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In the crystal structure of the title diamide, C
6H
6N
4O
2, linear tapes of carboxamide N—H
O and pyrazine C—H
N hydrogen-bond dimers are connected by N—H
O bonds to form a staircase-like pattern.
Supporting information
CCDC reference: 156186
Colourless crystals of (I) were obtained by crystallization of pyrazine-2,3-dicarboxamide from water (m.p. 541 K). The compound was purchased from Acros Chemicals and used as received.
Data collection: COLLECT (Nonius, 1998); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: SCALEPACK in DENZO-SMN; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976) and PLUTON (Spek, 1992); software used to prepare material for publication: SHELXL97.
Pyrazine-2,3-dicarboxamide
top
Crystal data top
C6H6N4O2 | F(000) = 172 |
Mr = 166.15 | Dx = 1.646 Mg m−3 |
Triclinic, P1 | Melting point: 541K K |
a = 5.0250 (3) Å | Mo Kα radiation, λ = 0.71073 Å |
b = 7.0977 (3) Å | Cell parameters from 1868 reflections |
c = 10.1196 (5) Å | θ = 3.1–30.0° |
α = 70.826 (3)° | µ = 0.13 mm−1 |
β = 81.868 (3)° | T = 153 K |
γ = 81.163 (3)° | Cubic, colourless |
V = 335.25 (3) Å3 | 0.32 × 0.30 × 0.30 mm |
Z = 2 | |
Data collection top
Nonius Kappa CCD diffractometer | 1754 reflections with I > 2σ(I) |
Radiation source: normal focus for the X-ray tube | Rint = 0.015 |
Graphite monochromator | θmax = 30.0°, θmin = 3.1° |
ω scans | h = −7→7 |
2623 measured reflections | k = −9→9 |
1868 independent reflections | l = −14→13 |
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)] = 0.035 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.101 | All H-atom parameters refined |
S = 1.06 | w = 1/[σ2(Fo2) + (0.0548P)2 + 0.0906P] where P = (Fo2 + 2Fc2)/3 |
1835 reflections | (Δ/σ)max < 0.001 |
133 parameters | Δρmax = 0.50 e Å−3 |
0 restraints | Δρmin = −0.20 e Å−3 |
Crystal data top
C6H6N4O2 | γ = 81.163 (3)° |
Mr = 166.15 | V = 335.25 (3) Å3 |
Triclinic, P1 | Z = 2 |
a = 5.0250 (3) Å | Mo Kα radiation |
b = 7.0977 (3) Å | µ = 0.13 mm−1 |
c = 10.1196 (5) Å | T = 153 K |
α = 70.826 (3)° | 0.32 × 0.30 × 0.30 mm |
β = 81.868 (3)° | |
Data collection top
Nonius Kappa CCD diffractometer | 1754 reflections with I > 2σ(I) |
2623 measured reflections | Rint = 0.015 |
1868 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.035 | 0 restraints |
wR(F2) = 0.101 | All H-atom parameters refined |
S = 1.06 | Δρmax = 0.50 e Å−3 |
1835 reflections | Δρmin = −0.20 e Å−3 |
133 parameters | |
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 on F2 for ALL reflections except for 33 with very negative F2 or flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The observed criterion of F2 > σ(F2) is used only for calculating R_factor_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 | |
O1 | 0.27403 (13) | 0.88931 (9) | 0.22860 (7) | 0.0176 (2) | |
O2 | 0.23121 (13) | 0.64845 (9) | 0.05365 (7) | 0.0165 (2) | |
N3 | 0.76290 (15) | 0.54499 (11) | 0.36956 (8) | 0.0144 (2) | |
N4 | 0.7104 (2) | 0.91373 (11) | 0.13368 (9) | 0.0185 (2) | |
H4A | 0.681 (3) | 1.044 (2) | 0.0973 (16) | 0.029 (4)* | |
H4B | 0.877 (3) | 0.857 (2) | 0.1358 (16) | 0.029 (4)* | |
N5 | 0.1634 (2) | 0.31990 (11) | 0.14050 (8) | 0.0148 (2) | |
H5A | 0.047 (3) | 0.332 (2) | 0.0798 (17) | 0.031 (4)* | |
H5B | 0.216 (3) | 0.201 (2) | 0.1966 (16) | 0.028 (4)* | |
N6 | 0.5181 (2) | 0.24527 (11) | 0.32782 (8) | 0.0162 (2) | |
C7 | 0.5066 (2) | 0.81334 (12) | 0.20777 (8) | 0.0129 (2) | |
C8 | 0.5817 (2) | 0.59011 (12) | 0.27475 (8) | 0.0117 (2) | |
C9 | 0.6917 (2) | 0.20298 (13) | 0.42416 (10) | 0.0174 (2) | |
H9 | 0.724 (3) | 0.064 (2) | 0.4801 (15) | 0.028 (3)* | |
C10 | 0.2751 (2) | 0.47817 (12) | 0.13919 (9) | 0.0120 (2) | |
C11 | 0.8183 (2) | 0.35200 (13) | 0.44334 (9) | 0.0153 (2) | |
H11 | 0.951 (3) | 0.316 (2) | 0.5142 (15) | 0.025 (3)* | |
C12 | 0.4643 (2) | 0.43856 (12) | 0.25113 (8) | 0.0118 (2) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
O1 | 0.0144 (3) | 0.0132 (3) | 0.0245 (3) | −0.0003 (2) | −0.0025 (2) | −0.0052 (2) |
O2 | 0.0204 (3) | 0.0114 (3) | 0.0170 (3) | −0.0024 (2) | −0.0080 (2) | −0.0009 (2) |
N3 | 0.0140 (3) | 0.0150 (4) | 0.0147 (3) | −0.0024 (2) | −0.0041 (3) | −0.0037 (3) |
N4 | 0.0158 (4) | 0.0117 (3) | 0.0243 (4) | −0.0023 (3) | −0.0005 (3) | −0.0010 (3) |
N5 | 0.0172 (4) | 0.0108 (3) | 0.0176 (4) | −0.0024 (3) | −0.0076 (3) | −0.0032 (3) |
N6 | 0.0175 (4) | 0.0113 (3) | 0.0190 (4) | −0.0023 (3) | −0.0070 (3) | −0.0013 (3) |
C7 | 0.0156 (4) | 0.0108 (3) | 0.0131 (4) | −0.0023 (3) | −0.0041 (3) | −0.0036 (3) |
C8 | 0.0119 (3) | 0.0106 (3) | 0.0121 (4) | −0.0014 (3) | −0.0020 (3) | −0.0027 (3) |
C9 | 0.0188 (4) | 0.0128 (4) | 0.0190 (4) | −0.0024 (3) | −0.0075 (3) | 0.0000 (3) |
C10 | 0.0119 (3) | 0.0117 (4) | 0.0129 (4) | −0.0010 (3) | −0.0028 (3) | −0.0040 (3) |
C11 | 0.0147 (4) | 0.0158 (4) | 0.0146 (4) | −0.0022 (3) | −0.0053 (3) | −0.0018 (3) |
C12 | 0.0121 (4) | 0.0110 (4) | 0.0123 (4) | −0.0018 (3) | −0.0029 (3) | −0.0024 (3) |
Geometric parameters (Å, º) top
O1—C7 | 1.2298 (10) | N5—H5B | 0.88 (2) |
O2—C10 | 1.2424 (10) | N6—C9 | 1.3301 (11) |
N3—C11 | 1.3346 (11) | N6—C12 | 1.3430 (10) |
N3—C8 | 1.3447 (11) | C7—C8 | 1.5151 (11) |
N4—C7 | 1.3322 (11) | C8—C12 | 1.4021 (11) |
N4—H4A | 0.87 (2) | C9—C11 | 1.3920 (12) |
N4—H4B | 0.87 (2) | C9—H9 | 0.962 (15) |
N5—C10 | 1.3263 (11) | C10—C12 | 1.5097 (11) |
N5—H5A | 0.88 (2) | C11—H11 | 0.994 (15) |
| | | |
C11—N3—C8 | 117.44 (7) | C12—C8—C7 | 124.94 (7) |
C7—N4—H4A | 119.0 (10) | N6—C9—C11 | 121.60 (8) |
C7—N4—H4B | 121.2 (10) | N6—C9—H9 | 116.5 (9) |
H4A—N4—H4B | 118.6 (14) | C11—C9—H9 | 121.9 (9) |
C10—N5—H5A | 120.5 (10) | O2—C10—N5 | 123.88 (7) |
C10—N5—H5B | 119.9 (10) | O2—C10—C12 | 121.01 (7) |
H5A—N5—H5B | 119.3 (14) | N5—C10—C12 | 115.12 (7) |
C9—N6—C12 | 117.52 (7) | N3—C11—C9 | 121.43 (8) |
O1—C7—N4 | 125.14 (8) | N3—C11—H11 | 118.7 (8) |
O1—C7—C8 | 119.84 (7) | C9—C11—H11 | 119.9 (8) |
N4—C7—C8 | 114.96 (7) | N6—C12—C8 | 121.00 (7) |
N3—C8—C12 | 120.90 (7) | N6—C12—C10 | 115.58 (7) |
N3—C8—C7 | 114.01 (7) | C8—C12—C10 | 123.41 (7) |
| | | |
C11—N3—C8—C12 | −2.40 (12) | C9—N6—C12—C10 | 177.59 (7) |
C11—N3—C8—C7 | 173.35 (7) | N3—C8—C12—N6 | 3.69 (13) |
O1—C7—C8—N3 | −114.85 (9) | C7—C8—C12—N6 | −171.58 (8) |
N4—C7—C8—N3 | 62.39 (10) | N3—C8—C12—C10 | −175.51 (7) |
O1—C7—C8—C12 | 60.71 (12) | C7—C8—C12—C10 | 9.22 (13) |
N4—C7—C8—C12 | −122.06 (9) | O2—C10—C12—N6 | −173.24 (8) |
C12—N6—C9—C11 | −1.38 (14) | N5—C10—C12—N6 | 6.84 (11) |
C8—N3—C11—C9 | −0.63 (13) | O2—C10—C12—C8 | 6.00 (13) |
N6—C9—C11—N3 | 2.64 (15) | N5—C10—C12—C8 | −173.92 (8) |
C9—N6—C12—C8 | −1.67 (13) | | |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N4—H4A···O2i | 0.873 (15) | 2.282 (15) | 3.097 (1) | 155.3 (14) |
N4—H4B···O1ii | 0.871 (15) | 2.393 (15) | 3.080 (1) | 136.0 (13) |
N4—H4B···O2ii | 0.871 (15) | 2.373 (15) | 3.153 (1) | 149.1 (13) |
N5—H5A···O2iii | 0.882 (16) | 2.037 (16) | 2.919 (1) | 177.5 (15) |
N5—H5B···O1iv | 0.874 (15) | 2.108 (15) | 2.876 (1) | 146.4 (14) |
N5—H5B···N6 | 0.874 (15) | 2.271 (15) | 2.657 (1) | 106.6 (12) |
C9—H9···N6v | 0.964 (15) | 2.725 (15) | 3.545 (1) | 143.3 (12) |
C11—H11···N3vi | 0.993 (15) | 2.470 (15) | 3.325 (1) | 144.0 (11) |
Symmetry codes: (i) −x+1, −y+2, −z; (ii) x+1, y, z; (iii) −x, −y+1, −z; (iv) x, y−1, z; (v) −x+1, −y, −z+1; (vi) −x+2, −y+1, −z+1. |
Experimental details
Crystal data |
Chemical formula | C6H6N4O2 |
Mr | 166.15 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 153 |
a, b, c (Å) | 5.0250 (3), 7.0977 (3), 10.1196 (5) |
α, β, γ (°) | 70.826 (3), 81.868 (3), 81.163 (3) |
V (Å3) | 335.25 (3) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 0.13 |
Crystal size (mm) | 0.32 × 0.30 × 0.30 |
|
Data collection |
Diffractometer | Nonius Kappa CCD diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 2623, 1868, 1754 |
Rint | 0.015 |
(sin θ/λ)max (Å−1) | 0.704 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.035, 0.101, 1.06 |
No. of reflections | 1835 |
No. of parameters | 133 |
H-atom treatment | All H-atom parameters refined |
Δρmax, Δρmin (e Å−3) | 0.50, −0.20 |
Selected torsion angles (º) topO1—C7—C8—N3 | −114.85 (9) | O2—C10—C12—N6 | −173.24 (8) |
N4—C7—C8—N3 | 62.39 (10) | N5—C10—C12—N6 | 6.84 (11) |
O1—C7—C8—C12 | 60.71 (12) | O2—C10—C12—C8 | 6.00 (13) |
N4—C7—C8—C12 | −122.06 (9) | N5—C10—C12—C8 | −173.92 (8) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N4—H4A···O2i | 0.873 (15) | 2.282 (15) | 3.097 (1) | 155.3 (14) |
N4—H4B···O1ii | 0.871 (15) | 2.393 (15) | 3.080 (1) | 136.0 (13) |
N4—H4B···O2ii | 0.871 (15) | 2.373 (15) | 3.153 (1) | 149.1 (13) |
N5—H5A···O2iii | 0.882 (16) | 2.037 (16) | 2.919 (1) | 177.5 (15) |
N5—H5B···O1iv | 0.874 (15) | 2.108 (15) | 2.876 (1) | 146.4 (14) |
N5—H5B···N6 | 0.874 (15) | 2.271 (15) | 2.657 (1) | 106.6 (12) |
C9—H9···N6v | 0.964 (15) | 2.725 (15) | 3.545 (1) | 143.3 (12) |
C11—H11···N3vi | 0.993 (15) | 2.470 (15) | 3.325 (1) | 144.0 (11) |
Symmetry codes: (i) −x+1, −y+2, −z; (ii) x+1, y, z; (iii) −x, −y+1, −z; (iv) x, y−1, z; (v) −x+1, −y, −z+1; (vi) −x+2, −y+1, −z+1. |
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The role of the carboxamide functional group in crystal packing and molecular recognition is well studied (Leiserowitz & Schmidt, 1969; Desiraju, 1989; Palmore & MacDonald, 2000). A common feature in the crystal structures of amides is the short 5.1 Å axis, a consequence of translation-related centrosymmetric amide dimers connected by N—H···O bonds. While benzamide [Cambridge Structual Database (CSD) refcode BZAMID; release? ref?] has the archetypical amide structure, pyrazine carboxamide is quite different and exists in five different polymorphic forms (CSD refcode PYRZIN). This shows that the isoelectronic CH → N replacement in the molecule has a profound effect on the crystal structure. The role of N—H···O– and C—H···N-mediated supramolecular synthons in the polymorphs of pyrazine carboxamide has been discussed recently by Desiraju (1997). With this background, and given our interest in understanding crystal structures with strong and weak hydrogen bonds (Kumar & Nangia, 2000), we report here the crystal structure of pyrazine-2,3-dicarboxamide, (I), which exhibits an interesting staircase-like architecture. Compound (I) has also been used as a ligand in metal complexes showing magnetic properties (Klein et al., 1983). \sch
The molecular geometry of (I) in the crystal is shown in Fig. 1. One of the carboxamide groups (C10) is in the plane of the heterocyclic ring while the other (C7) is out of plane (see Table 1 for torsion angles). The coplanar conformation of the C10 carboxamide in the crystal is stabilized by the intramolecular N5—H5B···N6 hydrogen bond (Table 2).
The carboxamide group that is coplanar with the heterocyclic ring (C10) forms centrosymmetric N—H···O dimers [N5—H5A···O2iii; symmetry code: (iii) −x, 1 − y, −z] which extend in a linear tape along [201] via C—H···N dimers [C11—H11···N3vi; symmetry code: (vi) 2 − x, 1 − y, 1 − z]. Such C—H···N dimers were noted recently in the crystal structures of some pyrazines (Thalladi et al., 2000). In the normal 5.1 Å packing, translation-related amide dimers are connected by N—H···O bonds to produce a sheet-like structure, as in benzamide (Desiraju, 1989). In (I) however, the N—H of the C10 carboxamide is bonded to the O atom of the out-of-plane C7 carboxamide group [N5—H5B···O1iv; symmetry code: (iv) x, y − 1, z], connecting the tapes mentioned above by translation along b. This produces a staircase-like pattern, with the tape along [201] constituting the flat step and the N—H···O bond along [010] giving the height to the staircase (Fig. 2). Such staircase networks are in turn connected by N4—H4A···O2i, N4—H4B···O1ii, N4—H4B···O2ii and C9—H9···N6v hydrogen bonds (Fig. 3) [symmetry codes: (i) 1 − x, 2 − y, −z; (ii) 1 + x, y, z; (v) 1 − x, −y, 1 − z]. A molecular staircase motif was identified recently in the crystal structure of the complex of benzene-1,2,4,5-tetracarboxylic acid and hexamethylenetetramine (Lough et al., 2000).
In (I), hydrogen bonding in both the amide groups is satisfied because the number of strong donors (four, two NH2 groups) and acceptors (four, two C=O groups) are matched. The weak C—H donors are bonded to the heterocyclic N atoms. The crystal structure may therefore be rationalized via the preferred combinations of hydrogen-bond donors and acceptors (Etter, 1990). It may be noted that each atom in (I) is either a donor (N—H, Csp2—H) or an acceptor (C=O, ring N) and further that all these groups are involved in hydrogen bonding. The title crystal structure may be compared with the structure of pyrazine-2,3-dicarboxylic acid, which crystallizes as a dihydrate (Takusagawa & Shimada, 1973); the imbalance of the donor-acceptor ratio in the diacid (2:4) is compensated for by the inclusion of the two water molecules.
In a recent survey of the Cambridge Structural Database (CSD) for bimolecular motifs in organic crystal structures, Allen et al. (1999) noted that the eight-membered carboxamide dimer synthon occurs in the maximum number of structures (627) and tops the list of 75 different ring motifs analysed. We have discussed this crystal structure in terms of robust amide dimer and pyrazine dimer supramolecular synthons (Desiraju, 1997), although larger hydrogen-bond patterns involving both the amide groups are present in the structure. The identification of robust, in other words recurring, supramolecular synthons is a current theme in crystal engineering.