RETRACTED ARTICLE

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Retracted: Oxonium picrate

The title compound, H₃O⁺·C₆H₂N₃O₇⁻, consists of one picrate anion and one oxonium cation. The oxonium cation is located on a crystallographic twofold axis and both its H atoms are disordered, each over two symmetry-equivalent positions with occupancy ratios of 0.75. The picrate anions are also located on twofold axes bis­ecting the phenolate and p-nitro groups. π–π inter­actions between the rings of the picrates [centroid-to-centroid distances of 3.324 (2) Å] connect the anions to form stacks along the a-axis direction. The stacks are further joined together by the protonated water mol­ecules through hydrogen bonds to form two-dimensional sheets extending parallel to the ab plane. The sheets are stacked on top of each other along the c-axis direction and connected through C—H⋯O inter­actions between the CH groups of the benzene rings and the picrate nitro groups, with C⋯O distances of 3.450 (2) Å.

Related literature

For general background to organic salts of picric acid, see Jin et al. (2010); Harrison et al. (2007); Muthamizhchelvan et al. (2005); Smith et al. (2004).

Experimental

Crystal data

• H₃O⁺·C₆H₂N₃O₇⁻

• M_r = 247.13

• Orthorhombic, I b c a

• a = 7.1510 (6) Å

• b = 19.80820 (18) Å

• c = 13.50610 (12) Å

• V = 1913.12 (16) ų

• Z = 8

• Mo Kα radiation

• μ = 0.16 mm⁻¹

• T = 298 K

• 0.45 × 0.34 × 0.31 mm

Data collection

• Bruker SMART CCD area-detector diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2002) T_min = 0.936, T_max = 0.951

• 3842 measured reflections

• 848 independent reflections

• 654 reflections with I > 2σ(I)

• R_int = 0.044

Refinement

• R[F² > 2σ(F²)] = 0.044

• wR(F²) = 0.140

• S = 1.12

• 848 reflections

• 89 parameters

• 2 restraints

• H atoms treated by a mixture of independent and constrained refinement

• Δρ_max = 0.21 e Å⁻³

• Δρ_min = −0.41 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O5—H5B⋯O2^i	0.91 (2)	2.17 (2)	3.061 (3)	166 (5)
O5—H5A⋯O1	0.92 (2)	1.93 (2)	2.848 (2)	172 (5)
C3—H3⋯O3^ii	0.93	2.52	3.450 (2)	175
Symmetry codes: (i) ; (ii) .

Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.

Supporting information

S1. Comment

It is well known that picric acid is used primarily to prepare explosives, and as an intermediate to manufacture dyes. As a strong organic acid, picric acid forms salts with many N-containing organic bases (Smith et al., 2004; Harrison et al., 2007; Muthamizhchelvan et al., 2005). As an extension of our study concerning organic salts based on picric acid (Jin et al., 2010), we herein report the crystal structure of oxonium picrate.

The single crystal of the title compound (Fig. 1) with the formula C₆H₅N₃O₈ was obtained by recrystallization of picric acid and 2-chloropyridine from a methanol solution. However the 2-chloropyridine molecules do not appear in the title compound. X-ray diffraction analysis indicated that in the title compound there are one protonated water molecule, and one picrate. The OH group of the picric acid is ionized and the proton is transferred to the water molecule. In the title compound all of the bond distances and angles are in the normal range. The oxonium cation is located on a crystallographic two-fold axis and both its H atoms are disordered over each two symmetry equivalent positions with occupancy rates of 0.75 each. The benzene ring of the picrate is almost planar. The ortho-nitro groups (N1—O2—O3, and N1A—O2A—O3A) deviate from the benzene ring plane and have a dihedral angle of 25.6 (2)° with the benzene plane, whereas the para-nitro group lies almost in the benzene plane [with a dihedral angle of 2.0 (1)° between the N2—O4—O4A group and the benzene ring]. These structural data are similar to those in other structurally described picrates (Muthamizhchelvan et al., 2005).

π–π Interactions between the phenyl rings of the picrates (with Cg–Cg distances of 3.324 (2) Å) connect the picrate anions to form stacks along the a axis direction. Within one stack molecules alternate and are arranged in an antiparallel fashion. The one-dimensional picrate stacks are further linked together by the oxonium ions to form a two-dimensional sheet structure when it is viewed from the c axis direction (Fig. 2). The sheets are further stacked along the c axis direction through CH—O interactions between CH of the benzene rings and the nitro groups of the picrates with C—O distances of 3.450 (2) Å to form a three-dimensional structure.

Related literature

For general background on organic salts of picric acid, see Jin et al. (2010); Harrison et al. (2007); Muthamizhchelvan et al. (2005); Smith et al. (2004).

S2. Experimental

Crystals of oxonium picrate were formed by slow evaporation of its methanol solution at room temperature. Picric acid (23 mg, 0.10 mmol) was dissolved in 4 ml of methanol, and 2-chloropyridine (11 mg, 0.10 mmol) was added to the methanol solution. The solution was then filtered into a test tube and left standing at room temperature. After about one week yellow block crystals were obtained.

S3. Refinement

H atoms H5A and H5B bonded to the oxonium O atom were located in a difference Fourier map and refined isotropically. The oxonium cation is located on a crystallographic two-fold axis and both H5A and H5B are disordered over each two symmetry equivalent positions, and both have an occupancy of 0.75. Other H atoms were positioned geometrically with C—H = 0.93 Å for aromatic H atoms, and constrained to ride on their parent atoms with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. The structure of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. Symmetry code: (i) -x + 1/2, y, -z.
	Fig. 2. Two-dimensional sheet structure formed through hydrogen bonds which is viewed along the c axis direction. The blue dashed lines represent O—H···O and π–π interactions.

Oxonium 2,4,6-trinitrophenolate

Crystal data

H3O^+·C6H2N3O7^−	Dx = 1.716 Mg m^−3
Mr = 247.13	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Ibca	Cell parameters from 1867 reflections
a = 7.1510 (6) Å	θ = 1.5–25.0°
b = 19.80820 (18) Å	µ = 0.16 mm^−1
c = 13.50610 (12) Å	T = 298 K
V = 1913.12 (16) Å^3	Block, yellow
Z = 8	0.45 × 0.34 × 0.31 mm
F(000) = 1008

Data collection

Bruker SMART CCD area-detector diffractometer	848 independent reflections
Radiation source: fine-focus sealed tube	654 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.044
ϕ and ω scans	θmax = 25.0°, θmin = 2.1°
Absorption correction: multi-scan (SADABS; Bruker, 2002)	h = −8→8
Tmin = 0.936, Tmax = 0.951	k = −22→23
3842 measured reflections	l = −16→6

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)] = 0.044	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.140	w = 1/[σ^2(Fo^2) + (0.0677P)^2 + 3.1011P] where P = (Fo^2 + 2Fc^2)/3
S = 1.12	(Δ/σ)max < 0.001
848 reflections	Δρmax = 0.21 e Å^−3
89 parameters	Δρmin = −0.41 e Å^−3
2 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.039 (4)

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	Occ. (<1)
N1	0.3838 (3)	0.11353 (11)	0.17214 (16)	0.0328 (7)
N2	0.2500	−0.09568 (15)	0.0000	0.0361 (8)
O1	0.2500	0.18513 (12)	0.0000	0.0369 (8)
O2	0.3327 (3)	0.17048 (10)	0.19325 (15)	0.0502 (7)
O3	0.4947 (3)	0.08131 (11)	0.22328 (15)	0.0497 (7)
O4	0.3100 (4)	−0.12491 (10)	0.07276 (19)	0.0630 (8)
O5	0.0000	0.2500	0.1338 (2)	0.0489 (9)
H5A	0.089 (6)	0.233 (3)	0.091 (3)	0.073*	0.75
H5B	0.052 (7)	0.279 (2)	0.177 (3)	0.073*	0.75
C1	0.2500	0.12179 (17)	0.0000	0.0270 (8)
C2	0.3107 (4)	0.08102 (13)	0.08289 (17)	0.0270 (7)
C3	0.3134 (4)	0.01147 (13)	0.08305 (17)	0.0286 (7)
H3	0.3569	−0.0122	0.1378	0.034*
C4	0.2500	−0.02233 (17)	0.0000	0.0282 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0376 (14)	0.0358 (13)	0.0250 (12)	−0.0067 (10)	−0.0014 (10)	0.0001 (9)
N2	0.0350 (19)	0.0269 (16)	0.046 (2)	0.000	0.0059 (15)	0.000
O1	0.0587 (19)	0.0226 (13)	0.0295 (14)	0.000	0.0085 (13)	0.000
O2	0.0748 (17)	0.0372 (12)	0.0387 (12)	0.0047 (10)	−0.0128 (11)	−0.0126 (9)
O3	0.0569 (15)	0.0538 (13)	0.0385 (12)	0.0006 (11)	−0.0193 (10)	0.0019 (9)
O4	0.096 (2)	0.0300 (12)	0.0629 (15)	0.0117 (11)	−0.0140 (14)	0.0089 (10)
O5	0.061 (2)	0.0414 (17)	0.0443 (18)	−0.0008 (15)	0.000	0.000
C1	0.0273 (19)	0.0275 (18)	0.0260 (18)	0.000	0.0050 (14)	0.000
C2	0.0287 (14)	0.0305 (14)	0.0217 (13)	−0.0032 (10)	0.0009 (10)	−0.0014 (9)
C3	0.0279 (14)	0.0303 (14)	0.0275 (13)	0.0010 (11)	−0.0001 (11)	0.0051 (10)
C4	0.0262 (19)	0.0248 (17)	0.0337 (19)	0.000	0.0041 (15)	0.000

Geometric parameters (Å, º)

N1—O2	1.220 (3)	O5—H5B	0.91 (2)
N1—O3	1.230 (3)	C1—C2	1.447 (3)
N1—C2	1.463 (3)	C1—C2^i	1.447 (3)
N2—O4	1.219 (3)	C2—C3	1.378 (4)
N2—O4^i	1.219 (3)	C3—C4	1.383 (3)
N2—C4	1.453 (5)	C3—H3	0.9300
O1—C1	1.255 (4)	C4—C3^i	1.383 (3)
O5—H5A	0.92 (2)
O2—N1—O3	122.8 (2)	C3—C2—C1	124.3 (2)
O2—N1—C2	119.5 (2)	C3—C2—N1	115.7 (2)
O3—N1—C2	117.7 (2)	C1—C2—N1	119.9 (2)
O4—N2—O4^i	123.3 (3)	C2—C3—C4	118.6 (2)
O4—N2—C4	118.37 (17)	C2—C3—H3	120.7
O4^i—N2—C4	118.37 (17)	C4—C3—H3	120.7
H5A—O5—H5B	111 (5)	C3^i—C4—C3	122.1 (3)
O1—C1—C2	123.92 (15)	C3^i—C4—N2	118.97 (16)
O1—C1—C2^i	123.92 (15)	C3—C4—N2	118.97 (16)
C2—C1—C2^i	112.2 (3)
O1—C1—C2—C3	−179.13 (18)	C1—C2—C3—C4	−1.7 (3)
C2^i—C1—C2—C3	0.87 (18)	N1—C2—C3—C4	−178.59 (19)
O1—C1—C2—N1	−2.4 (3)	C2—C3—C4—C3^i	0.81 (17)
C2^i—C1—C2—N1	177.6 (3)	C2—C3—C4—N2	−179.19 (17)
O2—N1—C2—C3	−155.8 (3)	O4—N2—C4—C3^i	178.42 (19)
O3—N1—C2—C3	23.8 (3)	O4^i—N2—C4—C3^i	−1.58 (19)
O2—N1—C2—C1	27.2 (3)	O4—N2—C4—C3	−1.58 (19)
O3—N1—C2—C1	−153.3 (2)	O4^i—N2—C4—C3	178.42 (19)

Symmetry code: (i) −x+1/2, y, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O5—H5B···O2^ii	0.91 (2)	2.17 (2)	3.061 (3)	166 (5)
O5—H5A···O1	0.92 (2)	1.93 (2)	2.848 (2)	172 (5)
C3—H3···O3^iii	0.93	2.52	3.450 (2)	175

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