2-Pyridone–tartronic acid (1/1), 3-hydroxy­pyridinium hydrogen tartronate and 4-hydroxy­pyridinium hydrogen tartronate

Tartronic acid forms a hydrogen-bonded complex, C₅H₅NO·C₃H₄O₅, (I), with 2-pyridone, while it forms acid salts, namely 3-hydroxy­pyridinium hydrogen tartronate, (II), and 4-hy­droxy­pyridinium hydrogen tartronate, (III), both C₅H₆NO⁺·C₃H₃O₅⁻, with 3-hydroxy­pyridine and 4-hydroxy­pyridine, respectively. In (I), the pyridone mol­ecules and the acid mol­ecules form R(8) and R(10) hydrogen-bonded rings, respectively, around the inversion centres. In (II) and (III), the cations and anions are linked by N—H...O and O—H...O hydrogen bonds to form a hydrogen-bonded chain. In each of (I), (II) and (III), an intermolecular hydrogen bond is formed between a carboxyl group and the hydroxyl group attached to the central C atom, and in (I), the hydroxyl group participates in an intramolecular hydrogen bond with a carbonyl group. No intermolecular hydrogen bond is formed between the carboxyl groups in (I), or between the carboxyl and carboxyl­ate groups in (II) and (III).

S1. Comment

Tartronic acid, a member of a family of hydroxycarboxylic acids, is of potential interest in crystal engineering for the formation of two- and three-dimensional aggregates with organic bases, as shown in several organic salts of tartaric acid (Aakeröy et al., 1992; Aakeröy & Hitchcock, 1993; Aakeröy Bahra & Niewenhuzen, 1996), malonic acid (Aakeröy & Niewenhuzen, 1994, 1996), dihydroxymalonic acid (Aakeröy Niewenhuzen & Robinson, 1998) and oxamic acid (Aakeröy Hughes & Niewenhuyzen, 1996). Furthermore, tartronic acid is an interesting candidate for the selective synthesis and crystallization of optically active substances, because its acidic anion, the hydrogen tartronate ion, is optically active. Previously, we have reported the three-dimensional hydrogen-bonded structure of imidazolium hydrogen tartronate, where the anions form a homochiral infinite chain but the chains aggregate to form a heterochiral layer (Fukunaga & Ishida, 2003). In the present study, we have selected hydroxypyridines as the counter-base in order to extend the previous examination further, and report here the structures of the title compounds, (I)-(III). Fig. 1 shows the asymmetric units of compounds (I), (II) and (III). \sch

In (I), the base molecule is in the lactam form (Yang & Craven, 1998), and no acid-base interaction involving H-atom transfer is observed. Two pyridone molecules are held together by N—H···O hydrogen bonds, forming a centrosymmetric hydrogen-bonded ring with graph-set discriptor R₄⁴(8) (Bernstein et al., 1995), and two molecules of tartronic acid are held together by O—H···O hydrogen bonds between the hydroxyl and carbonyl groups, forming a centrosymmetric R₂²(10) ring (Fig. 2a and Table 2). The dimeric unit composed of pyridone molecules is connected to that composed of acid molecules via an O6—H9···O1 hydrogen bond on one side, and by C6—H5···O3^iv and C6—H5···O5ⁱ bifurcated hydrogen bonds on the other side, to afford a molecular tape running along [011] [symmetry codes: (i) 1 − x, −y, 1 − z; (iv) x, y − 1, 1 + z; Fig. 2a and Table 2]. The molecular tapes are stacked parallel to the c direction through an O4—H8···O2ⁱⁱⁱ hydrogen bond, resulting in a layer parallel to (202) [symmetry code: (iii) 1 + x, y, z; Figs. 2 b and 2c, and Table 2]. The closest separation between the pyridone rings in the layer is 3.428 Å, and the centre-to-centre separation is 3.735 (3) Å.

The hydrogen-bonding motif formed between the pyridone dimer and the acid moiety is similar to that reported for 2:1 co-crystals of 2-pyridone and several dicarboxylic acids, namely oxalic acid, succinic acid, adipic acid dihydrate, suberic acid and sebacic acid (Aakeröy, Beatty & Zou, 1998), fumaric acid and meso-2,3-dibromosuccinic acid (Aakeröy et al., 2000), oxalic acid and trans-β-hydromuconic acid (Kashino et al., 2001), and malonic acid and pimeric acid (Edwards et al., 2002). The pyridone dimer is also formed in 1:1 co-crystals of 2-pyridone and some non-centrosymmetric dicarboxylic acids, namely glutaric acid and azelaic acid (Edwards et al., 2002). The pyridone dimer is not formed in the 1:1 co-crystals of 2-pyridone with trans-glutaconic acid and L-tartaric acid (Kashino et al., 2001).

In (II) and (III), H-atom transfer occurs from the acid to the base moiety and a chiral hydrogen tartronate anion is induced in these crystals. In (II), a cation is linked to two neighbouring anions related by a glide plane through the N1—H1···O6, N1—H1···O2, O1—H3···O5^v and C4—H4···O5^v hydrogen bonds, to form a zigzag chain running along [102] [symmetry code: (v) 1 + x, −y, z − 1/2; Fig. 3a and Table 4]. On the other hand, the anions aggregate through O—H···O hydrogen bonds between the hydroxyl and carboxylate groups (O2—H8···O6^vi) and between the carboxyl and hydroxyl groups (O4—H9···O2^vii) to form a homochiral plane parallel to (001) [symmetry codes: (vi) x, 1 + y, z; (vii) x − 1, y, z; Fig. 3 b]. The planes related by a glide plane are bridged by cations through the N—H···O, O—H···O and C—H···O hydrogen bonds mentioned above, resulting in a three-dimensional hydrogen-bonded network. It is noted that such a homochiral plane has also been found in some chiral crystals, namely 3-hydroxypyridinium hydrogen L-tartarate (Tafeenko et al., 1990) and 3-hydroxypyridinium hydrogen L-maleate (Aakeröy & Niewenhuyzen, 1994). In these crystals, planes with the same chirality were bridged by the cations.

In (III), an intramolecular O—H···O hydrogen bond is observed between the carboxyl and carboxylate groups in the anion (Fig. 1 and Table 6). A cation is linked to two neighbouring anions, which are related to each other by a translation along [101], through the O1—H4···O5^ix, C5—H5···O5^ix and bifurcated N—H···O hydrogen bonds to form a zigzag chain running along [121] [symmetry codes: (ix) x − 1, y, 1 + z; Fig. 4a and Table 6). The chains are linked by an O2—H8···O3^x hydrogen bond between the hydroxyl and carboxyl groups, resulting in a heterochiral layer parallel to (101) [symmetry code: (x) 1/2 + x, 1 − y, 1/2 + z; Fig. 4 b]. The layers are connected via an C7—H7···O2^xiii hydrogen bond [symmetry code: (xiii) 1 + x, y, z; Table 6].

In the crystal of tartronic acid, neighbouring molecules related by a 2₁ axis form a molecular chain through O—H···O hydrogen bonds between the carboxyl groups (van Eijck et al., 1965). In the crystal of ammonium hydrogen tartronate, hydrogen tartronate anions related by a 2₁ axis form a very short O—H···O hydrogen bond between the carboxyl and carboxylate groups (Taka et al., 1998; Moritani et al., 2001). This is an indication that a strong intermolecular hydrogen bond is formed between the carboxyl and carboxylate groups of the anions. However, in the crystals of (I), (II) and (III), no such type of hydrogen-bonding is observed. This fact shows that the hydroxyl group attached to the central C atom of tartronic acid or the hydrogen tartronate anion can form stable intermolecular hydrogen bond(s) in place of the carboxyl group.

S2. Experimental

Crystals of (I), (II) and (III) were grown by slow evaporation at room temperature of ethanol solutions of tartronic acid and the respective hydroxypyridines, in a molar ratio of 1:1.

S3. Refinement

For all compounds, H atoms attached to C atoms were treated as riding, with C—H = 0.98 (methine H) or 0.93 Å (aromatic H), and with U_iso(H) = 1.2U_eq(C). For (I) and (II), H atoms involved in O—H···O and N—H···O hydrogen bonds were refined. For (III), the O—H distances and the C—O—H angles were fixed to 0.82 Å and 109.5°, respectively, while the torsion angles around the C—O bonds were refined, with U_iso(H) = 1.5U_eq(O). H atoms attached to N atoms were constrained in the riding model, with N—H = 0.86 Å and U_iso(H) = 1.2U_eq(N). For (II) and (III), Friedel opposites were merged.

Computing details

For all compounds, data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1990); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: TEXSAN for Windows (Molecular Structure Corporation, 1997-1999); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: TEXSAN for Windows.

Figures

	Fig. 1. A view of the asymmetric units of (a) (I), (b) (II) and (c) (III). Displacement ellipsoids are drawn at the 50% probability level. The N—H···O and O—H···O hydrogen bonds are indicated by dashed lines.
	Fig. 2. The crystal structure and hydrogen-bonding scheme for (I). (a) Hydrogen-bonded rings centred on inversion centres. (b) The pyridone molecules linked to the hydrogen-bonded ribbons of the acid molecules. (c) A packing diagram viewed along the a direction, showing the N—H···O, O—H···O and C—H···O hydrogen bonds (symmetry codes as in Table 2).
	Fig. 3. The crystal structure and hydrogen-bonding scheme for (II). (a) The hydrogen-bonded chain formed by the anion and cation. (b) The homochiral anions, forming a hydrogen-bonded plane across the c axis. (c) A packing diagram viewed along the b direction, showing the N—H···O, O—H···O and C—H···O hydrogen bonds (symmetry codes as in Table 4).
	Fig. 4. The crystal structure and hydrogen-bonding scheme for (III). (a) The hydrogen-bonded chain formed by the anion and cation. (b) The hydrogen-bonded net formed by the N—H···O, O—H···O and C—H···O hydrogen bonds, viewed along the (101) plane (symmetry codes as in Table 6).

(I)

Crystal data

C5H5NO·C3H4O5	Z = 2
Mr = 215.16	F(000) = 224
Triclinic, P1	Dx = 1.549 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 5.879 (4) Å	Cell parameters from 25 reflections
b = 6.859 (4) Å	θ = 10.3–11.5°
c = 12.588 (8) Å	µ = 0.14 mm^−1
α = 74.61 (5)°	T = 296 K
β = 80.94 (6)°	Plate, colourless
γ = 70.95 (5)°	0.30 × 0.20 × 0.08 mm
V = 461.2 (5) Å^3

Data collection

Rigaku AFC-5R diffractometer	Rint = 0.032
Radiation source: Rigaku rotating anode	θmax = 30.0°, θmin = 3.2°
Graphite monochromator	h = −8→8
ω/2θ scans	k = −9→1
3319 measured reflections	l = −17→17
2698 independent reflections	3 standard reflections every 97 reflections
1323 reflections with I > 2σ(I)	intensity decay: 0.0%

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)] = 0.065	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.191	H atoms treated by a mixture of independent and constrained refinement
S = 1.00	w = 1/[σ^2(Fo^2) + (0.08P)^2] where P = (Fo^2 + 2Fc^2)/3
2698 reflections	(Δ/σ)max = 0.001
153 parameters	Δρmax = 0.26 e Å^−3
0 restraints	Δρmin = −0.24 e Å^−3
0 constraints

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.5760 (4)	0.2370 (4)	0.44393 (17)	0.0441 (6)
O2	0.4022 (4)	0.7641 (4)	0.01997 (18)	0.0366 (6)
O3	0.8635 (4)	0.7274 (4)	−0.05312 (16)	0.0403 (6)
O4	0.9596 (4)	0.7379 (4)	0.10989 (19)	0.0426 (7)
O5	0.5145 (4)	0.3892 (4)	0.17429 (18)	0.0455 (7)
O6	0.6360 (5)	0.5405 (4)	0.28236 (19)	0.0421 (6)
N1	0.6855 (5)	0.0014 (4)	0.6052 (2)	0.0349 (6)
C2	0.6995 (6)	0.1784 (5)	0.5281 (2)	0.0331 (7)
C3	0.8526 (6)	0.2838 (6)	0.5480 (3)	0.0422 (8)
C4	0.9782 (7)	0.2080 (6)	0.6388 (3)	0.0477 (9)
C5	0.9599 (6)	0.0227 (6)	0.7161 (3)	0.0414 (8)
C6	0.8131 (6)	−0.0764 (6)	0.6969 (2)	0.0392 (8)
C7	0.5646 (5)	0.7342 (5)	0.0989 (2)	0.0282 (6)
C8	0.8142 (5)	0.7321 (5)	0.0429 (2)	0.0274 (6)
C9	0.5710 (5)	0.5335 (5)	0.1894 (2)	0.0310 (7)
H1	0.586 (5)	−0.074 (5)	0.590 (3)	0.033 (8)*
H2	0.867	0.407	0.498	0.051*
H3	1.079	0.280	0.650	0.057*
H4	1.047	−0.030	0.779	0.050*
H5	0.798	−0.200	0.747	0.047*
H6	0.505	0.855	0.134	0.034*
H7	0.477 (7)	0.712 (6)	−0.042 (3)	0.058 (12)*
H8	1.081 (7)	0.733 (6)	0.077 (3)	0.054 (13)*
H9	0.614 (9)	0.444 (8)	0.330 (4)	0.083 (16)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0575 (15)	0.0457 (15)	0.0328 (12)	−0.0280 (13)	−0.0139 (10)	0.0069 (11)
O2	0.0284 (11)	0.0495 (15)	0.0319 (11)	−0.0128 (11)	−0.0086 (9)	−0.0038 (11)
O3	0.0419 (13)	0.0536 (15)	0.0254 (11)	−0.0181 (12)	−0.0009 (9)	−0.0055 (10)
O4	0.0300 (13)	0.0721 (19)	0.0351 (12)	−0.0244 (13)	−0.0032 (10)	−0.0158 (12)
O5	0.0609 (16)	0.0472 (15)	0.0382 (12)	−0.0334 (13)	−0.0081 (11)	−0.0024 (11)
O6	0.0614 (16)	0.0451 (15)	0.0274 (11)	−0.0306 (13)	−0.0129 (10)	0.0029 (11)
N1	0.0461 (16)	0.0363 (15)	0.0277 (12)	−0.0233 (13)	−0.0080 (11)	0.0007 (11)
C2	0.0380 (17)	0.0341 (18)	0.0273 (14)	−0.0152 (14)	−0.0010 (12)	−0.0028 (13)
C3	0.055 (2)	0.042 (2)	0.0351 (17)	−0.0297 (18)	−0.0065 (15)	0.0029 (15)
C4	0.054 (2)	0.056 (2)	0.0438 (19)	−0.0329 (19)	−0.0122 (16)	−0.0036 (17)
C5	0.049 (2)	0.047 (2)	0.0305 (16)	−0.0212 (17)	−0.0111 (14)	0.0016 (15)
C6	0.052 (2)	0.0400 (19)	0.0268 (15)	−0.0212 (17)	−0.0080 (14)	0.0032 (14)
C7	0.0263 (14)	0.0325 (16)	0.0263 (13)	−0.0126 (13)	−0.0062 (11)	−0.0004 (12)
C8	0.0265 (14)	0.0253 (15)	0.0279 (14)	−0.0084 (12)	−0.0013 (11)	−0.0016 (11)
C9	0.0272 (15)	0.0387 (18)	0.0299 (15)	−0.0166 (14)	−0.0008 (12)	−0.0049 (13)

Geometric parameters (Å, º)

O1—C2	1.279 (7)	C2—C3	1.409 (10)
O2—C7	1.416 (5)	C3—C4	1.350 (9)
O2—H7	0.92 (4)	C3—H2	0.93
O3—C8	1.204 (3)	C4—C5	1.404 (11)
O4—C8	1.308 (4)	C4—H3	0.93
O4—H8	0.76 (4)	C5—C6	1.342 (10)
O5—C9	1.208 (7)	C5—H4	0.93
O6—C9	1.304 (4)	C6—H5	0.93
O6—H9	0.79 (5)	C7—C8	1.522 (4)
N1—C2	1.355 (4)	C7—C9	1.530 (4)
N1—C6	1.365 (8)	C7—H6	0.98
N1—H1	0.97 (3)
O1···O6	2.569 (4)	O4···H4^vii	2.72
O1···N1^i	2.809 (4)	O4···C5^vii	3.234 (5)
O2···H8^ii	1.97 (4)	O4···C4^vii	3.370 (5)
O2···O4^ii	2.712 (4)	O5···H7^iii	1.96 (4)
O2···O5^iii	2.825 (4)	O5···H5^i	2.52
O2···C8^iv	3.192 (5)	O5···C6^i	3.286 (5)
O3···H5^v	2.50	O6···H3^vii	2.72
O3···H4^v	2.64	O6···C3^viii	3.383 (5)
O3···O3^vi	3.049 (4)	O6···C2	3.399 (4)
O3···C8^vi	3.084 (5)	C2···H9	2.68 (5)
O3···C6^v	3.096 (4)	C2···H1^i	2.77 (3)
O3···C5^v	3.157 (5)	C7···H8^ii	2.90 (4)
C7—O2—H7	113 (2)	C4—C5—H4	121.1
C8—O4—H8	107 (3)	C5—C6—N1	120.8 (3)
C9—O6—H9	110 (3)	C5—C6—H5	119.6
C2—N1—C6	123.3 (3)	N1—C6—H5	119.6
C2—N1—H1	116.3 (19)	O2—C7—C8	110.6 (2)
C6—N1—H1	120.3 (19)	O2—C7—C9	110.9 (3)
O1—C2—N1	118.7 (3)	C8—C7—C9	112.1 (3)
O1—C2—C3	125.1 (3)	O2—C7—H6	107.7
N1—C2—C3	116.2 (6)	C8—C7—H6	107.7
C4—C3—C2	120.7 (4)	C9—C7—H6	107.7
C4—C3—H2	119.6	O3—C8—O4	125.8 (3)
C2—C3—H2	119.6	O3—C8—C7	121.6 (3)
C3—C4—C5	121.1 (7)	O4—C8—C7	112.5 (2)
C3—C4—H3	119.4	O5—C9—O6	125.2 (6)
C5—C4—H3	119.4	O5—C9—C7	122.0 (3)
C6—C5—C4	117.9 (6)	O6—C9—C7	112.8 (3)
C6—C5—H4	121.1
C6—N1—C2—O1	178.8 (3)	O2—C7—C8—O3	−9.4 (4)
C6—N1—C2—C3	−1.0 (5)	C9—C7—C8—O3	114.9 (6)
O1—C2—C3—C4	−179.2 (4)	O2—C7—C8—O4	170.1 (3)
N1—C2—C3—C4	0.7 (5)	C9—C7—C8—O4	−65.7 (6)
C2—C3—C4—C5	−0.1 (6)	O2—C7—C9—O5	23.5 (4)
C3—C4—C5—C6	−0.1 (6)	C8—C7—C9—O5	−100.6 (4)
C4—C5—C6—N1	−0.2 (5)	O2—C7—C9—O6	−154.7 (3)
C2—N1—C6—C5	0.8 (5)	C8—C7—C9—O6	81.2 (6)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1^i	0.96 (3)	1.85 (3)	2.809 (4)	174 (4)
O2—H7···O5^iii	0.93 (4)	1.96 (4)	2.825 (4)	155 (4)
O4—H8···O2^ix	0.76 (4)	1.97 (4)	2.712 (4)	164 (4)
O6—H9···O1	0.80 (5)	1.77 (5)	2.569 (4)	175 (3)
O2—H7···O3	0.93 (4)	2.29 (4)	2.675 (4)	104 (3)
C6—H5···O3^x	0.93	2.50	3.096 (4)	122
C6—H5···O5^i	0.93	2.52	3.286 (5)	140

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

(II)

Crystal data

C5H6NO^+·C3H3O5^−	F(000) = 224
Mr = 215.16	Dx = 1.467 Mg m^−3
Monoclinic, Pc	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P -2yc	Cell parameters from 25 reflections
a = 5.7563 (11) Å	θ = 11.0–11.5°
b = 5.1871 (7) Å	µ = 0.13 mm^−1
c = 16.3206 (19) Å	T = 298 K
β = 92.186 (13)°	Plate, colourless
V = 486.95 (13) Å^3	0.50 × 0.50 × 0.10 mm
Z = 2

Data collection

Rigaku AFC-5R diffractometer	Rint = 0.016
Radiation source: Rigaku rotating anode	θmax = 31.0°, θmin = 2.5°
Graphite monochromator	h = −1→8
ω/2θ scans	k = −1→7
2353 measured reflections	l = −23→23
1562 independent reflections	3 standard reflections every 97 reflections
1394 reflections with I > 2σ(I)	intensity decay: 0.2%

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)] = 0.042	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.119	w = 1/[σ^2(Fo^2) + (0.0945P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.00	(Δ/σ)max = 0.001
1562 reflections	Δρmax = 0.43 e Å^−3
153 parameters	Δρmin = −0.18 e Å^−3
2 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: 0.115 (19)

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.9138 (5)	−0.0907 (5)	0.08939 (14)	0.0655 (6)
O2	0.2852 (2)	0.4262 (2)	0.34707 (11)	0.0335 (3)
O3	−0.1582 (3)	0.4706 (4)	0.28672 (12)	0.0503 (5)
O4	−0.2977 (3)	0.3127 (4)	0.40281 (12)	0.0473 (5)
O5	0.0705 (4)	−0.0990 (3)	0.45448 (12)	0.0529 (5)
O6	0.2425 (3)	−0.0767 (3)	0.33621 (11)	0.0442 (5)
N1	0.4292 (4)	0.1192 (5)	0.20162 (13)	0.0466 (5)
C2	0.6141 (5)	−0.0148 (5)	0.17989 (14)	0.0466 (6)
C3	0.7280 (5)	0.0497 (5)	0.10891 (14)	0.0462 (5)
C4	0.6415 (6)	0.2591 (7)	0.06331 (15)	0.0555 (6)
C5	0.4496 (6)	0.3944 (7)	0.08893 (17)	0.0597 (7)
C6	0.3427 (5)	0.3205 (7)	0.15909 (18)	0.0556 (7)
C7	0.1089 (3)	0.3168 (3)	0.39297 (12)	0.0253 (3)
C8	−0.1301 (3)	0.3763 (3)	0.35368 (13)	0.0286 (3)
C9	0.1436 (3)	0.0219 (3)	0.39551 (13)	0.0300 (3)
H1	0.344 (8)	0.059 (9)	0.237 (3)	0.073 (13)*
H2	0.667	−0.152	0.212	0.056*
H3	0.968 (9)	−0.025 (10)	0.043 (3)	0.082 (15)*
H4	0.713	0.308	0.016	0.067*
H5	0.393	0.535	0.059	0.072*
H6	0.213	0.409	0.177	0.067*
H7	0.118	0.386	0.449	0.030*
H8	0.271 (6)	0.591 (7)	0.344 (2)	0.042 (7)*
H9	−0.421 (8)	0.375 (8)	0.383 (3)	0.062 (10)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0825 (16)	0.0663 (13)	0.0497 (11)	0.0027 (12)	0.0306 (11)	0.0030 (10)
O2	0.0223 (5)	0.0221 (5)	0.0570 (9)	−0.0003 (5)	0.0118 (5)	0.0016 (5)
O3	0.0352 (8)	0.0702 (12)	0.0451 (9)	−0.0014 (8)	−0.0030 (7)	0.0192 (8)
O4	0.0211 (6)	0.0715 (12)	0.0498 (9)	0.0010 (7)	0.0090 (6)	0.0114 (9)
O5	0.0744 (13)	0.0364 (8)	0.0501 (10)	0.0122 (8)	0.0326 (9)	0.0128 (7)
O6	0.0635 (11)	0.0224 (6)	0.0488 (9)	0.0011 (6)	0.0326 (8)	0.0010 (6)
N1	0.0561 (12)	0.0503 (11)	0.0343 (8)	−0.0167 (9)	0.0141 (8)	−0.0013 (8)
C2	0.0677 (15)	0.0407 (10)	0.0325 (10)	−0.0113 (10)	0.0171 (10)	0.0022 (9)
C3	0.0594 (14)	0.0481 (12)	0.0321 (9)	−0.0122 (11)	0.0142 (9)	−0.0013 (9)
C4	0.0677 (16)	0.0665 (15)	0.0331 (10)	−0.0093 (14)	0.0114 (10)	0.0112 (11)
C5	0.0651 (17)	0.0722 (18)	0.0415 (12)	−0.0028 (15)	−0.0016 (12)	0.0160 (13)
C6	0.0459 (14)	0.0736 (19)	0.0475 (13)	−0.0042 (12)	0.0030 (10)	−0.0020 (13)
C7	0.0195 (6)	0.0227 (6)	0.0339 (7)	0.0020 (5)	0.0037 (5)	−0.0024 (6)
C8	0.0229 (6)	0.0274 (7)	0.0357 (8)	0.0012 (6)	0.0038 (6)	−0.0001 (7)
C9	0.0291 (8)	0.0240 (6)	0.0377 (8)	0.0036 (6)	0.0111 (6)	0.0038 (7)

Geometric parameters (Å, º)

O1—C3	1.342 (4)	C2—C3	1.394 (3)
O1—H3	0.90 (5)	C2—H2	0.93
O2—C7	1.404 (2)	C3—C4	1.397 (4)
O2—H8	0.86 (4)	C4—C5	1.387 (5)
O3—C8	1.203 (3)	C4—H4	0.93
O4—C8	1.320 (2)	C5—C6	1.375 (4)
O4—H9	0.83 (5)	C5—H5	0.93
O5—C9	1.236 (3)	C6—H6	0.93
O6—C9	1.251 (2)	C7—C8	1.527 (2)
N1—C2	1.330 (4)	C7—C9	1.543 (2)
N1—C6	1.339 (4)	C7—H7	0.98
N1—H1	0.84 (5)
O2···H1	2.62 (5)	O5···H7^vii	2.69
O2···H6	2.79	O5···H8^vii	2.71 (3)
O2···N1	3.004 (3)	O5···C7^vii	3.203 (2)
O2···C6	3.146 (3)	O5···C4^vi	3.206 (4)
O2···C9^i	3.299 (2)	O5···C3^vi	3.269 (3)
O2···C8^ii	3.373 (2)	O5···C8^vii	3.362 (3)
O3···H2^iii	2.50	O6···C7^vii	3.377 (2)
O3···H6	2.86	C7···H9^ii	2.73 (5)
O3···N1^iv	3.262 (3)	C9···H8^vii	2.51 (4)
O3···C2^iv	3.305 (3)	C9···H3^vi	2.65 (5)
O4···H4^v	2.70	C9···H1	2.88 (5)
O5···H4^vi	2.56
C3—O1—H3	107 (3)	C4—C5—H5	120.1
C7—O2—H8	111 (2)	N1—C6—C5	118.7 (3)
C8—O4—H9	108 (3)	N1—C6—H6	120.7
C2—N1—C6	123.7 (2)	C5—C6—H6	120.7
C2—N1—H1	119 (3)	O2—C7—C8	110.62 (15)
C6—N1—H1	116 (3)	O2—C7—C9	108.66 (13)
N1—C2—C3	120.2 (2)	C8—C7—C9	108.96 (13)
N1—C2—H2	119.9	O2—C7—H7	109.5
C3—C2—H2	119.9	C8—C7—H7	109.5
O1—C3—C2	118.1 (2)	C9—C7—H7	109.5
O1—C3—C4	124.5 (2)	O3—C8—O4	125.29 (19)
C2—C3—C4	117.4 (3)	O3—C8—C7	123.47 (17)
C5—C4—C3	120.3 (2)	O4—C8—C7	111.24 (17)
C5—C4—H4	119.9	O5—C9—O6	125.01 (17)
C3—C4—H4	119.9	O5—C9—C7	118.45 (17)
C6—C5—C4	119.8 (3)	O6—C9—C7	116.53 (16)
C6—C5—H5	120.1
C6—N1—C2—C3	−0.6 (4)	O2—C7—C8—O3	10.1 (3)
N1—C2—C3—O1	180.0 (3)	C9—C7—C8—O3	−109.3 (2)
N1—C2—C3—C4	0.6 (4)	O2—C7—C8—O4	−169.49 (16)
O1—C3—C4—C5	−179.3 (3)	C9—C7—C8—O4	71.1 (2)
C2—C3—C4—C5	0.0 (4)	O2—C7—C9—O5	153.1 (2)
C3—C4—C5—C6	−0.7 (5)	C8—C7—C9—O5	−86.3 (3)
C2—N1—C6—C5	0.0 (4)	O2—C7—C9—O6	−27.8 (2)
C4—C5—C6—N1	0.6 (5)	C8—C7—C9—O6	92.8 (2)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H3···O5^viii	0.90 (5)	1.71 (5)	2.604 (3)	180 (7)
O2—H8···O6^i	0.86 (4)	1.74 (4)	2.5956 (19)	179 (4)
O4—H9···O2^iv	0.83 (5)	1.79 (5)	2.602 (2)	165 (4)
N1—H1···O6	0.83 (5)	1.88 (5)	2.682 (3)	162 (5)
C2—H2···O3^ix	0.93	2.50	3.422 (3)	174
C4—H4···O5^viii	0.93	2.56	3.206 (4)	127

Symmetry codes: (i) x, y+1, z; (iv) x−1, y, z; (viii) x+1, −y, z−1/2; (ix) x+1, y−1, z.

(III)

Crystal data

C5H6NO^+·C3H3O5^−	F(000) = 224
Mr = 215.16	Dx = 1.574 Mg m^−3
Monoclinic, Pn	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P -2yac	Cell parameters from 25 reflections
a = 4.0607 (13) Å	θ = 10.8–11.4°
b = 13.144 (3) Å	µ = 0.14 mm^−1
c = 8.696 (2) Å	T = 298 K
β = 101.99 (2)°	Plate, colourless
V = 454.0 (2) Å^3	0.46 × 0.26 × 0.17 mm
Z = 2

Data collection

Rigaku AFC-5R diffractometer	861 reflections with I > 2σ(I)
Radiation source: Rigaku rotating anode	Rint = 0.038
Graphite monochromator	θmax = 30.0°, θmin = 2.9°
ω/2θ scans	h = −1→5
Absorption correction: ψ scan (North et al., 1968)	k = −1→18
Tmin = 0.942, Tmax = 0.977	l = −12→12
1985 measured reflections	3 standard reflections every 97 reflections
1341 independent reflections	intensity decay: 2.0%

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)] = 0.051	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.133	H-atom parameters constrained
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0521P)^2] where P = (Fo^2 + 2Fc^2)/3
1341 reflections	(Δ/σ)max = 0.001
136 parameters	Δρmax = 0.21 e Å^−3
2 restraints	Δρmin = −0.19 e Å^−3

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.0432 (12)	0.8918 (2)	0.9464 (4)	0.0558 (9)
O2	0.5687 (8)	0.6265 (2)	0.4054 (3)	0.0357 (7)
O3	0.3569 (10)	0.4882 (2)	0.1718 (4)	0.0526 (9)
O4	0.6132 (9)	0.5659 (2)	0.0077 (3)	0.0494 (9)
O5	0.8864 (9)	0.7360 (2)	0.0931 (4)	0.0510 (9)
O6	0.7017 (9)	0.8064 (2)	0.2937 (4)	0.0458 (8)
N1	0.3879 (11)	0.8035 (3)	0.5608 (4)	0.0401 (9)
C2	0.3392 (13)	0.9020 (3)	0.5858 (5)	0.0426 (10)
C3	0.2261 (13)	0.9332 (3)	0.7144 (5)	0.0454 (12)
C4	0.1519 (12)	0.8613 (3)	0.8191 (5)	0.0392 (10)
C5	0.1983 (12)	0.7588 (3)	0.7885 (5)	0.0374 (9)
C6	0.3127 (13)	0.7327 (3)	0.6582 (5)	0.0432 (11)
C7	0.7267 (11)	0.6245 (3)	0.2768 (4)	0.0301 (8)
C8	0.5441 (12)	0.5539 (3)	0.1482 (4)	0.0348 (9)
C9	0.7685 (11)	0.7335 (3)	0.2199 (4)	0.0351 (10)
H1	0.469	0.785	0.481	0.048*
H2	0.383	0.950	0.514	0.051*
H3	0.199	1.002	0.732	0.054*
H4	0.001	0.842	0.996	0.084*
H5	0.151	0.709	0.857	0.045*
H6	0.339	0.664	0.636	0.052*
H7	0.953	0.597	0.314	0.036*
H8	0.630	0.577	0.462	0.053*
H9	0.720	0.619	0.006	0.074*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.093 (3)	0.0359 (15)	0.0512 (19)	0.004 (2)	0.0448 (19)	−0.0015 (15)
O2	0.0484 (17)	0.0332 (13)	0.0305 (15)	0.0042 (13)	0.0203 (14)	0.0028 (11)
O3	0.067 (3)	0.0397 (15)	0.0571 (18)	−0.0144 (17)	0.0257 (18)	−0.0135 (14)
O4	0.070 (3)	0.0503 (17)	0.0333 (14)	−0.0062 (18)	0.0236 (16)	−0.0125 (14)
O5	0.077 (3)	0.0431 (16)	0.0428 (17)	−0.0120 (18)	0.0340 (18)	−0.0003 (14)
O6	0.069 (2)	0.0318 (13)	0.0411 (15)	−0.0061 (16)	0.0218 (16)	−0.0010 (13)
N1	0.052 (3)	0.0410 (18)	0.0321 (17)	−0.0068 (18)	0.0204 (17)	−0.0014 (15)
C2	0.060 (3)	0.0318 (18)	0.042 (2)	−0.003 (2)	0.024 (2)	0.0086 (17)
C3	0.069 (3)	0.0207 (16)	0.054 (3)	0.0034 (19)	0.030 (3)	0.0045 (17)
C4	0.056 (3)	0.033 (2)	0.033 (2)	0.000 (2)	0.019 (2)	0.0013 (16)
C5	0.053 (3)	0.0297 (17)	0.0334 (18)	0.003 (2)	0.0185 (19)	0.0030 (16)
C6	0.064 (3)	0.0331 (18)	0.039 (2)	−0.002 (2)	0.026 (2)	−0.0009 (18)
C7	0.037 (2)	0.0311 (16)	0.0245 (17)	0.0060 (18)	0.0120 (16)	0.0000 (15)
C8	0.044 (3)	0.0267 (16)	0.037 (2)	0.0047 (18)	0.0161 (19)	−0.0048 (15)
C9	0.043 (3)	0.034 (2)	0.0306 (19)	−0.0057 (18)	0.0139 (19)	−0.0002 (16)

Geometric parameters (Å, º)

O1—C4	1.336 (5)	C2—C3	1.358 (6)
O1—H4	0.82	C2—H2	0.93
O2—C7	1.400 (4)	C3—C4	1.389 (5)
O2—H8	0.82	C3—H3	0.93
O3—C8	1.196 (5)	C4—C5	1.394 (5)
O4—C8	1.318 (5)	C5—C6	1.356 (6)
O4—H9	0.82	C5—H5	0.93
O5—C9	1.291 (5)	C6—H6	0.93
O6—C9	1.215 (5)	C7—C8	1.522 (6)
N1—C2	1.334 (5)	C7—C9	1.537 (5)
N1—C6	1.336 (5)	C7—H7	0.98
N1—H1	0.86
O2···H6	2.43	O4···C7^ii	3.385 (5)
O2···O3	2.729 (4)	O4···C5^iii	3.401 (6)
O2···C6	2.968 (5)	O5···H5^iv	2.53
O2···C7^i	3.370 (6)	O5···C5^iv	3.178 (6)
O3···H7^i	2.67	O5···C4^iv	3.258 (6)
O3···O4^i	3.226 (5)	O6···H3^v	2.57
O3···C8^i	3.376 (6)	O6···N1^vi	3.235 (5)
O3···C7^i	3.401 (6)	C2···C4^vi	3.537 (7)
O4···H8^ii	2.69	C2···C3^vi	3.566 (8)
O4···H7^ii	2.72	C5···C6^i	3.554 (7)
O4···H5^iii	2.78
C4—O1—H4	109.5	C4—C5—H5	120.4
C7—O2—H8	109.5	N1—C6—C5	121.1 (4)
C8—O4—H9	109.5	N1—C6—H6	119.4
C2—N1—C6	120.8 (4)	C5—C6—H6	119.4
C2—N1—H1	119.6	O2—C7—C8	111.3 (3)
C6—N1—H1	119.6	O2—C7—C9	109.8 (3)
N1—C2—C3	121.0 (4)	C8—C7—C9	113.7 (3)
N1—C2—H2	119.5	O2—C7—H7	107.2
C3—C2—H2	119.5	C8—C7—H7	107.2
C2—C3—C4	119.4 (3)	C9—C7—H7	107.2
C2—C3—H3	120.3	O3—C8—O4	120.7 (4)
C4—C3—H3	120.3	O3—C8—C7	123.0 (3)
O1—C4—C3	119.5 (3)	O4—C8—C7	116.3 (4)
O1—C4—C5	122.0 (3)	O6—C9—O5	126.5 (4)
C3—C4—C5	118.5 (4)	O6—C9—C7	120.9 (3)
C6—C5—C4	119.2 (4)	O5—C9—C7	112.6 (4)
C6—C5—H5	120.4
C6—N1—C2—C3	2.9 (9)	O2—C7—C8—O3	−19.9 (6)
N1—C2—C3—C4	−1.7 (8)	C9—C7—C8—O3	−144.6 (4)
C2—C3—C4—O1	179.5 (5)	O2—C7—C8—O4	162.7 (3)
C2—C3—C4—C5	0.3 (8)	C9—C7—C8—O4	38.0 (5)
O1—C4—C5—C6	−179.3 (5)	O2—C7—C9—O6	7.4 (6)
C3—C4—C5—C6	−0.2 (8)	C8—C7—C9—O6	132.9 (4)
C2—N1—C6—C5	−2.8 (8)	O2—C7—C9—O5	−174.4 (4)
C4—C5—C6—N1	1.4 (8)	C8—C7—C9—O5	−48.9 (5)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H4···O5^vii	0.82	1.74	2.562 (4)	177
O2—H8···O3^viii	0.82	2.05	2.808 (4)	153
O4—H9···O5	0.82	1.79	2.538 (4)	151
N1—H1···O2	0.86	2.25	2.862 (5)	128
N1—H1···O6	0.86	2.07	2.872 (5)	156
C2—H2···O1^v	0.93	2.29	3.149 (5)	153
C3—H3···O6^ix	0.93	2.57	3.497 (5)	173
C5—H5···O5^vii	0.93	2.54	3.179 (6)	127
C7—H7···O2^vi	0.98	2.49	3.369 (6)	149

Symmetry codes: (v) x+1/2, −y+2, z−1/2; (vi) x+1, y, z; (vii) x−1, y, z+1; (viii) x+1/2, −y+1, z+1/2; (ix) x−1/2, −y+2, z+1/2.