The title compound, C
6H
4N
2O
4, is a new unsolvated form of pyrazine-2,3-dicarboxylic acid. The asymmetric unit contains two independent molecules with different geometry. The planes of the carboxylic groups make dihedral angles with the planar pyrazine rings of 22.7 (2) and 50.0 (2)° in one molecule, and 9.7 (2) and 79.1 (2)° in the other. The molecules form layers in which hydrogen bonds occur, with O
O distances ranging from 2.728 (2) to 2.773 (2) Å. The shortest distance between two adjacent layers is 3.5 Å, indicating van der Waals interactions.
Supporting information
CCDC reference: 230702
Key indicators
- Single-crystal X-ray study
- T = 573 K
- Mean (C-C) = 0.003 Å
- R factor = 0.031
- wR factor = 0.110
- Data-to-parameter ratio = 9.7
checkCIF/PLATON results
No syntax errors found
Alert level C
PLAT088_ALERT_3_C Poor Data / Parameter Ratio .................... 9.73
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 .... 2.21
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor .... 2.32
0 ALERT level A = In general: serious problem
0 ALERT level B = Potentially serious problem
4 ALERT level C = Check and explain
0 ALERT level G = General alerts; check
0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
2 ALERT type 2 Indicator that the structure model may be wrong or deficient
1 ALERT type 3 Indicator that the structure quality may be low
1 ALERT type 4 Improvement, methodology, query or suggestion
Data collection: KM-4 Software (Kuma, 1996); cell refinement: KM-4 Software; data reduction: DATAPROC (Kuma, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Siemens, 1992); software used to prepare material for publication: SHELXL97.
Pyrazine-2,3-dicarboxylic acid
top
Crystal data top
C6H4N2O4 | F(000) = 688 |
Mr = 168.11 | Dx = 1.670 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
a = 7.9690 (16) Å | Cell parameters from 25 reflections |
b = 11.952 (2) Å | θ = 6–15° |
c = 14.336 (3) Å | µ = 0.14 mm−1 |
β = 101.69 (3)° | T = 573 K |
V = 1337.1 (5) Å3 | Block (cut from a needle), colourless |
Z = 8 | 0.24 × 0.22 × 0.20 mm |
Data collection top
Kuma KM-4 four-circle diffractometer | Rint = 0.051 |
Radiation source: fine-focus sealed tube | θmax = 25.2°, θmin = 2.2° |
Graphite monochromator | h = −9→9 |
ω/2θ scans | k = −14→0 |
2528 measured reflections | l = −17→0 |
2423 independent reflections | 2 standard reflections every 200 reflections |
1612 reflections with I > 2σ(I) | intensity decay: 0.6% |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.031 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.110 | All H-atom parameters refined |
S = 1.03 | w = 1/[σ2(Fo2) + (0.0769P)2] where P = (Fo2 + 2Fc2)/3 |
2423 reflections | (Δ/σ)max < 0.001 |
249 parameters | Δρmax = 0.32 e Å−3 |
0 restraints | Δρmin = −0.21 e Å−3 |
Special details top
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 (Å2) top | x | y | z | Uiso*/Ueq | |
N11 | 0.83384 (19) | 0.20060 (12) | 0.10809 (10) | 0.0271 (3) | |
C13 | 0.8536 (2) | 0.20076 (14) | 0.27556 (12) | 0.0238 (4) | |
N12 | 0.86993 (19) | 0.08886 (12) | 0.27947 (10) | 0.0286 (4) | |
O11 | 0.7152 (2) | 0.42577 (12) | 0.23719 (10) | 0.0450 (4) | |
O13 | 0.7845 (2) | 0.21101 (13) | 0.42547 (10) | 0.0426 (4) | |
O12 | 0.8042 (2) | 0.42058 (13) | 0.10019 (10) | 0.0512 (5) | |
C12 | 0.8277 (2) | 0.25609 (14) | 0.18842 (12) | 0.0246 (4) | |
C17 | 0.7772 (2) | 0.37728 (15) | 0.17857 (12) | 0.0286 (4) | |
O14 | 0.9747 (2) | 0.33392 (12) | 0.39283 (9) | 0.0453 (4) | |
C18 | 0.8764 (2) | 0.25802 (14) | 0.37055 (12) | 0.0261 (4) | |
C15 | 0.8704 (2) | 0.03494 (16) | 0.19917 (13) | 0.0316 (4) | |
C16 | 0.8581 (3) | 0.09075 (16) | 0.11383 (13) | 0.0317 (4) | |
C23 | 0.3589 (2) | 0.19334 (15) | 0.01549 (12) | 0.0267 (4) | |
N21 | 0.3049 (2) | 0.36346 (13) | −0.07025 (11) | 0.0368 (4) | |
C22 | 0.3038 (2) | 0.30360 (15) | 0.00898 (12) | 0.0285 (4) | |
C28 | 0.3736 (2) | 0.12331 (15) | 0.10399 (12) | 0.0283 (4) | |
O21 | 0.2102 (2) | 0.31038 (12) | 0.15590 (10) | 0.0423 (4) | |
N22 | 0.4123 (2) | 0.14145 (13) | −0.05638 (11) | 0.0345 (4) | |
C27 | 0.2383 (3) | 0.36031 (15) | 0.08799 (12) | 0.0314 (4) | |
O24 | 0.49070 (18) | 0.13160 (13) | 0.16930 (10) | 0.0435 (4) | |
O23 | 0.2485 (2) | 0.05011 (12) | 0.09745 (11) | 0.0428 (4) | |
O22 | 0.2159 (3) | 0.46678 (12) | 0.07261 (12) | 0.0629 (6) | |
C25 | 0.4118 (3) | 0.20179 (18) | −0.13315 (14) | 0.0384 (5) | |
C26 | 0.3590 (3) | 0.31210 (17) | −0.14075 (15) | 0.0421 (5) | |
H16 | 0.864 (3) | 0.0502 (18) | 0.0597 (16) | 0.043 (6)* | |
H15 | 0.874 (3) | −0.046 (2) | 0.2028 (16) | 0.045 (6)* | |
H25 | 0.454 (3) | 0.1690 (19) | −0.1850 (15) | 0.041 (6)* | |
H26 | 0.367 (3) | 0.355 (2) | −0.1992 (19) | 0.060 (7)* | |
H23 | 0.273 (3) | 0.010 (2) | 0.1473 (19) | 0.058 (8)* | |
H13 | 0.809 (3) | 0.234 (2) | 0.480 (2) | 0.052 (7)* | |
H12 | 0.764 (4) | 0.490 (3) | 0.091 (2) | 0.075 (9)* | |
H22 | 0.183 (4) | 0.505 (3) | 0.123 (2) | 0.089 (10)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
N11 | 0.0351 (8) | 0.0268 (8) | 0.0201 (7) | −0.0005 (6) | 0.0078 (6) | −0.0029 (6) |
C13 | 0.0272 (8) | 0.0220 (8) | 0.0232 (9) | −0.0002 (7) | 0.0077 (7) | 0.0011 (7) |
N12 | 0.0382 (8) | 0.0236 (8) | 0.0247 (8) | 0.0017 (6) | 0.0080 (6) | 0.0009 (6) |
O11 | 0.0773 (11) | 0.0318 (7) | 0.0302 (7) | 0.0135 (7) | 0.0207 (7) | −0.0003 (6) |
O13 | 0.0661 (10) | 0.0442 (8) | 0.0218 (7) | −0.0183 (7) | 0.0185 (7) | −0.0071 (6) |
O12 | 0.0997 (13) | 0.0297 (8) | 0.0317 (8) | 0.0166 (8) | 0.0309 (8) | 0.0118 (6) |
C12 | 0.0294 (9) | 0.0276 (9) | 0.0182 (8) | −0.0032 (7) | 0.0082 (6) | 0.0007 (7) |
C17 | 0.0409 (10) | 0.0249 (9) | 0.0199 (8) | −0.0003 (8) | 0.0058 (7) | −0.0004 (7) |
O14 | 0.0639 (10) | 0.0435 (9) | 0.0288 (7) | −0.0223 (7) | 0.0100 (7) | −0.0069 (6) |
C18 | 0.0358 (9) | 0.0232 (9) | 0.0190 (8) | 0.0022 (7) | 0.0050 (7) | 0.0035 (7) |
C15 | 0.0412 (11) | 0.0240 (9) | 0.0305 (10) | 0.0024 (8) | 0.0096 (8) | −0.0023 (7) |
C16 | 0.0413 (10) | 0.0291 (10) | 0.0262 (9) | 0.0009 (8) | 0.0102 (8) | −0.0065 (8) |
C23 | 0.0306 (9) | 0.0271 (10) | 0.0228 (9) | −0.0023 (7) | 0.0067 (7) | −0.0017 (7) |
N21 | 0.0587 (11) | 0.0295 (9) | 0.0250 (8) | 0.0032 (7) | 0.0146 (7) | 0.0040 (7) |
C22 | 0.0386 (10) | 0.0274 (10) | 0.0202 (9) | −0.0024 (7) | 0.0081 (7) | 0.0018 (7) |
C28 | 0.0346 (9) | 0.0269 (10) | 0.0252 (9) | 0.0037 (8) | 0.0104 (8) | 0.0007 (7) |
O21 | 0.0651 (10) | 0.0369 (8) | 0.0303 (8) | 0.0056 (7) | 0.0223 (7) | 0.0054 (6) |
N22 | 0.0449 (9) | 0.0328 (9) | 0.0276 (8) | 0.0044 (7) | 0.0114 (7) | 0.0000 (7) |
C27 | 0.0454 (11) | 0.0251 (9) | 0.0242 (9) | 0.0015 (8) | 0.0084 (8) | 0.0014 (8) |
O24 | 0.0388 (8) | 0.0622 (10) | 0.0278 (7) | −0.0034 (7) | 0.0030 (6) | 0.0084 (7) |
O23 | 0.0558 (9) | 0.0375 (8) | 0.0332 (8) | −0.0136 (7) | 0.0045 (7) | 0.0114 (6) |
O22 | 0.1319 (17) | 0.0259 (8) | 0.0429 (9) | 0.0170 (9) | 0.0463 (10) | 0.0041 (7) |
C25 | 0.0525 (12) | 0.0421 (12) | 0.0232 (9) | 0.0038 (9) | 0.0137 (9) | −0.0019 (9) |
C26 | 0.0654 (14) | 0.0383 (11) | 0.0269 (10) | 0.0060 (10) | 0.0196 (10) | 0.0060 (9) |
Geometric parameters (Å, º) top
N11—C16 | 1.327 (2) | C23—N22 | 1.343 (2) |
N11—C12 | 1.338 (2) | C23—C22 | 1.386 (3) |
C13—N12 | 1.344 (2) | C23—C28 | 1.504 (2) |
C13—C12 | 1.391 (2) | N21—C26 | 1.327 (3) |
C13—C18 | 1.502 (2) | N21—C22 | 1.344 (2) |
N12—C15 | 1.320 (2) | C22—C27 | 1.502 (2) |
O11—C17 | 1.206 (2) | C28—O24 | 1.184 (2) |
O13—C18 | 1.306 (2) | C28—O23 | 1.315 (2) |
O13—H13 | 0.81 (3) | O21—C27 | 1.201 (2) |
O12—C17 | 1.294 (2) | N22—C25 | 1.315 (3) |
O12—H12 | 0.90 (3) | C27—O22 | 1.298 (2) |
C12—C17 | 1.502 (2) | O23—H23 | 0.85 (3) |
O14—C18 | 1.199 (2) | O22—H22 | 0.93 (3) |
C15—C16 | 1.379 (3) | C25—C26 | 1.382 (3) |
C15—H15 | 0.97 (2) | C25—H25 | 0.96 (2) |
C16—H16 | 0.92 (2) | C26—H26 | 0.99 (3) |
| | | |
C16—N11—C12 | 117.85 (16) | N22—C23—C22 | 122.17 (16) |
N12—C13—C12 | 120.39 (16) | N22—C23—C28 | 114.04 (15) |
N12—C13—C18 | 115.01 (15) | C22—C23—C28 | 123.72 (15) |
C12—C13—C18 | 124.49 (15) | C26—N21—C22 | 117.14 (17) |
C15—N12—C13 | 117.83 (16) | N21—C22—C23 | 120.45 (16) |
C18—O13—H13 | 112.2 (18) | N21—C22—C27 | 117.39 (16) |
C17—O12—H12 | 112.8 (19) | C23—C22—C27 | 122.15 (15) |
N11—C12—C13 | 120.83 (16) | O24—C28—O23 | 125.18 (17) |
N11—C12—C17 | 116.92 (15) | O24—C28—C23 | 122.30 (17) |
C13—C12—C17 | 122.05 (15) | O23—C28—C23 | 112.43 (15) |
O11—C17—O12 | 125.21 (17) | C25—N22—C23 | 116.16 (17) |
O11—C17—C12 | 122.52 (16) | O21—C27—O22 | 125.68 (18) |
O12—C17—C12 | 112.25 (15) | O21—C27—C22 | 122.52 (17) |
O14—C18—O13 | 125.52 (17) | O22—C27—C22 | 111.80 (16) |
O14—C18—C13 | 122.59 (16) | C28—O23—H23 | 106.0 (18) |
O13—C18—C13 | 111.78 (15) | C27—O22—H22 | 113 (2) |
N12—C15—C16 | 121.68 (17) | N22—C25—C26 | 122.58 (19) |
N12—C15—H15 | 116.5 (13) | N22—C25—H25 | 118.9 (13) |
C16—C15—H15 | 121.8 (13) | C26—C25—H25 | 118.5 (13) |
N11—C16—C15 | 121.10 (17) | N21—C26—C25 | 121.48 (18) |
N11—C16—H16 | 119.9 (14) | N21—C26—H26 | 119.4 (15) |
C15—C16—H16 | 119.0 (14) | C25—C26—H26 | 119.0 (15) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O23—H23···O11i | 0.85 (3) | 1.92 (3) | 2.763 (2) | 169 (3) |
O13—H13···N11ii | 0.81 (3) | 1.97 (3) | 2.776 (2) | 172 (2) |
O13—H13···O12ii | 0.81 (3) | 2.54 (3) | 2.935 (2) | 112 (2) |
O12—H12···N21iii | 0.90 (3) | 1.83 (3) | 2.730 (2) | 176 (3) |
O22—H22···N12iv | 0.93 (3) | 1.84 (3) | 2.772 (2) | 175 (3) |
Symmetry codes: (i) −x+1, y−1/2, −z+1/2; (ii) x, −y+1/2, z+1/2; (iii) −x+1, −y+1, −z; (iv) −x+1, y+1/2, −z+1/2. |