Crystal structure of 4-hy­droxy­pyridin-1-ium 3,5-di­carb­oxy­benzoate

Staun, S.L.; Oliver, A.G.

doi:10.1107/S2056989015011780

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ISSN: 2056-9890

Volume 71| Part 7| July 2015| Pages 861-863

doi:10.1107/S2056989015011780

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Crystal structure of 4-hydroxypyridin-1-ium 3,5-dicarboxybenzoate

Selena L. Staun ^a and Allen G. Oliver ^a ^*

^aDepartment of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556-5670, USA
^*Correspondence e-mail: aoliver2@nd.edu

Edited by S. Parkin, University of Kentucky, USA (Received 7 June 2015; accepted 19 June 2015; online 27 June 2015)

The structure of the title salt, C₅H₆NO⁺·C₉H₅O₆⁻, (I), shows that 4-hydroxypyridine has abstracted an H atom from benzene-1,3,5-tricarboxylic acid, yielding a pyridinium cation and carboxylate anion. The two ions form an extensive three-dimensional hydrogen-bonded network throughout the crystal. The hydrogen bonds that comprise the core of the network are considered strong, with O—H⋯O and N—H⋯O donor-to-acceptor distances ranging from 2.533 (2) to 2.700 (2) Å. Packing is further enhanced by π-stacking of the cations and anions with like species [centroid–centroid distance = 3.6206 (13) Å].

Keywords: crystal structure; 4-hydroxypyridin-1-ium; 3,5-dicarboxybenzoate; hydrogen bonding; cocrystal.

CCDC reference: 1407819

1. Chemical Context

As a study in crystal engineering utilizing hydrogen bonding between disparate molecules (Desiraju, 2003 ), we have been investigating the cocrystallization of various pyridine compounds with benzene carboxylic acids (Staun & Oliver, 2012 ). From previous work, 4-hydroxypyridine undergoes hydrogen migration from the hydroxy O to the pyridine N atom, yielding 4-pyridone (Tyl et al., 2008 ). We were surprised to find that in the case of 4-hydroxypyridin-1-ium 3,5-dicarboxybenzoate, (I), an H atom is abstracted from one carboxylic acid group, yielding a pyridinium salt. This result allows for the hydroxy O and pyridine N atom to both act as hydrogen-bond donors, rather than the donor/acceptor situation of the 4-pyridone species. These two molecules have been incorporated as linker species in metal–organic frameworks (Guo et al., 2011 ).

2. Structural Commentary

The structure of (I) shows that the 4-hydroxypyridine has abstracted an H atom from the benzenetricarboxylic acid, yielding a pyridinium cation and a carboxylate anion (Fig. 1). Bond distances about the pyridine ring show some localization of the bonds: C1—C2 and C4—C5 are slightly shorter than the ideal aromatic distance [1.367 (3) and 1.369 (3) Å, respectively, cf. 1.390 Å for an aromatic C—C bond]. The N1—C1 and N1—C5 distances are typical for an aromatic N atom [1.345 (3) and 1.348 (3) Å, respectively]. The remaining bonds within the ring display typical aromatic distances [C2—C3 = 1.405 (3) Å and C3—C4 = 1.402 (3) Å]. The C3—O1 distance of 1.326 (2) Å is typical for a hydroxy O atom bound to an aromatic ring. Bond angles within the pyridine ring are unexceptional.

Figure 1
Labeling scheme for (I). Displacement ellipsoids are depicted at the 50% probability level. The inter-ion hydrogen bond is shown as a dashed red line.

Two of the three carboxylic acid groups show distinct single- and double-bond character [C12—O3 = 1.305 (3) Å and C14—O7 = 1.332 (3) Å; C12—O2 = 1.224 (2) Å and C14—O6 = 1.204 (3) Å]. The remaining carboxylate group displays C—O bond distances that are similar to each other and indicate delocalization of the C—O bonds [1.268 (3) and 1.249 (2) Å for C13—O4 and C4—O5, respectively], supporting the proposed single negative charge on the benzenetricarboxylic acid molecule. This is further supported by the presence of H atoms, located in a difference Fourier map, on atoms O3 and O7. Bond distances and angles within the benzene ring are as expected.

3. Supramolecular Features

The local intermolecular contacts consist of the pyridinium cation forming a hydrogen bond from the hydroxy group to the anionic carboxylate group (O1⋯O5; see Table 1 for detailed contacts) and from pyridine atom N1 to carboxylate atom O4ⁱ [symmetry code: (i) −x + $[{1\over 2}]$ , y + $[{1\over 2}]$ , z − $[{1\over 2}]$ ]. Carboxylic acid atoms O3 and O7 are donors for hydrogen bonds to atoms O4ⁱⁱ and O2ⁱⁱⁱ, respectively [symmetry codes: (ii) −x, −y, z − $[{1\over 2}]$ ; (iii) −x, −y + 1, z + $[{1\over 2}]$ ]. Since these hydrogen bonds extend over several molecules, an extensive hydrogen-bonded network exists in this structure.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1O⋯O5	0.95 (3)	1.59 (4)	2.533 (2)	171 (3)
N1—H1N⋯O4ⁱ	0.98 (3)	1.73 (3)	2.700 (2)	173 (4)
O3—H3O⋯O4ⁱⁱ	0.93 (3)	1.65 (3)	2.574 (2)	172 (3)
O7—H7O⋯O2ⁱⁱⁱ	0.90 (3)	1.79 (3)	2.678 (2)	166 (3)
Symmetry codes: (i) $[-x+{\script{1\over 2}}, y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ ; (ii) $[-x, -y, z-{\script{1\over 2}}]$ ; (iii) $[-x, -y+1, z+{\script{1\over 2}}]$ .

Pertinent features of this extended network are an R₄⁴(28) ring comprised of 3,5-dicarboxybenzoate ions (Fig. 2) (Bernstein et al., 1995 ). The carboxylic acid groups are involved in the hydrogen bonding within this ring. There is also an R₆⁶(44) ring of 3,5-dicarboxybenzoate ions, that incorporate a different chain of carboxylic acid groups. These rings are bridged by the 4-hydroxypyridinium cations resulting in the three-dimensional network. The hydrogen bonds within the structure are surprisingly strong, with O—H⋯O and N—H⋯O distances ranging from 2.533 (2) to 2.700 (2) Å (Table 1).

Figure 2
A view of (I) approximately along the crystallographic c axis. Color code: blue represents the R₄⁴(28) ring, purple the R₆⁶(44) ring, and green the bridging 4-hydroxypyridinium cations.

The cations and anions form homogeneous π-stacked columns parallel to the c axis, that is, 4-pyridinium cations stacking with other cations and 3,5-dicarboxybenzoate anions stacking with other anions. The centroid-to-centroid distances for both the pyridinium and the dicarboxybenzoate interactions are 3.6206 (13) Å, i.e. the c-axis spacing. The centroid-to-perpendicular distances are 3.3629 (9) Å for the cation and 3.4372 (9) Å for the anion. Both measurements are within accepted π–π contact ranges (see Table 2; Spek, 2009 ).

Table 2
π-stacking interactions within (I)

Interaction	Cg⋯Cg (Å)	Cg⋯perp (Å)
Cg1⋯Cg1ⁱ	3.6206 (13)	3.4373 (9)
Cg2⋯Cg2ⁱ	3.6206 (13)	3.3627 (9)
Cg1 is the centroid of the 3,5-dicarboxybenzoate ring, Cg2 is the centroid of the 4-hydroxypyridinium ring [symmetry code: (i) x, y, 1 + z], Cg⋯Cg is the centroid-to-centroid distance, and Cg⋯perp is the distance to the plane perpendicular to the ring centroid.

4. Database Survey

A search of the Cambridge Structural Database (CSD, Version 5.36 plus 3 updates; Groom & Allen, 2014 ) for 4-hydroxypyridine and benzenetricarboxylic acid gave only five hits. In the compound that is most closely related to the title compound, namely benzene-1,3,5-tricarboxylic acid pyridin-4(1H)-one (Campos-Gaxiola et al., 2014 ), there are three molecules of 4-pyridone present in the asymmetric unit. Benzenetricarboxylic acid and a tetrakis[(pyridin-4-yloxy)methyl]methane moiety (incorporating a 4-hydroxypyridine functionality) have been utilized in the devlopment of frameworks incorporating copper and cadmium (Guo et al., 2011).

5. Synthesis and Crystallization

To a solution of benzene-1,3,5-tricarboxylic acid (0.035 g, 1.24 mmol) in MeOH (3 ml) in a 20 ml vial was added a solution of 4-hydroxypyridine (0.0218 g, 1.77 mmol) in MeOH (3 ml). The mixture was shaken vigorously, covered with perforated Parafilm and allowed to evaporate slowly over a period of 5 d, yielding colorless rod-like crystals.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3. Carboxylic, hydroxy, and pyridinium H atoms were initally located in a difference Fourier map. H atoms on the 4-hydroxypyridinium cation were refined freely. H atoms on the carboxylic acid groups were included with refined coordinates and atomic displacement parameters tied to that of the O atom to which they are bonded. C—H hydrogens were included in idealized positions riding on the C atom to which they are bonded, with C—H distances constrained to 0.95 Å and U_iso(H) = 1.2 U_eq(C).

Table 3
Experimental details

Crystal data
Chemical formula	C₅H₆NO⁺·C₉H₅O₆⁻
M_r	305.24
Crystal system, space group	Orthorhombic, Pna2₁
Temperature (K)	122
a, b, c (Å)	29.3465 (10), 12.2113 (5), 3.6206 (2)
V (Å³)	1297.47 (10)
Z	4
Radiation type	Cu Kα
μ (mm⁻¹)	1.10
Crystal size (mm)	0.11 × 0.06 × 0.06

Data collection
Diffractometer	Bruker APEXII
Absorption correction	Numerical (SADABS; Krause et al., 2015 )
T_min, T_max	0.694, 0.753
No. of measured, independent and observed [I > 2σ(I)] reflections	6000, 2322, 2172
R_int	0.018
(sin θ/λ)_max (Å⁻¹)	0.614

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.028, 0.071, 1.05
No. of reflections	2322
No. of parameters	213
No. of restraints	1
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.15, −0.19
Absolute structure	Flack x determined using 786 quotients [(I⁺) − (I⁻)]/[(I⁺) + (I⁻)] (Parsons et al., 2013)
Absolute structure parameter	0.20 (8)
Computer programs: APEX2 and SAINT (Bruker 2012 ), SHELXS97 (Sheldrick, 2008 ), SHELXL2014 (Sheldrick, 2015 ), OLEX2 (Dolomanov et al., 2009 ), Mercury (Macrae et al., 2008 ), POVRay (Cason, 2003 ), publCIF (Westrip, 2010 ) and PLATON (Spek, 2009).

The compound is achiral, but crystallizes with a noncentrosymmetric, polar space group. The Flack x parameter refined to 0.20 (8), which suggests the possibility of a small amount of inversion twinnning (Parsons et al., 2013 ), but the strength of the anomalous signal is very weak. We compared both a model twinned by inversion and the untwinned model, and there was no significant difference. We therefore elected to model the structure without inclusion of a twin component.

Supporting information

CCDC reference: 1407819

Crystal structure: contains datablocks I, New_Global_Publ_Block. DOI: 10.1107/S2056989015011780/pk2555sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S2056989015011780/pk2555Isup2.hkl

Supporting information file. DOI: 10.1107/S2056989015011780/pk2555Isup3.cml

checkCIF report

Chemical Context top

As a study in crystal engineering utilizing hydrogen bonding between disparate molecules (Desiraju, 2003), we have been investigating the cocrystallization of various pyridine compounds with benzene carboxylic acids (Staun & Oliver, 2012). From previous work, 4-hydroxypyridine undergoes hydrogen migration from the hydroxy O to the pyridine N atom, yielding 4-pyridone (Tyl et al., 2008). We were surprised to find that in the case of 4-hydroxypyridin-1-ium 3,5-dicarboxybenzoate, (I), an H atom is abstracted from one carboxylic acid group, yielding a pyridinium salt. This result allows for the hydroxy O and pyridine N atom to both act as hydrogen-bond donors, rather than the donor/acceptor situation of the 4-pyridone species. These two molecules have been incorporated as linker species in metal–organic frameworks (Guo et al., 2011).

Structural Commentary top

Supramolecular Features top

The local intermolecular contacts consist of the pyridinium cation forming a hydrogen bond from the hydroxy group to the anionic carboxylate group (O1···O5; see Table 1 for detailed contacts) and from pyridine atom N1 to carboxylate atom O4ⁱ [symmetry code: (i) -x+1/2, y+1/2, z-1/2]. Carboxylic acid atoms O3 and O7 are donors for hydrogen bonds to atoms O4ⁱⁱ and O2ⁱⁱⁱ, respectively [symmetry codes: (ii) -x, -y, z-1/2; (iii) -x, -y+1, z+1/2]. Since these hydrogen bonds extend over several molecules, an extensive hydrogen-bonded network exists in this structure.

Pertinent features of this extended network are an R₄⁴(28) ring comprised of 3,5-dicarboxybenzoate ions (Fig. 2) (Bernstein et al., 1995). The carboxylic acid groups are involved in the hydrogen bonding within this ring. There is also an R₆⁶(44) ring of 3,5-dicarboxybenzoate ions, that incorporate a different chain of carboxylic acid groups. These rings are bridged by the 4-hydroxypyridinium cations resulting in the three-dimensional network. The hydrogen bonds within the structure are surprisingly strong, with O—H···O and N—H···O distances ranging from 2.533 (2) to 2.700 (2) Å (Table 1).

Database Survey top

A search of the Cambridge Structural Database (CSD, Version 5.36 plus 3 updates; Groom & Allen, 2014) for 4-hydroxypyridine and benzenetricarboxylic acid gave only five hits. In the compound that is most closely related to the title compound, namely benzene-1,3,5-tricarboxylic acid pyridin-4(1H)-one (Campos-Gaxiola et al., 2014), there are three molecules of 4-pyridone present in the asymmetric unit. Benzenetricarboxylic acid and a tetrakis[(pyridin-4-yloxy)methyl]methane moiety (incorporating a 4-hydroxypyridine functionality) have been utilized in the devlopment of frameworks incorporating copper and cadmium (Guo et al., 2011).

Synthesis and Crystallization top

Refinement top

The compound is achiral, but crystallizes with a noncentrosymmetric, polar space group. The Flack x parameter refined to 0.20 (8), which suggests the possibility of a small amount of inversion twinnning (Parsons et al., 2013), but the strength of the anomalous signal is very weak. We compared both a model twinned by inversion and the untwinned model, and there was no significant difference. We therefore elected to model the structure without inclusion of a twin component.

Computing details top

Data collection: APEX2 (Bruker, 2012); cell refinement: SAINT (Bruker 2012); data reduction: SAINT (Bruker 2012); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: OLEX2 (Dolomanov et al., 2009), Mercury (Macrae et al., 2008) and POVRay (Cason, 2003); software used to prepare material for publication: publCIF (Westrip, 2010) and PLATON (Spek, 2009).

Figures top

	Fig. 1. Labeling scheme for (I). Displacement ellipsoids are depicted at the 50% probability level. The inter-ion hydrogen bond is shown as a dashed red line.
	Fig. 2. A view of (I) approximately along the crystallographic c axis. Color code: blue represents the R₄⁴(28) ring, purple the R₆⁶(44) ring, and green the bridging 4-hydroxypyridinium cations.

4-Hydroxypyridin-1-ium 3,5dicarboxybenzoate top

Crystal data top

C₅H₆NO⁺·C₉H₅O₆⁻	D_x = 1.563 Mg m⁻³
M_r = 305.24	Cu Kα radiation, λ = 1.54184 Å
Orthorhombic, Pna2₁	Cell parameters from 2373 reflections
a = 29.3465 (10) Å	θ = 3.4–71.2°
b = 12.2113 (5) Å	µ = 1.10 mm⁻¹
c = 3.6206 (2) Å	T = 122 K
V = 1297.47 (10) Å³	Rod, colorless
Z = 4	0.11 × 0.06 × 0.06 mm
F(000) = 632

Data collection top

Bruker APEXII diffractometer	2322 independent reflections
Radiation source: Incoatec micro-focus	2172 reflections with I > 2σ(I)
Detector resolution: 8.33 pixels mm^-1	R_int = 0.018
combination of ω and ϕ–scans	θ_max = 71.2°, θ_min = 3.0°
Absorption correction: numerical SADABS (Krause et al., 2015)	h = −27→35
T_min = 0.694, T_max = 0.753	k = −13→14
6000 measured reflections	l = −4→4

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: mixed
R[F² > 2σ(F²)] = 0.028	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.071	w = 1/[σ²(F_o²) + (0.0441P)² + 0.1815P] where P = (F_o² + 2F_c²)/3
S = 1.05	(Δ/σ)_max = 0.001
2322 reflections	Δρ_max = 0.15 e Å⁻³
213 parameters	Δρ_min = −0.19 e Å⁻³
1 restraint	Absolute structure: Flack x determined using 786 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.20 (8)

Crystal data top

C₅H₆NO⁺·C₉H₅O₆⁻	V = 1297.47 (10) Å³
M_r = 305.24	Z = 4
Orthorhombic, Pna2₁	Cu Kα radiation
a = 29.3465 (10) Å	µ = 1.10 mm⁻¹
b = 12.2113 (5) Å	T = 122 K
c = 3.6206 (2) Å	0.11 × 0.06 × 0.06 mm

Data collection top

Bruker APEXII diffractometer	2322 independent reflections
Absorption correction: numerical SADABS (Krause et al., 2015)	2172 reflections with I > 2σ(I)
T_min = 0.694, T_max = 0.753	R_int = 0.018
6000 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.028	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.071	Δρ_max = 0.15 e Å⁻³
S = 1.05	Δρ_min = −0.19 e Å⁻³
2322 reflections	Absolute structure: Flack x determined using 786 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
213 parameters	Absolute structure parameter: 0.20 (8)
1 restraint

Special details top

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.

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

	x	y	z	U_iso*/U_eq
O1	0.23997 (5)	0.04165 (12)	0.3072 (5)	0.0195 (4)
H1O	0.2112 (11)	0.062 (3)	0.405 (11)	0.057 (11)*
N1	0.32385 (6)	0.30371 (16)	0.1767 (5)	0.0181 (4)
H1N	0.3450 (9)	0.365 (3)	0.166 (11)	0.048 (10)*
C1	0.33796 (7)	0.2029 (2)	0.0796 (6)	0.0186 (5)
H1A	0.3679	0.1933	−0.0157	0.022*
C2	0.30997 (6)	0.11410 (19)	0.1159 (7)	0.0169 (4)
H2A	0.3201	0.0433	0.0444	0.020*
C3	0.26602 (6)	0.12932 (17)	0.2608 (6)	0.0145 (4)
C4	0.25177 (7)	0.23551 (18)	0.3521 (6)	0.0160 (4)
H4A	0.2218	0.2481	0.4424	0.019*
C5	0.28155 (7)	0.32085 (18)	0.3095 (6)	0.0174 (4)
H5A	0.2723	0.3929	0.3741	0.021*
O2	−0.06609 (4)	0.25817 (12)	0.5787 (5)	0.0182 (3)
O3	−0.04180 (5)	0.08670 (13)	0.5070 (5)	0.0215 (4)
H3O	−0.0703 (9)	0.067 (2)	0.417 (9)	0.032*
O4	0.11707 (4)	−0.02696 (12)	0.7027 (5)	0.0196 (4)
O5	0.16718 (4)	0.10740 (13)	0.6111 (6)	0.0252 (4)
O6	0.11934 (5)	0.47723 (13)	1.1519 (5)	0.0220 (4)
O7	0.05337 (5)	0.53129 (13)	0.8992 (5)	0.0204 (4)
H7O	0.0611 (8)	0.598 (3)	0.987 (9)	0.031*
C6	0.01288 (6)	0.21569 (17)	0.6846 (6)	0.0127 (4)
C7	0.04618 (7)	0.13490 (17)	0.6462 (6)	0.0128 (4)
H7A	0.0380	0.0638	0.5628	0.015*
C8	0.09153 (6)	0.15874 (17)	0.7304 (6)	0.0133 (4)
C9	0.10330 (6)	0.26321 (18)	0.8480 (6)	0.0142 (4)
H9A	0.1341	0.2795	0.9056	0.017*
C10	0.07019 (6)	0.34410 (18)	0.8820 (6)	0.0131 (4)
C11	0.02463 (6)	0.32021 (17)	0.8012 (6)	0.0134 (4)
H11A	0.0019	0.3751	0.8261	0.016*
C12	−0.03557 (6)	0.18988 (17)	0.5860 (6)	0.0138 (4)
C13	0.12794 (6)	0.07323 (18)	0.6782 (6)	0.0150 (4)
C14	0.08419 (7)	0.45642 (18)	0.9953 (6)	0.0156 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0143 (7)	0.0151 (8)	0.0291 (9)	−0.0021 (6)	0.0044 (7)	−0.0012 (7)
N1	0.0152 (8)	0.0205 (10)	0.0185 (9)	−0.0067 (8)	−0.0004 (7)	0.0002 (8)
C1	0.0122 (9)	0.0270 (12)	0.0166 (11)	−0.0006 (9)	0.0006 (8)	0.0004 (10)
C2	0.0142 (9)	0.0208 (11)	0.0157 (10)	0.0018 (8)	0.0008 (8)	−0.0017 (9)
C3	0.0133 (9)	0.0166 (11)	0.0135 (10)	−0.0014 (8)	−0.0015 (8)	−0.0005 (9)
C4	0.0132 (9)	0.0180 (11)	0.0170 (10)	0.0010 (8)	0.0016 (8)	−0.0006 (10)
C5	0.0190 (10)	0.0171 (11)	0.0161 (11)	−0.0012 (8)	0.0000 (8)	−0.0007 (9)
O2	0.0116 (6)	0.0130 (7)	0.0299 (9)	0.0009 (5)	−0.0012 (6)	0.0000 (7)
O3	0.0124 (7)	0.0138 (8)	0.0382 (11)	−0.0007 (6)	−0.0073 (7)	−0.0059 (7)
O4	0.0122 (6)	0.0134 (7)	0.0331 (9)	0.0017 (6)	0.0034 (6)	0.0022 (7)
O5	0.0120 (7)	0.0220 (9)	0.0417 (11)	−0.0023 (6)	0.0085 (7)	−0.0032 (8)
O6	0.0179 (7)	0.0204 (8)	0.0277 (9)	−0.0050 (6)	−0.0047 (7)	−0.0032 (7)
O7	0.0179 (8)	0.0126 (8)	0.0308 (10)	0.0003 (6)	−0.0019 (7)	−0.0057 (7)
C6	0.0125 (8)	0.0126 (10)	0.0130 (9)	0.0008 (8)	0.0013 (7)	0.0010 (8)
C7	0.0142 (8)	0.0112 (10)	0.0129 (10)	−0.0014 (7)	0.0007 (7)	0.0018 (8)
C8	0.0128 (9)	0.0143 (10)	0.0129 (10)	−0.0005 (8)	0.0009 (8)	0.0022 (9)
C9	0.0111 (9)	0.0166 (11)	0.0150 (10)	−0.0017 (8)	−0.0008 (8)	0.0002 (9)
C10	0.0139 (9)	0.0136 (10)	0.0117 (10)	−0.0017 (8)	0.0003 (8)	0.0002 (8)
C11	0.0139 (9)	0.0138 (10)	0.0127 (10)	0.0024 (8)	0.0004 (8)	0.0006 (8)
C12	0.0152 (9)	0.0125 (10)	0.0137 (10)	0.0000 (8)	−0.0002 (8)	0.0009 (9)
C13	0.0129 (9)	0.0159 (11)	0.0164 (10)	0.0001 (8)	0.0000 (8)	−0.0007 (9)
C14	0.0139 (9)	0.0168 (11)	0.0162 (11)	−0.0012 (8)	0.0026 (9)	−0.0015 (9)

Geometric parameters (Å, º) top

O1—C3	1.326 (2)	O5—C13	1.249 (2)
O1—H1O	0.95 (3)	O6—C14	1.204 (3)
N1—C1	1.345 (3)	O7—C14	1.332 (3)
N1—C5	1.348 (3)	O7—H7O	0.90 (3)
N1—H1N	0.98 (3)	C6—C11	1.388 (3)
C1—C2	1.367 (3)	C6—C7	1.396 (3)
C1—H1A	0.9500	C6—C12	1.499 (3)
C2—C3	1.405 (3)	C7—C8	1.396 (3)
C2—H2A	0.9500	C7—H7A	0.9500
C3—C4	1.402 (3)	C8—C9	1.389 (3)
C4—C5	1.369 (3)	C8—C13	1.506 (3)
C4—H4A	0.9500	C9—C10	1.391 (3)
C5—H5A	0.9500	C9—H9A	0.9500
O2—C12	1.224 (2)	C10—C11	1.399 (3)
O3—C12	1.305 (3)	C10—C14	1.489 (3)
O3—H3O	0.93 (3)	C11—H11A	0.9500
O4—C13	1.268 (3)

C3—O1—H1O	111 (2)	C6—C7—C8	119.90 (19)
C1—N1—C5	121.26 (19)	C6—C7—H7A	120.1
C1—N1—H1N	119.9 (18)	C8—C7—H7A	120.1
C5—N1—H1N	118.7 (18)	C9—C8—C7	119.70 (18)
N1—C1—C2	121.04 (19)	C9—C8—C13	119.95 (17)
N1—C1—H1A	119.5	C7—C8—C13	120.29 (19)
C2—C1—H1A	119.5	C8—C9—C10	120.39 (18)
C1—C2—C3	118.9 (2)	C8—C9—H9A	119.8
C1—C2—H2A	120.6	C10—C9—H9A	119.8
C3—C2—H2A	120.6	C9—C10—C11	120.1 (2)
O1—C3—C4	123.01 (18)	C9—C10—C14	119.06 (17)
O1—C3—C2	118.02 (19)	C11—C10—C14	120.86 (18)
C4—C3—C2	118.97 (19)	C6—C11—C10	119.51 (18)
C5—C4—C3	119.15 (19)	C6—C11—H11A	120.2
C5—C4—H4A	120.4	C10—C11—H11A	120.2
C3—C4—H4A	120.4	O2—C12—O3	123.40 (18)
N1—C5—C4	120.7 (2)	O2—C12—C6	123.77 (19)
N1—C5—H5A	119.7	O3—C12—C6	112.83 (17)
C4—C5—H5A	119.7	O5—C13—O4	124.62 (19)
C12—O3—H3O	117.1 (18)	O5—C13—C8	116.56 (19)
C14—O7—H7O	110.8 (17)	O4—C13—C8	118.82 (17)
C11—C6—C7	120.42 (17)	O6—C14—O7	124.0 (2)
C11—C6—C12	120.09 (17)	O6—C14—C10	124.07 (19)
C7—C6—C12	119.45 (18)	O7—C14—C10	111.89 (17)

C5—N1—C1—C2	−0.7 (3)	C7—C6—C11—C10	−0.3 (3)
N1—C1—C2—C3	−0.7 (3)	C12—C6—C11—C10	−178.11 (19)
C1—C2—C3—O1	−177.5 (2)	C9—C10—C11—C6	−0.5 (3)
C1—C2—C3—C4	2.1 (3)	C14—C10—C11—C6	177.9 (2)
O1—C3—C4—C5	177.3 (2)	C11—C6—C12—O2	4.8 (4)
C2—C3—C4—C5	−2.2 (3)	C7—C6—C12—O2	−173.0 (2)
C1—N1—C5—C4	0.5 (3)	C11—C6—C12—O3	−175.4 (2)
C3—C4—C5—N1	0.9 (3)	C7—C6—C12—O3	6.7 (3)
C11—C6—C7—C8	0.9 (3)	C9—C8—C13—O5	−25.5 (3)
C12—C6—C7—C8	178.7 (2)	C7—C8—C13—O5	151.8 (2)
C6—C7—C8—C9	−0.7 (3)	C9—C8—C13—O4	154.9 (2)
C6—C7—C8—C13	−178.04 (19)	C7—C8—C13—O4	−27.8 (3)
C7—C8—C9—C10	−0.1 (3)	C9—C10—C14—O6	−20.3 (3)
C13—C8—C9—C10	177.3 (2)	C11—C10—C14—O6	161.3 (2)
C8—C9—C10—C11	0.7 (3)	C9—C10—C14—O7	159.0 (2)
C8—C9—C10—C14	−177.74 (19)	C11—C10—C14—O7	−19.4 (3)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1O···O5	0.95 (3)	1.59 (4)	2.533 (2)	171 (3)
N1—H1N···O4ⁱ	0.98 (3)	1.73 (3)	2.700 (2)	173 (4)
O3—H3O···O4ⁱⁱ	0.93 (3)	1.65 (3)	2.574 (2)	172 (3)
O7—H7O···O2ⁱⁱⁱ	0.90 (3)	1.79 (3)	2.678 (2)	166 (3)

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

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1O···O5	0.95 (3)	1.59 (4)	2.533 (2)	171 (3)
N1—H1N···O4ⁱ	0.98 (3)	1.73 (3)	2.700 (2)	173 (4)
O3—H3O···O4ⁱⁱ	0.93 (3)	1.65 (3)	2.574 (2)	172 (3)
O7—H7O···O2ⁱⁱⁱ	0.90 (3)	1.79 (3)	2.678 (2)	166 (3)

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

π-stacking interactions within (I) top

Interaction	Cg···Cg (Å)	Cg···perp (Å)
Cg1···Cg1ⁱ	3.6206 (13)	3.4373 (9)
Cg2···Cg2ⁱ	3.6206 (13)	3.3627 (9)

Cg1 is the centroid of the 3,5-dicarboxybenzoate ring, Cg2 is the centroid of the 4-hydroxypyridinium ring [symmetry code: (i) x, y, 1+z], Cg···Cg is the centroid-to-centroid distance, and Cg···perp is the distance to the plane perpendicular to the ring centroid.

Experimental details

Crystal data
Chemical formula	C₅H₆NO⁺·C₉H₅O₆⁻
M_r	305.24
Crystal system, space group	Orthorhombic, Pna2₁
Temperature (K)	122
a, b, c (Å)	29.3465 (10), 12.2113 (5), 3.6206 (2)
V (Å³)	1297.47 (10)
Z	4
Radiation type	Cu Kα
µ (mm⁻¹)	1.10
Crystal size (mm)	0.11 × 0.06 × 0.06

Data collection
Diffractometer	Bruker APEXII diffractometer
Absorption correction	Numerical SADABS (Krause et al., 2015)
T_min, T_max	0.694, 0.753
No. of measured, independent and observed [I > 2σ(I)] reflections	6000, 2322, 2172
R_int	0.018
(sin θ/λ)_max (Å⁻¹)	0.614

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.028, 0.071, 1.05
No. of reflections	2322
No. of parameters	213
No. of restraints	1
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.15, −0.19
Absolute structure	Flack x determined using 786 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
Absolute structure parameter	0.20 (8)

Computer programs: APEX2 (Bruker, 2012), SAINT (Bruker 2012), SHELXS97 (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2015), OLEX2 (Dolomanov et al., 2009), Mercury (Macrae et al., 2008) and POVRay (Cason, 2003), publCIF (Westrip, 2010) and PLATON (Spek, 2009).

Acknowledgements

We thank the University of Notre Dame for generous support of the micro-focus source used in this project. SLS thanks the Indiana Academy of Science for a Junior Research Grant and the Henderson lab for kind donation of materials and research space.

References

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Volume 71| Part 7| July 2015| Pages 861-863

doi:10.1107/S2056989015011780

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