Redetermination of picolinic acid hydro­chloride at 150 K

The structure of the title compound, C₆H₆NO₂⁺·Cl⁻, was previously determined at ambient temperature [Laurent (1965). Acta Cryst. 18, 799–806]. This redetermination at 150 K is to a far higher precision. On cooling to 150 K, the unit cell contracts most in the π–π stacking direction, b, and rather less so in the directions involving the strongly hydrogen-bonded chains, a and c. The π–π stacking distance is b/2 (3.263 Å)All of the atoms lie on a mirror plane. There are two strong hydrogen bonds, O—H...Cl and N—H...Cl. Cations and anions form hydrogen-bonded, zigzag chains parallel to the a axis.

Key indicators

• Single-crystal X-ray study
• T = 150 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.029
• wR factor = 0.082
• Data-to-parameter ratio = 16.1

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT094_ALERT_2_C Ratio of Maximum / Minimum Residual Density ....       2.25
PLAT213_ALERT_2_C Atom O2      has ADP max/min Ratio .............       3.60 prola
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....       3.97

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

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   3 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
   0 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

As part of our studies into complexes, co-crystals and solvates of pyridine and pyrazine (poly)carboxylates we inadvertently produced crystals of pyridine-2-carboxylic acid hydrochloride (I). Fig. 1. shows the asymmetric unit. The structure had been determined previously at ambient temperature with an R factor of 0.147 (Laurent, 1965). Comparison of the unit-cell parameters reveals that on cooling to 150 K, taking into account the different unit cell and space group settings, a contracts by 0.45%, b by 1.85% and c by 0.13% (see Figs. 2 & 3). We note that b/2 is the interlayer spacing with soft π-π stacking interactions only, while a and c incorporate the strong, less compressable, hydrogen bonds. The basic structure was discussed in datail in Laurent's paper. See tables for hydrogen bond geomery which has been determined here more precisely. Laurent notes an apparently very short C═O bond length of 1.17 Å, but the current study suggests a more normal value of 1.200 (2) Å.

Related literature

Laurent (1965) previously determined the stucture of the title compound at ambient temperature with R1 = 0.147.

S2. Experimental

Picolinic acid (0.115 g; 0.934 mmol) in methanol/ethanol (10 ml, 1:1) was added dropwise to a solution of Cu(PPh₃)₂(BH₄) (0.450 g; 0.746 mmol) in CH₂Cl₂ (10 ml). The solution was stirred for 15 min, then reduced in volume to give a yellow precipitate (0.468 g). Crystals were obtained by vapour diffusion from methanol/ethanol (1:1) with diethylether as precipitant. The source of the HCl is thought to have been the dichloromethane solvent in the initial reaction.

S3. Refinement

Aromatic H atoms were placed in geometric positions (C—H distance = 0.95 Å) using a riding model. NH and OH hydrogen coordinates were freely refined.U_iso values were set to 1.2U_eq of the carrier atom for CH and NH, 1.5U_eq for OH.

Computing details

Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT (Bruker, 2006); data reduction: SAINT (Bruker, 2006); program(s) used to solve structure: SHELXTL (Bruker, 2000); program(s) used to refine structure: SHELXTL (Bruker, 2000); molecular graphics: SHELXTL (Bruker, 2000); software used to prepare material for publication: SHELXTL (Bruker, 2000) and local programs.

Figures

	Fig. 1. View of I, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. Packing plot of I viewed parallel to b, showing the strong hydrogen bonds. Most hydrogen atoms have been removed for clarity. Symmetry code: (i) x + 1/2, y, -z + 3/2
	Fig. 3. Packing plot of I viewed parallel to c, showing the π-π stacked layer structure. Most hydrogen atoms have been removed for clarity.

picolinic acid hydrochloride

Crystal data

C6H6NO2^+·Cl^−	F(000) = 328
Mr = 159.57	Dx = 1.519 Mg m^−3
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 3266 reflections
a = 13.7876 (15) Å	θ = 3.0–30.4°
b = 6.5268 (7) Å	µ = 0.48 mm^−1
c = 7.7517 (9) Å	T = 150 K
V = 697.57 (13) Å^3	Plate, colourless
Z = 4	0.54 × 0.33 × 0.10 mm

Data collection

Bruker APEXII CCD diffractometer	1045 independent reflections
Radiation source: fine-focus sealed tube	939 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.024
ω rotation with narrow frames scans	θmax = 29.5°, θmin = 3.0°
Absorption correction: multi-scan (SADABS; Sheldrick, 2007)	h = −19→18
Tmin = 0.782, Tmax = 0.954	k = −9→9
7281 measured reflections	l = −10→10

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.029	Hydrogen site location: geom except NH & OH coords freely refined
wR(F^2) = 0.082	H atoms treated by a mixture of independent and constrained refinement
S = 1.13	w = 1/[σ^2(Fo^2) + (0.0415P)^2 + 0.234P] where P = (Fo^2 + 2Fc^2)/3
1045 reflections	(Δ/σ)max < 0.001
65 parameters	Δρmax = 0.42 e Å^−3
0 restraints	Δρmin = −0.19 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.

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	0.12483 (3)	0.2500	0.87284 (5)	0.02637 (14)
C1	0.36168 (11)	0.2500	0.35614 (19)	0.0214 (3)
C2	0.31249 (12)	0.2500	0.20260 (19)	0.0245 (3)
H2	0.2436	0.2500	0.2010	0.029*
C3	0.36462 (12)	0.2500	0.0493 (2)	0.0270 (4)
H3	0.3315	0.2500	−0.0582	0.032*
C4	0.46489 (13)	0.2500	0.0538 (2)	0.0294 (4)
H4	0.5014	0.2500	−0.0502	0.035*
C5	0.51094 (12)	0.2500	0.2117 (2)	0.0292 (4)
H5	0.5798	0.2500	0.2173	0.035*
N1	0.45886 (11)	0.2500	0.35628 (17)	0.0233 (3)
H1	0.4884 (16)	0.2500	0.448 (3)	0.028*
C6	0.31613 (13)	0.2500	0.5312 (2)	0.0302 (4)
O1	0.22104 (9)	0.2500	0.52598 (16)	0.0299 (3)
H1A	0.204 (2)	0.2500	0.628 (3)	0.045*
O2	0.36553 (11)	0.2500	0.65865 (18)	0.0631 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.0215 (2)	0.0388 (2)	0.0188 (2)	0.000	0.00604 (13)	0.000
C1	0.0184 (7)	0.0329 (8)	0.0129 (6)	0.000	0.0009 (5)	0.000
C2	0.0178 (7)	0.0410 (9)	0.0147 (7)	0.000	−0.0002 (5)	0.000
C3	0.0252 (8)	0.0440 (10)	0.0118 (6)	0.000	−0.0018 (6)	0.000
C4	0.0254 (8)	0.0478 (11)	0.0150 (7)	0.000	0.0046 (6)	0.000
C5	0.0186 (7)	0.0475 (11)	0.0216 (8)	0.000	0.0023 (6)	0.000
N1	0.0186 (6)	0.0378 (8)	0.0135 (6)	0.000	−0.0029 (5)	0.000
C6	0.0229 (8)	0.0544 (11)	0.0134 (7)	0.000	0.0019 (6)	0.000
O1	0.0211 (6)	0.0534 (8)	0.0150 (5)	0.000	0.0035 (4)	0.000
O2	0.0252 (7)	0.152 (2)	0.0117 (6)	0.000	−0.0012 (5)	0.000

Geometric parameters (Å, º)

C1—N1	1.340 (2)	C4—H4	0.9500
C1—C2	1.370 (2)	C5—N1	1.331 (2)
C1—C6	1.495 (2)	C5—H5	0.9500
C2—C3	1.389 (2)	N1—H1	0.82 (2)
C2—H2	0.9500	C6—O2	1.200 (2)
C3—C4	1.383 (2)	C6—O1	1.312 (2)
C3—H3	0.9500	O1—H1A	0.82 (3)
C4—C5	1.379 (2)
N1—C1—C2	119.72 (14)	C3—C4—H4	120.6
N1—C1—C6	114.79 (14)	N1—C5—C4	119.94 (16)
C2—C1—C6	125.48 (15)	N1—C5—H5	120.0
C1—C2—C3	119.16 (15)	C4—C5—H5	120.0
C1—C2—H2	120.4	C5—N1—C1	122.61 (14)
C3—C2—H2	120.4	C5—N1—H1	117.5 (16)
C4—C3—C2	119.72 (15)	C1—N1—H1	119.9 (16)
C4—C3—H3	120.1	O2—C6—O1	126.34 (16)
C2—C3—H3	120.1	O2—C6—C1	120.58 (16)
C5—C4—C3	118.85 (16)	O1—C6—C1	113.08 (14)
C5—C4—H4	120.6	C6—O1—H1A	105 (2)
N1—C1—C2—C3	0.0	C2—C1—N1—C5	0.0
C6—C1—C2—C3	180.0	C6—C1—N1—C5	180.0
C1—C2—C3—C4	0.0	N1—C1—C6—O2	0.0
C2—C3—C4—C5	0.0	C2—C1—C6—O2	180.0
C3—C4—C5—N1	0.0	N1—C1—C6—O1	180.0
C4—C5—N1—C1	0.0	C2—C1—C6—O1	0.0

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···Cl1^i	0.82 (2)	2.34 (2)	3.1058 (14)	156 (2)
O1—H1A···Cl1	0.82 (3)	2.19 (3)	2.9982 (13)	167 (3)

Symmetry code: (i) x+1/2, y, −z+3/2.