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

A 1:1.4 molar equivalent of benzene-1,3,5-tri­carb­oxy­lic acid cocrystallized with 4-hy­droxy­pyridine yields the 4-hy­droxy­pyridin-1-ium 3,5-di­carb­oxy­benzoate salt.

Key indicators

• Single-crystal X-ray study
• T = 122 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.028
• wR factor = 0.071
• Data-to-parameter ratio = 10.9

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT089_ALERT_3_C Poor Data / Parameter Ratio (Zmax < 18) ........       6.85 Note
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600          6 Report
PLAT915_ALERT_3_C Low Friedel Pair Coverage ......................         82 %

Alert level G
PLAT432_ALERT_2_G Short Inter X...Y Contact  O3     ..  C7      ..       3.01 Ang.
PLAT912_ALERT_4_G Missing # of FCF Reflections Above STh/L=  0.600         12 Note

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

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

---

S1. 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).

S2. 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.

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.

S3. 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+1/2, 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).

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).

S4. 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).

S5. 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.

S6. 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).

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

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

	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 R4^4(28) ring, purple the R6^6(44) ring, and green the bridging 4-hydroxypyridinium cations.

4-Hydroxypyridin-1-ium 3,5dicarboxybenzoate

Crystal data

C5H6NO^+·C9H5O6^−	Dx = 1.563 Mg m^−3
Mr = 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) Å^3	Rod, colorless
Z = 4	0.11 × 0.06 × 0.06 mm
F(000) = 632

Data collection

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

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: mixed
R[F^2 > 2σ(F^2)] = 0.028	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.071	w = 1/[σ^2(Fo^2) + (0.0441P)^2 + 0.1815P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max = 0.001
2322 reflections	Δρmax = 0.15 e Å^−3
213 parameters	Δρmin = −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)

Special details

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

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

	x	y	z	Uiso*/Ueq
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 (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
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)

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)

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···O4^i	0.98 (3)	1.73 (3)	2.700 (2)	173 (4)
O3—H3O···O4^ii	0.93 (3)	1.65 (3)	2.574 (2)	172 (3)
O7—H7O···O2^iii	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.