Ammonium 6-carboxy­pyridine-2-carboxyl­ate

In the title compound, NH₄⁺·C₇H₄NO₄⁻, the cations and anions are situated on twofold rotation axes. The carboxyl and carboxylate groups are thus disordered; this is consistent with the short and strong O—H...O hydrogen bond across an inversion centre between these groups in neighbouring anions. Ion pairing, and inter­molecular O—H...O and N—H...O hydrogen bonds contribute to the crystal packing stability.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](C-C) = 0.001 Å
• R factor = 0.034
• wR factor = 0.101
• Data-to-parameter ratio = 18.7

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ ....          ?
PLAT066_ALERT_1_C Predicted and Reported Transmissions Identical .          ?
PLAT094_ALERT_2_C Ratio of Maximum / Minimum Residual Density ....       2.50
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....       2.19
PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) .       1.14 Ratio

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   5 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   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
   0 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. Comment

There are some instances of ion pairing between ammonium ion and a counter ion, such as a proton transfer compound containing ammonium cation and an anionic complex [Co(CO)₄]^- (Casanova et al., 2006), supramolecular complexes of p-tert-butylcalix[6]arene and ammonium cations (Lazzarotto et al., 2005). Another example is proton transfer from acidic zeolites to NH₃ and the interaction of NH₄⁺ cation with the zeolite lattice (Teunissen et al., 1993).

In continuation of our study of proton transfer compounds containing pyridine-2,6-dicarboxylate ion (Aghabozorg et al., 2005; Aghabozorg, Ghadermazi & Attar Gharamaleki, 2006; Aghabozorg, Ghadermazi, Manteghi & Nakhjavan, 2006; Aghabozorg, Ghadermazi & Ramezanipour, 2006; Sheshmani et al., 2006), we present here the crystal structure of the title compound (I).

In (I), the cations and anions are situated on twofold rotational symmetry axes (Fig. 1), that causes the disorder of the acidic H atom. Various types of intermolecular hydrogen bonds (Table 1) are observed in (I), which form the layered supramolecular structure (Fig. 2).

Related literature

For related crystal structures, see: Teunissen et al. (1993); Lazzarotto et al. (2005); Casanova et al. (2006). For crystal structures of similar compounds with the same anionic fragment synthesized by our group, see: Aghabozorg et al. (2005); Aghabozorg, Ghadermazi & Attar Gharamaleki (2006); Aghabozorg, Ghadermazi, Manteghi & Nakhjavan (2006); Aghabozorg, Ghadermazi & Ramezanipour (2006); Sheshmani et al. (2006)

S2. Experimental

A 150 ml solution of 4 mmol (668 mg) pyridine-2,6-dicarboxylic acid and a 20 ml solution of 4 mmol (560 mg) hexamethylenetetramine in THF were mixed. The resulting white precipitate with 90% yield was recrystallized in water to shiny colourless cubic crystals (m.p.: 330°C) after four weeks.

S3. Refinement

All H atoms were found in Fourier difference map, placed in idealized postions (C—H 0.93 Å, N—H 0.90 Å, O—H 0.84 Å) and refined as riding, with U_eq(H) = 1.2Ueq of the parent atom. For disordered by symmetry atom H2, the occupancy was fixed to 0.5.

Computing details

Data collection: APEX2 (Bruker, 2005); cell refinement: APEX2 (Bruker, 2005); data reduction: APEX2 (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 1998); program(s) used to refine structure: SHELXTL (Sheldrick, 1998); molecular graphics: SHELXTL (Sheldrick, 1998); software used to prepare material for publication: SHELXTL (Sheldrick, 1998).

Figures

	Fig. 1. View of (I) showing the atomic numbering and 50% probability displacement ellipsoids [symmetry code: (A) 2 - x, y, 1/2 - z]. In the anion, only one position of teh disordered atom H2 is shown. Dashed lines indicate hydrogen bonds.
	Fig. 2. A portion of the crystal packing viewed along c axis. Hydrogen bonds are shown with dashed lines. In the anions, only one position of the disordered hydroxyl H-atom is shown.

Ammonium 6-carboxypyridine-2-carboxylate

Crystal data

H4N^+·C7H4NO4^−	F(000) = 384
Mr = 184.15	Dx = 1.615 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 1992 reflections
a = 10.7033 (11) Å	θ = 2.9–34.8°
b = 12.0722 (12) Å	µ = 0.14 mm^−1
c = 7.2121 (7) Å	T = 100 K
β = 125.651 (2)°	Cube, colourless
V = 757.24 (13) Å^3	0.50 × 0.50 × 0.50 mm
Z = 4

Data collection

Bruker SMART APEXII CCD area-detector diffractometer	1158 independent reflections
Radiation source: fine-focus sealed tube	1081 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.020
φ and ω scans	θmax = 30.5°, θmin = 2.9°
Absorption correction: multi-scan (APEX2; Bruker, 2005)	h = −15→14
Tmin = 0.936, Tmax = 0.936	k = −16→17
3303 measured reflections	l = −10→10

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.034	H-atom parameters constrained
wR(F^2) = 0.102	w = 1/[σ^2(Fo^2) + (0.0629P)^2 + 0.3876P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max < 0.001
1158 reflections	Δρmax = 0.55 e Å^−3
62 parameters	Δρmin = −0.22 e Å^−3
0 restraints	Extinction correction: SHELXTL (Sheldrick, 1998), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.016 (4)

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.

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 (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
O1	0.73809 (7)	0.61754 (5)	0.13711 (11)	0.01439 (18)
O2	0.62331 (7)	0.45370 (5)	0.08777 (12)	0.01787 (19)
H1	0.5518	0.5000	0.0356	0.027*	0.50
N1	1.0000	0.50758 (8)	0.2500	0.0100 (2)
C1	0.73808 (9)	0.51498 (7)	0.14117 (13)	0.01132 (19)
C2	0.87885 (8)	0.44959 (6)	0.20657 (12)	0.00989 (19)
C3	0.87534 (9)	0.33428 (7)	0.21115 (14)	0.01224 (19)
H3A	0.7893	0.2967	0.1881	0.015*
C4	1.0000	0.27524 (9)	0.2500	0.0135 (2)
H4A	1.0000	0.1966	0.2500	0.016*
N2	1.0000	0.75422 (8)	0.2500	0.0144 (2)
H2	0.9523	0.7984	0.1263	0.017*
H3	0.9317	0.7089	0.2460	0.017*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0108 (3)	0.0103 (3)	0.0208 (3)	0.00095 (19)	0.0085 (3)	−0.0002 (2)
O2	0.0092 (3)	0.0123 (3)	0.0316 (4)	−0.0001 (2)	0.0115 (3)	0.0008 (2)
N1	0.0080 (4)	0.0092 (4)	0.0121 (4)	0.000	0.0054 (4)	0.000
C1	0.0087 (4)	0.0116 (4)	0.0136 (4)	0.0003 (2)	0.0064 (3)	0.0001 (2)
C2	0.0076 (3)	0.0095 (4)	0.0117 (4)	0.0001 (2)	0.0052 (3)	0.0000 (2)
C3	0.0094 (3)	0.0102 (4)	0.0156 (4)	−0.0011 (2)	0.0064 (3)	0.0001 (2)
C4	0.0112 (5)	0.0087 (4)	0.0180 (5)	0.000	0.0070 (4)	0.000
N2	0.0119 (4)	0.0107 (4)	0.0183 (5)	0.000	0.0076 (4)	0.000

Geometric parameters (Å, º)

O1—C1	1.2385 (10)	C3—C4	1.3896 (9)
O2—C1	1.2857 (9)	C3—H3A	0.9500
O2—H1	0.8389	C4—C3^i	1.3896 (9)
N1—C2	1.3402 (9)	C4—H4A	0.9500
N1—C2^i	1.3402 (9)	N2—H2	0.8999
C1—C2	1.5125 (11)	N2—H3	0.9000
C2—C3	1.3934 (11)
C1—O2—H1	102.4	C4—C3—C2	118.76 (7)
C2—N1—C2^i	117.01 (9)	C4—C3—H3A	120.6
O1—C1—O2	125.55 (7)	C2—C3—H3A	120.6
O1—C1—C2	121.02 (7)	C3^i—C4—C3	118.29 (10)
O2—C1—C2	113.41 (7)	C3^i—C4—H4A	120.9
N1—C2—C3	123.51 (7)	C3—C4—H4A	120.9
N1—C2—C1	116.90 (7)	H2—N2—H3	110.3
C3—C2—C1	119.54 (7)
C2^i—N1—C2—C3	1.91 (5)	O2—C1—C2—C3	−2.04 (10)
C2^i—N1—C2—C1	−175.78 (7)	N1—C2—C3—C4	−3.76 (11)
O1—C1—C2—N1	−2.72 (10)	C1—C2—C3—C4	173.87 (6)
O2—C1—C2—N1	175.75 (6)	C2—C3—C4—C3^i	1.74 (5)
O1—C1—C2—C3	179.50 (7)

Symmetry code: (i) −x+2, y, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H1···O2^ii	0.84	1.64	2.434 (1)	158
N2—H2···O1^iii	0.90	2.07	2.897 (1)	153
N2—H3···O1	0.90	2.06	2.930 (1)	163
N2—H3···N1	0.90	2.53	2.977 (1)	111

Symmetry codes: (ii) −x+1, −y+1, −z; (iii) −x+3/2, −y+3/2, −z.