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Achiral p-nitro­phenyl isocyanide, C7H4N2O2, crystallizes in the orthorhombic chiral space group P212121. Attractive intermolecular interactions between the nitro O atoms and both aromatic H and nitro N atoms of neighbouring mol­ecules are observed. The O...N interaction is surprisingly strong [N...O = 2.869 (2) Å] compared with other aromatic nitro compounds.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270104007115/sq1151sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270104007115/sq1151Isup2.hkl
Contains datablock I

CCDC reference: 243606

Comment top

The title compound, p-nitroisocyanobenzene, (I), is achiral in solution but crystallizes in the orthorhombic chiral space group P212121, with four symmetry-equivalent molecules in the unit cell. Intramolecular bond lengths and angles of (I) are in the expected range for an aromatic isonitrile. The arene moiety is basically planar and the isocyano group, as well as the N atom of the nitro substituent, are located within 0.053 (3) Å of the mean plane of the benzene ring. The nitro group is rotated by 5.9 (2)° out of the benzene plane. \sch

While the cyano isomer of (I), p-nitrobenzonitrile, is essentially isosteric with (I), it is not isostructural, and crystallizes in the space group P21 (Higashi & Osaki, 1977). In the Cambridge Structural Database (CSD, Version?; Allen, 2002), we found ten aromatic nitrile/isonitrile pairs. As with (I), the majority of these were not isostructural and, indeed, only four had at least one isomorphous nitrile/isonitrile pair.

In the case presented here, the formation of isomorphous crystals is prevented by surprisingly strong interactions of the nitro group with neighbouring molecules. Thus, each of the nitro O atoms is in close contact with either a neighbouring aromatic H atom or with the N atom of a next molecule's nitro group (Fig. 1). The O1···H7ii distance is 2.46 (2) Å and the corresponding O1···C7ii distance is 3.246 (2) Å [symmetry code: (ii) x − 1, y + 1, z]. While this O···H—C interaction is definitely attractive and stabilizing, it is in the usual range found for aromatic nitro compounds.

In sharp contrast, the N—O···N interaction of atom O2 with the neighbouring nitro group is surprisingly strong. Thus, the intermolecular distance between atoms O2 and N2i is 2.869 (2) Å [symmetry code: (i) x + 1/2, 1/2 − y, −z]. Such a short intermolecular N···O distance is very rare for aromatic nitro compounds and only the extremely electron-poor superacid N,N-dipicrylamine, DPA, and some of its derivatives exhibit similarly short intermolecular N···O contacts (Woźniak et al., 1994, 1997; Szumma et al., 2000). Indeed, only the N···O distance of 2.826 Å observed for DPA itself is shorter than that observed for (I) (Woźniak et al., 1994).

DPA has been analyzed in detail, both by a charge-density study (Platts et al., 1995) and by computational methods using HNO2 and FNO2 as model compounds (Woźniak et al., 2002). Both studies indicate that these types of bonds are mainly dispersive van der Waals-type interactions. Electrostatic stabilization seems to play only a minor role. The calculated N···O distance found by Platts et al. for HNO2 lies between 2.8 and 2.9 Å, and both (I) and DPA fall well within that range. The strength of this interaction was estimated to be at least 10–13 kJ mol−1, thus being comparable with weak hydrogen-bond interactions.

Based on these findings, short N···O contacts between nitro groups should be common among nitrobenzene derivatives, but the opposite is the case. For the bulk of organic nitro compounds, the average non-bonding distance between two nitro groups is around 3.3 Å and only a small fraction are shorter than the van der Waals radius of 3.07 Å (Szczesna & Urbańczyk-Lipkowska, 2002). Of all 5921 aromatic nitro compounds in the CSD (Version?), only m-chloro-nitrobenzene has an N···O distance shorter than 3.2 Å (Scharma et al., 1985) (DPA and some of its derivatives are not listed in the CSD). This makes both (I) and DPA unusual cases, and a closer look at the geometry of the N···O interaction found in (I) seems appropriate.

As with hydrogen bonds, directionality is important for N···O interactions. The O atom in (I) is located directly atop the p-orbital of the N atom of the neighbouring molecule, i.e. the line of the N···O interaction in (I) is perpendicular to the plane of the nitro group (Figs. 1 and 2).

The relative orientation of the O atom is not as important. For (I), an `end-on coordination' of the O atom is observed and the direction of the O···N interaction is parallel with the C—N bond [(a) in the second scheme], resulting in the formation of an infinite zigzag chain of perpendicular molecules (Fig. 2). This end-on coordination was also found for DPA and some of its anions, but other alternative types of coordination, such as `side-on', `parallel' and bipyramidal are also observed [(b)-(d) in the second scheme] (Woźniak et al., 1994).

The strengths of the N—O···H and N—O···N interactions found in (I) seem to be of the same order of magnitude, and neither of the two N—O bonds in the nitro group seems to be stabilized more than the other. The N—O bond lengths are 1.228 (2) and 1.226 (2) Å, respectively, and are thus basically identical.

Given the large structural difference between (I) and DPA, the fundamental reason for the anomalously short Ar—NO2 Ar—NO2 interactions which they share is not apparent. In particular, the relative poles of the electron-withdrawing groups on the arenes and the lattice effects remain unclear, and more detailed experimental and computational investigations will be necessary to explain the reasons for the observations made.

Experimental top

The requisite intermediate, 1-formamido-4-nitrobenzene, was prepared by refluxing p-nitroaniline in 75% formic acid for 2 h. Addition of water precipitated the formamide, which was washed with water until neutral, dried in vacuo and recrystallized from hot acetone. The isocyanide, (I), was synthesized as described by Efraty et al. (1980) for 1,4-diisocyanobenzene, using two equivalents of diphosgene. It was purified by sublimation in vacuo. Single crystals of (I) were grown by sublimation in vacuo. Spectroscopic analysis: IR (toluene, CaF2, ν, cm−1): 2121 (s, isonitrile), 1520 (s, as NO2), 1345 (s, sy NO2); IR (KBr, ν, cm−1): 2130 (br, isonitrile), 1541 (br, as NO2), 1349 (br, sy NO2); 1H NMR (399.905 MHz, CDCl3, δ, p.p.m.): 8.23 [d, 3J(1H1H) = 9.0 Hz, 2H], 7.508 [d, 3J(1H1H) = 9.0 Hz, 2H]; 13C NMR (100.565 MHz, CDCl3, δ, p.p.m.): 169.3 (s, C isonitrile), 147.3 (s, C—NO2), 131.0 [t, 1J(13C14N) = 16 Hz, C—NC], 127.4 (s, C arom), 124.9 (s, C arom).

Refinement top

Since compound (I) is achiral and is without heavy atoms, and since Mo radiation was used for the measurement, it was decided to omit refinement of chirality. Thus, despite (I) having a chiral space group, Friedel equivalents were merged. All H atoms were taken from a difference Fourier calculation and were refined isotropically.

Computing details top

Data collection: SMART (Bruker, 2000); cell refinement: SAINT-Plus (Bruker 2000); data reduction: SAINT-Plus (Bruker 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXL97; software used to prepare material for publication: Please provide missing details.

Figures top
[Figure 1] Fig. 1. A plot of three molecules of (I), viewed along the a axis, showing the intermolecular O···N and O···H—C interactions. Displacement ellipsoids are drawn at the 30% probability level [symmetry codes: (i) x + 1/2, 1/2 − y, −z; (ii) x − 1, y + 1, z].
[Figure 2] Fig. 2. A diagram showing only the N···O intermolecular contacts in the structure of (I), viewed along the b axis. An infinite zigzag chain of molecules is formed by the N···O bridges.
p-Nitrophenyl isocyanide top
Crystal data top
C7H4N2O2Dx = 1.493 Mg m3
Mr = 148.12Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, P212121Cell parameters from 6022 reflections
a = 5.0127 (8) Åθ = 3.4–28.3°
b = 6.0320 (9) ŵ = 0.11 mm1
c = 21.790 (3) ÅT = 90 K
V = 658.86 (18) Å3Plate, colourless
Z = 40.60 × 0.29 × 0.08 mm
F(000) = 304
Data collection top
Bruker SMART APEX CCD area-detector
diffractometer
966 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.042
Graphite monochromatorθmax = 28.3°, θmin = 1.9°
ω scansh = 66
6766 measured reflectionsk = 87
997 independent reflectionsl = 2929
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.030Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.081All H-atom parameters refined
S = 1.07 w = 1/[σ2(Fo2) + (0.0698P)2 + 0.6662P]
where P = (Fo2 + 2Fc2)/3
997 reflections(Δ/σ)max < 0.001
116 parametersΔρmax = 0.29 e Å3
0 restraintsΔρmin = 0.23 e Å3
Crystal data top
C7H4N2O2V = 658.86 (18) Å3
Mr = 148.12Z = 4
Orthorhombic, P212121Mo Kα radiation
a = 5.0127 (8) ŵ = 0.11 mm1
b = 6.0320 (9) ÅT = 90 K
c = 21.790 (3) Å0.60 × 0.29 × 0.08 mm
Data collection top
Bruker SMART APEX CCD area-detector
diffractometer
966 reflections with I > 2σ(I)
6766 measured reflectionsRint = 0.042
997 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0300 restraints
wR(F2) = 0.081All H-atom parameters refined
S = 1.07Δρmax = 0.29 e Å3
997 reflectionsΔρmin = 0.23 e Å3
116 parameters
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.

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 (Å2) top
xyzUiso*/Ueq
N20.9952 (3)0.1846 (2)0.05838 (5)0.0156 (3)
O21.1083 (2)0.08980 (18)0.01585 (5)0.0204 (2)
N10.1867 (3)0.2688 (2)0.18229 (5)0.0179 (3)
C60.7026 (3)0.1394 (2)0.06865 (6)0.0157 (3)
O11.0504 (2)0.37257 (17)0.07555 (5)0.0216 (3)
C50.7827 (3)0.0656 (2)0.09092 (6)0.0148 (3)
C30.4719 (3)0.0496 (2)0.17331 (6)0.0182 (3)
C70.5023 (3)0.2517 (2)0.09935 (6)0.0165 (3)
C20.3901 (3)0.1565 (2)0.15112 (6)0.0157 (3)
C40.6724 (3)0.1617 (2)0.14264 (6)0.0176 (3)
C10.0132 (3)0.3569 (3)0.20720 (6)0.0231 (3)
H70.446 (4)0.390 (3)0.0854 (8)0.022 (5)*
H60.775 (4)0.198 (3)0.0333 (8)0.020 (5)*
H40.732 (4)0.300 (3)0.1570 (9)0.024 (5)*
H30.385 (4)0.106 (3)0.2088 (8)0.026 (5)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N20.0144 (5)0.0161 (5)0.0165 (5)0.0013 (5)0.0014 (4)0.0017 (4)
O20.0189 (5)0.0203 (5)0.0221 (5)0.0003 (4)0.0048 (4)0.0005 (4)
N10.0190 (6)0.0186 (6)0.0160 (5)0.0020 (5)0.0004 (4)0.0002 (4)
C60.0169 (6)0.0151 (6)0.0151 (6)0.0013 (6)0.0005 (5)0.0010 (5)
O10.0232 (5)0.0168 (5)0.0247 (5)0.0068 (5)0.0002 (4)0.0016 (4)
C50.0138 (6)0.0138 (6)0.0166 (6)0.0011 (5)0.0001 (5)0.0027 (5)
C30.0205 (6)0.0170 (6)0.0170 (6)0.0003 (6)0.0026 (6)0.0023 (5)
C70.0177 (7)0.0143 (6)0.0176 (6)0.0024 (6)0.0018 (5)0.0000 (5)
C20.0146 (6)0.0161 (6)0.0163 (5)0.0017 (6)0.0005 (5)0.0025 (5)
C40.0203 (7)0.0142 (6)0.0183 (6)0.0016 (6)0.0003 (5)0.0021 (5)
C10.0245 (7)0.0243 (7)0.0204 (6)0.0043 (7)0.0019 (6)0.0007 (6)
Geometric parameters (Å, º) top
N2—O11.2259 (16)C5—C41.3828 (19)
N2—O21.2275 (16)C3—C41.383 (2)
N2—C51.4671 (18)C3—C21.396 (2)
N1—C11.155 (2)C3—H30.950 (19)
N1—C21.3999 (18)C7—C21.3849 (19)
C6—C71.384 (2)C7—H70.93 (2)
C6—C51.3876 (18)C4—H40.94 (2)
C6—H60.922 (18)
O1—N2—O2123.85 (13)C4—C3—H3123.3 (12)
O1—N2—C5117.95 (12)C2—C3—H3117.9 (12)
O2—N2—C5118.19 (11)C6—C7—C2119.06 (13)
C1—N1—C2177.85 (16)C6—C7—H7120.0 (12)
C7—C6—C5118.49 (12)C2—C7—H7120.9 (12)
C7—C6—H6120.2 (12)C7—C2—C3122.14 (13)
C5—C6—H6121.2 (12)C7—C2—N1119.38 (12)
C4—C5—C6122.88 (13)C3—C2—N1118.48 (12)
C4—C5—N2118.64 (12)C5—C4—C3118.64 (13)
C6—C5—N2118.48 (12)C5—C4—H4121.1 (12)
C4—C3—C2118.78 (13)C3—C4—H4120.3 (12)
C7—C6—C5—C40.5 (2)C6—C7—C2—C30.2 (2)
C7—C6—C5—N2179.95 (13)C6—C7—C2—N1179.76 (12)
O1—N2—C5—C45.97 (18)C4—C3—C2—C70.3 (2)
O2—N2—C5—C4173.62 (12)C4—C3—C2—N1179.85 (13)
O1—N2—C5—C6174.52 (12)C6—C5—C4—C30.5 (2)
O2—N2—C5—C65.90 (18)N2—C5—C4—C3179.97 (12)
C5—C6—C7—C20.3 (2)C2—C3—C4—C50.4 (2)

Experimental details

Crystal data
Chemical formulaC7H4N2O2
Mr148.12
Crystal system, space groupOrthorhombic, P212121
Temperature (K)90
a, b, c (Å)5.0127 (8), 6.0320 (9), 21.790 (3)
V3)658.86 (18)
Z4
Radiation typeMo Kα
µ (mm1)0.11
Crystal size (mm)0.60 × 0.29 × 0.08
Data collection
DiffractometerBruker SMART APEX CCD area-detector
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
6766, 997, 966
Rint0.042
(sin θ/λ)max1)0.668
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.030, 0.081, 1.07
No. of reflections997
No. of parameters116
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.29, 0.23

Computer programs: SMART (Bruker, 2000), SAINT-Plus (Bruker 2000), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), SHELXL97, Please provide missing details.

Selected geometric parameters (Å, º) top
N2—O11.2259 (16)N1—C11.155 (2)
N2—O21.2275 (16)N1—C21.3999 (18)
N2—C51.4671 (18)
O1—N2—O2123.85 (13)C4—C5—N2118.64 (12)
O1—N2—C5117.95 (12)C6—C5—N2118.48 (12)
O2—N2—C5118.19 (11)C7—C2—N1119.38 (12)
C1—N1—C2177.85 (16)C3—C2—N1118.48 (12)
O1—N2—C5—C45.97 (18)O1—N2—C5—C6174.52 (12)
O2—N2—C5—C4173.62 (12)O2—N2—C5—C65.90 (18)
 

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