Synthesis and crystal structures of 3,6-di­hydroxy­picolinic acid and its labile inter­mediate dipotassium 3-hy­droxy-6-(sulfonato­oxy)pyridine-2-carboxyl­ate monohydrate

Behrman, E.J.; Parkin, S.

doi:10.1107/S2056989021004904

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ISSN: 2056-9890

Volume 77| Part 6| June 2021| Pages 623-628

https://doi.org/10.1107/S2056989021004904

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Synthesis and crystal structures of 3,6-dihydroxypicolinic acid and its labile intermediate dipotassium 3-hydroxy-6-(sulfonatooxy)pyridine-2-carboxylate monohydrate

Edward J. Behrman ^a ^* and Sean Parkin ^b

^aDepartment of Chemistry & Biochemistry, The Ohio State University, 484 W. 12th Avenue, Columbus, Ohio, 43210, USA, and ^bDepartment of Chemistry, University of Kentucky, 505 Rose Street, Lexington, Kentucky, 40506, USA
^*Correspondence e-mail: behrman.1@osu.edu

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 6 May 2021; accepted 10 May 2021; online 14 May 2021)

A simplified two-step synthesis of 3,6-dihydroxypicolinic acid (3-hydroxy-6-oxo-1,6-dihydropyridine-2-carboxylic acid), C₆H₅NO₄ (II), an intermediate in the metabolism of picolinic acid, is described. The crystal structure of II, along with that of a labile intermediate, dipotassium 3-hydroxy-6-(sulfonatooxy)pyridine-2-carboxylate monohydrate, 2K⁺·C₆H₃NO₇S²⁻·H₂O (I), is also described. Compound I comprises a pyridine ring with carboxylate, hydroxyl (connected by an intramolecular O—H⋯O hydrogen bond), and sulfate groups at the 2-, 3-, and 6-positions, respectively, along with two potassium cations for charge balance and one water molecule of crystallization. These components are connected into a three-dimensional network by O—H⋯O hydrogen bonds arising from the water molecule, C—H⋯O interactions and π–π stacking of pyridine rings. In II, the ring nitrogen atom is protonated, with charge balance provided by the carboxylate group (i.e., a zwitterion). The intramolecular O—H⋯O hydrogen bond observed in I is preserved in II. Crystals of II have unusual space-group symmetry of type Abm2 in which extended planar networks of O—H⋯O and N—H⋯O hydrogen-bonded molecules form sheets lying parallel to the ac plane, constrained to b = 0.25 (and 0.75). The structure was refined as a 50:50 inversion twin. A minor disorder component was modeled by reflection of the major component across a mirror plane perpendicular to c.

Keywords: Elbs oxidation; crystal structure; space group Abm2; hydrogen bonding; inversion twinning; disorder.

CCDC references: 2082685; 2082684

1. Chemical context

3,6-Dihydroxypicolinic acid (3-hydroxy-6-pyridone-2-carboxylic acid), C₆H₅NO₄, is an intermediate in the metabolism of picolinic acid by several microorganisms (Shukla & Kaul, 1973 ; Shukla et al., 1977 ; Qiu et al., 2019 ). It was isolated from culture media and partially characterized by Shukla & Kaul (1973; Shukla et al., 1977) whose work is misrepresented by Qiu et al. (2019) by stating that their work was only theoretical. It was synthesized by a six-step procedure from 3-hydroxypicolinic acid and characterized by mass spectrometry and NMR data (Qiu et al., 2019, with C. Shen).

We report here a two-step synthesis also starting with 3-hydroxypicolinic acid by an Elbs oxidation (Behrman, 1988 ; 2021 ) and crystal structures of both the intermediate sulfate ester (I) and of 3,6-dihydroxypicolinic acid (II). We considered two routes, as shown in Fig. 1. Both give the desired product but we chose the pathway from 3-hydroxypicolinic acid because in the first step, the dipotassium salt of the 6-sulfate ester precipitates from the mixture in an almost pure state.

Figure 1
Two synthetic routes to 3,6-dihydroxypicolinic acid (II), showing tautomerism of the product.

This sulfate ester is extraordinarily sensitive to acid-catalyzed hydrolysis; acidification at room temperature (RT) gives complete hydrolysis in a few minutes. The isomeric 6-oxo-picolinic acid-3-sulfate is much more stable although subject to anchimeric assistance (Benkovic, 1966 ); it is not completely hydrolyzed after 22 h, RT, pH 2. Nantka-Namirski & Rykowski (1972a ,b ) used boiling 20% sulfuric acid for four hours to effect the hydrolyses of the 5-sulfate esters of two dihydroxynicotinic acids. For the rapid hydrolysis of pyridyl-4-sulfate see Jerfy & Roy (1970 ) and Goren & Kochansky (1973 ) for the effects of impurities. A reasonable representation of the mechanism of the hydrolysis for the 4-sulfate is shown in Fig. 2a. The 2-sulfate should behave similarly (Fig. 2b). Jerfy & Roy (1970) also showed that sulfation of 2-pyridone gives the sulfamate, so that it has not yet been possible to prepare the pyridyl-2-sulfate for comparative purposes. However, a route to 5-hydroxypyridine-2-sulfate together with the isomeric 4- and 6-sulfate esters is known (Behrman & Pitt, 1958 ). Examination of these mixed esters by electrophoresis shows that all three are rapidly hydrolyzed under acid catalysis, as predicted by the model. The reaction between potassium peroxydisulfate and 3-hydroxypicolinic acid was carried out as usual in KOH solution except that if there is excess peroxy-disulfate, the sulfate ester and the peroxide precipitate from the reaction mixture together: to avoid this the persulfate was used as the limiting reagent. The ester was crystallized from water and 3,6-dihydroxypicolinic acid obtained by hydrolysis.

Figure 2
(a) A reasonable representation for the mechanism of hydrolysis for the 4-sulfate. (b) The o-sulfate analog ought to behave similarly.

2. Structural commentary

The asymmetric unit in I (Fig. 3) contains a single pyridine ring with a carboxylate group at the 2-position, a hydroxyl group at the 3-position, and a sulfate group attached to the 6-position. Charge balance is provided by a pair of K⁺ cations. There is also a single water molecule of crystallization present. The carboxylate C—O distances are 1.2510 (16) and 1.2758 (16) Å for C7—O3 and C7—O4, respectively. The longer of these is part of an S(6) intramolecular hydrogen-bonded ring with the hydroxyl group. In the sulfate group, the oxygen atom bound at the 6-position [C6—O2 = 1.3968 (14) Å] is longer [S1—O2 = 1.6343 (9) Å] than the other three S=O bonds [range 1.4361 (9) to 1.4486 (9) Å], as would be expected for this bonding arrangement.

Figure 3
An ellipsoid (50% probability) plot of the asymmetric unit of I. The intramolecular hydrogen bond is shown by the thick dashed line. Dotted lines indicate close contacts of the K⁺ cations.

In II (Fig. 4), the nitrogen atom of the ring is protonated. Charge balance is provided by the deprotonated 2-carboxylate group [C7—O3 = 1.262 (3), C7—O4 = 1.259 (3) Å], leading to a zwitterionic molecule. The intramolecular S(6) hydrogen-bonded ring from I is preserved in II. The 6-position of the ring is occupied by a second hydroxyl group. As discussed in more detail in section 6 (Refinement), there is a small minor disorder component [refined occupancy 4.7 (3)%] and probable inversion twinning.

Figure 4
An ellipsoid (50% probability) plot of the asymmetric unit of II with the intramolecular hydrogen bond shown as a thick dashed line.

3. Supramolecular features

In the packing of I, strong O_w—H⋯O (w = water) hydrogen bonds exist in which the water molecule acts as a linker between c-glide-related anions. The water oxygen is also coordinated to the K⁺ cations, both of which are seven coordinate. Around K1, coordination distances range from 2.7376 (9)–2.9102 (10) Å (for K⋯O) and 2.7869 (11) Å (K1⋯N). For K2, coordination distances range from 2.6769 (9) to 2.9525 (10) Å (all K⋯O). The coordination geometry about each K⁺ cation is very roughly pentagonal bipyramidal, with K1 much more distorted than K2. As each K⁺ cation is coordinated to the water molecule, the KO₆N and KO₇ polyhedra augment the extended chains that propagate parallel to c (Fig. 5, Table 1). In addition, there are weaker C—H⋯O contacts: pairs of C5—H5⋯O6ⁱⁱ interactions form R₂²(12) inversion-related dimers and C4—H4⋯O5ⁱ contacts link molecules via c-glide symmetry (symmetry codes as per Table 1). This in turn joins c-glide-related pyridine rings into an extended π–π stack along the c-axis direction. Adjacent rings within the stacks are almost parallel; the dihedral angle being 0.38 (4)° with a centroid–centroid distance of 3.698 (1) Å. These columns of hydrogen-bonded and π-stacked molecules are interlinked by the aforementioned chains of K⁺ cations and water molecules into a three-dimensional network (Fig. 5).

Table 1
Hydrogen-bond geometry (Å, °) for I

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1O⋯O4	0.843 (19)	1.760 (19)	2.5429 (13)	153.6 (17)
C4—H4⋯O5ⁱ	0.95	2.64	3.3682 (16)	133
C5—H5⋯O6ⁱⁱ	0.95	2.35	3.2943 (15)	175
O1W—H1W⋯O3ⁱⁱⁱ	0.83 (2)	1.97 (2)	2.7852 (13)	165 (2)
O1W—H2W⋯O4^iv	0.83 (2)	2.09 (2)	2.8910 (14)	161 (2)
Symmetry codes: (i) $[x, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ ; (ii) ; (iii) x+1, y, z; (iv) $[x+1, -y+{\script{1\over 2}}, z+{\script{1\over 2}}]$ .

Figure 5
A view of the packing in I, viewed down the c axis. Intramolecular hydrogen bonds are shown as thick dashed lines, open dashed lines indicate strong intermolecular hydrogen bonds, and thin dashed lines denote weaker C—H⋯O interactions. Dangling hydrogen bonds extend beyond the depth of the view.

The most remarkable feature of the packing in II are extended di-periodic hydrogen-bonded networks lying parallel to the ac plane (Fig. 6, Table 2) that are constrained to b = 0.25 (and 0.75) as a consequence of the unusual space-group symmetry of type Abm2. Strong O2—H2O⋯O3ⁱ and N1—H1N⋯O4ⁱ hydrogen bonds link pairs of 2₁ screw-related molecules into R₂²(8) motifs that extend to form ribbons parallel to c. Weaker C4—H4⋯O2ⁱⁱⁱ and C5—H5⋯O1ⁱⁱ (symmetry codes as per Table 2) interactions join 2₁ screw-related ribbons to form the aforementioned networks. Contacts between these planar networks are limited to weak van der Waals interactions.

Table 2
Hydrogen-bond geometry (Å, °) for II

The D⋯A distance for C4—H4⋯O2ⁱⁱⁱ is rather long, but within the bounds noted by Desiraju & Steiner (1999 ).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1N⋯O4ⁱ	0.99	1.77	2.755 (3)	169
O1—H1O⋯O4	0.89	1.76	2.535 (3)	145
C5—H5⋯O1ⁱⁱ	0.95	2.34	3.269 (3)	166
C4—H4⋯O2ⁱⁱⁱ	0.95	2.76	3.712 (4)	180
O2—H2O⋯O3ⁱ	0.94	1.57	2.459 (3)	156
O2—H2O⋯O4ⁱ	0.94	2.56	3.372 (3)	144
Symmetry codes: (i) $[-x+1, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ ; (ii) $[-x, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ ; (iii) $[-x, -y+{\script{1\over 2}}, z+{\script{1\over 2}}]$ .

Figure 6
A view of the planar diperiodic network in crystalline II, viewed normal to the ac plane. Intramolecular hydrogen bonds are drawn as thick dashed lines, strong intermolecular hydrogen bonds (O—H⋯O and N—H⋯O) are drawn as double dashed lines. Weaker hydrogen bonds (C—H⋯O) are drawn as thin dashed lines.

4. Database survey

A search of the Cambridge Structure Database (CSD v5.42, Nov. 2020; Groom et al., 2016 ) on a fragment composed of 3-picolinic acid with `any non-H' at the 6-position gave only seven hits. None of these have much in common with I or II, but the most similar were AGUMEV (ammonium 2,4,6-tricarboxypyridine-3-olate monohydrate; Li et al., 2010 ) and MAFTEU (6-chloro-3-trifluoromethoxy pyridine-2-carboxylic acid; Manteau et al., 2010 ) in that their main components consist of a single pyridine ring with a carboxylic acid group adjacent to the ring nitrogen and an oxygen (O⁻ in AGUMEV; O—CF₃ in MAFTEU) at the 3-position.

Space group Abm2 is not common, with only 62 entries listed in v5.42 of the CSD. Excluding polymers, entries flagged with known errors, and those without deposited coordinates left only 47 hits, i.e. <0.005% of known structures. Of these, only 29 have R₁ ≤ 5% and none form planar networks in a manner similar to II. By any measure, the crystal structure of II is unusual.

5. Synthesis and crystallization

3-Hydroxypyridine-2-carboxylic acid-6-sulfate dipotassium salt monohydrate (I): Potassium hydroxide (85%, 1 g, 15 mmol) was dissolved in 10 ml of water and cooled. 3-Hydroxypicolinic acid (0.82 g, 6 mmol) followed by potassium peroxydisulfate (0.9 g, 3.3 mmol) were added. The reaction mixture was stirred at RT for 24 h. The precipitate was filtered and dried by washing with acetone, yielding 0.46–0.49 g (∼44%) of the dipotassium salt of 3-hydroxypyridine-2-carboxylic acid-6-sulfate monohydrate (I). Compound I migrates on paper electrophoresis at pH 7.5 with R_p = 2 as a fluorescent spot. R_p is the migration distance relative to picric acid at R_p = 1 (the starting material has R_p = 1.1). Crystals of I grow from aqueous solution when treated as follows: 0.16 g were suspended in 2.0 ml of water, dissolved by heating carefully to about 313 K, and then cooled slowly to RT. Further cooling to 278 K overnight gave 0.12 g of needles. Analysis (%) calculated for C₆H₅NO₈K₂S: C, 2l.88; H, 1.53; N, 4.25. Found: C, 21.97; H, 1.44; N, 4.25. IR(Nujol): 3485, 3310, 3096, 1701, 1684, 1624, 1574, 1250, 1059, 957, 860, 833, 768, 716, 638 cm⁻¹. NMR(D₂O, 600 MHz) δ 7.27 (d, J = 8.82 Hz), 7.45 (d, J = 8.82 Hz). UV (in water): λ_max, (nm), ɛ (l mol⁻¹ cm⁻¹): 307, 1120; 230, 1200; 205, 4180. Heating behavior: I begins to discolor at about 448 K and then gets darker without melting up to 523 K.

3,6-Dihydroxypicolinic acid (II): The crude sulfate (I, 150 mg), was suspended in 2 ml of water and then heated to about 313 K to dissolve it. HCl was then added to about pH 2. A heavy precipitate formed immediately. After cooling, the colorless solid was filtered and washed with cold water to yield 50–60 mg of the product (yield 67–80%), R_p = 1. The proton NMR spectrum of II agreed with that reported by Qiu et al. (2019) except that our spectrum was taken in D₂O, 600 MHz, δ 6.69 (d, J = 9.65 Hz) and 7.45 (d, J = 9.65 Hz). These are shifted because of the solvent difference from Qiu et al. (2019), but the couplings are the same, as is the difference between the two resonances (δ 0.76). 50 mg of II was crystallized from 11 ml of hot water under argon to form 35 mg of crystals. Analytical results show that the precipitate is very nearly as clean as the crystals. Analysis (%): calculated for C₆H₅NO₄: C, 46.46; H, 3.25; N, 9.03. Found (crystals), C, 46.22; H, 3.20; N, 9.07. (precipitate), C, 45.65; H, 3.16; N, 9.10. IR: Nujol, 3120, 1614, 1540, 1360, 1269, 1100, 845, 810, 760, 621 cm⁻¹. Later, larger crystals were obtained using 88% formic acid as solvent. Upon heating, II carbonizes above 473 K without melting. UV (in water): λ_max, (nm), ɛ (l mol⁻¹ cm⁻¹) at pH 7: 346, 5970; 243, 4350; 221.5, 9450. Shukla & Kaul (1973) reported the pH-dependence of the spectrum. [See also Qiu et al. (2019), but on p. S2, line 3, read `240' for `360'.]

6. Data collection, structure solution and refinement

The crystals were mounted using polyisobutene oil on the tip of fine glass fibers, which were fastened in copper mounting pins with electrical solder. Crystals of I were placed directly into the cold gas stream of a liquid-N₂ based cryostat, while crystals of II were handled using methods developed for macromolecular cryocrystallography (Parkin & Hope, 1998b ). Diffraction data were collected with the crystals at 90 K. Crystal data, data collection and refinement details are summarized in Table 3. In II, a small minor disorder component was apparent in a difference map. It was modeled by reflection of the major component across a mirror plane perpendicular to its c axis, with coordinates related by the mirror plane and constrained by mapping its coordinates to the major component via SHELXL FVAR parameters. A test for twinning by inversion using the Flack parameter [x = 0.5 (3); Flack & Bernardinelli, 1999 ] was indeterminate. The Hooft (Hooft et al., 2008 ) and Parsons (Parsons et al., 2013 ) parameters [y = 0.63 (7); z = 0.62 (10), respectively], however, each gave a much stronger suggestion of twinning by inversion. Since the space group itself has a twofold parallel to its c axis, this results in a mirror operation (i.e. a twofold rotation combined with inversion). Thus, the twinning and disorder in II may effectively be treated by the same operation, not unlike that in uric acid dihydrate (Parkin & Hope, 1998a ; Parkin, 2000 ). To ensure satisfactory refinement of disorder, constraints (SHELXL command EADP) were used to equalize displacement parameters of superimposed groups. Full occupancy (and major component for II) hydrogen atoms were found in difference-Fourier maps. Carbon-bound hydrogen atoms were included using riding models with constrained distances set to 0.95 Å (Csp²H). In I, the water H atoms were refined but subject to distance and angle–distance restraints, while the hydroxyl H atom was refined freely. In II, for O—H and N—H groups, riding models that allowed the bond distance to refine were used. U_iso(H) parameters were set to values of either 1.2U_eq or 1.5U_eq (OH only) of the attached atom. The structures were validated using PLATON and checkCIF (Spek, 2020 ).

Table 3
Experimental details

	I	II
Crystal data
Chemical formula	2K⁺·C₆H₃NO₇S²⁻·H₂O	C₆H₅NO₄
M_r	329.37	155.11
Crystal system, space group	Monoclinic, P2₁/c	Orthorhombic, Abm2
Temperature (K)	90	90
a, b, c (Å)	13.3366 (4), 11.5467 (3), 7.3078 (2)	10.2045 (6), 6.1282 (4), 9.7293 (6)
α, β, γ (°)	90, 103.553 (1), 90	90, 90, 90
V (Å³)	1094.02 (5)	608.42 (7)
Z	4	4
Radiation type	Mo Kα	Cu Kα
μ (mm⁻¹)	1.09	1.27
Crystal size (mm)	0.18 × 0.16 × 0.13	0.14 × 0.10 × 0.02

Data collection
Diffractometer	Bruker D8 Venture dual source	Bruker D8 Venture dual source
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )	Multi-scan (SADABS; Krause et al., 2015)
T_min, T_max	0.793, 0.862	0.799, 0.971
No. of measured, independent and observed [I > 2σ(I)] reflections	22347, 2505, 2423	4025, 700, 690
R_int	0.036	0.025
(sin θ/λ)_max (Å⁻¹)	0.650	0.634

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.020, 0.056, 1.08	0.024, 0.068, 1.11
No. of reflections	2505	700
No. of parameters	174	74
No. of restraints	3	4
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.40, −0.44	0.20, −0.25
Absolute structure	–	Refined as a perfect inversion twin
Absolute structure parameter	–	0.5
Computer programs: APEX3 (Bruker, 2016 ), SHELXT (Sheldrick, 2015a ), SHELXL2018/3 (Sheldrick, 2015b ), XP in SHELXTL (Sheldrick, 2008 ) and CIFFIX (Parkin, 2013 ).

Supporting information

CCDC references: 2082685; 2082684

Crystal structure: contains datablocks I, II, global. DOI: https://doi.org/10.1107/S2056989021004904/hb7975sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989021004904/hb7975Isup2.hkl

Structure factors: contains datablock II. DOI: https://doi.org/10.1107/S2056989021004904/hb7975IIsup3.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2056989021004904/hb7975Isup4.cml

Supporting information file. DOI: https://doi.org/10.1107/S2056989021004904/hb7975IIsup5.cml

checkCIF report

Computing details top

For both structures, data collection: APEX3 (Bruker, 2016); cell refinement: APEX3 (Bruker, 2016); data reduction: APEX3 (Bruker, 2016); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: XP in SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELX (Sheldrick, 2008) and CIFFIX (Parkin, 2013).

Dipotassium 3-hydroxy-6-(sulfonatooxy)pyridine-2-carboxylate monohydrate (I) top

Crystal data top

2K⁺·C₆H₃NO₇S²⁻·H₂O	F(000) = 664
M_r = 329.37	D_x = 2.000 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 13.3366 (4) Å	Cell parameters from 9459 reflections
b = 11.5467 (3) Å	θ = 3.1–27.5°
c = 7.3078 (2) Å	µ = 1.09 mm⁻¹
β = 103.553 (1)°	T = 90 K
V = 1094.02 (5) Å³	Block, colourless
Z = 4	0.18 × 0.16 × 0.13 mm

Data collection top

Bruker D8 Venture dual source diffractometer	2505 independent reflections
Radiation source: microsource	2423 reflections with I > 2σ(I)
Detector resolution: 7.41 pixels mm^-1	R_int = 0.036
φ and ω scans	θ_max = 27.5°, θ_min = 1.6°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −17→17
T_min = 0.793, T_max = 0.862	k = −14→14
22347 measured reflections	l = −9→9

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: mixed
R[F² > 2σ(F²)] = 0.020	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.056	w = 1/[σ²(F_o²) + (0.0254P)² + 0.7213P] where P = (F_o² + 2F_c²)/3
S = 1.08	(Δ/σ)_max = 0.001
2505 reflections	Δρ_max = 0.40 e Å⁻³
174 parameters	Δρ_min = −0.44 e Å⁻³
3 restraints	Extinction correction: SHELXL2018/3 (Sheldrick 2015b), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0116 (12)

Special details top

Experimental. The crystal was mounted using polyisobutene oil on the tip of a fine glass fibre, which was fastened in a copper mounting pin with electrical solder. It was placed directly into the cold gas stream of a liquid-nitrogen based cryostat (Hope, 1994; Parkin & Hope, 1998).

Diffraction data were collected with the crystal at 90K, which is standard practice in this laboratory for the majority of flash-cooled crystals.

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refinement progress was checked using Platon (Spek, 2020) and by an R-tensor (Parkin, 2000). The final model was further checked with the IUCr utility checkCIF.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
K1	−0.11303 (2)	0.44196 (2)	0.29817 (4)	0.01068 (9)
K2	0.65851 (2)	0.37254 (2)	0.80722 (4)	0.01048 (9)
S1	0.39446 (2)	0.56402 (3)	0.68497 (4)	0.00841 (9)
O1	0.18689 (8)	0.05598 (7)	0.56350 (13)	0.01168 (19)
H1O	0.1278 (15)	0.0662 (15)	0.584 (3)	0.018*
O2	0.32641 (7)	0.49448 (8)	0.50302 (12)	0.00997 (18)
O3	0.01000 (7)	0.34563 (8)	0.61547 (13)	0.01185 (19)
O4	0.02411 (7)	0.15242 (8)	0.61413 (13)	0.01227 (19)
O5	0.32663 (7)	0.58023 (8)	0.81136 (13)	0.01295 (19)
O6	0.41500 (7)	0.66929 (8)	0.59303 (13)	0.01295 (19)
O7	0.48251 (7)	0.49241 (8)	0.76027 (14)	0.0149 (2)
N1	0.20276 (8)	0.37108 (9)	0.55903 (14)	0.0088 (2)
C2	0.16613 (9)	0.26318 (11)	0.57169 (17)	0.0088 (2)
C3	0.22393 (10)	0.16468 (11)	0.55284 (17)	0.0093 (2)
C4	0.32289 (10)	0.17884 (11)	0.52150 (17)	0.0105 (2)
H4	0.363874	0.113328	0.509029	0.013*
C5	0.35984 (9)	0.28931 (11)	0.50905 (17)	0.0104 (2)
H5	0.426568	0.302283	0.487955	0.013*
C6	0.29543 (10)	0.38126 (10)	0.52862 (17)	0.0089 (2)
C7	0.05895 (9)	0.25453 (11)	0.60404 (17)	0.0096 (2)
O1W	0.85262 (7)	0.30218 (9)	0.79832 (14)	0.0151 (2)
H1W	0.8909 (13)	0.3167 (17)	0.726 (2)	0.023*
H2W	0.8914 (13)	0.3145 (17)	0.903 (2)	0.023*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
K1	0.00957 (14)	0.00968 (14)	0.01288 (14)	0.00117 (9)	0.00285 (10)	−0.00086 (9)
K2	0.00967 (14)	0.01126 (14)	0.01074 (14)	0.00044 (9)	0.00281 (10)	0.00146 (9)
S1	0.00738 (15)	0.00825 (15)	0.00966 (15)	−0.00042 (10)	0.00215 (11)	−0.00085 (10)
O1	0.0117 (5)	0.0075 (4)	0.0169 (5)	−0.0005 (3)	0.0054 (4)	0.0000 (3)
O2	0.0121 (4)	0.0089 (4)	0.0087 (4)	−0.0027 (3)	0.0019 (3)	−0.0002 (3)
O3	0.0096 (4)	0.0123 (4)	0.0142 (4)	0.0010 (3)	0.0038 (3)	0.0002 (3)
O4	0.0109 (4)	0.0112 (4)	0.0154 (4)	−0.0017 (3)	0.0044 (3)	0.0009 (3)
O5	0.0123 (4)	0.0164 (5)	0.0111 (4)	−0.0004 (4)	0.0048 (3)	−0.0019 (4)
O6	0.0147 (5)	0.0093 (4)	0.0160 (4)	−0.0028 (3)	0.0059 (4)	−0.0002 (3)
O7	0.0108 (4)	0.0139 (4)	0.0180 (5)	0.0033 (3)	−0.0005 (4)	−0.0017 (4)
N1	0.0096 (5)	0.0093 (5)	0.0072 (5)	−0.0002 (4)	0.0015 (4)	−0.0006 (4)
C2	0.0086 (5)	0.0101 (6)	0.0076 (5)	−0.0008 (4)	0.0018 (4)	0.0005 (4)
C3	0.0112 (6)	0.0082 (6)	0.0078 (5)	−0.0010 (4)	0.0008 (4)	0.0000 (4)
C4	0.0104 (6)	0.0109 (6)	0.0101 (6)	0.0021 (4)	0.0023 (4)	−0.0014 (4)
C5	0.0087 (5)	0.0132 (6)	0.0096 (5)	−0.0002 (5)	0.0026 (4)	−0.0014 (4)
C6	0.0108 (6)	0.0082 (5)	0.0070 (5)	−0.0021 (4)	0.0010 (4)	−0.0001 (4)
C7	0.0091 (6)	0.0129 (6)	0.0065 (5)	−0.0007 (4)	0.0011 (4)	0.0002 (4)
O1W	0.0113 (5)	0.0165 (5)	0.0181 (5)	0.0005 (4)	0.0044 (4)	0.0003 (4)

Geometric parameters (Å, º) top

K1—O4ⁱ	2.7376 (9)	K2—K2^x	4.6216 (3)
K1—O3	2.7428 (10)	S1—O7	1.4361 (9)
K1—O5ⁱⁱ	2.7843 (10)	S1—O6	1.4457 (9)
K1—N1ⁱⁱ	2.7869 (11)	S1—O5	1.4486 (9)
K1—O3ⁱⁱ	2.8099 (10)	S1—O2	1.6343 (9)
K1—O1Wⁱⁱⁱ	2.856 (1)	O1—C3	1.3577 (15)
K1—O1^iv	2.9102 (10)	O1—H1O	0.843 (19)
K1—S1ⁱⁱ	3.7848 (4)	O2—C6	1.3968 (14)
K1—K1ⁱⁱ	3.9268 (5)	O3—C7	1.2510 (16)
K1—K2^v	4.2041 (4)	O4—C7	1.2758 (16)
K1—K2ⁱⁱⁱ	4.7508 (4)	N1—C6	1.3112 (16)
K2—O7	2.6769 (9)	N1—C2	1.3492 (16)
K2—O6^vi	2.7084 (10)	C2—C3	1.3988 (17)
K2—O1W	2.7286 (10)	C2—C7	1.5057 (17)
K2—O2^vii	2.7842 (9)	C3—C4	1.4010 (17)
K2—O5^viii	2.8012 (9)	C4—C5	1.3781 (18)
K2—O6^vii	2.8993 (10)	C4—H4	0.9500
K2—O1^ix	2.9525 (10)	C5—C6	1.3940 (17)
K2—S1^vii	3.5751 (4)	C5—H5	0.9500
K2—S1^vi	3.6348 (4)	O1W—H1W	0.832 (15)
K2—K2ⁱ	4.6216 (3)	O1W—H2W	0.831 (15)

O4ⁱ—K1—O3	85.28 (3)	O5^viii—K2—K1^xi	41.02 (2)
O4ⁱ—K1—O5ⁱⁱ	125.34 (3)	O6^vii—K2—K1^xi	154.00 (2)
O3—K1—O5ⁱⁱ	125.08 (3)	O1^ix—K2—K1^xi	43.784 (19)
O4ⁱ—K1—N1ⁱⁱ	152.53 (3)	S1^vii—K2—K1^xi	138.793 (10)
O3—K1—N1ⁱⁱ	102.82 (3)	S1^vi—K2—K1^xi	106.147 (8)
O5ⁱⁱ—K1—N1ⁱⁱ	71.26 (3)	O7—K2—K2ⁱ	112.19 (2)
O4ⁱ—K1—O3ⁱⁱ	96.31 (3)	O6^vi—K2—K2ⁱ	75.48 (2)
O3—K1—O3ⁱⁱ	90.00 (3)	O1W—K2—K2ⁱ	67.86 (2)
O5ⁱⁱ—K1—O3ⁱⁱ	123.94 (3)	O2^vii—K2—K2ⁱ	71.370 (18)
N1ⁱⁱ—K1—O3ⁱⁱ	58.00 (3)	O5^viii—K2—K2ⁱ	153.22 (2)
O4ⁱ—K1—O1Wⁱⁱⁱ	74.51 (3)	O6^vii—K2—K2ⁱ	33.178 (19)
O3—K1—O1Wⁱⁱⁱ	70.34 (3)	O1^ix—K2—K2ⁱ	124.254 (19)
O5ⁱⁱ—K1—O1Wⁱⁱⁱ	75.87 (3)	S1^vii—K2—K2ⁱ	50.703 (5)
N1ⁱⁱ—K1—O1Wⁱⁱⁱ	132.96 (3)	S1^vi—K2—K2ⁱ	56.517 (8)
O3ⁱⁱ—K1—O1Wⁱⁱⁱ	158.67 (3)	K1^xi—K2—K2ⁱ	131.084 (6)
O4ⁱ—K1—O1^iv	81.77 (3)	O7—K2—K2^x	104.80 (2)
O3—K1—O1^iv	163.61 (3)	O6^vi—K2—K2^x	35.86 (2)
O5ⁱⁱ—K1—O1^iv	71.02 (3)	O1W—K2—K2^x	90.71 (2)
N1ⁱⁱ—K1—O1^iv	84.60 (3)	O2^vii—K2—K2^x	174.19 (2)
O3ⁱⁱ—K1—O1^iv	81.53 (3)	O5^viii—K2—K2^x	49.13 (2)
O1Wⁱⁱⁱ—K1—O1^iv	115.26 (3)	O6^vii—K2—K2^x	129.27 (2)
O4ⁱ—K1—S1ⁱⁱ	142.24 (2)	O1^ix—K2—K2^x	108.403 (19)
O3—K1—S1ⁱⁱ	111.50 (2)	S1^vii—K2—K2^x	152.157 (10)
O5ⁱⁱ—K1—S1ⁱⁱ	18.571 (19)	S1^vi—K2—K2^x	49.568 (8)
N1ⁱⁱ—K1—S1ⁱⁱ	59.06 (2)	K1^xi—K2—K2^x	64.932 (5)
O3ⁱⁱ—K1—S1ⁱⁱ	116.43 (2)	K2ⁱ—K2—K2^x	104.485 (11)
O1Wⁱⁱⁱ—K1—S1ⁱⁱ	79.72 (2)	O7—S1—O6	115.80 (6)
O1^iv—K1—S1ⁱⁱ	84.87 (2)	O7—S1—O5	114.01 (6)
O4ⁱ—K1—K1ⁱⁱ	91.22 (2)	O6—S1—O5	113.72 (6)
O3—K1—K1ⁱⁱ	45.69 (2)	O7—S1—O2	106.09 (5)
O5ⁱⁱ—K1—K1ⁱⁱ	143.23 (2)	O6—S1—O2	99.47 (5)
N1ⁱⁱ—K1—K1ⁱⁱ	77.04 (2)	O5—S1—O2	105.75 (5)
O3ⁱⁱ—K1—K1ⁱⁱ	44.305 (19)	O7—S1—K2^vii	117.03 (4)
O1Wⁱⁱⁱ—K1—K1ⁱⁱ	115.57 (2)	O6—S1—K2^vii	51.28 (4)
O1^iv—K1—K1ⁱⁱ	124.38 (2)	O5—S1—K2^vii	127.54 (4)
S1ⁱⁱ—K1—K1ⁱⁱ	125.061 (11)	O2—S1—K2^vii	48.78 (3)
O4ⁱ—K1—K2^v	86.50 (2)	O7—S1—K2^ix	134.65 (4)
O3—K1—K2^v	144.54 (2)	O6—S1—K2^ix	40.71 (4)
O5ⁱⁱ—K1—K2^v	41.328 (19)	O5—S1—K2^ix	73.18 (4)
N1ⁱⁱ—K1—K2^v	100.27 (2)	O2—S1—K2^ix	114.92 (3)
O3ⁱⁱ—K1—K2^v	125.21 (2)	K2^vii—S1—K2^ix	79.729 (8)
O1Wⁱⁱⁱ—K1—K2^v	74.21 (2)	O7—S1—K1ⁱⁱ	134.83 (4)
O1^iv—K1—K2^v	44.587 (19)	O6—S1—K1ⁱⁱ	109.13 (4)
S1ⁱⁱ—K1—K2^v	59.892 (7)	O5—S1—K1ⁱⁱ	37.75 (4)
K1ⁱⁱ—K1—K2^v	168.952 (12)	O2—S1—K1ⁱⁱ	69.61 (3)
O4ⁱ—K1—K2ⁱⁱⁱ	101.95 (2)	K2^vii—S1—K1ⁱⁱ	94.176 (9)
O3—K1—K2ⁱⁱⁱ	86.38 (2)	K2^ix—S1—K1ⁱⁱ	79.600 (8)
O5ⁱⁱ—K1—K2ⁱⁱⁱ	46.95 (2)	C3—O1—K1^xii	114.60 (7)
N1ⁱⁱ—K1—K2ⁱⁱⁱ	104.70 (2)	C3—O1—K2^vi	116.45 (7)
O3ⁱⁱ—K1—K2ⁱⁱⁱ	161.00 (2)	K1^xii—O1—K2^vi	91.63 (3)
O1Wⁱⁱⁱ—K1—K2ⁱⁱⁱ	30.91 (2)	C3—O1—H1O	104.4 (12)
O1^iv—K1—K2ⁱⁱⁱ	106.07 (2)	K1^xii—O1—H1O	95.2 (12)
S1ⁱⁱ—K1—K2ⁱⁱⁱ	48.809 (6)	K2^vi—O1—H1O	131.0 (12)
K1ⁱⁱ—K1—K2ⁱⁱⁱ	129.234 (11)	C6—O2—S1	118.44 (7)
K2^v—K1—K2ⁱⁱⁱ	61.786 (6)	C6—O2—K2^vii	134.86 (7)
O7—K2—O6^vi	96.93 (3)	S1—O2—K2^vii	105.02 (4)
O7—K2—O1W	163.59 (3)	C7—O3—K1	120.18 (8)
O6^vi—K2—O1W	98.84 (3)	C7—O3—K1ⁱⁱ	120.90 (8)
O7—K2—O2^vii	80.73 (3)	K1—O3—K1ⁱⁱ	90.00 (3)
O6^vi—K2—O2^vii	142.83 (3)	C7—O4—K1^x	133.68 (8)
O1W—K2—O2^vii	83.96 (3)	S1—O5—K1ⁱⁱ	123.68 (5)
O7—K2—O5^viii	83.24 (3)	S1—O5—K2^viii	138.63 (5)
O6^vi—K2—O5^viii	81.17 (3)	K1ⁱⁱ—O5—K2^viii	97.65 (3)
O1W—K2—O5^viii	103.61 (3)	S1—O6—K2^ix	118.92 (5)
O2^vii—K2—O5^viii	134.52 (3)	S1—O6—K2^vii	105.82 (5)
O7—K2—O6^vii	82.98 (3)	K2^ix—O6—K2^vii	110.96 (3)
O6^vi—K2—O6^vii	93.96 (2)	S1—O7—K2	163.84 (6)
O1W—K2—O6^vii	91.42 (3)	C6—N1—C2	117.72 (11)
O2^vii—K2—O6^vii	48.87 (3)	C6—N1—K1ⁱⁱ	119.90 (8)
O5^viii—K2—O6^vii	164.72 (3)	C2—N1—K1ⁱⁱ	119.70 (8)
O7—K2—O1^ix	101.29 (3)	N1—C2—C3	121.82 (11)
O6^vi—K2—O1^ix	143.63 (3)	N1—C2—C7	116.38 (11)
O1W—K2—O1^ix	68.03 (3)	C3—C2—C7	121.79 (11)
O2^vii—K2—O1^ix	71.74 (3)	O1—C3—C2	121.99 (11)
O5^viii—K2—O1^ix	70.16 (3)	O1—C3—C4	119.11 (11)
O6^vii—K2—O1^ix	119.21 (3)	C2—C3—C4	118.90 (11)
O7—K2—S1^vii	78.73 (2)	C5—C4—C3	118.94 (11)
O6^vi—K2—S1^vii	116.72 (2)	C5—C4—H4	120.5
O1W—K2—S1^vii	90.11 (2)	C3—C4—H4	120.5
O2^vii—K2—S1^vii	26.201 (18)	C4—C5—C6	117.37 (11)
O5^viii—K2—S1^vii	155.84 (2)	C4—C5—H5	121.3
O6^vii—K2—S1^vii	22.895 (18)	C6—C5—H5	121.3
O1^ix—K2—S1^vii	97.67 (2)	N1—C6—C5	125.24 (11)
O7—K2—S1^vi	109.94 (2)	N1—C6—O2	115.26 (11)
O6^vi—K2—S1^vi	20.38 (2)	C5—C6—O2	119.36 (11)
O1W—K2—S1^vi	84.12 (2)	O3—C7—O4	124.78 (11)
O2^vii—K2—S1^vi	127.21 (2)	O3—C7—C2	118.96 (11)
O5^viii—K2—S1^vi	98.27 (2)	O4—C7—C2	116.25 (11)
O6^vii—K2—S1^vi	80.302 (19)	K2—O1W—K1^xiii	116.56 (4)
O1^ix—K2—S1^vi	145.27 (2)	K2—O1W—H1W	132.9 (13)
S1^vii—K2—S1^vi	102.902 (10)	K1^xiii—O1W—H1W	94.4 (14)
O7—K2—K1^xi	116.69 (2)	K2—O1W—H2W	108.4 (13)
O6^vi—K2—K1^xi	99.86 (2)	K1^xiii—O1W—H2W	96.0 (14)
O1W—K2—K1^xi	64.86 (2)	H1W—O1W—H2W	102.0 (15)
O2^vii—K2—K1^xi	114.43 (2)

O7—S1—O2—C6	55.28 (10)	K1ⁱⁱ—S1—O7—K2	142.06 (18)
O6—S1—O2—C6	175.77 (9)	C6—N1—C2—C3	−0.18 (17)
O5—S1—O2—C6	−66.14 (10)	K1ⁱⁱ—N1—C2—C3	−161.62 (9)
K2^vii—S1—O2—C6	167.38 (11)	C6—N1—C2—C7	−179.2 (1)
K2^ix—S1—O2—C6	−144.57 (8)	K1ⁱⁱ—N1—C2—C7	19.36 (14)
K1ⁱⁱ—S1—O2—C6	−77.22 (8)	K1^xii—O1—C3—C2	101.95 (11)
O7—S1—O2—K2^vii	−112.10 (5)	K2^vi—O1—C3—C2	−152.82 (9)
O6—S1—O2—K2^vii	8.39 (5)	K1^xii—O1—C3—C4	−77.87 (12)
O5—S1—O2—K2^vii	126.48 (5)	K2^vi—O1—C3—C4	27.36 (14)
K2^ix—S1—O2—K2^vii	48.05 (4)	N1—C2—C3—O1	−179.28 (11)
K1ⁱⁱ—S1—O2—K2^vii	115.40 (3)	C7—C2—C3—O1	−0.31 (18)
O7—S1—O5—K1ⁱⁱ	−133.28 (6)	N1—C2—C3—C4	0.54 (18)
O6—S1—O5—K1ⁱⁱ	90.99 (7)	C7—C2—C3—C4	179.51 (11)
O2—S1—O5—K1ⁱⁱ	−17.12 (7)	O1—C3—C4—C5	179.41 (11)
K2^vii—S1—O5—K1ⁱⁱ	32.58 (8)	C2—C3—C4—C5	−0.41 (18)
K2^ix—S1—O5—K1ⁱⁱ	94.73 (5)	C3—C4—C5—C6	−0.03 (18)
O7—S1—O5—K2^viii	43.85 (10)	C2—N1—C6—C5	−0.32 (18)
O6—S1—O5—K2^viii	−91.88 (9)	K1ⁱⁱ—N1—C6—C5	161.09 (9)
O2—S1—O5—K2^viii	160.01 (7)	C2—N1—C6—O2	175.49 (10)
K2^vii—S1—O5—K2^viii	−150.29 (5)	K1ⁱⁱ—N1—C6—O2	−23.10 (13)
K2^ix—S1—O5—K2^viii	−88.14 (7)	C4—C5—C6—N1	0.42 (19)
K1ⁱⁱ—S1—O5—K2^viii	177.13 (12)	C4—C5—C6—O2	−175.23 (11)
O7—S1—O6—K2^ix	−129.41 (6)	S1—O2—C6—N1	94.96 (11)
O5—S1—O6—K2^ix	5.50 (8)	K2^vii—O2—C6—N1	−102.36 (12)
O2—S1—O6—K2^ix	117.46 (5)	S1—O2—C6—C5	−88.96 (12)
K2^vii—S1—O6—K2^ix	125.55 (7)	K2^vii—O2—C6—C5	73.72 (14)
K1ⁱⁱ—S1—O6—K2^ix	45.88 (6)	K1—O3—C7—O4	−88.64 (13)
O7—S1—O6—K2^vii	105.04 (6)	K1ⁱⁱ—O3—C7—O4	160.99 (9)
O5—S1—O6—K2^vii	−120.05 (5)	K1—O3—C7—C2	89.91 (11)
O2—S1—O6—K2^vii	−8.09 (5)	K1ⁱⁱ—O3—C7—C2	−20.46 (14)
K2^ix—S1—O6—K2^vii	−125.55 (7)	K1^x—O4—C7—O3	−30.63 (18)
K1ⁱⁱ—S1—O6—K2^vii	−79.67 (4)	K1^x—O4—C7—C2	150.78 (8)
O6—S1—O7—K2	−44.2 (2)	N1—C2—C7—O3	0.67 (17)
O5—S1—O7—K2	−179.00 (19)	C3—C2—C7—O3	−178.36 (11)
O2—S1—O7—K2	65.0 (2)	N1—C2—C7—O4	179.34 (10)
K2^vii—S1—O7—K2	13.6 (2)	C3—C2—C7—O4	0.31 (17)
K2^ix—S1—O7—K2	−89.3 (2)

Symmetry codes: (i) x, −y+1/2, z−1/2; (ii) −x, −y+1, −z+1; (iii) x−1, −y+1/2, z−1/2; (iv) −x, y+1/2, −z+1/2; (v) x−1, y, z−1; (vi) −x+1, y−1/2, −z+3/2; (vii) −x+1, −y+1, −z+1; (viii) −x+1, −y+1, −z+2; (ix) −x+1, y+1/2, −z+3/2; (x) x, −y+1/2, z+1/2; (xi) x+1, y, z+1; (xii) −x, y−1/2, −z+1/2; (xiii) x+1, −y+1/2, z+1/2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1O···O4	0.843 (19)	1.760 (19)	2.5429 (13)	153.6 (17)
C4—H4···O5ⁱ	0.95	2.64	3.3682 (16)	133
C5—H5···O6^vii	0.95	2.35	3.2943 (15)	175
O1W—H1W···O3^xiv	0.83 (2)	1.97 (2)	2.7852 (13)	165 (2)
O1W—H2W···O4^xiii	0.83 (2)	2.09 (2)	2.8910 (14)	161 (2)

Symmetry codes: (i) x, −y+1/2, z−1/2; (vii) −x+1, −y+1, −z+1; (xiii) x+1, −y+1/2, z+1/2; (xiv) x+1, y, z.

3-Hydroxy-6-oxo-1,6-dihydropyridine-2-carboxylic acid (II) top

Crystal data top

C₆H₅NO₄	D_x = 1.693 Mg m⁻³
M_r = 155.11	Cu Kα radiation, λ = 1.54178 Å
Orthorhombic, Abm2	Cell parameters from 3820 reflections
a = 10.2045 (6) Å	θ = 4.3–78.5°
b = 6.1282 (4) Å	µ = 1.27 mm⁻¹
c = 9.7293 (6) Å	T = 90 K
V = 608.42 (7) Å³	Plate, colourless
Z = 4	0.14 × 0.10 × 0.02 mm
F(000) = 320

Data collection top

Bruker D8 Venture dual source diffractometer	700 independent reflections
Radiation source: microsource	690 reflections with I > 2σ(I)
Detector resolution: 7.41 pixels mm^-1	R_int = 0.025
φ and ω scans	θ_max = 77.8°, θ_min = 4.3°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −11→12
T_min = 0.799, T_max = 0.971	k = −7→7
4025 measured reflections	l = −11→12

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.024	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.068	w = 1/[σ²(F_o²) + (0.050P)² + 0.0512P] where P = (F_o² + 2F_c²)/3
S = 1.11	(Δ/σ)_max = 0.024
700 reflections	Δρ_max = 0.20 e Å⁻³
74 parameters	Δρ_min = −0.25 e Å⁻³
4 restraints	Absolute structure: Refined as a perfect inversion twin
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.5

Special details top

Diffraction data were collected with the crystal at 90K, which is standard practice in this laboratory for the majority of flash-cooled crystals.

Refinement. Refined as a two-component perfect inversion twin.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
N1	0.3327 (2)	0.250000	0.44103 (19)	0.0146 (4)	0.953 (3)
H1N	0.421 (3)	0.25000 (2)	0.3976 (15)	0.017*	0.953 (3)
C2	0.3260 (2)	0.250000	0.5827 (2)	0.0131 (5)	0.953 (3)
C3	0.2033 (3)	0.250000	0.6458 (3)	0.0148 (5)	0.953 (3)
O1	0.19022 (19)	0.250000	0.7831 (2)	0.0188 (4)	0.953 (3)
H1O	0.269 (4)	0.25000 (2)	0.8219 (19)	0.028*	0.953 (3)
C4	0.0919 (3)	0.250000	0.5626 (3)	0.0194 (6)	0.953 (3)
H4	0.007769	0.250000	0.604343	0.023*	0.953 (3)
C5	0.1011 (2)	0.250000	0.4226 (3)	0.0191 (5)	0.953 (3)
H5	0.024166	0.250000	0.367711	0.023*	0.953 (3)
C6	0.2280 (2)	0.250000	0.3592 (3)	0.0154 (5)	0.953 (3)
O2	0.2369 (2)	0.250000	0.22580 (18)	0.0186 (4)	0.953 (3)
H2O	0.326 (3)	0.25000 (2)	0.200 (1)	0.028*	0.953 (3)
C7	0.4488 (2)	0.250000	0.6616 (2)	0.0158 (5)	0.953 (3)
O3	0.55590 (18)	0.250000	0.59684 (19)	0.0182 (4)	0.953 (3)
O4	0.43850 (17)	0.250000	0.7906 (2)	0.0224 (5)	0.953 (3)
N1'	0.3327 (2)	0.250000	0.55897 (19)	0.0131 (5)	0.047 (3)
H1'N	0.421 (3)	0.25000 (2)	0.6024 (16)	0.016*	0.047 (3)
C2'	0.3260 (2)	0.250000	0.4173 (2)	0.0146 (4)	0.047 (3)
C3'	0.2033 (3)	0.250000	0.3542 (3)	0.0154 (5)	0.047 (3)
O1'	0.19022 (19)	0.250000	0.2169 (2)	0.0186 (4)	0.047 (3)
H1'O	0.269 (4)	0.25000 (2)	0.178 (2)	0.028*	0.047 (3)
C4'	0.0919 (3)	0.250000	0.4374 (3)	0.0191 (5)	0.047 (3)
H4'	0.007769	0.250000	0.395657	0.023*	0.047 (3)
C5'	0.1011 (2)	0.250000	0.5774 (3)	0.0194 (6)	0.047 (3)
H5'	0.024166	0.250000	0.632289	0.023*	0.047 (3)
C6'	0.2280 (2)	0.250000	0.6408 (3)	0.0148 (5)	0.047 (3)
O2'	0.2369 (2)	0.250000	0.77420 (18)	0.0188 (4)	0.047 (3)
H2'O	0.326 (4)	0.25000 (2)	0.8001 (11)	0.028*	0.047 (3)
C7'	0.4488 (2)	0.250000	0.3384 (2)	0.0158 (5)	0.047 (3)
O3'	0.55590 (18)	0.250000	0.40316 (19)	0.0182 (4)	0.047 (3)
O4'	0.43850 (17)	0.250000	0.2094 (2)	0.0224 (5)	0.047 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
N1	0.0142 (9)	0.0190 (8)	0.0105 (11)	0.000	0.0000 (9)	0.000
C2	0.0127 (12)	0.0155 (9)	0.0112 (10)	0.000	−0.0016 (9)	0.000
C3	0.0151 (10)	0.0180 (11)	0.0113 (11)	0.000	0.0040 (8)	0.000
O1	0.0167 (9)	0.0274 (9)	0.0123 (8)	0.000	0.0041 (7)	0.000
C4	0.0159 (12)	0.0222 (10)	0.0202 (13)	0.000	0.0025 (10)	0.000
C5	0.0150 (11)	0.0259 (10)	0.0166 (10)	0.000	−0.0017 (9)	0.000
C6	0.0150 (12)	0.017 (1)	0.0141 (12)	0.000	−0.0031 (9)	0.000
O2	0.0163 (9)	0.0295 (8)	0.0101 (8)	0.000	0.0003 (6)	0.000
C7	0.0167 (10)	0.0196 (12)	0.0112 (14)	0.000	−0.0002 (9)	0.000
O3	0.0141 (8)	0.0268 (7)	0.0137 (8)	0.000	−0.0008 (6)	0.000
O4	0.0148 (12)	0.0368 (11)	0.0157 (9)	0.000	−0.0014 (7)	0.000
N1'	0.0127 (12)	0.0155 (9)	0.0112 (10)	0.000	−0.0016 (9)	0.000
C2'	0.0142 (9)	0.0190 (8)	0.0105 (11)	0.000	0.0000 (9)	0.000
C3'	0.0150 (12)	0.017 (1)	0.0141 (12)	0.000	−0.0031 (9)	0.000
O1'	0.0163 (9)	0.0295 (8)	0.0101 (8)	0.000	0.0003 (6)	0.000
C4'	0.0150 (11)	0.0259 (10)	0.0166 (10)	0.000	−0.0017 (9)	0.000
C5'	0.0159 (12)	0.0222 (10)	0.0202 (13)	0.000	0.0025 (10)	0.000
C6'	0.0151 (10)	0.0180 (11)	0.0113 (11)	0.000	0.0040 (8)	0.000
O2'	0.0167 (9)	0.0274 (9)	0.0123 (8)	0.000	0.0041 (7)	0.000
C7'	0.0167 (10)	0.0196 (12)	0.0112 (14)	0.000	−0.0002 (9)	0.000
O3'	0.0141 (8)	0.0268 (7)	0.0137 (8)	0.000	−0.0008 (6)	0.000
O4'	0.0148 (12)	0.0368 (11)	0.0157 (9)	0.000	−0.0014 (7)	0.000

Geometric parameters (Å, º) top

N1—C6	1.333 (3)	N1'—C6'	1.333 (3)
N1—C2	1.381 (3)	N1'—C2'	1.381 (3)
N1—H1N	0.99 (3)	N1'—H1'N	0.99 (4)
C2—C3	1.394 (3)	C2'—C3'	1.394 (3)
C2—C7	1.470 (3)	C2'—C7'	1.470 (3)
C3—O1	1.342 (3)	C3'—O1'	1.342 (3)
C3—C4	1.395 (4)	C3'—C4'	1.395 (4)
O1—H1O	0.89 (4)	O1'—H1'O	0.89 (4)
C4—C5	1.365 (3)	C4'—C5'	1.365 (3)
C4—H4	0.9500	C4'—H4'	0.9500
C5—C6	1.434 (3)	C5'—C6'	1.434 (3)
C5—H5	0.9500	C5'—H5'	0.9500
C6—O2	1.301 (3)	C6'—O2'	1.301 (3)
O2—H2O	0.94 (4)	O2'—H2'O	0.94 (4)
C7—O4	1.259 (3)	C7'—O4'	1.259 (3)
C7—O3	1.262 (3)	C7'—O3'	1.262 (3)

C6—N1—C2	123.81 (19)	C6'—N1'—C2'	123.81 (19)
C6—N1—H1N	118.1	C6'—N1'—H1'N	118.1
C2—N1—H1N	118.1	C2'—N1'—H1'N	118.1
N1—C2—C3	119.0 (2)	N1'—C2'—C3'	119.0 (2)
N1—C2—C7	118.6 (2)	N1'—C2'—C7'	118.6 (2)
C3—C2—C7	122.41 (19)	C3'—C2'—C7'	122.41 (19)
O1—C3—C2	121.8 (2)	O1'—C3'—C2'	121.8 (2)
O1—C3—C4	119.8 (2)	O1'—C3'—C4'	119.8 (2)
C2—C3—C4	118.4 (2)	C2'—C3'—C4'	118.4 (2)
C3—O1—H1O	109.5	C3'—O1'—H1'O	109.5
C5—C4—C3	121.5 (2)	C5'—C4'—C3'	121.5 (2)
C5—C4—H4	119.2	C5'—C4'—H4'	119.2
C3—C4—H4	119.2	C3'—C4'—H4'	119.2
C4—C5—C6	119.5 (2)	C4'—C5'—C6'	119.5 (2)
C4—C5—H5	120.3	C4'—C5'—H5'	120.3
C6—C5—H5	120.3	C6'—C5'—H5'	120.3
O2—C6—N1	122.7 (2)	O2'—C6'—N1'	122.7 (2)
O2—C6—C5	119.5 (2)	O2'—C6'—C5'	119.5 (2)
N1—C6—C5	117.8 (2)	N1'—C6'—C5'	117.8 (2)
C6—O2—H2O	109.5	C6'—O2'—H2'O	109.5
O4—C7—O3	124.8 (2)	O4'—C7'—O3'	124.8 (2)
O4—C7—C2	116.7 (2)	O4'—C7'—C2'	116.7 (2)
O3—C7—C2	118.53 (19)	O3'—C7'—C2'	118.53 (19)

C6—N1—C2—C3	0.000 (1)	C6'—N1'—C2'—C3'	0.000 (1)
C6—N1—C2—C7	180.000 (1)	C6'—N1'—C2'—C7'	180.000 (1)
N1—C2—C3—O1	180.000 (1)	N1'—C2'—C3'—O1'	180.000 (1)
C7—C2—C3—O1	0.000 (1)	C7'—C2'—C3'—O1'	0.000 (1)
N1—C2—C3—C4	0.000 (1)	N1'—C2'—C3'—C4'	0.000 (1)
C7—C2—C3—C4	180.000 (1)	C7'—C2'—C3'—C4'	180.000 (1)
O1—C3—C4—C5	180.000 (1)	O1'—C3'—C4'—C5'	180.000 (1)
C2—C3—C4—C5	0.000 (1)	C2'—C3'—C4'—C5'	0.000 (1)
C3—C4—C5—C6	0.000 (1)	C3'—C4'—C5'—C6'	0.000 (1)
C2—N1—C6—O2	180.000 (1)	C2'—N1'—C6'—O2'	180.000 (1)
C2—N1—C6—C5	0.000 (1)	C2'—N1'—C6'—C5'	0.000 (1)
C4—C5—C6—O2	180.000 (1)	C4'—C5'—C6'—O2'	180.000 (1)
C4—C5—C6—N1	0.000 (1)	C4'—C5'—C6'—N1'	0.000 (1)
N1—C2—C7—O4	180.000 (1)	N1'—C2'—C7'—O4'	180.000 (1)
C3—C2—C7—O4	0.000 (1)	C3'—C2'—C7'—O4'	0.000 (1)
N1—C2—C7—O3	0.000 (1)	N1'—C2'—C7'—O3'	0.000 (1)
C3—C2—C7—O3	180.000 (1)	C3'—C2'—C7'—O3'	180.000 (1)

Hydrogen-bond geometry (Å, º) top

The D···A distance for C4—H4···O2ⁱⁱⁱ is rather long, but within the bounds noted by Desiraju & Steiner (1999).

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N···O4ⁱ	0.99	1.77	2.755 (3)	169
O1—H1O···O4	0.89	1.76	2.535 (3)	145
C5—H5···O1ⁱⁱ	0.95	2.34	3.269 (3)	166
C4—H4···O2ⁱⁱⁱ	0.95	2.76	3.712 (4)	180
O2—H2O···O3ⁱ	0.94	1.57	2.459 (3)	156
O2—H2O···O4ⁱ	0.94	2.56	3.372 (3)	144

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

Acknowledgements

Analytical data were provided by Robertson Microlit Laboratories. The D8 Venture diffractometer was funded by the NSF (MRI CHE1625732), and by the University of Kentucky.

Funding information

Funding for this research was provided by: The OSU Emeritus Academy.

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