Hydro­gen-bonded chains in N-(2-nitrophenyl)phenylamine

Molecules of the title compound, C₁₂H₁₀N₂O₂, are markedly non-planar. There is an intramolecular N-H...O hydrogen bond, and the mol­ecules are linked into zigzag chains by a single C-H...O hydrogen bond. Comparisons are made with the supramolecular aggregation in isomeric amino-nitro derivatives, and in some N-methylnitro­anilines.

S1. Comment

The structures of C-methylated nitroanilines exhibit a wide range of supramolecular aggregation patterns (Cannon et al., 2001; Ferguson et al., 2001); in general, where there are no N-substituents, both N—H bonds and both N—O bonds participate in the hydrogen bonding. However, N-substitution necessarily produces a mismatch in the numbers of N—H and N—O bonds, opening the possibility of C—H···O hydrogen-bond formation wherever there is an excess of hard hydrogen-bond acceptors over hard hydrogen-bond donors. Here we report the structure of such a nitroaniline, N-phenyl-2-nitroaniline (2-nitrodiphenylamine), (I). \sch

Molecules of (I) exhibit a very wide C—N—C angle (Table 1), together with a conrotatory twist of the two independent aryl rings out of the central C—N—C plane. The wide angle is typical of sterically hindered secondary amines and the twisting of the rings, which is similar to that observed in Ph₃N (Sobolev et al., 1985), may be ascribed to a compromise between minimization of repulsive H···H contacts between the rings and maximization of conjugative overlap between the rings and the imino N. The C—N distances are unusual: the two independent distance to N1 are not only significantly different, but they are both very long for their type, where the mean value is 1.353 Å (Allen et al., 1987); the larger C—N—C—C torsional angles are associated with the longer C—N bond. The C—NO₂ distance is intermediate between the rather short bonds typically found in 2- and 4-nitroanilines, where electronic delocalization is possible, and the longer bonds found in unconjugated systems, such as 3-nitroanilines; at the same time, the nitro group is significantly twisted out of the plane of the adjacent aryl ring, so reducing the possible conjugation. While the C—C distances in the un-nitrated ring fall in a rather narrow range, those in the nitrated ring are consistent with a modest degree of conjugation, as in (Ia).

In compound (I) (Fig. 1) there is an intramolecular N—H···O hydrogen bond, as typically found in 2-nitroanilines (Table 2). In addition, the molecules are weakly linked by C—H···O hydrogen bonds: C25 in the molecule at (x, y, z) acts as hydrogen-bond donor to O1 in the molecule at (-0.5 + x, 2 - y, z), and propagation of this hydrogen bond produces a C(9) chain parallel to [100], generated by the glide plane at y = 1.0 (Fig. 2). There are two chains of this type running through each unit cell and they lie in the domains -0.08 < z < 0.48 and 0.42 < z < 0.98; there are neither hydrogen bonds nor aromatic π···π stacking interactions between the chains. It is striking that the same O atom, O1, is acceptor of both hydrogen bonds in this structure (Table 2): despite the abundance of aromatic C—H bonds, O2 does not participate in the hydrogen bonding.

Despite repeated efforts to crystallize the isomeric 4-nitrodiphenylamine, (II), no crystals suitable for single-crystal X-ray analysis have been obtained. However, the structures of three further isomeric aminonitrobiphenyls (III)-(V) are available in the Cambridge Structural Database (CSD; Allen & Kennard, 1993). In compound (III) (CSD code KEFLEM; Graham et al., 1989) the amino group acts as a double donor and the nitro group as a double acceptor of N—H···O hydrogen bonds: each molecule is thereby linked to four others in a (4,4) net (Batten & Robson, 1998) built from a single type of R⁴₄(30) ring, analogous to the (4,4) net of R⁴₄(22) rings found in 4-nitroaniline itself (Tonogaki et al., 1993). In the isomeric biphenyl (IV) (CSD code NIAMBP; Fallon & Ammon, 1974), the supramolecular structure is again two-dimensional. The amino group at (x, y, z) acts as donor, via H11, to both O atoms in the molecule at (1 + x, -0.5 - y, 0.5 + z), so generating a C(10)[R²₁(4)] chain of rings parallel to [201]; the same amino group acts as donor, via H12, to O11 at (x, -0.5 - y, 0.5 + z) producing a C(10) chain parallel to [001]. The combination of the [201] and [001] chains generates a sheet structure (Fig. 3). Thus, while in both (III) and (IV), all the N—H and N—O bonds participate in the formation of hard hydrogen bonds, the pattern of these hydrogen bonds is entirely different: in (II) there is a simple pairing of N—H and N—O bonds, whereas in (IV) one N—H bond is linked to two O acceptors and one O acts as a double acceptor.

By contrast in compound (V) (CSD code DIWFEU; Sutherland & Ali-Adib, 1986), one of the N—H bonds of the amino group plays no role in the hydrogen bonding, despite the numerical match between N—H and N—O bonds. The amino group at (x, y, z) acts, via a single H, as donor to both O atoms in the molecule at (1 - x, -y, 1 - z). The resulting centrosymmetric dimer, centred at (1/2, 0, 1/2), thus contains two R²₁(4) rings and an R²₂(20) ring. Dimers of this type are linked into chains parallel to [110]; atom C11 at (x, y, z) acts as hydrogen-bond donor to O2 at (-0.5 + x, 0.5 + y, z) and propagation of this interaction yields a chain of fused, alternating R²₂(20) and R²₄(12) rings (Fig. 4). Both O atoms in (V) participate in the hydrogen bonding, and the C—H···O hydrogen bond involves O2, which forms the longer of the two N—H···O hydrogen bonds in the R²₁(4) ring: thus the expected hydrogen-bonding role of one of the N—H bonds has apparently been usurped by a C—H bond.

Also in the CSD are the structures of the N-methyl derivatives (VI) (CSD code MNOMAN10; Chiaroni, 1971) and (VII) (CSD code FUXNAN; Panunto et al., 1987). In (VI), there is a single N—H···O hydrogen bond linking the molecules into C(7) translational chains, while in (VII) the molecules are linked by a single N—H···O hydrogen bond into zigzag C(8) chains. In neither compound are there any aromatic C—H···O hydrogen bonds so that, as in compound (I), one of the O atoms plays no role in the hydrogen bonding.

Thus even where there is a numerical match between the N—H and N—O bonds, not all of these are necessarily participants in the hydrogen bonding, as with compound (V). In compounds (I), (VI) and (VII), where there is an excess of hydrogen-bond acceptors, this does not necessarily lead to the formation of C—H···O hydrogen bonds.

Related literature

For related literature, see: Allen & Kennard (1993); Allen et al. (1987); Batten & Robson (1998); Cannon et al. (2001); Chiaroni (1971); Fallon & Ammon (1974); Ferguson et al. (2001); Flack (1983); Flack & Bernardinelli (2000); Graham et al. (1989); Panunto et al. (1987); Sobolev et al. (1985); Sutherland & Ali-Adib (1986); Tonogaki et al. (1993).

S2. Experimental

Crystals of (I) suitable for single-crystal X-ray diffraction were obtained by recrystallization from ethanol of a commercial sample, purchased from Aldrich. Two different commercial samples of (II) were purified by thin-layer chromatography: attempts were made to obtain material suitable for single-crystal X-ray diffraction by crystallization from anhydrous ethanol, aqueous ethanol, chloroform and ethyl acetate, in all cases without success.

S3. Refinement

Compound (I) crystallized in the orthorhombic system. Space groups Pca2₁ and Pcam were permitted by the systematic absences; the unit-cell volume indicated that Z = 4, and hence Pca2₁ was chosen, and confirmed by the successful structure analysis. H atoms were treated as riding atoms with C—H 0.95 Å, N—H 0.88 Å. In the absence of any significant anomalous scatterers, attempts to determine the absolute structure by Flack refinement (Flack, 1983) led to an inconclusive (Flack & Bernardinelli, 2000) value of the Flack parameter, 1.1 (15): hence the Friedel equivalents were merged before the final refinements.

Computing details

Data collection: Kappa-CCD server software (Nonius, 1997); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2001); software used to prepare material for publication: SHELXL97 and PRPKAPPA (Ferguson, 1999).

Figures

	Fig. 1. The asymmetric unit of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.
	Fig. 2. Part of the crystal structure of (II), showing formation of a C(9) zigzag chain. For the sake of clarity, H atoms not participating in the hydrogen-bonding are omitted. Atoms marked with a star (*) or hash (#) are at the symmetry positions (1/2 + x, 2 - y, z) and (-1/2 + x, 2 - y, z), respectively.
	Fig. 3. Part of the crystal structure of NIAMBP (Fallon & Ammon, 1974) showing formation of a (010) sheet. For the sake of clarity, H atoms bonded to C are omitted.
	Fig. 4. Part of the crystal structure of DIWFEU (Sutherland & Ali-Adib, 1986), showing formation of a chain of fused rings. For the sake of clarity, H atoms not participating in the hydrogen bonding are omitted. Atoms marked with a star (*) are at the symmetry position (1 - x, -y, 1 - z).

2-Nitrodiphenylamine

Crystal data

C12H10N2O2	F(000) = 448
Mr = 214.22	Dx = 1.403 Mg m^−3
Orthorhombic, Pca21	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2c -2ac	Cell parameters from 1246 reflections
a = 14.7077 (5) Å	θ = 3.4–27.4°
b = 10.1602 (4) Å	µ = 0.10 mm^−1
c = 6.7878 (2) Å	T = 150 K
V = 1014.32 (6) Å^3	Plate, orange
Z = 4	0.18 × 0.10 × 0.04 mm

Data collection

Kappa-CCD diffractometer	1246 independent reflections
Radiation source: fine-focus sealed X-ray tube	1071 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.078
ϕ scans, and ω scans with κ offsets	θmax = 27.4°, θmin = 3.4°
Absorption correction: multi-scan (DENZO-SMN; Otwinowski & Minor, 1997)	h = −18→16
Tmin = 0.983, Tmax = 0.996	k = −13→13
9187 measured reflections	l = −7→8

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)] = 0.046	H-atom parameters constrained
wR(F^2) = 0.111	w = 1/[σ^2(Fo^2) + (0.0708P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.08	(Δ/σ)max < 0.001
1246 reflections	Δρmax = 0.28 e Å^−3
143 parameters	Δρmin = −0.32 e Å^−3
1 restraint	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.029 (7)

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

	x	y	z	Uiso*/Ueq
C11	0.10776 (15)	0.6247 (2)	0.2121 (4)	0.0220 (5)
N1	0.08211 (14)	0.74980 (18)	0.2639 (4)	0.0268 (5)
C12	0.19915 (16)	0.5831 (2)	0.2064 (4)	0.0234 (5)
N2	0.27326 (12)	0.6698 (2)	0.2587 (3)	0.0268 (5)
O1	0.25536 (13)	0.77348 (15)	0.3512 (3)	0.0325 (5)
O2	0.35155 (11)	0.63978 (18)	0.2152 (3)	0.0384 (5)
C13	0.22414 (16)	0.4559 (2)	0.1465 (4)	0.0268 (6)
C14	0.15829 (16)	0.3664 (2)	0.0961 (4)	0.0280 (6)
C15	0.06768 (16)	0.4027 (2)	0.1096 (4)	0.0265 (6)
C16	0.04220 (16)	0.5275 (2)	0.1662 (4)	0.0251 (6)
C21	−0.00247 (15)	0.8114 (2)	0.2271 (4)	0.0242 (5)
C22	−0.05434 (12)	0.78654 (16)	0.0613 (3)	0.0296 (6)
C23	−0.13509 (12)	0.85409 (16)	0.0307 (3)	0.0340 (6)
C24	−0.16349 (17)	0.9484 (2)	0.1644 (5)	0.0344 (7)
C25	−0.11106 (17)	0.9761 (2)	0.3274 (5)	0.0333 (7)
C26	−0.03084 (17)	0.9069 (2)	0.3609 (4)	0.0277 (6)
H1	0.1229	0.7971	0.3271	0.032*
H13	0.2865	0.4318	0.1409	0.032*
H14	0.1746	0.2807	0.0525	0.034*
H15	0.0220	0.3398	0.0791	0.032*
H16	−0.0206	0.5487	0.1746	0.030*
H22	−0.0346	0.7230	−0.0320	0.035*
H23	−0.1710	0.8356	−0.0824	0.041*
H24	−0.2191	0.9939	0.1439	0.041*
H25	−0.1297	1.0426	0.4171	0.040*
H26	0.0045	0.9249	0.4748	0.033*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C11	0.0242 (12)	0.0182 (11)	0.0235 (13)	−0.0009 (8)	0.0014 (11)	0.0008 (10)
N1	0.0216 (10)	0.0206 (10)	0.0384 (14)	−0.0002 (7)	−0.0034 (9)	−0.0036 (9)
C12	0.0230 (12)	0.0224 (11)	0.0248 (14)	0.0007 (9)	−0.0004 (10)	0.0026 (11)
N2	0.0237 (12)	0.0267 (10)	0.0301 (12)	−0.0015 (7)	−0.0007 (10)	0.0050 (10)
O1	0.0314 (9)	0.0248 (8)	0.0412 (13)	−0.0042 (8)	−0.0027 (9)	0.0004 (9)
O2	0.0211 (9)	0.0434 (11)	0.0507 (13)	0.0007 (7)	0.0041 (9)	0.0007 (10)
C13	0.0259 (14)	0.0262 (12)	0.0284 (14)	0.0041 (8)	0.0008 (10)	0.0036 (11)
C14	0.0327 (13)	0.0215 (11)	0.0298 (14)	0.0039 (9)	0.0007 (11)	−0.0009 (10)
C15	0.0333 (14)	0.0211 (11)	0.0251 (14)	−0.0012 (9)	0.0008 (11)	0.0021 (11)
C16	0.0224 (12)	0.0234 (11)	0.0295 (14)	−0.0008 (8)	0.0011 (10)	−0.0015 (11)
C21	0.0217 (12)	0.0174 (11)	0.0336 (14)	−0.0001 (8)	0.0019 (11)	0.0017 (11)
C22	0.0315 (13)	0.0223 (11)	0.0349 (15)	0.0023 (9)	−0.0016 (13)	−0.0018 (12)
C23	0.0314 (13)	0.0277 (12)	0.0429 (17)	−0.0005 (10)	−0.0090 (13)	0.0026 (13)
C24	0.0232 (13)	0.0267 (13)	0.0531 (19)	0.0031 (9)	−0.0022 (12)	0.0011 (13)
C25	0.0311 (14)	0.0226 (12)	0.0463 (18)	0.0055 (9)	0.0044 (13)	−0.0016 (13)
C26	0.0310 (13)	0.0195 (12)	0.0327 (15)	−0.0002 (9)	−0.0006 (12)	−0.0026 (11)

Geometric parameters (Å, º)

C11—C12	1.409 (3)	C26—C21	1.393 (4)
C12—C13	1.404 (3)	N1—C11	1.372 (3)
C13—C14	1.372 (3)	N1—C21	1.415 (3)
C14—C15	1.386 (3)	N1—H1	0.8800
C15—C16	1.377 (3)	C13—H13	0.9500
C16—C11	1.415 (3)	C14—H14	0.9500
C12—N2	1.446 (3)	C15—H15	0.9500
N2—O1	1.254 (3)	C16—H16	0.9500
N2—O2	1.227 (2)	C22—H22	0.9500
C21—C22	1.383 (3)	C23—H23	0.9500
C22—C23	1.387 (2)	C24—H24	0.9500
C23—C24	1.384 (4)	C25—H25	0.9500
C24—C25	1.378 (5)	C26—H26	0.9500
C25—C26	1.392 (3)
N1—C11—C12	123.1 (2)	C15—C16—C11	121.2 (2)
N1—C11—C16	121.0 (2)	C15—C16—H16	119.4
C12—C11—C16	115.78 (19)	C11—C16—H16	119.4
C11—N1—C21	127.3 (2)	C22—C21—C26	119.5 (2)
C11—N1—H1	116.3	C22—C21—N1	123.2 (2)
C21—N1—H1	116.3	C26—C21—N1	117.2 (2)
C13—C12—C11	122.2 (2)	C21—C22—C23	120.24 (12)
C13—C12—N2	115.8 (2)	C21—C22—H22	119.9
C11—C12—N2	122.00 (19)	C23—C22—H22	119.9
O2—N2—O1	121.8 (2)	C24—C23—C22	120.16 (14)
O2—N2—C12	119.8 (2)	C24—C23—H23	119.9
O1—N2—C12	118.44 (18)	C22—C23—H23	119.9
C14—C13—C12	119.9 (2)	C25—C24—C23	120.0 (2)
C14—C13—H13	120.1	C25—C24—H24	120.0
C12—C13—H13	120.1	C23—C24—H24	120.0
C13—C14—C15	119.1 (2)	C24—C25—C26	120.1 (3)
C13—C14—H14	120.5	C24—C25—H25	119.9
C15—C14—H14	120.5	C26—C25—H25	119.9
C16—C15—C14	121.7 (2)	C25—C26—C21	120.0 (3)
C16—C15—H15	119.2	C25—C26—H26	120.0
C14—C15—H15	119.2	C21—C26—H26	120.0
C21—N1—C11—C12	162.4 (3)	C11—N1—C21—C22	−32.9 (4)
C21—N1—C11—C16	−19.5 (5)	C11—N1—C21—C26	150.9 (3)
C11—C12—N2—O1	15.7 (4)	C11—C12—N2—O2	−165.5 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1	0.88	1.97	2.627 (3)	130
C25—H25···O1^i	0.95	2.56	3.219 (3)	127

Symmetry code: (i) x−1/2, −y+2, z.