2-Hydroxy­pyridinium 2,4,6-trinitro­phenolate

The title proton-transfer compound, C₅H₆NO⁺·C₆H₂N₃O₇⁻, consists of a 2,4,6-trinitro­phenolate anion and a protonated 2-hydroxy­pyridinium cation. Inter­molecular O—H...O and N—H...O hydrogen bonds link ions into dimers. The formation of hydrogen bonds with 2-pyridinol decreases the bitterness of 2,4,6-trinitro­phenol.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.005 Å
• R factor = 0.067
• wR factor = 0.170
• Data-to-parameter ratio = 12.2

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S1. Comment

Much effort has been made to decrease the bitterness of food and medicines (Suzuki et al., 2002, 2004; Hofmann, 1999; Shaw et al., 1984). 2,4,6-Trinitrophenol is a bitter compound; in order to investigate the influence of the hydrogen bonds on the bitterness of the compound, the title proton-transfer compound was synthesized and characterized.

The proton-transfer compound (I) (Fig. 1) consists of an unprotonated 2,4,6-trinitrophenolate anion and a protonated 2-hydroxypyridinium cation. The H atom of O2 is transferred to N1. The bond lengths and angles are within normal ranges (Allen et al., 1987) and comparable with the values observed in other similar compounds (Saminathan & Sivakumar, 2007a,b; Näther et al., 1997; In et al., 1997; Harrison et al., 2007; Soriano-García et al., 1990). The dihedral angles between C6—C11 phenyl ring and N2/O3/O4, N3/O5/O6, N4/O7/O8 planes are 32.6 (3), 10.5 (3) and 17.6 (3)°, respectively. The C6—C11 phenyl ring and the N1/C1—C5 pyridine ring form dihedral angle of 10.3 (3)°. Intramolecular O—H···O and N—H···O hydrogen bonds connect molecules into dimers (Fig. 2, Table 1). Both protons of cation are involved into bifurcated hydrogen bonds. Each of them acts as a donor to two acceptors of anion (Table 2).

Related literature

For related literature, see: Allen et al. (1987); Harrison et al. (2007); Hofmann (1999); In et al. (1997); Näther et al. (1997); Saminathan & Sivakumar (2007a,b); Shaw et al. (1984); Soriano-García et al. (1990); Suzuki et al. (2002, 2004).

S2. Experimental

All the reagents were of commercial grade and were used without further purification. 2,4,6-Trinitrophenol (0.1 mmol, 23.0 mg) and 2-pyridinol (0.1 mmol, 9.5 mg) were dissolved in MeOH/H₂O (10 ml, v:v = 1:1). The mixture was stirred at room temperature for 30 min to give a clear yellow solution. After keeping the solution in air for 10 d, yellow needle-shaped crystals were formed. Analysis found: C 40.62, H 2.54, N 17.37; calculated for C₁₁H₈N₄O₈: C 40.75, H 2.49, N 17.28%.

S3. Refinement

Atoms H1 and H1A were located in a difference Fourier map and refined isotropically, with the O–H distance restrained to 0.85 (1) Å, N–H distance restrained to 0.90 (1) Å, and with U_iso(H) values fixed at 0.08 Ų. The other H atoms were placed in idealized positions and constrained to ride on their parent atoms with C—H distances of 0.93 Å, and with U_iso(H) set to 1.2U_eq(C).

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SMART; data reduction: SAINT (Bruker, 1998); 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: SHELXTL.

Figures

	Fig. 1. The structure of (I) with the 30% probability displacement ellipsoids and the atom-numbering scheme.
	Fig. 2. Molecular packing of the compound, viewed along the b axis. Intramolecular hydrogen bonds are shown as dashed lines.

2-Hydroxypyridinium 2,4,6-trinitrophenolate

Crystal data

C5H6NO^+·C6H2N3O7^−	F(000) = 664
Mr = 324.21	Dx = 1.695 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 12.360 (3) Å	Cell parameters from 718 reflections
b = 3.7323 (10) Å	θ = 2.2–24.4°
c = 27.575 (7) Å	µ = 0.15 mm^−1
β = 93.128 (4)°	T = 298 K
V = 1270.2 (6) Å^3	Needle, yellow
Z = 4	0.45 × 0.03 × 0.03 mm

Data collection

Bruker SMART 1000 CCD area-detector diffractometer	2633 independent reflections
Radiation source: fine-focus sealed tube	1468 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.081
ω scans	θmax = 26.5°, θmin = 1.5°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −15→15
Tmin = 0.936, Tmax = 0.996	k = −4→4
9449 measured reflections	l = −34→34

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)] = 0.067	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.170	w = 1/[σ^2(Fo^2) + (0.0695P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.02	(Δ/σ)max < 0.001
2633 reflections	Δρmax = 0.26 e Å^−3
215 parameters	Δρmin = −0.28 e Å^−3
2 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.012 (2)

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	0.08847 (19)	0.7094 (8)	0.47182 (8)	0.0498 (7)
O2	0.19824 (18)	0.3631 (7)	0.41230 (8)	0.0510 (7)
O3	0.02968 (19)	0.7159 (7)	0.36716 (9)	0.0560 (8)
O4	−0.01971 (19)	0.4424 (8)	0.30070 (9)	0.0646 (9)
O5	0.2730 (2)	0.3254 (9)	0.19155 (9)	0.0718 (10)
O6	0.4134 (2)	0.0296 (8)	0.21813 (9)	0.0625 (9)
O7	0.4813 (2)	−0.1360 (8)	0.38769 (9)	0.0628 (8)
O8	0.3973 (2)	0.1652 (9)	0.43928 (9)	0.0698 (9)
N1	0.2547 (2)	0.5368 (8)	0.50557 (9)	0.0375 (7)
N2	0.0490 (2)	0.5260 (8)	0.33235 (10)	0.0401 (8)
N3	0.3295 (2)	0.1891 (9)	0.22435 (10)	0.0445 (8)
N4	0.4074 (2)	0.0611 (8)	0.39779 (10)	0.0396 (7)
C1	0.1554 (3)	0.6779 (9)	0.51021 (11)	0.0333 (8)
C2	0.1262 (3)	0.7854 (9)	0.55578 (11)	0.0385 (9)
H2	0.0580	0.8824	0.5599	0.046*
C3	0.1985 (3)	0.7474 (9)	0.59448 (12)	0.0450 (10)
H3	0.1792	0.8195	0.6251	0.054*
C4	0.3011 (3)	0.6021 (10)	0.58887 (12)	0.0451 (10)
H4	0.3503	0.5773	0.6154	0.054*
C5	0.3270 (3)	0.4985 (9)	0.54424 (12)	0.0426 (9)
H5	0.3948	0.3999	0.5398	0.051*
C6	0.2276 (2)	0.3217 (9)	0.36964 (11)	0.0316 (8)
C7	0.1595 (2)	0.3997 (9)	0.32664 (11)	0.0316 (8)
C8	0.1906 (2)	0.3560 (9)	0.28060 (11)	0.0332 (8)
H8	0.1437	0.4126	0.2542	0.040*
C9	0.2940 (3)	0.2251 (9)	0.27358 (11)	0.0338 (8)
C10	0.3629 (3)	0.1285 (9)	0.31213 (11)	0.0343 (8)
H10	0.4308	0.0340	0.3068	0.041*
C11	0.3303 (2)	0.1730 (9)	0.35853 (11)	0.0331 (8)
H1A	0.271 (3)	0.451 (11)	0.4762 (7)	0.080*
H1	0.123 (3)	0.645 (12)	0.4472 (9)	0.080*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0418 (15)	0.073 (2)	0.0338 (14)	0.0173 (13)	−0.0020 (11)	−0.0015 (14)
O2	0.0495 (15)	0.0755 (19)	0.0279 (13)	0.0175 (14)	0.0009 (11)	−0.0038 (13)
O3	0.0482 (16)	0.073 (2)	0.0474 (15)	0.0188 (14)	0.0067 (12)	−0.0105 (14)
O4	0.0418 (15)	0.098 (2)	0.0530 (17)	0.0125 (15)	−0.0116 (13)	−0.0109 (16)
O5	0.075 (2)	0.109 (3)	0.0312 (14)	0.0229 (18)	0.0043 (14)	0.0140 (16)
O6	0.0513 (17)	0.092 (2)	0.0461 (16)	0.0201 (16)	0.0166 (13)	−0.0088 (15)
O7	0.0494 (16)	0.077 (2)	0.0610 (18)	0.0301 (15)	−0.0064 (13)	−0.0058 (15)
O8	0.0608 (18)	0.115 (3)	0.0329 (15)	0.0300 (17)	−0.0056 (13)	−0.0064 (16)
N1	0.0374 (16)	0.0421 (19)	0.0334 (16)	0.0037 (14)	0.0048 (13)	0.0026 (14)
N2	0.0352 (17)	0.050 (2)	0.0350 (16)	0.0052 (15)	0.0000 (14)	0.0050 (15)
N3	0.0465 (19)	0.057 (2)	0.0307 (16)	−0.0029 (16)	0.0091 (14)	−0.0016 (15)
N4	0.0342 (16)	0.047 (2)	0.0372 (17)	0.0021 (15)	−0.0028 (13)	−0.0009 (15)
C1	0.0356 (19)	0.031 (2)	0.0332 (18)	−0.0004 (16)	0.0003 (15)	0.0027 (15)
C2	0.041 (2)	0.039 (2)	0.0355 (19)	0.0042 (16)	0.0064 (16)	−0.0029 (16)
C3	0.057 (2)	0.048 (2)	0.0309 (19)	−0.005 (2)	0.0072 (17)	−0.0098 (17)
C4	0.042 (2)	0.056 (3)	0.036 (2)	−0.0053 (19)	−0.0078 (16)	0.0041 (18)
C5	0.0341 (19)	0.045 (2)	0.048 (2)	0.0061 (17)	−0.0020 (17)	0.0097 (19)
C6	0.0357 (19)	0.0324 (19)	0.0270 (17)	−0.0027 (15)	0.0040 (14)	−0.0026 (15)
C7	0.0274 (17)	0.031 (2)	0.0364 (19)	0.0033 (14)	0.0047 (14)	0.0011 (15)
C8	0.0338 (19)	0.037 (2)	0.0289 (17)	−0.0019 (16)	−0.0016 (14)	0.0049 (15)
C9	0.040 (2)	0.036 (2)	0.0262 (17)	−0.0033 (16)	0.0063 (14)	−0.0026 (15)
C10	0.0310 (18)	0.033 (2)	0.0390 (19)	−0.0003 (15)	0.0078 (15)	−0.0016 (16)
C11	0.0335 (19)	0.035 (2)	0.0303 (17)	0.0011 (15)	−0.0020 (14)	0.0019 (16)

Geometric parameters (Å, º)

O1—C1	1.313 (4)	C2—C3	1.361 (4)
O1—H1	0.86 (3)	C2—H2	0.9300
O2—C6	1.260 (3)	C3—C4	1.395 (5)
O3—N2	1.227 (3)	C3—H3	0.9300
O4—N2	1.224 (3)	C4—C5	1.345 (4)
O5—N3	1.223 (4)	C4—H4	0.9300
O6—N3	1.216 (3)	C5—H5	0.9300
O7—N4	1.217 (3)	C6—C11	1.434 (4)
O8—N4	1.221 (3)	C6—C7	1.446 (4)
N1—C1	1.348 (4)	C7—C8	1.356 (4)
N1—C5	1.361 (4)	C8—C9	1.391 (4)
N1—H1A	0.906 (10)	C8—H8	0.9300
N2—C7	1.462 (4)	C9—C10	1.373 (4)
N3—C9	1.456 (4)	C10—C11	1.372 (4)
N4—C11	1.463 (4)	C10—H10	0.9300
C1—C2	1.385 (4)
C1—O1—H1	107 (3)	C5—C4—H4	120.8
C1—N1—C5	121.9 (3)	C3—C4—H4	120.8
C1—N1—H1A	118 (3)	C4—C5—N1	120.5 (3)
C5—N1—H1A	119 (3)	C4—C5—H5	119.7
O4—N2—O3	123.2 (3)	N1—C5—H5	119.7
O4—N2—C7	117.2 (3)	O2—C6—C11	123.4 (3)
O3—N2—C7	119.6 (3)	O2—C6—C7	123.8 (3)
O6—N3—O5	123.8 (3)	C11—C6—C7	112.7 (3)
O6—N3—C9	118.7 (3)	C8—C7—C6	124.1 (3)
O5—N3—C9	117.5 (3)	C8—C7—N2	117.0 (3)
O7—N4—O8	121.5 (3)	C6—C7—N2	118.8 (3)
O7—N4—C11	118.0 (3)	C7—C8—C9	118.8 (3)
O8—N4—C11	120.4 (3)	C7—C8—H8	120.6
O1—C1—N1	119.7 (3)	C9—C8—H8	120.6
O1—C1—C2	121.4 (3)	C10—C9—C8	121.3 (3)
N1—C1—C2	118.9 (3)	C10—C9—N3	119.5 (3)
C3—C2—C1	119.3 (3)	C8—C9—N3	119.2 (3)
C3—C2—H2	120.4	C11—C10—C9	119.3 (3)
C1—C2—H2	120.4	C11—C10—H10	120.4
C2—C3—C4	121.0 (3)	C9—C10—H10	120.4
C2—C3—H3	119.5	C10—C11—C6	123.6 (3)
C4—C3—H3	119.5	C10—C11—N4	116.3 (3)
C5—C4—C3	118.4 (3)	C6—C11—N4	120.0 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O3	0.86 (3)	2.45 (3)	2.937 (3)	117 (3)
O1—H1···O2	0.86 (3)	1.73 (2)	2.539 (3)	157 (4)
N1—H1A···O8	0.91 (1)	2.18 (3)	2.953 (4)	142 (3)
N1—H1A···O2	0.91 (1)	1.96 (3)	2.707 (4)	138 (3)