Bis(pyridinium-4-olate) succinic acid

In the title compound, 2C₅H₅NO·C₄H₆O₄, a phenolic proton is transferred to the pyridine N atom, yielding a zwitterionic pyridinium-4-olate. The succinic acid mol­ecule lies about a centre of symmetry which also generates the second pyridinium-4-olate mol­ecule. The crystal structure is stabilized by inter­molecular O—H...O and C—H...O hydrogen bonds, forming a network structure.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.066
• wR factor = 0.198
• Data-to-parameter ratio = 13.8

checkCIF/PLATON results

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Alert level B
PLAT230_ALERT_2_B Hirshfeld Test Diff for    C1     -   C2      ..       8.31 su
PLAT432_ALERT_2_B Short Inter X...Y Contact  O1     ..  C2      ..       2.79 Ang.

Alert level C
PLAT029_ALERT_3_C _diffrn_measured_fraction_theta_full Low .......       0.98
PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ ....          ?
PLAT066_ALERT_1_C Predicted and Reported Transmissions Identical .          ?
PLAT230_ALERT_2_C Hirshfeld Test Diff for    N1     -   C3      ..       6.35 su
PLAT230_ALERT_2_C Hirshfeld Test Diff for    N1     -   C4      ..       6.86 su
PLAT230_ALERT_2_C Hirshfeld Test Diff for    C2     -   C3      ..       6.43 su
PLAT420_ALERT_2_C D-H Without Acceptor       N1     -   H1     ...          ?

   0 ALERT level A = In general: serious problem
   2 ALERT level B = Potentially serious problem
   7 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

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

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S1. Comment

Proton transfer in molecular associations confers considerable stability in the structure-forming process (Smith et al., 2004, 2004a,b; Moghimi et al., 2004). In order to study the role of proton-exchange compounds in the construction of net-like structures, we have prepared the title compound, (I), and its structure is reported here.

In the reaction with succinic acid a phenolic proton is is transferred to the pyridine N atom, forming a zwitterionic pyridinium-4-olate. The structure of (I) thus has a neutral succinic acid residue and two pyridinium-4-olate moieties in the asymmetric unit, as the succinic acid molecule lies on a centre of symmetry located at the mid-point of the C7—C7ⁱ bond (see Fig. 1 for symmetry code). All bond lengths in the molecules are within normal ranges (Allen et al., 1987).

In the crystal structure, intermolecular O2—H2···O1 hydrogen bonds link succinic acid molecules to two adjacent pyridinium-4-olate residues along the a axis. The structure is further stabilized by a number of C—H···O hydrogen bonds (Table 1), forming a network parallel to the ac plane (Fig. 2).

S2. Experimental

Pyridin-4-ol (0.2 mmol, 19.1 mg) and succinic acid (0.1 mmol, 11.8 mg) were dissolved in distilled water (10 ml). The mixture was heated under reflux to form a clear colourless solution. Crystals of the title compound were grown by gradual evaporation of water over a period of one week at room temperature.

S3. Refinement

Atoms H1 and H2 were located in a difference Fourier map and refined isotropically, with the N—H distance restrained to 0.97 (1) Å and the O—H distance restrained to 0.84 (1) Å. The other H atoms were placed in idealized positions and constrained to ride on their parent atoms, with C—H distances in the range 0.93–0.97 Å, and with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997a); molecular graphics: SHELXTL (Sheldrick, 1997b); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. Labelled atoms are related to the equivalent unlabelled atoms by the symmetry operation (1 − x, 2 − y, 2 − z).
	Fig. 2. The crystal packing of (I). Intermolecular hydrogen bonds are drawn as dashed lines.

Bis(pyridinium-4-olate) succinic acid

Crystal data

2C5H5NO·C4H6O4	F(000) = 324
Mr = 308.29	Dx = 1.423 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 1725 reflections
a = 8.559 (2) Å	θ = 2.5–26.6°
b = 5.178 (1) Å	µ = 0.11 mm^−1
c = 16.387 (3) Å	T = 298 K
β = 97.891 (2)°	Plate, colourless
V = 719.4 (3) Å^3	0.34 × 0.20 × 0.07 mm
Z = 2

Data collection

Bruker SMART APEX area-detector diffractometer	1464 independent reflections
Radiation source: fine-focus sealed tube	1146 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.022
ϕ and ω scans	θmax = 26.5°, θmin = 2.5°
Absorption correction: multi-scan (SADABS; Bruker, 2002)	h = −10→10
Tmin = 0.963, Tmax = 0.992	k = −6→6
5307 measured reflections	l = −20→20

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)] = 0.066	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.198	H atoms treated by a mixture of independent and constrained refinement
S = 1.05	w = 1/[σ^2(Fo^2) + (0.1263P)^2 + 0.2431P] where P = (Fo^2 + 2Fc^2)/3
1464 reflections	(Δ/σ)max < 0.001
106 parameters	Δρmax = 0.53 e Å^−3
2 restraints	Δρmin = −0.43 e Å^−3

Special details

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

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	Uiso*/Ueq
O1	1.1054 (2)	1.2071 (4)	0.94140 (11)	0.0471 (5)
O2	0.2951 (2)	0.5851 (4)	0.91652 (11)	0.0473 (6)
O3	0.3129 (2)	0.6847 (4)	1.04893 (12)	0.0546 (6)
N1	0.9081 (3)	0.7293 (5)	0.75891 (16)	0.0568 (7)
C1	1.0473 (3)	1.0671 (4)	0.88184 (15)	0.0348 (6)
C2	0.9509 (2)	0.8682 (4)	0.89648 (12)	0.0253 (5)
H2A	0.9300	0.8441	0.9502	0.030*
C3	0.8833 (3)	0.7028 (5)	0.83773 (16)	0.0394 (6)
H3	0.8194	0.5699	0.8521	0.047*
C4	1.0057 (3)	0.9314 (5)	0.73969 (16)	0.0445 (7)
H4	1.0240	0.9539	0.6855	0.053*
C5	1.0741 (3)	1.0948 (5)	0.79883 (16)	0.0406 (6)
H5	1.1392	1.2266	0.7847	0.049*
C6	0.3518 (3)	0.7186 (4)	0.98233 (14)	0.0340 (6)
C7	0.4700 (3)	0.9172 (4)	0.96341 (15)	0.0370 (6)
H7A	0.4215	1.0272	0.9191	0.044*
H7B	0.5585	0.8300	0.9443	0.044*
H2	0.228 (4)	0.484 (6)	0.932 (2)	0.080*
H1	0.870 (4)	0.591 (5)	0.720 (2)	0.080*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0515 (11)	0.0494 (11)	0.0405 (10)	−0.0213 (8)	0.0065 (8)	−0.0024 (8)
O2	0.0489 (11)	0.0479 (11)	0.0472 (11)	−0.0186 (8)	0.0139 (8)	−0.0069 (8)
O3	0.0625 (12)	0.0612 (13)	0.0415 (11)	−0.0273 (10)	0.0121 (9)	0.0026 (9)
N1	0.0615 (16)	0.0567 (15)	0.0510 (15)	−0.0020 (12)	0.0036 (12)	−0.0080 (11)
C1	0.0306 (11)	0.0356 (12)	0.0380 (12)	−0.0022 (9)	0.0036 (9)	0.0022 (9)
C2	0.0252 (10)	0.0267 (10)	0.0247 (10)	−0.0065 (8)	0.0064 (7)	0.0002 (8)
C3	0.0403 (13)	0.0352 (12)	0.0424 (13)	−0.0067 (10)	0.0047 (10)	−0.0017 (10)
C4	0.0478 (14)	0.0507 (16)	0.0363 (13)	0.0027 (11)	0.0106 (10)	0.0047 (11)
C5	0.0403 (12)	0.0408 (13)	0.0418 (13)	−0.0034 (10)	0.0098 (10)	0.0066 (10)
C6	0.0307 (11)	0.0305 (11)	0.0407 (13)	0.0000 (9)	0.0043 (9)	0.0027 (9)
C7	0.0337 (11)	0.0352 (12)	0.0431 (13)	−0.0044 (10)	0.0092 (10)	0.0010 (10)

Geometric parameters (Å, º)

O1—C1	1.262 (3)	C2—H2A	0.9300
O2—C6	1.316 (3)	C3—H3	0.9300
O2—H2	0.84 (3)	C4—C5	1.357 (4)
O3—C6	1.197 (3)	C4—H4	0.9300
N1—C3	1.344 (4)	C5—H5	0.9300
N1—C4	1.402 (4)	C6—C7	1.504 (3)
N1—H1	0.98 (3)	C7—C7^i	1.506 (5)
C1—C2	1.362 (3)	C7—H7A	0.9700
C1—C5	1.417 (3)	C7—H7B	0.9700
C2—C3	1.357 (3)
C6—O2—H2	106 (3)	C5—C4—H4	119.4
C3—N1—C4	118.0 (2)	N1—C4—H4	119.4
C3—N1—H1	118 (2)	C4—C5—C1	120.8 (2)
C4—N1—H1	124 (2)	C4—C5—H5	119.6
O1—C1—C2	118.8 (2)	C1—C5—H5	119.6
O1—C1—C5	125.8 (2)	O3—C6—O2	123.5 (2)
C2—C1—C5	115.3 (2)	O3—C6—C7	124.6 (2)
C3—C2—C1	124.2 (2)	O2—C6—C7	111.90 (19)
C3—C2—H2A	117.9	C6—C7—C7^i	113.0 (2)
C1—C2—H2A	117.9	C6—C7—H7A	109.0
N1—C3—C2	120.6 (2)	C7^i—C7—H7A	109.0
N1—C3—H3	119.7	C6—C7—H7B	109.0
C2—C3—H3	119.7	C7^i—C7—H7B	109.0
C5—C4—N1	121.1 (2)	H7A—C7—H7B	107.8
O1—C1—C2—C3	−179.1 (2)	N1—C4—C5—C1	−0.6 (4)
C5—C1—C2—C3	0.3 (3)	O1—C1—C5—C4	179.6 (2)
C4—N1—C3—C2	0.2 (4)	C2—C1—C5—C4	0.3 (3)
C1—C2—C3—N1	−0.6 (4)	O3—C6—C7—C7^i	−3.1 (4)
C3—N1—C4—C5	0.3 (4)	O2—C6—C7—C7^i	176.8 (2)

Symmetry code: (i) −x+1, −y+2, −z+2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O1^ii	0.84 (3)	1.80 (2)	2.611 (2)	163 (4)
C2—H2A···O1^iii	0.93	1.86	2.792 (2)	178 (3)
C3—H3···O3^iv	0.93	2.48	3.340 (2)	154 (3)
C4—H4···O2^v	0.93	2.52	3.360 (2)	150 (3)

Symmetry codes: (ii) x−1, y−1, z; (iii) −x+2, −y+2, −z+2; (iv) −x+1, −y+1, −z+2; (v) −x+3/2, y+1/2, −z+3/2.