A monoclinic polymorph of hypoxanthine

A monoclinic polymorph of hypoxanthine (systematic name: 1,7-dihydro-6H-purin-6-one), C₅H₄N₄O, is reported. The hydrogen-bonding motifs involve a layered structure of N—H...O and N—H...N hydrogen-bonded mol­ecules. The mean stacking distance between adjacent layers is 3.672 Å.

Key indicators

• Single-crystal X-ray study
• T = 292 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.036
• wR factor = 0.109
• Data-to-parameter ratio = 12.1

checkCIF/PLATON results

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PLAT125_ALERT_4_C No _symmetry_space_group_name_Hall Given .......          ?
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....       2.57

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   0 ALERT level B = Potentially serious problem
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S1. Comment

A triclinic polymorph of hypoxanthine (I) has been reported (Schmalle et al., 1988). Here we describe a monoclinic polymorph (Figure1). There are two hydrogen bonds of the type N1—H1···O1ⁱ with N1—O1ⁱ donor-acceptor distance of 2.7846 (18) Å and N4—H4···N3ⁱⁱ with N4—N3ⁱⁱ donor-acceptor distance of 2.8208 (19) Å (Figure 2). In addition, there are different weak intermolecular contacts (Taylor & Kennard,1982) of the form C2—H2···N2ⁱⁱⁱ with C2—N2ⁱⁱⁱ distance of 3.376 (2) Å and C5—H5···O1ⁱⁱ with C5—O1ⁱⁱ distance of 3.1933 (19) Å (Table 1). Thus, the hypoxanthine molecules form sheets approximately parallel to the (102) plane. The separations between parallel hypoxanthine molecules stacked along the a axis is 3.672 Å (Figure 3).

Related literature

The triclinic polymorph of hypoxanthine was described by Schmalle et al. (1988). There are different weak intermolecular contacts of the form C2—H2···N2ⁱⁱⁱ and C5—H5···O1ⁱⁱ (Taylor & Kennard, 1982).

S2. Experimental

Hydrothermal treatment of Ba(ClO₄)₂.6H₂O(0.1332 g, 0.3 mmol), Inosine(0.1610 g, 0.6 mmol), And 95% ethanol solution(4 ml) over three days at 70 ^oC yielded colorless plate crystals of hypoxanthine(I). The product was isolated, washed three times with 70% ethanol solution, and dried in a vacuum desiccator using CaCl₂. Yield: 15%. CH&N analysis: Calculated for C₅H₄N₄O: C 44.12, H 2.96, N 41.16%; found: C 44.05, H 2.93, N 41.04%.

S3. Refinement

H atoms bonded to C or N atoms were placed in calculated positions, with C—H = 0.95 Å and N—H= 0.88 Å, and were included in the refinement in the riding-model approximation, and U_iso(H) = 1.2U_eq(C or N).

Computing details

Data collection: SMART (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 2004); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The asymmetric unit of compound (I), with displacement ellipsoids drawn at the 30% probability level.
	Fig. 2. The hydrogen-bonding motif in (I). Dashed lines indicate the hydrogen bonds.
	Fig. 3. The packing of (I) in the crystal.

1,7-dihydro-6H-purin-6-one

Crystal data

C5H4N4O	Z = 4
Mr = 136.12	F(000) = 280
Monoclinic, P21/c	Dx = 1.595 Mg m^−3
a = 3.6725 (19) Å	Mo Kα radiation, λ = 0.71073 Å
b = 17.960 (9) Å	µ = 0.12 mm^−1
c = 9.010 (5) Å	T = 292 K
β = 107.469 (19)°	Plate, colorless
V = 566.9 (5) Å^3	0.48 × 0.13 × 0.11 mm

Data collection

Bruker SMART APEXII CCD area-detector diffractometer	1113 independent reflections
Radiation source: fine-focus sealed tube	964 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.016
φ and ω scans	θmax = 26.0°, θmin = 2.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −4→4
Tmin = 0.979, Tmax = 0.988	k = −22→21
2981 measured reflections	l = −6→11

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)] = 0.036	H-atom parameters constrained
wR(F^2) = 0.109	w = 1/[σ^2(Fo^2) + (0.0758P)^2 + 0.069P] where P = (Fo^2 + 2Fc^2)/3
S = 1.04	(Δ/σ)max < 0.001
1113 reflections	Δρmax = 0.19 e Å^−3
92 parameters	Δρmin = −0.19 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.067 (11)

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
O1	0.5544 (3)	0.40375 (5)	0.51583 (12)	0.0469 (3)
N1	0.1515 (3)	0.46886 (6)	0.31417 (13)	0.0374 (3)
H1	0.2213	0.5107	0.3658	0.045*
N2	−0.2451 (3)	0.41739 (6)	0.08071 (13)	0.0388 (3)
N3	0.2692 (3)	0.26683 (6)	0.31153 (13)	0.0367 (3)
N4	−0.1664 (3)	0.28307 (6)	0.08049 (13)	0.0377 (3)
H4	−0.3275	0.2721	−0.0109	0.045*
C1	0.3174 (4)	0.40330 (7)	0.38534 (16)	0.0339 (3)
C2	−0.1094 (4)	0.47339 (8)	0.17154 (16)	0.0395 (4)
H2	−0.2006	0.5216	0.1350	0.047*
C3	−0.0906 (4)	0.35170 (7)	0.14506 (15)	0.0329 (3)
C4	0.1784 (3)	0.34128 (7)	0.28815 (14)	0.0317 (3)
C5	0.0550 (4)	0.23473 (8)	0.18446 (16)	0.0394 (4)
H5	0.0552	0.1826	0.1670	0.047*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0569 (7)	0.0343 (6)	0.0312 (6)	−0.0004 (4)	−0.0145 (5)	−0.0024 (4)
N1	0.0449 (7)	0.0273 (6)	0.0308 (7)	0.0004 (4)	−0.0026 (5)	0.0000 (4)
N2	0.0406 (6)	0.0380 (7)	0.0284 (6)	0.0014 (5)	−0.0038 (5)	0.0046 (5)
N3	0.0422 (6)	0.0294 (6)	0.0289 (6)	0.0001 (4)	−0.0039 (5)	0.0000 (4)
N4	0.0407 (6)	0.0380 (7)	0.0233 (6)	−0.0042 (4)	−0.0075 (5)	−0.0041 (4)
C1	0.0358 (6)	0.0322 (7)	0.0261 (7)	−0.0012 (5)	−0.0023 (5)	0.0016 (5)
C2	0.0429 (7)	0.0355 (7)	0.0318 (8)	0.0036 (5)	−0.0013 (6)	0.0062 (5)
C3	0.0340 (6)	0.0348 (7)	0.0244 (7)	−0.0014 (5)	0.0004 (5)	0.0012 (5)
C4	0.0338 (7)	0.0299 (7)	0.0247 (7)	−0.0005 (5)	−0.0014 (5)	0.0018 (5)
C5	0.0446 (8)	0.0320 (7)	0.0317 (8)	−0.0016 (5)	−0.0035 (6)	−0.0029 (5)

Geometric parameters (Å, º)

O1—C1	1.2352 (17)	N4—C5	1.3546 (17)
N1—C2	1.3553 (18)	N4—C3	1.3557 (17)
N1—C1	1.3908 (17)	N4—H4	0.8800
N1—H1	0.8800	C1—C4	1.4141 (18)
N2—C2	1.2980 (18)	C2—H2	0.9500
N2—C3	1.3612 (17)	C3—C4	1.3815 (19)
N3—C5	1.3118 (17)	C5—H5	0.9500
N3—C4	1.3788 (18)
C2—N1—C1	125.10 (11)	N2—C2—H2	117.3
C2—N1—H1	117.4	N1—C2—H2	117.3
C1—N1—H1	117.4	N4—C3—N2	126.84 (12)
C2—N2—C3	111.78 (12)	N4—C3—C4	105.93 (11)
C5—N3—C4	103.81 (11)	N2—C3—C4	127.22 (12)
C5—N4—C3	106.41 (11)	N3—C4—C3	110.26 (11)
C5—N4—H4	126.8	N3—C4—C1	130.06 (12)
C3—N4—H4	126.8	C3—C4—C1	119.69 (12)
O1—C1—N1	121.29 (11)	N3—C5—N4	113.58 (13)
O1—C1—C4	127.93 (11)	N3—C5—H5	123.2
N1—C1—C4	110.78 (12)	N4—C5—H5	123.2
N2—C2—N1	125.43 (13)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1^i	0.88	1.91	2.7846 (18)	172
N4—H4···N3^ii	0.88	1.95	2.8208 (19)	168
C2—H2···N2^iii	0.95	2.60	3.376 (2)	139
C5—H5···O1^ii	0.95	2.48	3.1933 (19)	132

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