6)	0.0092 (7)	−0.0025 (6)
N5	0.0624 (10)	0.0307 (7)	0.0325 (8)	−0.0015 (6)	0.0113 (7)	0.0043 (6)
N6	0.0625 (10)	0.0265 (6)	0.0315 (8)	0.0040 (6)	0.0109 (7)	−0.0020 (6)
C1	0.0311 (8)	0.0280 (7)	0.0297 (8)	0.0000 (6)	0.0031 (6)	0.0003 (6)
C2	0.0316 (8)	0.0295 (7)	0.0321 (9)	−0.0005 (6)	0.0043 (7)	0.0007 (6)
C3	0.0309 (8)	0.0271 (7)	0.0311 (8)	0.0028 (6)	0.0040 (6)	0.0005 (6)
N7	0.0470 (8)	0.0232 (6)	0.0335 (8)	−0.0008 (5)	0.0088 (6)	0.0002 (5)
N8	0.0414 (8)	0.0278 (6)	0.0257 (7)	0.0005 (5)	0.0043 (6)	0.0008 (5)
N9	0.0429 (8)	0.0266 (6)	0.0273 (7)	0.0006 (5)	0.0047 (6)	0.0012 (5)
N10	0.0630 (10)	0.0299 (7)	0.0327 (8)	−0.0008 (6)	0.0085 (7)	−0.0045 (6)
N11	0.0620 (10)	0.0255 (6)	0.0289 (7)	0.0046 (6)	0.0057 (7)	0.0015 (6)
N12	0.0669 (10)	0.0271 (6)	0.0319 (8)	0.0004 (6)	0.0046 (7)	0.0056 (6)
C4	0.0329 (8)	0.0309 (8)	0.0314 (9)	−0.0029 (6)	0.0058 (7)	−0.0014 (7)
C5	0.0321 (8)	0.0283 (7)	0.0285 (8)	0.0001 (6)	0.0053 (6)	0.0010 (6)
C6	0.0358 (8)	0.0270 (7)	0.0308 (8)	−0.0020 (6)	0.0060 (7)	0.0012 (6)
P1	0.0436 (3)	0.0258 (2)	0.0342 (2)	−0.00159 (17)	0.00568 (18)	−0.00082 (17)
O1	0.0623 (8)	0.0311 (6)	0.0351 (7)	0.0025 (5)	−0.0014 (6)	−0.0029 (5)
O2	0.0581 (8)	0.0348 (6)	0.0339 (7)	−0.0022 (5)	0.0056 (6)	0.0002 (5)
O3	0.0670 (9)	0.0262 (6)	0.0694 (10)	0.0037 (6)	0.0131 (7)	−0.0038 (6)
O4	0.0575 (9)	0.0380 (6)	0.0552 (9)	0.0027 (6)	0.0031 (7)	−0.0046 (6)
O5	0.0759 (11)	0.0360 (7)	0.0581 (9)	−0.0046 (7)	0.0193 (8)	−0.0054 (6)
O6	0.0548 (8)	0.0496 (7)	0.0407 (8)	0.0084 (7)	0.0101 (7)	0.0093 (6)
O7	0.0477 (8)	0.0519 (8)	0.0461 (8)	−0.0044 (6)	0.0009 (6)	0.0065 (6)

Geometric parameters (Å, º)

N1—C2	1.3305 (19)	N9—C5	1.3620 (19)
N1—C1	1.3516 (19)	N10—C4	1.318 (2)
N2—C2	1.356 (2)	N10—H10A	0.8600
N2—C3	1.365 (2)	N10—H10B	0.8600
N2—H3	0.9227	N11—C5	1.3192 (19)
N3—C3	1.3351 (19)	N11—H11A	0.8600
N3—C1	1.3502 (19)	N11—H11B	0.8600
N4—C1	1.3248 (19)	N12—C6	1.322 (2)
N4—H4A	0.8600	N12—H12A	0.8600
N4—H4B	0.8600	N12—H12B	0.8600
N5—C2	1.317 (2)	P1—O3	1.5080 (13)
N5—H5A	0.8600	P1—O2	1.5154 (12)
N5—H5B	0.8600	P1—O1	1.5242 (12)
N6—C3	1.309 (2)	P1—H1	1.32
N6—H6A	0.8600	O4—H41	0.76 (3)
N6—H6B	0.8600	O4—H42	0.85 (2)
N7—C6	1.355 (2)	O5—H51	0.84 (3)
N7—C4	1.359 (2)	O5—H52	0.88 (3)
N7—H7	0.9545	O6—H61	0.78 (2)
N8—C4	1.3281 (19)	O6—H62	0.89 (3)
N8—C5	1.3491 (19)	O7—H71	0.91 (2)
N9—C6	1.3292 (19)	O7—H72	0.85 (3)
C2—N1—C1	115.54 (13)	C4—N10—H10A	120.0
C2—N2—C3	119.40 (13)	C4—N10—H10B	120.0
C2—N2—H3	118.3	H10A—N10—H10B	120.0
C3—N2—H3	122.0	C5—N11—H11A	120.0
C3—N3—C1	115.59 (13)	C5—N11—H11B	120.0
C1—N4—H4A	120.0	H11A—N11—H11B	120.0
C1—N4—H4B	120.0	C6—N12—H12A	120.0
H4A—N4—H4B	120.0	C6—N12—H12B	120.0
C2—N5—H5A	120.0	H12A—N12—H12B	120.0
C2—N5—H5B	120.0	N10—C4—N8	120.18 (15)
H5A—N5—H5B	120.0	N10—C4—N7	117.95 (13)
C3—N6—H6A	120.0	N8—C4—N7	121.87 (14)
C3—N6—H6B	120.0	N11—C5—N8	117.79 (14)
H6A—N6—H6B	120.0	N11—C5—N9	116.39 (14)
N4—C1—N3	116.97 (14)	N8—C5—N9	125.81 (13)
N4—C1—N1	116.77 (14)	N12—C6—N9	120.03 (14)
N3—C1—N1	126.25 (13)	N12—C6—N7	117.98 (14)
N5—C2—N1	119.98 (15)	N9—C6—N7	121.98 (14)
N5—C2—N2	118.18 (13)	O3—P1—O2	113.31 (8)
N1—C2—N2	121.83 (14)	O3—P1—O1	111.77 (8)
N6—C3—N3	120.89 (14)	O2—P1—O1	111.54 (7)
N6—C3—N2	117.73 (14)	O3—P1—H1	106.6
N3—C3—N2	121.37 (14)	O2—P1—H1	106.6
C6—N7—C4	119.24 (13)	O1—P1—H1	106.6
C6—N7—H7	121.1	H41—O4—H42	109 (2)
C4—N7—H7	119.4	H51—O5—H52	108 (2)
C4—N8—C5	115.69 (13)	H61—O6—H62	105 (2)
C6—N9—C5	115.36 (13)	H71—O7—H72	108 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H3···O1	0.92	1.80	2.7171 (17)	174
N4—H4A···O4^i	0.86	2.03	2.873 (2)	169
N4—H4B···O7^ii	0.86	2.51	3.335 (2)	162
N5—H5A···N9^iii	0.86	2.14	2.991 (2)	173
N5—H5B···O5	0.86	2.31	2.9200 (19)	128
N6—H6A···N8	0.86	2.19	3.0444 (19)	177
N6—H6B···O2	0.86	1.98	2.8141 (17)	164
N7—H7···O3^i	0.95	1.65	2.5970 (17)	170
N10—H10A···N3	0.86	2.18	3.030 (2)	168
N10—H10B···O4^i	0.86	2.25	2.863 (2)	128
N11—H11A···O6	0.86	2.06	2.8702 (19)	156
N11—H11B···O5^iv	0.86	2.13	2.923 (2)	154
N12—H12A···N1^iv	0.86	2.16	3.006 (2)	168
N12—H12B···O7^i	0.86	2.38	3.0951 (19)	141
O4—H41···O1^v	0.76 (3)	2.07 (3)	2.824 (2)	169 (3)
O4—H42···O6	0.85 (2)	2.02 (3)	2.864 (2)	171 (3)
O5—H51···O3^vi	0.84 (3)	1.91 (3)	2.739 (2)	169 (2)
O5—H52···O7	0.88 (3)	2.05 (3)	2.903 (2)	163 (2)
O6—H61···O7^vii	0.78 (2)	2.11 (2)	2.873 (2)	168 (3)
O6—H62···O2	0.89 (3)	1.82 (3)	2.691 (2)	166 (2)
O7—H71···O1	0.91 (2)	1.91 (2)	2.8046 (19)	169 (2)
O7—H72···O2^viii	0.85 (3)	1.83 (3)	2.6743 (19)	171 (2)

Symmetry codes: (i) −x+1/2, y+1/2, −z+1/2; (ii) −x+1/2, y+1/2, −z+3/2; (iii) x, y, z+1; (iv) x, y, z−1; (v) x−1/2, −y+1/2, z−1/2; (vi) x−1/2, −y+1/2, z+1/2; (vii) x+1/2, −y+1/2, z−1/2; (viii) x+1/2, −y+1/2, z+1/2.