A monoclinic polymorph of pyrazinic acid

The title compound (pyrazine-2-carboxylic acid), C₅H₄N₂O₂, had been previously characterized in space group Pna2₁ and has now been obtained as a monoclinic polymorph crystallizing in space group P2₁. The mol­ecule is almost planar and is connected to symmetry-related mol­ecules through O—H...N and C—H...O hydrogen bonds, and weak π–π inter­actions, giving a three-dimensional network.

Key indicators

• Single-crystal X-ray study
• T = 294 K
• Mean [sigma](C-C) = 0.005 Å
• R factor = 0.037
• wR factor = 0.079
• Data-to-parameter ratio = 6.9

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT066_ALERT_1_C Predicted and Reported Transmissions Identical .          ?
PLAT089_ALERT_3_C Poor Data / Parameter Ratio (Zmax .LT. 18) .....       6.88
PLAT152_ALERT_1_C Supplied and Calc Volume s.u. Inconsistent .....          ?
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....       2.01
PLAT340_ALERT_3_C Low Bond Precision on C-C bonds (x 1000) Ang ...          5

Alert level G
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           26.50
           From the CIF: _reflns_number_total                571
           Count of symmetry unique reflns          575
           Completeness (_total/calc)             99.30%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured         0
           Fraction of Friedel pairs measured     0.000
           Are heavy atom types Z>Si present         no

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   5 ALERT level C = Check and explain
   1 ALERT level G = General alerts; check

   2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion

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S1. Comment

Pyrazinic acid (pyrazine-2-carboxylic acid) is one of the most important materials for the preparation of pyrazine derivatives of pyrazinoyl chloride and pyrazinamide. Some pyrazine derivatives possess bacteriostatic activity. They are widely used in the treatment of tuberculosis and also exhibit fungicidal activity (Kushner et al., 1952). We have designed and synthesized a number of compounds for testing their effective antibacterial activity compared with that of pyrazinic acid. When recrystallizing a commercial impure batch of the title molecule, (I), we get single crystals of a new monoclinic polymorph for this compound.

The title compound, C₅H₄N₂O₂, crystallizes in space group P2₁ with the expected geometry (Table 1). The molecule is almost planar. A weak intramolecular hydrogen bond involves the C3/H3 and hydroxy groups (Fig. 1). Atom N2 of the pyrazine ring is connected to atom H1 of the hydroxy group, while atom H3 is linked to atom O2 of the carbonyl group (Table 2). As a result, molecules form zigzag chains along the [010] axis. Between two neighbouring zigzag chains, carboxylic O2 atoms interact with atoms H2 of the pyrazine rings to form C—H···O hydrogen bonds (Table 2). These hydrogen bonds further extend the one-dimensional zigzag chains along the bc plane, forming a quasi-two-dimensional network, as illustrated in Fig. 2.

In addition, face-to-face π–π stacking interactions are observed in the crystal, with a separation of ca 3.36 Å between the centroids of the pyrazine rings (Fig. 3). The complete crystal structure presents a different topology from that of the previously reported orthorhombic polymorph (Tukusagawa et al., 1974).

S2. Experimental

The title compound was obtained by recrystallization of an impure batch of this compound. The crystal used for data collection was obtained by slow evaporation at 298 K of a methanol solution, over a period of one week.

S3. Refinement

C bound H atoms were placed in calculated positions and allowed to ride on their parent atoms, with C—H distances constrained to 0.93 Å and U_iso(H) = 1.2U_eq(parent C atom). The H atom of the hydroxy group was found in a difference map and refined with the O—H distance constrained to 0.82 Å and U_iso(H) = 1.5U_eq(O). In the absence of significant anomalous scattering effects, measured Friedel pairs were merged.

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SAINT (Bruker, 1997); 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, 1997); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The molecular structure of (I), showing 30% probability displacement ellipsoids. H atoms are drawn as small spheres of arbitrary radii. The dashed line indicates the intramolecular hydrogen bond.
	Fig. 2. The one-dimensional zigzag chains and two-dimensional structure of compound (I), formed by O—H···N and C—H···O hydrogen bonds (dashed lines) between adjacent molecules.
	Fig. 3. The packing of (I) viewed along the b axis, showing the layered structure. Dashed lines indicate hydrogen bonds.

pyrazine-2-carboxylic acid

Crystal data

C5H4N2O2	F(000) = 128
Mr = 124.10	Dx = 1.558 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2yb	Cell parameters from 477 reflections
a = 3.7249 (14) Å	θ = 3.5–23.7°
b = 11.281 (4) Å	µ = 0.12 mm^−1
c = 6.298 (2) Å	T = 294 K
β = 91.936 (7)°	Plate, colourless
V = 264.48 (18) Å^3	0.30 × 0.16 × 0.10 mm
Z = 2

Data collection

Bruker SMART CCD area-detector diffractometer	571 independent reflections
Radiation source: fine-focus sealed tube	440 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.037
ϕ and ω scans	θmax = 26.5°, θmin = 3.2°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −4→4
Tmin = 0.962, Tmax = 0.988	k = −14→6
1501 measured reflections	l = −7→7

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: inferred from neighbouring sites
wR(F^2) = 0.079	H-atom parameters constrained
S = 1.07	w = 1/[σ^2(Fo^2) + (0.032P)^2 + 0.0353P] where P = (Fo^2 + 2Fc^2)/3
571 reflections	(Δ/σ)max = 0.002
83 parameters	Δρmax = 0.14 e Å^−3
1 restraint	Δρmin = −0.18 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
O1	0.5363 (7)	0.1006 (2)	0.4275 (3)	0.0448 (7)
H1	0.6043	0.0385	0.3744	0.067*
O2	0.2901 (7)	−0.0206 (2)	0.6633 (4)	0.0514 (9)
N1	0.1339 (7)	0.1712 (2)	0.9153 (4)	0.0389 (8)
N2	0.2844 (7)	0.3970 (2)	0.7595 (4)	0.0354 (7)
C1	0.0647 (9)	0.2716 (4)	1.0242 (6)	0.0405 (9)
H1A	−0.0381	0.2652	1.1563	0.049*
C2	0.1399 (8)	0.3820 (3)	0.9478 (5)	0.0374 (8)
H2	0.0887	0.4482	1.0294	0.045*
C3	0.3559 (8)	0.2983 (3)	0.6483 (5)	0.0343 (8)
H3	0.4584	0.3054	0.5163	0.041*
C4	0.2812 (9)	0.1876 (3)	0.7253 (6)	0.0294 (7)
C5	0.3672 (9)	0.0771 (3)	0.6041 (5)	0.0342 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0725 (16)	0.0214 (11)	0.0421 (14)	0.0013 (13)	0.0255 (12)	−0.0038 (11)
O2	0.078 (2)	0.0279 (14)	0.0505 (17)	−0.0045 (15)	0.0307 (16)	0.0017 (13)
N1	0.0465 (16)	0.0352 (19)	0.0357 (14)	0.0023 (15)	0.0104 (13)	0.0031 (14)
N2	0.0453 (15)	0.0243 (16)	0.0374 (16)	0.0001 (13)	0.0106 (13)	−0.0027 (12)
C1	0.048 (2)	0.043 (2)	0.0310 (18)	0.000 (2)	0.0082 (16)	−0.0014 (18)
C2	0.0439 (18)	0.029 (2)	0.0403 (19)	0.0030 (18)	0.0079 (15)	−0.0092 (17)
C3	0.040 (2)	0.0281 (19)	0.0354 (19)	0.0027 (18)	0.0106 (15)	0.0006 (16)
C4	0.0336 (15)	0.0261 (15)	0.0289 (19)	−0.0013 (18)	0.0058 (13)	−0.0004 (16)
C5	0.0396 (19)	0.0267 (19)	0.0368 (19)	−0.0004 (18)	0.0078 (14)	−0.0019 (16)

Geometric parameters (Å, º)

O1—C5	1.324 (4)	C1—C2	1.368 (5)
O1—H1	0.8200	C1—H1A	0.9300
O2—C5	1.201 (4)	C2—H2	0.9300
N1—C4	1.346 (4)	C3—C4	1.372 (5)
N1—C1	1.354 (5)	C3—H3	0.9300
N2—C2	1.329 (4)	C4—C5	1.502 (4)
N2—C3	1.346 (4)
C5—O1—H1	109.5	N2—C3—C4	121.5 (3)
C4—N1—C1	115.2 (3)	N2—C3—H3	119.2
C2—N2—C3	116.9 (3)	C4—C3—H3	119.2
N1—C1—C2	122.6 (3)	N1—C4—C3	122.2 (3)
N1—C1—H1A	118.7	N1—C4—C5	116.0 (3)
C2—C1—H1A	118.7	C3—C4—C5	121.8 (3)
N2—C2—C1	121.6 (3)	O2—C5—O1	124.8 (3)
N2—C2—H2	119.2	O2—C5—C4	123.1 (3)
C1—C2—H2	119.2	O1—C5—C4	112.1 (3)
C4—N1—C1—C2	−0.3 (5)	N2—C3—C4—N1	−0.2 (5)
C3—N2—C2—C1	−0.5 (5)	N2—C3—C4—C5	−178.7 (3)
N1—C1—C2—N2	0.5 (6)	N1—C4—C5—O2	4.8 (4)
C2—N2—C3—C4	0.4 (4)	C3—C4—C5—O2	−176.5 (4)
C1—N1—C4—C3	0.1 (4)	N1—C4—C5—O1	−175.0 (3)
C1—N1—C4—C5	178.7 (3)	C3—C4—C5—O1	3.6 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···N2^i	0.82	1.86	2.676 (3)	175
C2—H2···O2^ii	0.93	2.46	3.168 (4)	133
C3—H3···O1	0.93	2.40	2.725 (4)	101
C3—H3···O2^iii	0.93	2.47	3.152 (4)	131

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