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

Fernandes, J.A.; Liu, B.; Tomé, J.P.C.; Cunha-Silva, L.; Almeida Paz, F.A.

doi:10.1107/S205698901501172X

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ISSN: 2056-9890

Volume 71| Part 7| July 2015| Pages 840-843

doi:10.1107/S205698901501172X

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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

José A. Fernandes,^a Bing Liu,^b João P. C. Tomé,^c,^d Luís Cunha-Silva ^b and Filipe A. Almeida Paz ^a ^*

^aDepartment of Chemistry, CICECO – Aveiro Institute of Materials, University of Aveiro, 3810-193 Aveiro, Portugal, ^bREQUIMTE / LAQV & Departamento de Química e Bioquímica, Faculdade de Ciencias, Universidade do Porto, 4169-007 Porto, Portugal, ^cDepartment of Chemistry, QOPNA, University of Aveiro, 3810-193 Aveiro, Portugal, and ^dDepartment of Organic and Macromolecular Chemistry, Ghent University, B-9000 Ghent, Belgium
^*Correspondence e-mail: filipe.paz@ua.pt

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 13 June 2015; accepted 17 June 2015; online 24 June 2015)

Both the 3-amino-2H,4H-1,2,4-triazolium cation and the pyrazine-2-carboxylate anion in the title salt, C₂H₅N₄⁺·C₅H₃N₂O₂⁻, were formed by an unexpected decarboxylation reaction, from 5-amino-1H-1,2,4-triazole-3-carboxylic acid and pyrazine-2,3-dicarboxylic acid, respectively. The dihedral angle between the pyrazine ring (r.m.s. deviation = 0.008 Å) and the carboxylate group in the anion is 3.7 (3)°. The extended structure of the salt contains a supramolecular zigzag tape in which cations and anions are engaged in strong and highly directional N—H⋯N,O hydrogen bonds, forming R₂²(8) and R₂²(9) graph-set motifs. The packing between the tapes is mediated by π–π stacking interactions between the triazole and pyrazine rings.

Keywords: crystal structure; ionothermal synthesis; decarboxylation; triazolium salt; hydrogen bonding; π–π stacking interactions.

CCDC reference: 1407396

1. 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.

2. 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.

Figure 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.

3. 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).

Table 1
Hydrogen-bond geometry (Å, °)

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⋯O1ⁱ	0.90 (1)	1.73 (1)	2.632 (3)	176 (3)
N6—H6B⋯O2ⁱ	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) $[-x+1, y-{\script{1\over 2}}, -z+{\script{3\over 2}}]$ .

Figure 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.

4. 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 NO³⁻ ions (Chen et al., 2009 ).

5. 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.

6. Refinement details

Crystal data, data collection and structure refinement details are summarized in Table 2. 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).

Table 2
Experimental details

Crystal data
Chemical formula	C₂H₅N₄⁺·C₅H₃N₂O₂⁻
M_r	208.19
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	296
a, b, c (Å)	7.0599 (5), 12.1868 (8), 10.8385 (6)
β (°)	103.593 (4)
V (Å³)	906.40 (10)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.12
Crystal size (mm)	0.09 × 0.04 × 0.03

Data collection
Diffractometer	Bruker X8 Kappa CCD APEXII
Absorption correction	Multi-scan (SADABS; Sheldrick, 1998 )
T_min, T_max	0.989, 0.997
No. of measured, independent and observed [I > 2σ(I)] reflections	12089, 1858, 1037
R_int	0.077
(sin θ/λ)_max (Å⁻¹)	0.625

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.059, 0.133, 1.02
No. of reflections	1858
No. of parameters	148
No. of restraints	5
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.19, −0.20
Computer programs: APEX2 (Bruker, 2006 ), SAINT-Plus (Bruker, 2005 ), SHELXS97 and SHELXTL (Sheldrick, 2008 ), SHELXL2014 (Sheldrick, 2015 ) and DIAMOND (Brandenburg, 2009 ).

Supporting information

CCDC reference: 1407396

Crystal structure: contains datablocks I, New_Global_Publ_Block. DOI: 10.1107/S205698901501172X/hb7446sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S205698901501172X/hb7446Isup2.hkl

Supporting information file. DOI: 10.1107/S205698901501172X/hb7446Isup3.cml

checkCIF report

Chemical context top

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.

Structural commentary top

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.

Supramolecular features top

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).

Database survey top

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) .

Synthesis and crystallization top

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.

Refinement details top

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 top

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 top

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 top

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 top

Crystal data top

C₂H₅N₄⁺·C₅H₃N₂O₂⁻	F(000) = 432
M_r = 208.19	D_x = 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) Å³	Block, colourless
Z = 4	0.09 × 0.04 × 0.03 mm

Data collection top

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

Refinement top

Refinement on F²	5 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F² > 2σ(F²)] = 0.059	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.133	w = 1/[σ²(F_o²) + (0.0599P)²] where P = (F_o² + 2F_c²)/3
S = 1.01	(Δ/σ)_max < 0.001
1858 reflections	Δρ_max = 0.19 e Å⁻³
148 parameters	Δρ_min = −0.20 e Å⁻³

Crystal data top

C₂H₅N₄⁺·C₅H₃N₂O₂⁻	V = 906.40 (10) Å³
M_r = 208.19	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 7.0599 (5) Å	µ = 0.12 mm⁻¹
b = 12.1868 (8) Å	T = 296 K
c = 10.8385 (6) Å	0.09 × 0.04 × 0.03 mm
β = 103.593 (4)°

Data collection top

Bruker X8 Kappa CCD APEXII diffractometer	1858 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 1998)	1037 reflections with I > 2σ(I)
T_min = 0.989, T_max = 0.997	R_int = 0.077
12089 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.059	5 restraints
wR(F²) = 0.133	H atoms treated by a mixture of independent and constrained refinement
S = 1.01	Δρ_max = 0.19 e Å⁻³
1858 reflections	Δρ_min = −0.20 e Å⁻³
148 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
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 (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
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) top

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) top

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···O1ⁱ	0.90 (1)	1.73 (1)	2.632 (3)	176 (3)
N6—H6B···O2ⁱ	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.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N4—H4A···O2	0.902 (10)	1.769 (12)	2.655 (3)	166 (3)
N5—H5···O1ⁱ	0.901 (10)	1.733 (11)	2.632 (3)	176 (3)
N6—H6B···O2ⁱ	0.896 (10)	1.968 (12)	2.853 (3)	169 (3)
N6—H6A···N1	0.899 (10)	2.212 (12)	3.099 (3)	169 (3)

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

Experimental details

Crystal data
Chemical formula	C₂H₅N₄⁺·C₅H₃N₂O₂⁻
M_r	208.19
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	296
a, b, c (Å)	7.0599 (5), 12.1868 (8), 10.8385 (6)
β (°)	103.593 (4)
V (Å³)	906.40 (10)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.12
Crystal size (mm)	0.09 × 0.04 × 0.03

Data collection
Diffractometer	Bruker X8 Kappa CCD APEXII diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 1998)
T_min, T_max	0.989, 0.997
No. of measured, independent and observed [I > 2σ(I)] reflections	12089, 1858, 1037
R_int	0.077
(sin θ/λ)_max (Å⁻¹)	0.625

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.059, 0.133, 1.01
No. of reflections	1858
No. of parameters	148
No. of restraints	5
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.19, −0.20

Computer programs: APEX2 (Bruker, 2006), SAINT-Plus (Bruker, 2005), SHELXS97 (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2015), DIAMOND (Brandenburg, 2009), SHELXTL (Sheldrick, 2008).

Acknowledgements

Funding Sources and Entities: The Fundação para a Ciência e a Tecnologia (FCT, Portugal), the European Union, QREN, FEDER through Programa Operacional Factores de Competitividade (COMPETE), CICECO-Aveiro Institute of Materials (Ref. FCT UID/CTM/50011/2013), REQUIMTE/LAQV (Ref. FCT UID/QUI/50006/2013) financed by national funds through the FCT/MEC and when applicable co-financed by FEDER under the PT2020 Partnership Agreement.Projects and Individual grants: We wish to thank the FCT for funding the R&D projects FCOMP-01–0124-FEDER-041282 (Ref. FCT EXPL/CTM-NAN/0013/2013) and FCOMP-01–0124-FEDER-041445 (Ref. FCT EXPL/QEQ-QUI/0199/2013), and also CICECO for specific funding towards the purchase of the single-crystal diffractometer. The FCT is gratefully acknowledged for the post-doctoral research grants Nos. SFRH/BPD/63736/2009 and SFRH/BPD/47566/2008 (to JAF and BL, respectively).

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research communications\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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

1. Chemical context

2. Structural commentary

3. Supra­molecular features

4. Database survey

5. Synthesis and crystallization

6. Refinement details

Supporting information

Acknowledgements

References

research communications

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

3. Supramolecular features