Crystal structure of N-hy­droxy­picolinamide monohydrate

In C₆H₆N₂O₂·H₂O, the N-hy­droxy­picolinamide mol­ecule adopts a strongly flattened conformation. O—H...O inter­actions and π–π stacking inter­actions between the pyridine rings organize the crystal components into columns extending along the b axis while N—H...N hydrogen bonds link these columns into a two-dimensional framework parallel to (100).

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.053
• wR factor = 0.143
• Data-to-parameter ratio = 13.7

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT906_ALERT_3_C Large K value in the Analysis of Variance ......      5.025 Check
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600         19 Report

Alert level G
PLAT007_ALERT_5_G Number of Unrefined Donor-H Atoms ..............          4 Report
PLAT720_ALERT_4_G Number of Unusual/Non-Standard Labels ..........          2 Note
PLAT870_ALERT_4_G ALERTS Related to Twinning Effects Suppressed ..          ! Info
PLAT910_ALERT_3_G Missing # of FCF Reflection(s) Below Th(Min) ...          3 Report
PLAT961_ALERT_5_G Dataset Contains no Negative Intensities .......     Please Check

   0 ALERT level A = Most likely a serious problem - resolve or explain
   0 ALERT level B = A potentially serious problem, consider carefully
   2 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   5 ALERT level G = General information/check it is not something unexpected

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   2 ALERT type 5 Informative message, check

---

S1. Chemical context

Hydroxamic acids (HA) are weak organic acids with the general formula R—C(═O)—NH—OH. HA can exist as keto and imino­(enol) tautomers with two isomers, E and Z, for each form, and in the zwitterionic form (see Scheme below). They have found broad application in coordination chemistry due to their diversity and comparatively facile synthesis (Świątek-Kozłowska et al., 2000; Dobosz et al., 1999). In addition, they exhibit biological activities related to their enzyme-inhibitory properties (Marmion et al., 2013). HA are widely used in coordination and supra­molecular chemistry as scaffolds in the preparation of metallacrowns (Seda et al., 2007; Jankolovits et al., 2013; Safyanova et al., 2015) and as building blocks of coordination polymers (Gumienna-Kontecka et al., 2007; Golenya et al., 2014; Pavlishchuk et al., 2010, 2011).

N-Hy­droxy­picolinamide, known also as picoline-2-hydroxamic acid (o-PicHA), has been used extensively for the synthesis of polynuclear complexes, especially in the synthesis of diverse metallacrowns (Stemmler et al., 1999; Seda et al., 2007; Jankolovits et al., 2013; Golenya et al., 2012; Gumienna-Kontecka et al., 2013). Presently, the Cambridge Structural Database (Groom & Allen, 2014) contains more than 20 entries of coordination compounds based on N-hy­droxy­picolinamide.

Our inter­est in N-hy­droxy­picolinamide stems also from the fact that in the course of synthesis of the title and related compounds from 2-picolinic acid esters (Hynes, 1970), the products are frequently contaminated with impurities that result from hydrolysis of the ester or hydroxamic groups to the carb­oxy­lic group. Structural information about the title compound will be helpful in controlling the purity of the synthesized ligand by powder diffraction.

S2. Structural commentary

The molecular structure of the title compound is presented in Fig. 1. The crystal structure of the title compound consists of an N-hy­droxy­picolinamide molecule in the Z-keto tautomeric form and a water molecule. The N-hy­droxy­picolinamide molecule adopts a strongly flattened conformation and only the O—H group H atom deviates significantly from the molecular best plane. The maximum deviation from this plane for non-hydrogen atom is 0.083 (1) Å for O1 and the hydroxyl group H2 atom is displaced from the mean plane by 0.80 (1) Å in the direction of the water molecule. The dihedral angle between the hydroxamic group and the pyridine ring is 5.6 (2)°. The configuration about the hydroxamic group C—N bond is Z and that about the C—C bond between the pyridine and hydroxamic groups is E [torsion angles O2—N2—C6—O1 − 0.4 (3)°, N1—C1—C6—O1 175.6 (2)°].

S3. Supra­molecular features

The molecular components of the title compound are connected by O—H···O and N—H···N hydrogen bonds (Table 1) into a two-dimensional framework parallel to (100) (Fig. 2). The O—H···O inter­actions and π–π stacking inter­actions between the pyridine rings [centroid–centroid distance 3.427 (1) Å] organize the crystal components into columns extending along the b axis while the N—H···N hydrogen bonds link these columns into a two-dimensional framework parallel to (100) (Fig.2).

S4. Database survey

A search of the Cambridge Structural Database (Version 5.36, last update February 2015; Groom & Allen, 2014) reveals two crystal structures of isomeric pyridine hydroxamic acids and the crystal structure of 2,6-pyridinedi­hydroxamic acid (Golenya et al., 2007; Makhmudova et al., 2001; Griffith et al., 2008).

S5. Synthesis and crystallization

The title compound was obtained by the reaction of methyl 2-picolinate and hydroxyl­amine in methanol according to a reported procedure (Hynes, 1970). Colorless crystals suitable for X-ray diffraction were obtained from a methanol solution by slow evaporation at room temperature (yield 79%).

S6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. The crystal was refined as a non-merohedral twin with the volume ratio of two twin domains refined at 89:19. The C—H, N—H and O—H hydrogen atoms of the organic molecule were found from the difference Fourier maps but for further calculations they were positioned geometrically and constrained to ride on their parent atoms with C—H = 0.93 Å, N—H = 0.86 Å and O—H = 0.82 Å, and with U_iso = 1.2U_eq(C,N) or U_iso = 1.5U_eq(O). The H atoms of the water molecule were located in the difference Fourier maps, the O—H distances standardized to 0.85 Å and refined in riding-model approximation with U_iso(H) = 1.5U_eq(O).

Structure description

Hydroxamic acids (HA) are weak organic acids with the general formula R—C(═O)—NH—OH. HA can exist as keto and imino­(enol) tautomers with two isomers, E and Z, for each form, and in the zwitterionic form (see Scheme below). They have found broad application in coordination chemistry due to their diversity and comparatively facile synthesis (Świątek-Kozłowska et al., 2000; Dobosz et al., 1999). In addition, they exhibit biological activities related to their enzyme-inhibitory properties (Marmion et al., 2013). HA are widely used in coordination and supra­molecular chemistry as scaffolds in the preparation of metallacrowns (Seda et al., 2007; Jankolovits et al., 2013; Safyanova et al., 2015) and as building blocks of coordination polymers (Gumienna-Kontecka et al., 2007; Golenya et al., 2014; Pavlishchuk et al., 2010, 2011).

N-Hy­droxy­picolinamide, known also as picoline-2-hydroxamic acid (o-PicHA), has been used extensively for the synthesis of polynuclear complexes, especially in the synthesis of diverse metallacrowns (Stemmler et al., 1999; Seda et al., 2007; Jankolovits et al., 2013; Golenya et al., 2012; Gumienna-Kontecka et al., 2013). Presently, the Cambridge Structural Database (Groom & Allen, 2014) contains more than 20 entries of coordination compounds based on N-hy­droxy­picolinamide.

Our inter­est in N-hy­droxy­picolinamide stems also from the fact that in the course of synthesis of the title and related compounds from 2-picolinic acid esters (Hynes, 1970), the products are frequently contaminated with impurities that result from hydrolysis of the ester or hydroxamic groups to the carb­oxy­lic group. Structural information about the title compound will be helpful in controlling the purity of the synthesized ligand by powder diffraction.

The molecular structure of the title compound is presented in Fig. 1. The crystal structure of the title compound consists of an N-hy­droxy­picolinamide molecule in the Z-keto tautomeric form and a water molecule. The N-hy­droxy­picolinamide molecule adopts a strongly flattened conformation and only the O—H group H atom deviates significantly from the molecular best plane. The maximum deviation from this plane for non-hydrogen atom is 0.083 (1) Å for O1 and the hydroxyl group H2 atom is displaced from the mean plane by 0.80 (1) Å in the direction of the water molecule. The dihedral angle between the hydroxamic group and the pyridine ring is 5.6 (2)°. The configuration about the hydroxamic group C—N bond is Z and that about the C—C bond between the pyridine and hydroxamic groups is E [torsion angles O2—N2—C6—O1 − 0.4 (3)°, N1—C1—C6—O1 175.6 (2)°].

The molecular components of the title compound are connected by O—H···O and N—H···N hydrogen bonds (Table 1) into a two-dimensional framework parallel to (100) (Fig. 2). The O—H···O inter­actions and π–π stacking inter­actions between the pyridine rings [centroid–centroid distance 3.427 (1) Å] organize the crystal components into columns extending along the b axis while the N—H···N hydrogen bonds link these columns into a two-dimensional framework parallel to (100) (Fig.2).

A search of the Cambridge Structural Database (Version 5.36, last update February 2015; Groom & Allen, 2014) reveals two crystal structures of isomeric pyridine hydroxamic acids and the crystal structure of 2,6-pyridinedi­hydroxamic acid (Golenya et al., 2007; Makhmudova et al., 2001; Griffith et al., 2008).

Synthesis and crystallization

The title compound was obtained by the reaction of methyl 2-picolinate and hydroxyl­amine in methanol according to a reported procedure (Hynes, 1970). Colorless crystals suitable for X-ray diffraction were obtained from a methanol solution by slow evaporation at room temperature (yield 79%).

Refinement details

Crystal data, data collection and structure refinement details are summarized in Table 2. The crystal was refined as a non-merohedral twin with the volume ratio of two twin domains refined at 89:19. The C—H, N—H and O—H hydrogen atoms of the organic molecule were found from the difference Fourier maps but for further calculations they were positioned geometrically and constrained to ride on their parent atoms with C—H = 0.93 Å, N—H = 0.86 Å and O—H = 0.82 Å, and with U_iso = 1.2U_eq(C,N) or U_iso = 1.5U_eq(O). The H atoms of the water molecule were located in the difference Fourier maps, the O—H distances standardized to 0.85 Å and refined in riding-model approximation with U_iso(H) = 1.5U_eq(O).

Computing details

Data collection: CrysAlis PRO (Agilent, 2013); cell refinement: CrysAlis PRO (Agilent, 2013); data reduction: CrysAlis PRO (Agilent, 2013); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Figures

	Fig. 1. The asymmetric unit of the title compound, with displacement ellipsoids drawn at the 50% probability level. H atoms are shown as spheres of arbitrary radius. The dashed line indicates a hydrogen bond.
	Fig. 2. A packing diagram of the title compound. Hydrogen bonds are indicated by dashed lines. H atoms not involved in hydrogen bonding have been omitted for clarity.

N-Hydroxypyridine-2-carboxamide monohydrate

Crystal data

C6H6N2O2·H2O	Dx = 1.441 Mg m^−3
Mr = 156.14	Melting point: 393 K
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 18.7471 (13) Å	Cell parameters from 893 reflections
b = 3.8129 (4) Å	θ = 4.1–29.0°
c = 20.4813 (17) Å	µ = 0.12 mm^−1
β = 100.570 (7)°	T = 298 K
V = 1439.2 (2) Å^3	Plate, clear colourless
Z = 8	0.4 × 0.4 × 0.1 mm
F(000) = 656

Data collection

Agilent Xcalibur, Sapphire3 diffractometer	1401 independent reflections
Radiation source: Enhance (Mo) X-ray Source	1053 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.037
Detector resolution: 16.1827 pixels mm^-1	θmax = 26.0°, θmin = 3.3°
ω scans	h = −22→22
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2013)	k = −4→4
Tmin = 0.476, Tmax = 1.000	l = −24→24
2491 measured reflections

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)] = 0.053	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.143	H-atom parameters constrained
S = 0.99	w = 1/[σ^2(Fo^2) + (0.0751P)^2] where P = (Fo^2 + 2Fc^2)/3
1401 reflections	(Δ/σ)max < 0.001
102 parameters	Δρmax = 0.19 e Å^−3
0 restraints	Δρmin = −0.25 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. Refined as a 2-component twin. 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	0.52649 (8)	0.3700 (4)	0.43254 (7)	0.0468 (5)
O2	0.40179 (7)	0.5190 (5)	0.35109 (7)	0.0506 (5)
H2	0.3916	0.6429	0.3808	0.076*
N1	0.59448 (9)	0.8106 (5)	0.30306 (8)	0.0366 (5)
N2	0.46909 (9)	0.6163 (5)	0.33806 (8)	0.0410 (5)
H2A	0.4722	0.7305	0.3025	0.049*
C1	0.59810 (10)	0.6575 (5)	0.36271 (9)	0.0323 (5)
C2	0.66231 (11)	0.6152 (6)	0.40743 (11)	0.0428 (6)
H2B	0.6628	0.5119	0.4487	0.051*
C3	0.72601 (11)	0.7308 (6)	0.38915 (13)	0.0519 (7)
H3	0.7703	0.7030	0.4178	0.062*
C4	0.72296 (11)	0.8863 (6)	0.32857 (13)	0.0482 (6)
H4	0.7650	0.9656	0.3154	0.058*
C5	0.65653 (12)	0.9234 (6)	0.28737 (11)	0.0434 (6)
H5	0.6549	1.0327	0.2465	0.052*
C6	0.52864 (10)	0.5321 (6)	0.38079 (9)	0.0332 (5)
O1W	0.39862 (8)	0.9488 (5)	0.45255 (8)	0.0501 (5)
H1WA	0.4308	1.0938	0.4455	0.075*
H1WB	0.4202	0.8351	0.4861	0.075*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0447 (8)	0.0657 (11)	0.0287 (8)	0.0009 (7)	0.0035 (6)	0.0147 (7)
O2	0.0332 (8)	0.0832 (13)	0.0350 (9)	−0.0121 (8)	0.0051 (6)	0.0062 (8)
N1	0.0370 (9)	0.0465 (11)	0.0267 (9)	−0.0051 (8)	0.0069 (7)	−0.0036 (8)
N2	0.0307 (9)	0.0670 (13)	0.0252 (9)	−0.0038 (8)	0.0048 (7)	0.0107 (9)
C1	0.0344 (10)	0.0371 (11)	0.0252 (10)	0.0012 (8)	0.0047 (8)	−0.0061 (8)
C2	0.0369 (11)	0.0543 (14)	0.0347 (12)	0.0052 (9)	0.0000 (9)	−0.0030 (11)
C3	0.0322 (11)	0.0640 (17)	0.0554 (16)	0.0028 (11)	−0.0027 (10)	−0.0116 (13)
C4	0.0351 (11)	0.0569 (15)	0.0552 (15)	−0.0091 (10)	0.0156 (10)	−0.0148 (12)
C5	0.0435 (12)	0.0538 (15)	0.0348 (12)	−0.0062 (11)	0.0121 (9)	−0.0047 (11)
C6	0.0359 (11)	0.0409 (12)	0.0224 (10)	−0.0012 (9)	0.0043 (8)	−0.0013 (9)
O1W	0.0408 (8)	0.0687 (11)	0.0404 (9)	0.0044 (8)	0.0068 (7)	0.0163 (8)

Geometric parameters (Å, º)

O1—C6	1.234 (2)	C2—C3	1.387 (3)
O2—N2	1.387 (2)	C2—H2B	0.9300
O2—H2	0.8200	C3—C4	1.367 (3)
N1—C5	1.334 (3)	C3—H3	0.9300
N1—C1	1.344 (3)	C4—C5	1.378 (3)
N2—C6	1.325 (2)	C4—H4	0.9300
N2—H2A	0.8600	C5—H5	0.9300
C1—C2	1.382 (3)	O1W—H1WA	0.8503
C1—C6	1.496 (3)	O1W—H1WB	0.8499
N2—O2—H2	109.5	C4—C3—H3	120.4
C5—N1—C1	117.26 (17)	C2—C3—H3	120.4
C6—N2—O2	119.60 (16)	C3—C4—C5	118.9 (2)
C6—N2—H2A	120.2	C3—C4—H4	120.6
O2—N2—H2A	120.2	C5—C4—H4	120.6
N1—C1—C2	123.08 (19)	N1—C5—C4	123.4 (2)
N1—C1—C6	117.54 (16)	N1—C5—H5	118.3
C2—C1—C6	119.38 (18)	C4—C5—H5	118.3
C1—C2—C3	118.2 (2)	O1—C6—N2	122.15 (18)
C1—C2—H2B	120.9	O1—C6—C1	122.66 (17)
C3—C2—H2B	120.9	N2—C6—C1	115.17 (17)
C4—C3—C2	119.2 (2)	H1WA—O1W—H1WB	102.7
C5—N1—C1—C2	0.3 (3)	C3—C4—C5—N1	−1.0 (4)
C5—N1—C1—C6	179.67 (17)	O2—N2—C6—O1	−0.4 (3)
N1—C1—C2—C3	−1.2 (3)	O2—N2—C6—C1	−178.54 (17)
C6—C1—C2—C3	179.4 (2)	N1—C1—C6—O1	175.6 (2)
C1—C2—C3—C4	1.0 (3)	C2—C1—C6—O1	−5.0 (3)
C2—C3—C4—C5	0.0 (4)	N1—C1—C6—N2	−6.2 (3)
C1—N1—C5—C4	0.8 (3)	C2—C1—C6—N2	173.20 (18)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O1W	0.82	1.86	2.656 (2)	163
N2—H2A···N1^i	0.86	2.31	3.010 (2)	139
O1W—H1WA···O1^ii	0.85	2.14	2.976 (2)	168
O1W—H1WB···O1^iii	0.85	1.94	2.788 (2)	173

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