Strong intramolecular O—H...O hydrogen bonds in quinaldic acid N-oxide and picolinic acid N-oxide

The title compounds contain very short intramolecular hydrogen bonds of the type C—O—H...O—N. The O...O distances are 2.425 (2) Å in picolinic acid N-oxide (2-carboxy­pyridine N-oxide), C₆H₅NO₃, (I), and 2.435 (2) Å in quinaldic acid N-oxide (2-carboxy­quinoline N-oxide), C₁₀H₇NO₃, (II). In (II), this is associated with slight molecular distortion from planarity, while in (I), such an effect cannot be observed because the mol­ecule crystallizes on a mirror plane.

S1. Comment

There is a current revival of interest in the so-called very strong hydrogen bonds (Jeffrey, 1997). For the best studied of these hydrogen bonds, O—H···O, the majority of examples belong to a small number of chemical situations, i.e. the combination of acid and complementary base (O—H···O^-), the combination of base and complementary acid (O···H—O⁺), and `resonance assisted hydrogen bonding' (Hibbert & Emsley, 1990; Gilli et al., 1994). It is characteristic for all these cases that proton transfer leads to a chemically identical situation (O—H···O^- → ^-O···H—O, etc.). Not all very strong hydrogen bonds, however, belong to one of these categories. An example are intramolecular hydrogen bonds in 2-carboxypyridine-N-oxide (picolinic acid N-oxide), (I), and many of its derivatives. Although donor and acceptor groups of (I) are chemically very different, intramolecular hydrogen bonds are very short. In 6-methyl-2-carboxypyridine-N-oxide, the intramolecular O···O distance was reported as 2.41 Å, and the H atom was found bonded to the acid group (Dideberg & Dupont, 1975). In the 6-carboxy derivative of (I), 2,6-dicarboxypyridine-N-oxide, which crystallizes with two symmetry-independent molecules, the four independent intramolecular hydrogen bonds have O···O separations in the range 2.45–2.48 Å, and H atoms are bonded at the acid groups (Rychlewska & Gdaniec, 1977). For (I), the crystal structure was reported only with relatively low accuracy, and an intramolecular O···O distance of about 2.39 Å (Laing & Nicholson, 1971). The H atom position in the hydrogen bond could not be located. Because the short C—O—H···O—N hydrogen bonds in (I) and derivatives of (I) are chemically unusual, and to investigate the hydrogen-bond geometry with high reliability, we have determined the low-temperature crystal structure of quinaldic acid N-oxide (II), and repeated the crystal structure determination of (I), also at low temperature. In parallel, Hadzi and coworkers have performed extensive IR-spectroscopic and computational investigations of (I), (II), and related molecules (Stare et al., 2000). In particular, hydrogen-bond energies are calculated around -15 kcal/mol (in vacuo). \sch

The molecular structures of (I) and (II) are shown in Figure 1. In both molecules, very short intramolecular hydrogen bonds are formed, with O···O distances of 2.425 (2) in (I) and 2.435 (2) Å in (II). The relevant H atoms are much closer to the acid than to the N-oxide O atoms, so that the hydrogen bonds are of the type C—O—H···O—N (geometries in Tables 1 and 2). In the carboxyl group, the C=O and C—O bonds are clearly distinct [C=O = 1.208 (2) in (I) and 1.214 (2) Å in (II); C—O = 1.309 (2) in (I) and 1.305 (2) Å in (II)]. Because of stereochemical restriction of the C—O—H angle, the hydrogen bonds are relatively non-linear with O—H···O angles around 160°. The N—O distances are 1.342 (2) and 1.333 (2) Å in (I) and (II), respectively, which is slightly but significantly elongated compared to the average value of 1.304 Å in pyridine N-oxides (Allen et al., 1992; σ of sample = 0.012 Å). Because (I) crystallizes on a mirror plane, the observed geometry is restricted to be perfectly planar. Compound (II) crystallizes on a general position, so that deviations from planarity can be observed. Actually, O1 and O2 are displaced from the pyridine least-squares plane in opposite directions by +0.092 (2) and -0.049 (3) Å, respectively, and the resulting torsion angle O1—N1···C11—O2 is 3.3 (1)°. This is only a small distortion from planarity.

The edges of molecules (I) and (II) are constituted exclusively with O atoms and C—H groups. Therefore, it must be expected that weak C—H···O hydrogen bonds are formed in the crystal structures (Steiner, 1997; Desiraju & Steiner, 1999). Actually, there are many such interactions (Tables 1 and 2), but the geometries are all unfavourable with strongly bent angles. C—H···O hydrogen bonding does not seem to be particularly important in these compounds.

S2. Experimental

Picolinic acid N-oxide, (I), was obtained from Sigma, and quinaldic acid N-oxide was synthesized as described by Stare et al. (2000). Both compounds were recrystallized from MeOH.

S3. Refinement

The area detector data are 98.3% and 98.9% complete to 2 θ = 55° for (I) and (II), respectively. The H-atoms were located in difference Fourier calculations and refined isotropically. All H-atom displacement parameters refined to realistic values [H-atoms bonded to C: 0.031–0.038 Ų in (I) and 0.019–0.033 in (II); carboxylic acid H-atom: 0.072 (9) Ų in (I) and 0.059 (8) in (II)].

Computing details

For both compounds, data collection: COLLECT (Nonius, 1998); cell refinement: COLLECT; data reduction: COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997). Molecular graphics: ORTEPII (Johnson, 1976) for (I); ORTEPII (Johnson, 1996) for (II). For both compounds, software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. Molecular structure of (I), top, and (II), bottom. Displacement ellipsoids are drawn at the 50% probability level.

(I) 2-carboxypyridine-N-oxide'

Crystal data

C6H5NO3	F(000) = 144
Mr = 139.11	Dx = 1.554 Mg m^−3
Monoclinic, P21/m	Mo Kα radiation, λ = 0.71073 Å
a = 6.8020 (11) Å	Cell parameters from 28 reflections
b = 6.066 (2) Å	θ = 4.7–18.7°
c = 7.8040 (13) Å	µ = 0.13 mm^−1
β = 112.610 (11)°	T = 125 K
V = 297.25 (12) Å^3	Block, colourless
Z = 2	0.40 × 0.25 × 0.25 mm

Data collection

Nonius Kappa CCD diffractometer	654 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.023
Graphite monochromator	θmax = 27.4°, θmin = 2.8°
ω scans	h = −5→8
2264 measured reflections	k = −7→7
741 independent reflections	l = −9→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 atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.096	w = 1/[σ^2(Fo^2) + (0.0453P)^2 + 0.0912P] where P = (Fo^2 + 2Fc^2)/3
S = 1.12	(Δ/σ)max < 0.001
741 reflections	Δρmax = 0.36 e Å^−3
77 parameters	Δρmin = −0.24 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.07 (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
O1	0.57949 (17)	0.2500	0.43581 (16)	0.0254 (3)
O2	0.5744 (2)	0.2500	0.74478 (16)	0.0305 (4)
O3	0.2628 (2)	0.2500	0.77797 (17)	0.0388 (4)
N1	0.36573 (19)	0.2500	0.36202 (16)	0.0153 (3)
C2	0.2519 (2)	0.2500	0.4725 (2)	0.0168 (3)
C3	0.0326 (3)	0.2500	0.3903 (2)	0.0225 (4)
C4	−0.0703 (3)	0.2500	0.1985 (2)	0.0251 (4)
C5	0.0506 (3)	0.2500	0.0916 (2)	0.0233 (4)
C6	0.2686 (3)	0.2500	0.1748 (2)	0.0205 (4)
C7	0.3661 (3)	0.2500	0.6819 (2)	0.0235 (4)
H2	0.611 (5)	0.2500	0.627 (4)	0.072 (9)*
H3	−0.040 (3)	0.2500	0.466 (3)	0.031 (5)*
H4	−0.220 (4)	0.2500	0.142 (3)	0.038 (6)*
H5	−0.012 (4)	0.2500	−0.045 (3)	0.037 (6)*
H6	0.365 (3)	0.2500	0.110 (3)	0.032 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0105 (6)	0.0359 (7)	0.0281 (6)	0.000	0.0054 (4)	0.000
O2	0.0326 (7)	0.0288 (7)	0.0175 (6)	0.000	−0.0044 (5)	0.000
O3	0.0598 (10)	0.0421 (8)	0.0224 (6)	0.000	0.0246 (6)	0.000
N1	0.0128 (6)	0.0171 (6)	0.0157 (6)	0.000	0.0051 (5)	0.000
C2	0.0199 (7)	0.0156 (7)	0.0156 (7)	0.000	0.0076 (6)	0.000
C3	0.0208 (8)	0.0221 (8)	0.0288 (8)	0.000	0.0140 (7)	0.000
C4	0.0142 (7)	0.0228 (8)	0.0319 (9)	0.000	0.0016 (6)	0.000
C5	0.0279 (9)	0.0181 (7)	0.0159 (7)	0.000	−0.0002 (6)	0.000
C6	0.0269 (8)	0.0208 (8)	0.0152 (7)	0.000	0.0096 (6)	0.000
C7	0.0354 (9)	0.0191 (7)	0.0146 (7)	0.000	0.0080 (7)	0.000

Geometric parameters (Å, º)

O1—N1	1.3424 (16)	C2—C7	1.516 (2)
O1—H2	1.42 (3)	C3—C4	1.387 (2)
O2—C7	1.309 (2)	C3—H3	0.91 (2)
O2—H2	1.04 (3)	C4—C5	1.378 (2)
O3—C7	1.208 (2)	C4—H4	0.94 (2)
N1—C6	1.3527 (19)	C5—C6	1.371 (2)
N1—C2	1.3625 (19)	C5—H5	0.99 (2)
C2—C3	1.379 (2)	C6—H6	0.97 (2)
N1—O1—H2	98.6 (12)	C5—C4—H4	120.6 (13)
C7—O2—H2	105.0 (16)	C3—C4—H4	120.6 (13)
O1—N1—C6	117.53 (12)	C6—C5—C4	120.14 (14)
O1—N1—C2	120.93 (12)	C6—C5—H5	116.8 (13)
C6—N1—C2	121.54 (13)	C4—C5—H5	123.1 (13)
N1—C2—C3	118.82 (14)	N1—C6—C5	120.09 (14)
N1—C2—C7	120.12 (14)	N1—C6—H6	114.4 (13)
C3—C2—C7	121.06 (14)	C5—C6—H6	125.5 (13)
C2—C3—C4	120.59 (15)	O3—C7—O2	124.81 (15)
C2—C3—H3	117.4 (13)	O3—C7—C2	119.33 (16)
C4—C3—H3	122.0 (13)	O2—C7—C2	115.86 (14)
C5—C4—C3	118.81 (15)
O1—N1—C2—C3	180.0	O1—N1—C6—C5	180.0
C6—N1—C2—C3	0.0	C2—N1—C6—C5	0.0
O1—N1—C2—C7	0.0	C4—C5—C6—N1	0.0
C6—N1—C2—C7	180.0	N1—C2—C7—O3	180.0
N1—C2—C3—C4	0.0	C3—C2—C7—O3	0.0
C7—C2—C3—C4	180.0	N1—C2—C7—O2	0.0
C2—C3—C4—C5	0.0	C3—C2—C7—O2	180.0
C3—C4—C5—C6	0.0

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O1	1.04 (3)	1.42 (3)	2.425 (2)	159 (3)
C3—H3···O1^i	0.91 (2)	2.51 (2)	3.235 (2)	138 (2)
C4—H4···O2^ii	0.94 (2)	2.87 (2)	3.435 (2)	120 (2)
C5—H5···O2^ii	0.99 (2)	2.66 (2)	3.328 (2)	126 (2)
C5—H5···O3^iii	0.99 (2)	2.72 (2)	3.285 (2)	117 (2)
C6—H6···O3^iii	0.97 (2)	2.41 (2)	3.082 (2)	126 (2)

Symmetry codes: (i) x−1, y, z; (ii) x−1, y, z−1; (iii) x, y, z−1.

(II) 2-carboxyquinoline-N-oxide

Crystal data

C10H7NO3	F(000) = 392
Mr = 189.17	Dx = 1.550 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 3.821 (3) Å	Cell parameters from 26 reflections
b = 16.2406 (10) Å	θ = 3.3–18.4°
c = 13.062 (3) Å	µ = 0.12 mm^−1
β = 91.01 (1)°	T = 125 K
V = 810.5 (7) Å^3	Needle, yellow
Z = 4	0.5 × 0.1 × 0.1 mm

Data collection

Nonius kappa CCD diffractometer	1449 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.083
Graphite monochromator	θmax = 27.5°, θmin = 2.0°
ω–scans	h = −4→4
8148 measured reflections	k = −21→19
1829 independent reflections	l = −15→16

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)] = 0.044	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.115	w = 1/[σ^2(Fo^2) + (0.0351P)^2 + 0.5447P] where P = (Fo^2 + 2Fc^2)/3
S = 1.09	(Δ/σ)max < 0.001
1829 reflections	Δρmax = 0.30 e Å^−3
156 parameters	Δρmin = −0.21 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.008 (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
O1	0.1911 (3)	0.59674 (8)	0.01160 (9)	0.0233 (3)
O2	−0.1087 (3)	0.71560 (8)	−0.06214 (9)	0.0262 (3)
H2	0.030 (7)	0.6661 (18)	−0.0461 (19)	0.059 (8)*
O3	−0.3819 (4)	0.80210 (8)	0.04224 (10)	0.0322 (4)
N1	0.0758 (3)	0.61709 (8)	0.10397 (10)	0.0160 (3)
C2	−0.1093 (4)	0.68663 (10)	0.11830 (12)	0.0168 (4)
C3	−0.2132 (4)	0.70880 (10)	0.21682 (13)	0.0182 (4)
H3	−0.348 (5)	0.7586 (13)	0.2224 (15)	0.027 (5)*
C4	−0.1263 (4)	0.66081 (10)	0.29952 (13)	0.0187 (4)
H4	−0.193 (5)	0.6760 (12)	0.3695 (15)	0.025 (5)*
C5	0.0599 (4)	0.58659 (10)	0.28427 (12)	0.0173 (4)
C6	0.1561 (4)	0.56377 (10)	0.18441 (12)	0.0160 (3)
C7	0.3294 (4)	0.48881 (10)	0.16478 (14)	0.0206 (4)
H7	0.385 (5)	0.4746 (13)	0.0945 (16)	0.027 (5)*
C8	0.4025 (4)	0.43789 (11)	0.24559 (15)	0.0256 (4)
H8	0.513 (5)	0.3856 (15)	0.2322 (16)	0.038 (6)*
C9	0.3184 (4)	0.45986 (11)	0.34693 (14)	0.0254 (4)
H9	0.375 (5)	0.4235 (13)	0.4030 (16)	0.033 (5)*
C10	0.1524 (4)	0.53244 (11)	0.36586 (14)	0.0225 (4)
H10	0.100 (5)	0.5497 (12)	0.4338 (14)	0.019 (5)*
C11	−0.2104 (4)	0.74042 (11)	0.02758 (13)	0.0214 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0278 (6)	0.0267 (7)	0.0158 (6)	0.0025 (5)	0.0062 (5)	−0.0024 (5)
O2	0.0306 (7)	0.0271 (7)	0.0208 (7)	−0.0010 (5)	0.0000 (5)	0.0066 (5)
O3	0.0406 (8)	0.0225 (7)	0.0333 (8)	0.0096 (6)	−0.0058 (6)	0.0039 (6)
N1	0.0157 (6)	0.0160 (7)	0.0164 (7)	−0.0024 (5)	0.0024 (5)	−0.0020 (5)
C2	0.0142 (7)	0.0149 (8)	0.0212 (8)	−0.0029 (6)	−0.0008 (6)	0.0010 (6)
C3	0.0157 (8)	0.0155 (8)	0.0235 (9)	−0.0022 (6)	0.0006 (6)	−0.0042 (6)
C4	0.0164 (8)	0.0204 (8)	0.0193 (8)	−0.0034 (6)	0.0017 (6)	−0.0047 (7)
C5	0.0130 (7)	0.0181 (8)	0.0206 (8)	−0.0046 (6)	0.0000 (6)	0.0008 (6)
C6	0.0127 (7)	0.0155 (8)	0.0196 (8)	−0.0031 (6)	0.0000 (6)	0.0013 (6)
C7	0.0164 (8)	0.0184 (8)	0.0271 (9)	−0.0011 (6)	0.0009 (7)	−0.0029 (7)
C8	0.0193 (8)	0.0165 (8)	0.0409 (11)	0.0011 (7)	−0.0009 (7)	0.0037 (8)
C9	0.0210 (9)	0.0249 (9)	0.0304 (10)	−0.0031 (7)	−0.0036 (7)	0.0113 (8)
C10	0.0207 (8)	0.0250 (9)	0.0217 (9)	−0.0050 (7)	−0.0002 (7)	0.0046 (7)
C11	0.0204 (8)	0.0195 (8)	0.0242 (9)	−0.0043 (7)	−0.0035 (7)	0.0038 (7)

Geometric parameters (Å, º)

O1—N1	1.3332 (17)	C4—C5	1.416 (2)
O2—C11	1.305 (2)	C5—C6	1.411 (2)
O3—C11	1.214 (2)	C5—C10	1.421 (2)
N1—C2	1.348 (2)	C6—C7	1.411 (2)
N1—C6	1.392 (2)	C7—C8	1.366 (3)
C2—C3	1.400 (2)	C8—C9	1.413 (3)
C2—C11	1.517 (2)	C9—C10	1.363 (3)
C3—C4	1.368 (2)
O1—N1—C2	121.07 (13)	N1—C6—C5	118.49 (14)
O1—N1—C6	117.20 (13)	N1—C6—C7	119.84 (14)
C2—N1—C6	121.73 (13)	C5—C6—C7	121.68 (15)
N1—C2—C3	120.07 (15)	C8—C7—C6	118.17 (16)
N1—C2—C11	120.09 (14)	C7—C8—C9	121.60 (17)
C3—C2—C11	119.83 (15)	C10—C9—C8	120.16 (16)
C4—C3—C2	120.69 (15)	C9—C10—C5	120.60 (17)
C3—C4—C5	119.31 (15)	O3—C11—O2	124.51 (16)
C6—C5—C4	119.57 (15)	O3—C11—C2	118.87 (16)
C6—C5—C10	117.73 (15)	O2—C11—C2	116.61 (15)
C4—C5—C10	122.69 (15)
O1—N1—C2—C3	−176.90 (13)	C10—C5—C6—N1	−178.33 (14)
C6—N1—C2—C3	2.8 (2)	C4—C5—C6—C7	−177.39 (14)
O1—N1—C2—C11	4.0 (2)	C10—C5—C6—C7	1.8 (2)
C6—N1—C2—C11	−176.26 (13)	N1—C6—C7—C8	−179.73 (15)
N1—C2—C3—C4	0.5 (2)	C5—C6—C7—C8	0.2 (2)
C11—C2—C3—C4	179.61 (14)	C6—C7—C8—C9	−1.9 (2)
C2—C3—C4—C5	−2.2 (2)	C7—C8—C9—C10	1.7 (3)
C3—C4—C5—C6	0.7 (2)	C8—C9—C10—C5	0.4 (3)
C3—C4—C5—C10	−178.46 (15)	C6—C5—C10—C9	−2.0 (2)
O1—N1—C6—C5	175.45 (13)	C4—C5—C10—C9	177.10 (15)
C2—N1—C6—C5	−4.3 (2)	N1—C2—C11—O3	178.86 (15)
O1—N1—C6—C7	−4.7 (2)	C3—C2—C11—O3	−0.2 (2)
C2—N1—C6—C7	175.58 (14)	N1—C2—C11—O2	−0.1 (2)
C4—C5—C6—N1	2.5 (2)	C3—C2—C11—O2	−179.20 (14)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O1	0.98 (3)	1.48 (3)	2.435 (2)	161 (2)
C4—H4···O2^i	0.98 (2)	2.54 (2)	3.288 (2)	132 (1)
C4—H4···O3^ii	0.98 (2)	2.56 (2)	3.344 (2)	137 (1)
C7—H7···O1^iii	0.97 (2)	2.44 (2)	3.278 (2)	144 (1)
C7—H7···O1^iv	0.97 (2)	2.83 (2)	3.322 (2)	112 (1)
C9—H9···O3^v	0.96 (2)	2.83 (2)	3.395 (2)	119 (1)
C10—H10···O3^ii	0.96 (2)	2.79 (2)	3.544 (2)	136 (1)

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