Two new polymorphs of 2,6-diamino­pyrimidin-4(3H)-one monohydrate

The title compound, C₄H₆N₄O·H₂O, crystallized simultaneously as a triclinic and a monoclinic polymorph from an aqueous solution of 2,4-diamino­pyrimidin-6-ol. Previously, an ortho­rhom­bic polymorph was isolated under the same experimental conditions. The mol­ecular geometric parameters in the two present polymorphs and the previously reported ortho­rhom­bic polymorph are similar, but the structures differ in the details of their crystal packing. In the triclinic system, the diamino­pyrimidinone mol­ecules are connected to one another via N—H...O and N—H...N hydrogen bonding to form infinite chains in the [011] direction. The chains are further hydrogen bonded to the water mol­ecules, resulting in a three-dimensional network. In the monoclinic system, the diamino­pyrimidinone mol­ecules are hydrogen bonded together into two-dimensional networks parallel to the bc plane. The water mol­ecules link the planes to form a three-dimensional polymeric structure.

S1. Comment

Diaminopyrimidines are a class of organic compounds with interesting biological properties (Desharnais et al., 2003) and applications in supramolecular chemistry (Yagai, 2006). Some years ago Skoweranda et al. (1990) reported the crystal structure of 2,6-diamino-4-oxo-3,4-dihydropyrimidinone, cocrystallized with one molecule of water, in an orthorhombic crystal system, (I). During our studies on the crystallization behavior of 2,4-diamino-6-hydroxypyrimidine, we obtained two new polymorphs of the reported compound in triclinic, (II), and monoclinic, (III), systems. Our subsequent efforts to get the orthorhombic form all failed, and therefore it can be regarded as a disappearing polymorph. In fact, recrystallization of 2,4-diamino-6-hydroxypyrimidine from an aqueous solution, the condition which was used by Skoweranda et al., led to concomitant formation of the triclinic and monoclinic crystals.

The thermal ellipsoid drawing of the three polymorphs is given in Fig. 1. In the three polymorphs, the molecules form three-dimensional hydrogen-bonded networks, however with different hydrogen-bond systems. In contrast to the orthorhombic polymorph, (I), in which the water molecules are hydrogen bonded together into infinite chains along the a axis, there is no interaction between the water molecules in the two present polymorphs. Moreover, polymorph (I) shows N4—H4B···N4 hydrogen bonding (Fig. 2) which was not observed in polymorphs (II) and (III). In polymorph (II) the adjacent diaminopyrimidinone molecules are connected to one another via N—H···O and N—H···N hydrogen bonding around centers of inversion to form parallel infinite chains in the [0 1 1] direction. The water molecule has five hydrogen-bonding interactions that involve five different neighboring pyrimidinone molecules (Fig. 3). As a result, the pyrimidinone chains are linked into a three-dimensional network.

In polymorph (III) each two diaminopyrimidinone molecules is N—H···N hydrogen bonded together around centers of inversion. The resulting dimers are further connected together around twofold screw axes along b via N3—H3···O2 hydrogen bonding in a bifurcated system to form two-dimensional networks parallel to the bc plane. The water molecule is engaged in five hydrogen-bonding interactions with five neighboring pyrimidinone molecules (Fig. 4), resulting in a three-dimensional hydrogen-bonded network. Fig. 5 represents the stereoviews of polymorphs (II) and (III).

In both polymorphs, weak π–π stacking occurs between the planar molecules in the direction of the shortest crystallographic axis. The diaminopyrimidinone molecule, including all hydrogen atoms, in the three polymorphs is almost planar [r.m.s deviation: (I) 0.049 Å, (II) 0.031 Å, (III) 0.053 Å] and the bond lengths and angles are similar (Tables 1 and 3). The amino groups do not appear to be pyramidalized to within the uncertainty of the structure determinations. For (II), the sums of the angles at nitrogen are 359.3 (14) and 359.4 (15)° for N2 and N4, respectively, whereas for (III) the corresponding values are 359 (2) and 356 (2)°. Polymorph (III) does exhibit slightly greater deviations than (II) of the NH₂ groups from the least-squares planes of the pyrimidinone molecule. These displacements are of opposite sign for the N2 and N4 groups in both polymorphs. The density of the monoclinic polymorph (1.538 Mg m^-3) is greater than that of the triclinic structure (1.492 Mg m^-3) which might be indicative of higher thermodynamic stability of the monoclinic system (Burger & Ramberger, 1979). The density of polymorph (I) was reported to be 1.476 Mg m^-3; however the data were collected at 293 K.

Related literature

For related literature, see: Burger & Ramberger (1979); Desharnais et al. (2003); Skoweranda et al. (1990); Yagai (2006).

S2. Experimental

A portion of commercially available 2,4-diaminopyrimidin-6-ol (0.6 g) was dissolved in distilled water (10 ml) by heating and stirring. The resulting solution was then left at room temperature. In less than an hour, crystals of polymorphs (II) and (III) were obtained simultaneously.

S3. Refinement

The C-bound H atoms were placed in idealized locations (C—H = 0.95 Å) and refined as riding on their parent carbon atoms. The nitrogen- and oxygen-bound H atoms were located in a difference Fourier map and were refined with distance restraints of N—H 0.88 (2) and O—H 0.84 (2) Å. U(H) were set to 1.2U_eq (parent atom).

Computing details

For both compounds, data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. The asymmetric units of the three polymorphs of the title compound, showing the atom-numbering scheme selected to conform to polymorph (I). Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. The position of the hydrate molecule has been selected in order to show the shortest hydrogen-bonding interaction between the hydrate and atom O2. The O1···O2 distances are displayed. The structure of polymorph (I) was determined at 293 K, whereas the data of polymorphs (II) and (III) were collected at 100 K.
	Fig. 2. A view of the hydrogen-bonding interactions in polymorph (I). [Symmetry codes: (i) -x+1, y+1/2, -z+1/2; (ii) x, -y-1/2, z+1/2; (iii) -x+1/2, -y, z+1/2; (iv) -x+1/2, y-1/2, z; (v) -x+1, -y-1, -z.]
	Fig. 3. A view of the hydrogen-bonding interactions in polymorph (II). [Symmetry codes: (i) x-1, y, z; (ii) -x+2, -y+1, -z+1; (iii) x-1, y-1, z; (iv) -x+1, -y+1, -z.]
	Fig. 4. A view of the hydrogen-bonding interactions in polymorph (III). [Symmetry codes: (i) x, y+1, z; (ii) -x+1/2, y+3/2, -z+1/2; (iii) x, -y+1, z+1/2; (iv) -x+1, y, -z+1/2; (v) <-x+1, y+1, -z+1/2.]
	Fig. 5. Stereoviews of polymorphs (II) and (III). The stacking of the planar molecules is only shown at the periphery of the figure in order to focus on the hydrogen-bonding patterns in the immediate vicinity of the title molecule. The view is selected such that the title molecules are placed in the same orientation. The stacking motif is in the direction of the shortest axial length, namely the a axis in (II) and the b axis in (III).

(II) 2,6-diaminopyrimidin-4(3H)-one monohydrate

Crystal data

C4H6N4O·H2O	Z = 2
Mr = 144.14	F(000) = 152
Triclinic, P1	Dx = 1.492 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 3.9293 (3) Å	Cell parameters from 1370 reflections
b = 8.6611 (7) Å	θ = 3.0–30.3°
c = 9.6044 (8) Å	µ = 0.12 mm^−1
α = 83.111 (5)°	T = 100 K
β = 88.090 (6)°	Block, colorless
γ = 81.479 (6)°	0.45 × 0.35 × 0.13 mm
V = 320.88 (4) Å^3

Data collection

Bruker APEXII CCD diffractometer	1113 independent reflections
Radiation source: fine-focus sealed tube	996 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.017
ϕ and ω scans	θmax = 25.1°, θmin = 2.4°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −4→4
Tmin = 0.948, Tmax = 0.984	k = −10→10
2138 measured reflections	l = −11→11

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)] = 0.036	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.112	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ^2(Fo^2) + (0.073P)^2 + 0.0912P] where P = (Fo^2 + 2Fc^2)/3
1113 reflections	(Δ/σ)max < 0.001
112 parameters	Δρmax = 0.20 e Å^−3
7 restraints	Δρmin = −0.26 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
O2	0.8723 (3)	0.42708 (12)	0.35218 (11)	0.0178 (3)
N1	1.0531 (3)	0.85718 (15)	0.16673 (13)	0.0163 (3)
N2	1.2801 (3)	0.89049 (16)	0.37701 (14)	0.0185 (4)
H2A	1.345 (5)	0.856 (2)	0.4627 (17)	0.022*
H2B	1.344 (4)	0.9798 (19)	0.3378 (19)	0.022*
N3	1.0696 (3)	0.65930 (14)	0.35786 (13)	0.0153 (3)
H3	1.105 (4)	0.632 (2)	0.4461 (16)	0.018*
N4	0.8325 (4)	0.82005 (17)	−0.04094 (14)	0.0227 (4)
H4A	0.877 (5)	0.914 (2)	−0.072 (2)	0.027*
H4B	0.713 (5)	0.772 (2)	−0.0924 (19)	0.027*
C2	1.1329 (4)	0.80288 (17)	0.29798 (16)	0.0151 (4)
C4	0.9195 (4)	0.55938 (17)	0.28491 (16)	0.0154 (4)
C5	0.8382 (4)	0.61166 (19)	0.14700 (16)	0.0178 (4)
H5	0.7390	0.5475	0.0908	0.021*
C6	0.9056 (4)	0.76208 (19)	0.09153 (16)	0.0171 (4)
O1	0.4541 (3)	0.21283 (13)	0.32544 (12)	0.0204 (3)
H1A	0.602 (5)	0.274 (2)	0.319 (2)	0.025*
H1B	0.269 (4)	0.271 (2)	0.3414 (19)	0.025*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O2	0.0224 (6)	0.0142 (6)	0.0169 (6)	−0.0062 (4)	−0.0023 (4)	0.0030 (4)
N1	0.0191 (7)	0.0153 (7)	0.0142 (7)	−0.0038 (5)	−0.0005 (5)	0.0014 (5)
N2	0.0273 (7)	0.0148 (7)	0.0138 (7)	−0.0075 (6)	−0.0046 (6)	0.0032 (5)
N3	0.0194 (7)	0.0148 (7)	0.0113 (7)	−0.0036 (5)	−0.0015 (5)	0.0019 (5)
N4	0.0367 (8)	0.0191 (7)	0.0143 (7)	−0.0134 (6)	−0.0065 (6)	0.0029 (5)
C2	0.0147 (7)	0.0140 (8)	0.0158 (8)	−0.0021 (6)	0.0018 (6)	0.0008 (6)
C4	0.0145 (7)	0.0137 (7)	0.0178 (8)	−0.0026 (6)	0.0016 (6)	−0.0004 (6)
C5	0.0197 (8)	0.0183 (8)	0.0162 (8)	−0.0064 (6)	−0.0011 (6)	−0.0006 (6)
C6	0.0171 (7)	0.0181 (8)	0.0157 (8)	−0.0032 (6)	0.0006 (6)	−0.0002 (6)
O1	0.0206 (6)	0.0161 (6)	0.0251 (6)	−0.0057 (5)	−0.0024 (5)	−0.0002 (5)

Geometric parameters (Å, º)

O2—C4	1.2815 (18)	N4—C6	1.335 (2)
N1—C2	1.322 (2)	N4—H4A	0.876 (16)
N1—C6	1.359 (2)	N4—H4B	0.874 (15)
N2—C2	1.336 (2)	C4—C5	1.379 (2)
N2—H2A	0.874 (15)	C5—C6	1.406 (2)
N2—H2B	0.885 (15)	C5—H5	0.9500
N3—C2	1.360 (2)	O1—H1A	0.837 (15)
N3—C4	1.383 (2)	O1—H1B	0.841 (15)
N3—H3	0.863 (15)
C2—N1—C6	117.07 (13)	N2—C2—N3	117.60 (14)
C2—N2—H2A	121.9 (13)	O2—C4—C5	126.64 (14)
C2—N2—H2B	119.1 (12)	O2—C4—N3	116.60 (13)
H2A—N2—H2B	118.3 (18)	C5—C4—N3	116.76 (14)
C2—N3—C4	122.12 (13)	C4—C5—C6	118.48 (15)
C2—N3—H3	119.7 (12)	C4—C5—H5	120.8
C4—N3—H3	118.0 (12)	C6—C5—H5	120.8
C6—N4—H4A	119.1 (13)	N4—C6—N1	115.37 (14)
C6—N4—H4B	120.7 (13)	N4—C6—C5	121.59 (15)
H4A—N4—H4B	119.6 (19)	N1—C6—C5	123.04 (14)
N1—C2—N2	119.89 (14)	H1A—O1—H1B	104.1 (18)
N1—C2—N3	122.51 (14)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1A···O2	0.84 (2)	1.88 (2)	2.6935 (15)	163 (2)
O1—H1B···O2^i	0.84 (2)	1.92 (2)	2.7485 (16)	170 (2)
N4—H4B···O1^ii	0.87 (2)	2.34 (2)	3.0501 (18)	139 (2)
N4—H4A···N1^iii	0.88 (2)	2.13 (2)	3.0004 (19)	173 (2)
N2—H2B···O1^iv	0.89 (2)	2.12 (2)	2.9527 (17)	158 (2)
N2—H2A···O1^v	0.87 (2)	2.19 (2)	3.0605 (18)	174 (2)
N3—H3···O2^v	0.86 (2)	1.95 (2)	2.8035 (17)	173 (2)

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

(III) 2,6-diaminopyrimidin-4(3H)-one monohydrate

Crystal data

C4H6N4O·H2O	F(000) = 608
Mr = 144.14	Dx = 1.538 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 353 reflections
a = 17.236 (11) Å	θ = 2.4–22.9°
b = 3.987 (3) Å	µ = 0.13 mm^−1
c = 18.717 (12) Å	T = 100 K
β = 104.450 (9)°	Lath, colorless
V = 1245.4 (14) Å^3	0.30 × 0.07 × 0.04 mm
Z = 8

Data collection

Bruker APEXII CCD diffractometer	1131 independent reflections
Radiation source: fine-focus sealed tube	757 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.055
ϕ and ω scans	θmax = 25.2°, θmin = 2.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −20→20
Tmin = 0.964, Tmax = 0.995	k = −3→4
2752 measured reflections	l = −22→21

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)] = 0.056	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.148	H atoms treated by a mixture of independent and constrained refinement
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0775P)^2] where P = (Fo^2 + 2Fc^2)/3
1131 reflections	(Δ/σ)max = 0.001
112 parameters	Δρmax = 0.28 e Å^−3
7 restraints	Δρmin = −0.37 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
O2	0.35162 (12)	0.3762 (5)	0.27734 (11)	0.0264 (6)
N1	0.32226 (15)	0.0450 (6)	0.06546 (12)	0.0211 (6)
N2	0.21025 (16)	−0.2299 (7)	0.08148 (14)	0.0241 (7)
H2A	0.1826 (16)	−0.305 (8)	0.1124 (15)	0.029*
H2B	0.2024 (18)	−0.327 (7)	0.0369 (12)	0.029*
N3	0.28471 (15)	0.0795 (6)	0.17834 (13)	0.0214 (6)
H3	0.2443 (14)	0.034 (8)	0.1980 (16)	0.026*
N4	0.43543 (17)	0.3218 (7)	0.05329 (14)	0.0262 (7)
H4A	0.4180 (18)	0.270 (8)	0.0079 (11)	0.031*
H4B	0.4732 (16)	0.477 (7)	0.0704 (16)	0.031*
C2	0.27324 (18)	−0.0356 (8)	0.10741 (15)	0.0200 (7)
C4	0.34835 (17)	0.2802 (7)	0.21173 (15)	0.0205 (7)
C5	0.40169 (18)	0.3600 (8)	0.16933 (16)	0.0241 (7)
H5	0.4481	0.4903	0.1895	0.029*
C6	0.38555 (18)	0.2447 (7)	0.09648 (15)	0.0216 (7)
O1	0.43094 (14)	0.7970 (6)	0.38734 (14)	0.0364 (7)
H1A	0.412 (2)	0.699 (9)	0.3477 (14)	0.044*
H1B	0.453 (2)	0.970 (7)	0.376 (2)	0.044*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O2	0.0349 (13)	0.0343 (14)	0.0112 (10)	0.0033 (11)	0.0084 (9)	−0.0002 (9)
N1	0.0269 (14)	0.0237 (15)	0.0139 (13)	0.0056 (12)	0.0073 (11)	0.0036 (10)
N2	0.0304 (15)	0.0286 (17)	0.0155 (13)	−0.0001 (12)	0.0098 (12)	0.0001 (11)
N3	0.0247 (14)	0.0264 (16)	0.0155 (13)	0.0020 (12)	0.0096 (11)	0.0029 (10)
N4	0.0314 (16)	0.0330 (17)	0.0172 (13)	0.0031 (13)	0.0120 (13)	0.0045 (12)
C2	0.0235 (16)	0.0245 (17)	0.0120 (15)	0.0089 (14)	0.0043 (13)	0.0054 (12)
C4	0.0223 (16)	0.0219 (17)	0.0176 (16)	0.0069 (13)	0.0056 (13)	0.0051 (12)
C5	0.0240 (16)	0.0300 (18)	0.0188 (16)	0.0019 (15)	0.0062 (13)	0.0046 (13)
C6	0.0240 (16)	0.0238 (18)	0.0194 (16)	0.0104 (13)	0.0101 (13)	0.0079 (13)
O1	0.0366 (15)	0.0299 (15)	0.0463 (16)	−0.0099 (12)	0.0174 (13)	−0.0100 (12)

Geometric parameters (Å, º)

O2—C4	1.274 (4)	N4—C6	1.354 (4)
N1—C2	1.328 (4)	N4—H4A	0.852 (18)
N1—C6	1.358 (4)	N4—H4B	0.897 (18)
N2—C2	1.323 (4)	C4—C5	1.393 (4)
N2—H2A	0.890 (18)	C5—C6	1.400 (4)
N2—H2B	0.898 (18)	C5—H5	0.9500
N3—C2	1.371 (4)	O1—H1A	0.828 (18)
N3—C4	1.375 (4)	O1—H1B	0.835 (19)
N3—H3	0.883 (18)
C2—N1—C6	116.8 (2)	N1—C2—N3	122.1 (3)
C2—N2—H2A	119 (2)	O2—C4—N3	116.8 (3)
C2—N2—H2B	121 (2)	O2—C4—C5	127.1 (3)
H2A—N2—H2B	119 (3)	N3—C4—C5	116.0 (3)
C2—N3—C4	122.7 (3)	C4—C5—C6	118.7 (3)
C2—N3—H3	113 (2)	C4—C5—H5	120.6
C4—N3—H3	123 (2)	C6—C5—H5	120.6
C6—N4—H4A	115 (2)	N4—C6—N1	116.1 (3)
C6—N4—H4B	117 (2)	N4—C6—C5	120.4 (3)
H4A—N4—H4B	124 (3)	N1—C6—C5	123.5 (3)
N2—C2—N1	120.6 (3)	H1A—O1—H1B	106 (4)
N2—C2—N3	117.2 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2A···O2^i	0.89 (2)	2.39 (3)	3.115 (4)	138 (3)
N2—H2A···O1^ii	0.89 (2)	2.52 (2)	3.245 (4)	139 (3)
N2—H2B···N1^iii	0.90 (2)	2.05 (2)	2.947 (4)	177 (3)
N3—H3···O2^i	0.88 (2)	1.93 (2)	2.800 (3)	168 (3)
N4—H4A···O1^iv	0.85 (2)	2.34 (2)	3.124 (4)	154 (3)
N4—H4B···O1^v	0.90 (2)	2.08 (2)	2.975 (4)	174 (3)
O1—H1A···O2	0.83 (2)	1.95 (2)	2.742 (3)	160 (4)
O1—H1B···N4^vi	0.84 (2)	2.48 (3)	3.105 (4)	133 (3)

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