3-Carboxy­pyridinium chloride

The synthesis, crystallization and structure determination of the title compound, nicotinic acid hydro­chloride, C₆H₆NO₂⁺·Cl^-, is part of a project on charge densities in crystals. The good quality crystals of the compound composed of light elements and in centrosymmetric space group P2₁/m indicate their suitability for charge-density study.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.031
• wR factor = 0.077
• Data-to-parameter ratio = 8.5

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S1. Comment

The crystal structure of the title compound, (I), is built of protonated nicotinic acid cations C₆H₆NO₂⁺ and chlorine anions. As expected, the nicotinic acid is protonated on the aromatic ring N atom and forms a 3-carboxypyridinium cation (Fig. 1). Interatomic distances and angles are within usual limits (Table 1).

Electrostatic interactions among the ions in the crystal are supplemented with hydrogen bonds (Table 1). The 3-carboxypyridinium O1 atom acts as donor to Cl1 within the asymmetric unit, the 3-carboxypyridinium N1 atom acts as donor to the 3-carboxypyridinium O2(x, y, z + 1) atom and, simultaneously,to Cl1(x, y, z + 1). In total, there is one two-centre and one three-centre hydrogen bond per cation (Table 2).

The compound crystallizes in the space group P2₁/m. Both ions present in the crystal are situated in the special Wyckoff positions e of multiplicity 2 and site symmetry m. This means that both ions lie on the mirror plane (x, 1/4, z) and the 3-carboxypyridinium cation is strictly planar. As a result, there are parallel planar layers in the crystal structure, on the mirror planes of space group P2₁/m. The distance between the layers is 3.3343 (3) Å, half of the lattice parameter b.

Within the layer, there are chains of larger 3-carboxypyridinium cations alternating with smaller Cl^- anions; they are linked through hydrogen bonds (Fig. 2).

There are no hydrogen-bonding interactions between the layers; examination of the structure with PLATON (Spek, 1990) shows that there are no solvent-accessible voids in the unit cell.

This work is a preliminary study, part of a project on charge densities in crystals (Slouf, 2000). The structure of nicotinic acid itself has already been determined (Wright & King, 1953) and redetermined (Gupta & Kumar, 1975; Kutoglu & Scheringer, 1983). In the Cambridge Structural Database (Allen & Kennard, 1993), neither the structure of 3-carboxypyridinium, which is reported here, nor any charge–density study on nicotinic acid was found.

S2. Experimental

An 0.1 M methanol solution of nicotinic acid (99% pure) was mixed with an equimolar amount of an 0.1 M methanol solution of hydrochloric acid (36% water solution). Crystals suitable for structure determination were grown by very slow evaporation of the mixture.

Computing details

Data collection: COLLECT (Nonius, 1995); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO and SCALEPACK (Otwinowski & Minor, 1997) and JANA2000 (Petricek & Dusek, 2000); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1990); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of the title compound with displacement ellipsoids at the 50% probability level.
	Fig. 2. A view of part of the crystal structure of (I), showing the layer identical with mirror plane (x, 1/4, z) of space group P21/m. Hydrogen bonds are indicated by dashed lines.

3-carboxypyridinium chloride

Crystal data

C6H6O2N^+·Cl^−	F(000) = 164
Mr = 159.57	Dx = 1.500 Mg m^−3
Monoclinic, P21/m	Mo Kα radiation, λ = 0.71070 Å
a = 7.1704 (3) Å	Cell parameters from 2406 reflections
b = 6.6685 (6) Å	θ = 1–25°
c = 7.4937 (6) Å	µ = 0.47 mm^−1
β = 99.555 (5)°	T = 293 K
V = 353.35 (5) Å^3	Prism, translucent colourless
Z = 2	0.3 × 0.2 × 0.2 mm

Data collection

Nonius KappaCCD diffractometer	608 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.015
Graphite monochromator	θmax = 25.0°, θmin = 2.8°
Detector resolution: 0.110 pixels mm^-1	h = −8→8
ϕ and ω scans	k = 0→7
2406 measured reflections	l = 0→8
679 independent reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.031	All H-atom parameters refined
wR(F^2) = 0.077	w = 1/[σ^2(Fo^2) + (0.0263P)^2 + 0.1615P] where P = (Fo^2 + 2Fc^2)/3
S = 1.11	(Δ/σ)max < 0.001
679 reflections	Δρmax = 0.21 e Å^−3
80 parameters	Δρmin = −0.22 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.090 (17)

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
Cl1	0.71876 (9)	0.2500	0.14792 (8)	0.0409 (3)
O1	0.5551 (2)	0.2500	0.4790 (2)	0.0510 (6)
O2	0.2816 (3)	0.2500	0.2907 (2)	0.0765 (9)
C7	0.3704 (4)	0.2500	0.4408 (3)	0.0427 (7)
C1	0.2747 (3)	0.2500	0.6036 (3)	0.0350 (6)
C2	0.3771 (4)	0.2500	0.7746 (3)	0.0353 (6)
N3	0.2875 (3)	0.2500	0.9170 (3)	0.0369 (6)
C4	0.1005 (4)	0.2500	0.9007 (4)	0.0443 (7)
C5	−0.0081 (4)	0.2500	0.7323 (4)	0.0501 (8)
C6	0.0793 (4)	0.2500	0.5825 (4)	0.0437 (7)
H1	0.610 (6)	0.2500	0.363 (6)	0.093 (13)*
H2	0.505 (4)	0.2500	0.801 (3)	0.038 (7)*
H3	0.359 (4)	0.2500	1.022 (4)	0.050 (9)*
H4	0.050 (4)	0.2500	1.006 (4)	0.047 (8)*
H5	−0.139 (5)	0.2500	0.728 (4)	0.059 (9)*
H6	0.012 (4)	0.2500	0.470 (4)	0.046 (8)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.0355 (4)	0.0539 (5)	0.0344 (4)	0.000	0.0089 (3)	0.000
O1	0.0328 (11)	0.0905 (17)	0.0301 (10)	0.000	0.0065 (8)	0.000
O2	0.0413 (12)	0.166 (3)	0.0220 (10)	0.000	0.0035 (8)	0.000
C7	0.0375 (15)	0.0633 (19)	0.0271 (13)	0.000	0.0052 (11)	0.000
C1	0.0328 (13)	0.0470 (17)	0.0250 (12)	0.000	0.0038 (10)	0.000
C2	0.0309 (14)	0.0467 (17)	0.0281 (13)	0.000	0.0047 (10)	0.000
N3	0.0394 (13)	0.0475 (14)	0.0229 (11)	0.000	0.0022 (9)	0.000
C4	0.0438 (16)	0.0583 (19)	0.0340 (15)	0.000	0.0161 (12)	0.000
C5	0.0311 (15)	0.079 (2)	0.0407 (16)	0.000	0.0086 (12)	0.000
C6	0.0350 (14)	0.065 (2)	0.0290 (14)	0.000	−0.0007 (11)	0.000

Geometric parameters (Å, º)

O1—C7	1.308 (3)	C5—C6	1.373 (4)
O2—C7	1.197 (3)	O1—H1	1.01 (4)
C7—C1	1.496 (3)	C2—H2	0.91 (3)
C1—C2	1.367 (3)	N3—H3	0.86 (3)
C1—C6	1.383 (4)	C4—H4	0.92 (3)
C2—N3	1.333 (3)	C5—H5	0.93 (3)
N3—C4	1.326 (4)	C6—H6	0.90 (3)
C4—C5	1.369 (4)
O2—C7—O1	124.5 (2)	C4—N3—H3	121 (2)
C7—O1—H1	110 (2)	C2—N3—H3	116 (2)
O2—C7—C1	121.5 (2)	N3—C4—C5	119.8 (2)
O1—C7—C1	114.0 (2)	N3—C4—H4	117.2 (18)
C2—C1—C6	118.9 (2)	C5—C4—H4	123.0 (18)
C2—C1—C7	121.1 (2)	C4—C5—C6	119.1 (3)
C6—C1—C7	120.0 (2)	C4—C5—H5	116.7 (19)
N3—C2—C1	119.6 (2)	C6—C5—H5	124.2 (19)
N3—C2—H2	115.5 (17)	C5—C6—C1	119.8 (2)
C1—C2—H2	124.8 (17)	C5—C6—H6	121.1 (18)
C4—N3—C2	122.7 (2)	C1—C6—H6	119.0 (18)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···Cl1	1.01 (4)	1.90 (4)	2.9154 (19)	179 (1)
N3—H3···O2^i	0.86 (3)	2.18 (3)	2.808 (3)	130 (3)
N3—H3···Cl1^i	0.86 (3)	2.60 (3)	3.283 (2)	137 (3)

Symmetry code: (i) x, y, z+1.