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In the crystal structure of the title di­amide, C6H6N4O2, 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

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270100013421/jz1424sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270100013421/jz1424Isup2.hkl
Contains datablock I

CCDC reference: 156186

Comment top

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.

Experimental top

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.

Computing details top

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.

Figures top
[Figure 1] Fig. 1. The ORTEPII (Johnson, 1976) diagram and atom-numbering scheme for (I). The C10 carboxamide is in the plane of the heterocyclic pyrazine ring and the C7 carboxamide is out-of-plane. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
[Figure 2] Fig. 2. The crystal structure of (I), showing the molecular staircase. The linear tapes of N—H···O and C—H···N dimers [the hydrogen bonds with symmetry codes (iii) and (vi)] along [201] form the steps of the staircase and the N—H···O bonds [the hydrogen bond with symmetry code (iv)] along [010] build the network upwards. Symmetry codes are given in Table 2.
[Figure 3] Fig. 3. A side view of the molecular staircase networks in (I). The hydrogen bonds with symmetry codes (iii) and (iv) are shown as thick dotted lines. The C7 carboxamide NH2 group connects these staircase networks via the hydrogen bonds with symmetry codes (i) and (ii), shown as thin dotted lines. The C—H···N interaction with symmetry code (v) is omitted for clarity. Symmetry codes are given in Table 2.
Pyrazine-2,3-dicarboxamide top
Crystal data top
C6H6N4O2F(000) = 172
Mr = 166.15Dx = 1.646 Mg m3
Triclinic, P1Melting point: 541K K
a = 5.0250 (3) ÅMo Kα radiation, λ = 0.71073 Å
b = 7.0977 (3) ÅCell parameters from 1868 reflections
c = 10.1196 (5) Åθ = 3.1–30.0°
α = 70.826 (3)°µ = 0.13 mm1
β = 81.868 (3)°T = 153 K
γ = 81.163 (3)°Cubic, colourless
V = 335.25 (3) Å30.32 × 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 tubeRint = 0.015
Graphite monochromatorθmax = 30.0°, θmin = 3.1°
ω scansh = 77
2623 measured reflectionsk = 99
1868 independent reflectionsl = 1413
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.035Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.101All 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 parametersΔρmax = 0.50 e Å3
0 restraintsΔρmin = 0.20 e Å3
Crystal data top
C6H6N4O2γ = 81.163 (3)°
Mr = 166.15V = 335.25 (3) Å3
Triclinic, P1Z = 2
a = 5.0250 (3) ÅMo Kα radiation
b = 7.0977 (3) ŵ = 0.13 mm1
c = 10.1196 (5) ÅT = 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 reflectionsRint = 0.015
1868 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0350 restraints
wR(F2) = 0.101All H-atom parameters refined
S = 1.06Δρmax = 0.50 e Å3
1835 reflectionsΔρmin = 0.20 e Å3
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
xyzUiso*/Ueq
O10.27403 (13)0.88931 (9)0.22860 (7)0.0176 (2)
O20.23121 (13)0.64845 (9)0.05365 (7)0.0165 (2)
N30.76290 (15)0.54499 (11)0.36956 (8)0.0144 (2)
N40.7104 (2)0.91373 (11)0.13368 (9)0.0185 (2)
H4A0.681 (3)1.044 (2)0.0973 (16)0.029 (4)*
H4B0.877 (3)0.857 (2)0.1358 (16)0.029 (4)*
N50.1634 (2)0.31990 (11)0.14050 (8)0.0148 (2)
H5A0.047 (3)0.332 (2)0.0798 (17)0.031 (4)*
H5B0.216 (3)0.201 (2)0.1966 (16)0.028 (4)*
N60.5181 (2)0.24527 (11)0.32782 (8)0.0162 (2)
C70.5066 (2)0.81334 (12)0.20777 (8)0.0129 (2)
C80.5817 (2)0.59011 (12)0.27475 (8)0.0117 (2)
C90.6917 (2)0.20298 (13)0.42416 (10)0.0174 (2)
H90.724 (3)0.064 (2)0.4801 (15)0.028 (3)*
C100.2751 (2)0.47817 (12)0.13919 (9)0.0120 (2)
C110.8183 (2)0.35200 (13)0.44334 (9)0.0153 (2)
H110.951 (3)0.316 (2)0.5142 (15)0.025 (3)*
C120.4643 (2)0.43856 (12)0.25113 (8)0.0118 (2)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0144 (3)0.0132 (3)0.0245 (3)0.0003 (2)0.0025 (2)0.0052 (2)
O20.0204 (3)0.0114 (3)0.0170 (3)0.0024 (2)0.0080 (2)0.0009 (2)
N30.0140 (3)0.0150 (4)0.0147 (3)0.0024 (2)0.0041 (3)0.0037 (3)
N40.0158 (4)0.0117 (3)0.0243 (4)0.0023 (3)0.0005 (3)0.0010 (3)
N50.0172 (4)0.0108 (3)0.0176 (4)0.0024 (3)0.0076 (3)0.0032 (3)
N60.0175 (4)0.0113 (3)0.0190 (4)0.0023 (3)0.0070 (3)0.0013 (3)
C70.0156 (4)0.0108 (3)0.0131 (4)0.0023 (3)0.0041 (3)0.0036 (3)
C80.0119 (3)0.0106 (3)0.0121 (4)0.0014 (3)0.0020 (3)0.0027 (3)
C90.0188 (4)0.0128 (4)0.0190 (4)0.0024 (3)0.0075 (3)0.0000 (3)
C100.0119 (3)0.0117 (4)0.0129 (4)0.0010 (3)0.0028 (3)0.0040 (3)
C110.0147 (4)0.0158 (4)0.0146 (4)0.0022 (3)0.0053 (3)0.0018 (3)
C120.0121 (4)0.0110 (4)0.0123 (4)0.0018 (3)0.0029 (3)0.0024 (3)
Geometric parameters (Å, º) top
O1—C71.2298 (10)N5—H5B0.88 (2)
O2—C101.2424 (10)N6—C91.3301 (11)
N3—C111.3346 (11)N6—C121.3430 (10)
N3—C81.3447 (11)C7—C81.5151 (11)
N4—C71.3322 (11)C8—C121.4021 (11)
N4—H4A0.87 (2)C9—C111.3920 (12)
N4—H4B0.87 (2)C9—H90.962 (15)
N5—C101.3263 (11)C10—C121.5097 (11)
N5—H5A0.88 (2)C11—H110.994 (15)
C11—N3—C8117.44 (7)C12—C8—C7124.94 (7)
C7—N4—H4A119.0 (10)N6—C9—C11121.60 (8)
C7—N4—H4B121.2 (10)N6—C9—H9116.5 (9)
H4A—N4—H4B118.6 (14)C11—C9—H9121.9 (9)
C10—N5—H5A120.5 (10)O2—C10—N5123.88 (7)
C10—N5—H5B119.9 (10)O2—C10—C12121.01 (7)
H5A—N5—H5B119.3 (14)N5—C10—C12115.12 (7)
C9—N6—C12117.52 (7)N3—C11—C9121.43 (8)
O1—C7—N4125.14 (8)N3—C11—H11118.7 (8)
O1—C7—C8119.84 (7)C9—C11—H11119.9 (8)
N4—C7—C8114.96 (7)N6—C12—C8121.00 (7)
N3—C8—C12120.90 (7)N6—C12—C10115.58 (7)
N3—C8—C7114.01 (7)C8—C12—C10123.41 (7)
C11—N3—C8—C122.40 (12)C9—N6—C12—C10177.59 (7)
C11—N3—C8—C7173.35 (7)N3—C8—C12—N63.69 (13)
O1—C7—C8—N3114.85 (9)C7—C8—C12—N6171.58 (8)
N4—C7—C8—N362.39 (10)N3—C8—C12—C10175.51 (7)
O1—C7—C8—C1260.71 (12)C7—C8—C12—C109.22 (13)
N4—C7—C8—C12122.06 (9)O2—C10—C12—N6173.24 (8)
C12—N6—C9—C111.38 (14)N5—C10—C12—N66.84 (11)
C8—N3—C11—C90.63 (13)O2—C10—C12—C86.00 (13)
N6—C9—C11—N32.64 (15)N5—C10—C12—C8173.92 (8)
C9—N6—C12—C81.67 (13)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N4—H4A···O2i0.873 (15)2.282 (15)3.097 (1)155.3 (14)
N4—H4B···O1ii0.871 (15)2.393 (15)3.080 (1)136.0 (13)
N4—H4B···O2ii0.871 (15)2.373 (15)3.153 (1)149.1 (13)
N5—H5A···O2iii0.882 (16)2.037 (16)2.919 (1)177.5 (15)
N5—H5B···O1iv0.874 (15)2.108 (15)2.876 (1)146.4 (14)
N5—H5B···N60.874 (15)2.271 (15)2.657 (1)106.6 (12)
C9—H9···N6v0.964 (15)2.725 (15)3.545 (1)143.3 (12)
C11—H11···N3vi0.993 (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, y1, z; (v) x+1, y, z+1; (vi) x+2, y+1, z+1.

Experimental details

Crystal data
Chemical formulaC6H6N4O2
Mr166.15
Crystal system, space groupTriclinic, 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)
V3)335.25 (3)
Z2
Radiation typeMo Kα
µ (mm1)0.13
Crystal size (mm)0.32 × 0.30 × 0.30
Data collection
DiffractometerNonius Kappa CCD
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
2623, 1868, 1754
Rint0.015
(sin θ/λ)max1)0.704
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.035, 0.101, 1.06
No. of reflections1835
No. of parameters133
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.50, 0.20

Computer programs: COLLECT (Nonius, 1998), DENZO-SMN (Otwinowski & Minor, 1997), SCALEPACK in DENZO-SMN, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), ORTEPII (Johnson, 1976) and PLUTON (Spek, 1992), SHELXL97.

Selected torsion angles (º) top
O1—C7—C8—N3114.85 (9)O2—C10—C12—N6173.24 (8)
N4—C7—C8—N362.39 (10)N5—C10—C12—N66.84 (11)
O1—C7—C8—C1260.71 (12)O2—C10—C12—C86.00 (13)
N4—C7—C8—C12122.06 (9)N5—C10—C12—C8173.92 (8)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N4—H4A···O2i0.873 (15)2.282 (15)3.097 (1)155.3 (14)
N4—H4B···O1ii0.871 (15)2.393 (15)3.080 (1)136.0 (13)
N4—H4B···O2ii0.871 (15)2.373 (15)3.153 (1)149.1 (13)
N5—H5A···O2iii0.882 (16)2.037 (16)2.919 (1)177.5 (15)
N5—H5B···O1iv0.874 (15)2.108 (15)2.876 (1)146.4 (14)
N5—H5B···N60.874 (15)2.271 (15)2.657 (1)106.6 (12)
C9—H9···N6v0.964 (15)2.725 (15)3.545 (1)143.3 (12)
C11—H11···N3vi0.993 (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, y1, z; (v) x+1, y, z+1; (vi) x+2, y+1, z+1.
 

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