Crystal structure of 5-amino-4H-1,2,4-triazol-1-ium pyrazine-2-carboxyl­ate: an unexpected salt arising from the deca­rboxylation of both precursors

The salt 3-amino-2H,4H-1,2,4-triazolium pyrazine-2-carboxyl­ate was isolated by reacting 5-amino-1H-1,2,4-triazole-3-carb­oxy­lic acid and pyrazine-2,3-di­carb­oxy­lic acid in the presence of silver nitrate and 1-butyl-3-methyl­imidazolium bromide in ionothermal conditions.

Key indicators

• Single-crystal X-ray study
• T = 296 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.059
• wR factor = 0.133
• Data-to-parameter ratio = 12.6

checkCIF/PLATON results

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Alert level C
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....        2.1 Note
PLAT906_ALERT_3_C Large K value in the Analysis of Variance ......     12.612 Check

Alert level G
PLAT002_ALERT_2_G Number of Distance or Angle Restraints on AtSite          7 Note
PLAT042_ALERT_1_G Calc. and Reported MoietyFormula Strings  Differ     Please Check
PLAT066_ALERT_1_G Predicted and Reported Tmin&Tmax Range Identical          ? Check
PLAT172_ALERT_4_G The CIF-Embedded .res File Contains DFIX Records         10 Report
PLAT860_ALERT_3_G Number of Least-Squares Restraints .............          5 Note

   0 ALERT level A = Most likely a serious problem - resolve or explain
   0 ALERT level B = A potentially serious problem, consider carefully
   2 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   5 ALERT level G = General information/check it is not something unexpected

   2 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
   2 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Chemical context

A remarkable feature of ionothermal synthesis is the fact that ionic liquids (ILs) can act simultaneously as sustainable solvents and structure-directing agents (also known as templates). This has been widely demonstrated by their potential in the discovery of unprecedented crystalline materials (Xu et al., 2013). Following our inter­est in the design and preparation of new types of metal-organic frameworks (MOFs), we have been exploring the use of 5-amino-1H-1,2,4-triazole-3-carb­oxy­lic acid (H₂atrc) and pyrazine-2,3-di­carb­oxy­lic acid (H₂Pzdc) as a double-ligand system in the presence of transition metal centers using ionothermal synthetic conditions. In the presence of AgNO₃ the obtained product revealed, however, to be an unexpected organic salt (Bond, 2007) composed of the 3-amino-2H,4H(+)-1,2,4-triazolium cation and the pyrazine-2-carboxyl­ato anion.

S2. Structural commentary

The title compound is a product of decomposition of the H₂atrc and H₂Pzdc organic molecules by way of de­carboxyl­ation leading to, respectively, 3-amino-2H,4H-1,2,4-triazolium [(C₂H₅N₄)⁺] and pyrazine-2-carboxyl­ate [(C₅H₃N₂O₂)^-]. The asymmetric unit is composed of one of each of these moieties, as depicted in both the chemical diagram and in Fig. 1.

S3. Supra­molecular features

The cation present in the title compound is rich in groups capable of forming strong N—H···N,O hydrogen-bonding inter­actions (see Table 1 for further geometrical details), many highly directional with the observed <(D—H···A) inter­action angles being above 165°. These supra­molecular contacts are the main driving force which mediate the crystal packing features of the title compound. Indeed, the donation of hydrogen atoms from the cation to the carboxyl­ate group of an adjacent anion (N6—H6B···O2 and N5—H5···O1) forms the known structurally robust R₂²(8) graph-set motif (dashed pink lines in Fig. 2) (Grell et al., 1999). This graph-set motif has already been found in salts containing the title compound cation and carb­oxy­lic acids (see Database survey below). Two other inter­actions, N6—H6A···N1 (dashed aqua lines) and N4—H4A···O2, describe a second R₂²(9) hydrogen-bond motif. In contrast to the previous graph-set motif, the R₂²(9) ring has not been observed in structures containing the title-compound cation. The zigzag alternation of these two graph-set motifs leads to the formation of a highly coplanar supra­molecular tape running parallel to the [010] direction of the unit cell (Fig. 2). Adjacent tapes inter­act by way of weak π–π stacking contacts between triazole and pyrazine rings, with the inter-centroid distance being 3.75 (3) Å (dashed orange lines in Fig. 2).

S4. Database survey

Triazole molecules have been extensively used in the preparation of organic co-crystals (Kastelic et al., 2011; Remenar et al., 2003), and a survey of the Cambridge Structural Database (Groom & Allen, 2014) revealed the existence of about a dozen of crystallographic reports of co-crystals of the title compound cation (Byriel et al., 1992; Essid et al., 2013; Joo et al., 2013; Luo et al., 2013; Lynch et al., 1992, 1998, 1999; Lynch, Smith, Byriel & Kennard, 1994; Lynch, Smith, Byriel, Kennard et al., 1994; Matulková et al., 2007; Smith et al., 1996). The only compounds known with both of the title compound entities present is a bimetallic complex also containing Cd²⁺ and NO^3- ions (Chen et al., 2009) .

S5. Synthesis and crystallization

5-Amino-1H-1,2,4-triazole-3-carb­oxy­lic acid (H₂atrc, 98% purity), pyrazine-2,3-di­carb­oxy­lic acid (H₂Pzdc, 97% purity), 1-methyl­imidazole (99%+ purity), 1-bromo­butane (99% purity) and AgNO₃ (99%+ purity) were purchased from Sigma–Aldrich and were used as received without further purification. 1-Butyl-3-methyl­imidazolium bromide ([BMI]Br) was prepared according to the literature method (Parnham & Morris, 2006) and was isolated as a pale-yellow oil (yield of ca 78%).

AgNO₃ (0.0687 g; 0.400 mmol), H₂atrc (0.0510 g; 0.400 mmol) and H₂Pzdc (0.0607 g; 0.361 mmol) were mixed with 0.49 g of [BMI]Br and 0.3 mL of distilled water in a ca 25 mL Teflon-lined stainless-steel reaction vessel. The resulting mixture was heated to 383 K for 7 days. The vessel was then allowed to cool to ambient temperature at a rate of ca 1 K h^-1. Small colourless crystals of the title compound were directly isolated from the vessel contents.

S6. Refinement details

Hydrogen atoms bound to carbon were placed at idealized positions with C—H = 0.95 Å, and included in the final structural model in a riding-motion approximation with the isotropic thermal displacement parameters fixed at 1.2U_eq of the carbon atom to which they are attached. Hydrogen atoms associated with nitro­gen atoms were located directly from difference Fourier maps and were included in the model with the N—H and H···H (only for the –NH₂ groups) distances restrained to 0.90 (1) and 1.55 (1) Å, respectively, in order to ensure a chemically reasonable environment for these groups. These hydrogen atoms were modelled with the isotropic thermal displacement parameters fixed at 1.5U_eq(N).

Related literature

For related literature, see: Allen (2002); Bond (2007); Byriel et al. (1992); Chen et al. (2009); Essid et al. (2013); Grell et al. (1999); Joo et al. (2013); Kastelic et al. (2011); Luo et al. (2013); Lynch et al. (1992, 1998, 1999); Lynch, Smith, Byriel & Kennard (1994); Lynch, Smith, Byriel, Kennard & Whittaker (1994); Matulková et al. (2007); Parnham & Morris (2006); Remenar et al. (2003); Smith et al. (1996).

Computing details

Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT-Plus (Bruker, 2005); data reduction: SAINT-Plus (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 2009); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

Fig. 1. The asymmetric unit of the title salt. Non-H atoms are represented as displacement ellipsoids drawn at the 50% probability level, while H atoms are depicted as small spheres with arbitrary radii. The atomic labelling scheme for all non-H atoms is provided. Hydrogen bonds are represented as dashed lines.

Fig. 2. Supramolecular tape running parallel to the [010] direction of the unit cell. N—H···N and N—H···N hydrogen bonds are depicted as dashed aqua and pink lines, respectively. Graph-set motifs present in the structure are highlighted. For geometric details of the represented supramolecular contacts, see Table 1. π–π stacking interactions between two adjacent supramolecular tapes are shown as orange dashed lines.

5-Amino-4H-1,2,4-triazol-1-ium pyrazine-2-carboxylate

Crystal data

C2H5N4^+·C5H3N2O2^−	F(000) = 432
Mr = 208.19	Dx = 1.526 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 7.0599 (5) Å	Cell parameters from 1298 reflections
b = 12.1868 (8) Å	θ = 2.6–19.7°
c = 10.8385 (6) Å	µ = 0.12 mm^−1
β = 103.593 (4)°	T = 296 K
V = 906.40 (10) Å^3	Block, colourless
Z = 4	0.09 × 0.04 × 0.03 mm

Data collection

Bruker X8 Kappa CCD APEXII diffractometer	1037 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.077
ω / ϕ scans	θmax = 26.4°, θmin = 2.6°
Absorption correction: multi-scan (SADABS; Sheldrick, 1998)	h = −8→8
Tmin = 0.989, Tmax = 0.997	k = −15→15
12089 measured reflections	l = −13→13
1858 independent reflections

Refinement

Refinement on F^2	5 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F^2 > 2σ(F^2)] = 0.059	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.133	w = 1/[σ^2(Fo^2) + (0.0599P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.01	(Δ/σ)max < 0.001
1858 reflections	Δρmax = 0.19 e Å^−3
148 parameters	Δρmin = −0.20 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
N1	0.2890 (3)	0.79063 (17)	0.49872 (19)	0.0389 (6)
N2	0.0664 (3)	0.79145 (18)	0.2472 (2)	0.0468 (6)
C1	0.2177 (4)	0.8840 (2)	0.4404 (2)	0.0334 (6)
C2	0.1066 (4)	0.8815 (2)	0.3165 (2)	0.0412 (7)
H2	0.0571	0.9476	0.2797	0.049*
C3	0.1381 (4)	0.6995 (2)	0.3059 (2)	0.0448 (7)
H3	0.1147	0.6334	0.2623	0.054*
C4	0.2461 (4)	0.6993 (2)	0.4297 (3)	0.0442 (7)
H4	0.2912	0.6326	0.4668	0.053*
C5	0.2560 (4)	0.9921 (2)	0.5101 (2)	0.0378 (7)
O1	0.1745 (3)	1.07442 (14)	0.45075 (15)	0.0481 (6)
O2	0.3628 (3)	0.99415 (14)	0.61986 (16)	0.0543 (6)
N3	0.7128 (4)	0.94320 (19)	0.8957 (2)	0.0622 (8)
N4	0.6167 (4)	0.88117 (19)	0.7929 (2)	0.0476 (6)
H4A	0.535 (3)	0.912 (2)	0.7253 (18)	0.071*
N5	0.7480 (3)	0.76575 (18)	0.93596 (19)	0.0417 (6)
H5	0.778 (4)	0.6996 (13)	0.972 (2)	0.063*
N6	0.5628 (4)	0.6942 (2)	0.7405 (2)	0.0540 (7)
H6A	0.473 (3)	0.714 (2)	0.6709 (19)	0.081*
H6B	0.585 (5)	0.6271 (13)	0.775 (3)	0.081*
C6	0.6369 (4)	0.7751 (2)	0.8181 (2)	0.0365 (7)
C7	0.7892 (5)	0.8695 (2)	0.9782 (3)	0.0553 (8)
H7	0.8649	0.8861	1.0584	0.066*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0450 (14)	0.0290 (13)	0.0400 (12)	−0.0006 (11)	0.0049 (10)	0.0005 (10)
N2	0.0557 (16)	0.0387 (14)	0.0406 (12)	0.0008 (12)	0.0005 (11)	−0.0086 (12)
C1	0.0331 (15)	0.0309 (15)	0.0355 (13)	−0.0004 (13)	0.0067 (11)	0.0022 (12)
C2	0.0495 (18)	0.0320 (16)	0.0367 (14)	0.0061 (14)	−0.0007 (13)	0.0020 (12)
C3	0.0487 (19)	0.0352 (17)	0.0478 (16)	−0.0016 (15)	0.0059 (14)	−0.0099 (13)
C4	0.0499 (18)	0.0299 (16)	0.0497 (16)	0.0036 (14)	0.0056 (14)	0.0028 (13)
C5	0.0420 (17)	0.0344 (16)	0.0330 (13)	0.0001 (14)	0.0006 (12)	0.0036 (12)
O1	0.0625 (14)	0.0319 (11)	0.0402 (10)	0.0058 (9)	−0.0074 (9)	0.0021 (8)
O2	0.0708 (14)	0.0375 (12)	0.0399 (10)	0.0067 (10)	−0.0165 (10)	−0.0025 (9)
N3	0.089 (2)	0.0419 (15)	0.0461 (14)	0.0029 (15)	−0.0032 (13)	0.0024 (12)
N4	0.0625 (18)	0.0367 (15)	0.0386 (13)	0.0037 (13)	0.0019 (12)	0.0061 (11)
N5	0.0480 (14)	0.0362 (15)	0.0359 (12)	0.0025 (12)	−0.0004 (11)	0.0083 (11)
N6	0.0607 (18)	0.0440 (16)	0.0491 (15)	−0.0005 (15)	−0.0038 (13)	0.0030 (13)
C6	0.0391 (17)	0.0349 (18)	0.0348 (13)	0.0044 (13)	0.0068 (12)	0.0057 (12)
C7	0.074 (2)	0.046 (2)	0.0383 (15)	0.0020 (17)	−0.0026 (15)	0.0012 (14)

Geometric parameters (Å, º)

N1—C4	1.335 (3)	N3—C7	1.293 (3)
N1—C1	1.341 (3)	N3—N4	1.384 (3)
N2—C2	1.323 (3)	N4—C6	1.322 (3)
N2—C3	1.328 (3)	N4—H4A	0.902 (10)
C1—C2	1.387 (3)	N5—C6	1.338 (3)
C1—C5	1.512 (3)	N5—C7	1.353 (3)
C2—H2	0.9300	N5—H5	0.901 (10)
C3—C4	1.379 (4)	N6—C6	1.321 (3)
C3—H3	0.9300	N6—H6A	0.899 (10)
C4—H4	0.9300	N6—H6B	0.896 (10)
C5—O2	1.250 (2)	C7—H7	0.9300
C5—O1	1.256 (3)
C4—N1—C1	115.6 (2)	C7—N3—N4	102.9 (2)
C2—N2—C3	114.9 (2)	C6—N4—N3	111.1 (2)
N1—C1—C2	120.2 (2)	C6—N4—H4A	126 (2)
N1—C1—C5	120.1 (2)	N3—N4—H4A	121.7 (19)
C2—C1—C5	119.8 (2)	C6—N5—C7	105.9 (2)
N2—C2—C1	124.4 (2)	C6—N5—H5	121.3 (18)
N2—C2—H2	117.8	C7—N5—H5	132.7 (18)
C1—C2—H2	117.8	C6—N6—H6A	115 (2)
N2—C3—C4	122.0 (2)	C6—N6—H6B	115 (2)
N2—C3—H3	119.0	H6A—N6—H6B	128 (3)
C4—C3—H3	119.0	N6—C6—N4	126.2 (2)
N1—C4—C3	123.0 (2)	N6—C6—N5	126.9 (2)
N1—C4—H4	118.5	N4—C6—N5	106.9 (2)
C3—C4—H4	118.5	N3—C7—N5	113.2 (2)
O2—C5—O1	125.0 (2)	N3—C7—H7	123.4
O2—C5—C1	119.3 (2)	N5—C7—H7	123.4
O1—C5—C1	115.7 (2)
C4—N1—C1—C2	0.3 (4)	N1—C1—C5—O1	−176.1 (2)
C4—N1—C1—C5	179.5 (2)	C2—C1—C5—O1	3.1 (4)
C3—N2—C2—C1	1.2 (4)	C7—N3—N4—C6	0.8 (3)
N1—C1—C2—N2	−1.4 (4)	N3—N4—C6—N6	179.8 (3)
C5—C1—C2—N2	179.4 (2)	N3—N4—C6—N5	−0.9 (3)
C2—N2—C3—C4	−0.1 (4)	C7—N5—C6—N6	179.9 (3)
C1—N1—C4—C3	0.8 (4)	C7—N5—C6—N4	0.6 (3)
N2—C3—C4—N1	−1.0 (4)	N4—N3—C7—N5	−0.4 (4)
N1—C1—C5—O2	3.7 (4)	C6—N5—C7—N3	−0.1 (4)
C2—C1—C5—O2	−177.1 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N4—H4A···O2	0.90 (1)	1.77 (1)	2.655 (3)	166 (3)
N5—H5···O1^i	0.90 (1)	1.73 (1)	2.632 (3)	176 (3)
N6—H6B···O2^i	0.90 (1)	1.97 (1)	2.853 (3)	169 (3)
N6—H6A···N1	0.90 (1)	2.21 (1)	3.099 (3)	169 (3)

Symmetry code: (i) −x+1, y−1/2, −z+3/2.