Hydro­gen bonding in C-methyl­ated nitro­anilines: the three-dimensional framework structure of 2-methyl-4-nitro­aniline

Molecules of 2-methyl-4-nitro­aniline, C₇H₈N₂O₂, act as double donors and as double acceptors of N-H...O hydrogen bonds [N...O 3.117 (3) and 3.239 (3) Å; N-H...O 169 and 136°]. The mol­ecules are thereby linked into a three-dimensional framework.

S1. Comment

The introduction of C-methyl groups into 2- or 3-nitroanilines gives rise to patterns of supramolecular aggregation very different from those observed in the unsubstituted analogues (Cannon et al., 2001). In this paper, we report the structure of 2-methyl-4-nitroaniline, (I), where again the supramolecular structure is markedly different from that found in 4-nitroaniline itself [Cambridge Structural Database (CSD) refcode (Allen & Kennard, 1993) NANILI02 (Tonogaki et al., 1993)]. Compound (I) is listed in the CSD (BAJCIY; Lipscomb et al., 1981), but there are no atomic coordinates recorded either in the CSD or in the original report, nor does this report discuss the supramolecular aggregation. It seems clear, however, from both the cell dimensions and the space group that the structure reported here is for the same polymorph of (I) as BAJCIY.

The molecules of (I) (Fig. 1) lie in general positions and each acts as double donor and as a double acceptor of N—H···O hydrogen bonds. The three-dimensional structure is readily analysed in terms of two independent C(8) chain motifs (Bernstein et al., 1995). The amino N1 atom at (x, y, z) acts as a hydrogen-bond donor, via H1B, to O2 in the molecule at (1/2 + x, -y, 1 + z), while N1 at (1/2 + x, -y, 1 + z) in turn acts as donor to O2 at (1 + x, y, 2 + z); this hydrogen bond thus produces a zigzag chain running parallel to the [102] direction and generated by the glide plane at y = 0. A t the same time, N1 at (x, y, z) also acts as donor, this time via H1A, to O1 in the molecule at (1/2 + x, 1/2 + y, 1/2 + z), so producing by translation a chain running parallel to the [111] direction; the glide plane at y = 0 generates an entirely similar chain parallel to [1\-11]. The combination of the [102] and [111] chains generates continuous sheets parallel to (\-211) and built from a single type of R⁸₈(54) ring (Fig. 2); similarly, the combination of the [102] and [1\-11] chains generates continuous sheets parallel to (21\-1). Every intersection between the stacked sheets generates a [102] chain, and the molecules are thus linked into a continuous three-dimensional framework.

The structure of (I) thus differs from that of 4-nitroaniline itself (Tonogaki et al., 1993) in two ways. In 4-nitroaniline, the molecules are linked by N—H···O hydrogen bonds into two-dimensional sheets, which are weakly linked by aromatic π–π stacking interactions; in compound (I), the hydrogen-bonded structure is three dimensional and there are no π–π-stacking interactions. The structure of (I) also differs from those of the isomeric compounds 4-methyl-2-nitroaniline, (II), and 4-methyl-3-nitroaniline, (III), in both of which the supramolecular structure is one-dimensional; the supramolecular structure of (II) consists of chains, while that of (III) contains both simple chains and molecular ladders (Cannon et al., 2001). Thus, very simple nitroanilines can have supramolecular structures in one, two or three dimensions.

The C—NH₂ bond in (I (Table 1) is marginally longer than the analogous bonds in (II) and in 3,4-dimethyl-2-nitroaniline, (IV), in each of which Z' = 2 (Cannon et al., 2001) [range 1.341 (5)–1.347 (4) Å, mean 1.345 (5) Å], but significantly shorter than those in (III) where Z' = 4 [range 1.370 (2)–1.380 (2) Å, mean 1.376 (2) Å]. Likewise, the C—NO₂ bond in (I) is slightly longer than those in (II) and (IV) [range 1.413 (4)–1.437 (5) Å, mean 1.426 (3) Å], but much shorter than those in (III) [range 1.465 (2)–1.469 (2) Å, mean 1.467 (2) Å]. Despite this, the C—C bond lengths in the aromatic ring of (I) indicate only a modest contribution from the quinonoid form (Ia).

Related literature

For related literature, see: Allen & Kennard (1993); Bernstein et al. (1995); Lipscomb et al. (1981); Spek (2000); Tonogaki et al. (1993).

S2. Experimental

A sample of compound (I) was obtained from Aldrich. Crystals suitable for single-crystal X-ray diffraction were grown from a solution in ethanol.

S3. Refinement

Compound (I) is monoclinic and the systematic absences permitted Cc and C2/c as possible space groups. The unit-cell dimensions were consistent with Z = 4, so space group Cc was chosen and confirmed by the successful structure solution and refinement. Before the final refinement, the space group setting was transformed from the standard setting Cc, in which β = 139.104 (2)°, to the non-standard setting Ia, in which β = 94.050 (2)°. H atoms were treated as riding with N—H = 0.86 Å and C—H = 0.93 (aromatic) or 0.96 Å (methyl). In the absence of any significant anomalous scatterers, Friedel equivalents were merged before refinement. Examination of the structure with PLATON (Spek, 2000) showed that there were no solvent-accessible voids in the crystal lattice.

Computing details

Data collection: XPREP (Bruker, 1997); cell refinement: XPREP; data reduction: XPREP; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2000); software used to prepare material for publication: SHELXL97 and WORDPERFECT macro PRPKAPPA (Ferguson, 1999).

Figures

	Fig. 1. The molecule of (I) showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.
	Fig. 2. Part of the crystal structure of (I) showing the intersection of [102] chains with [111] and [1\-11] chains. Atoms marked with an asterisk (*), hash (#) or dollar ($) sign are at the symmetry positions (1/2 + x, -y, 1 + z), (1/2 + x, 1/2 + y, 1/2 + z) and (1 + x, -1/2 - y, 3/2 + z) respectively. H atoms bonded to C atoms have been omitted for clarity.

2-Methyl-4-nitroaniline

Crystal data

C7H8N2O2	F(000) = 320
Mr = 152.15	Dx = 1.391 Mg m^−3
Monoclinic, Ia	Mo Kα radiation, λ = 0.71073 Å
a = 7.6113 (5) Å	Cell parameters from 1316 reflections
b = 11.6304 (7) Å	θ = 3.0–32.5°
c = 8.2286 (5) Å	µ = 0.10 mm^−1
β = 94.050 (2)°	T = 150 K
V = 726.60 (8) Å^3	Block, orange
Z = 4	0.30 × 0.20 × 0.20 mm

Data collection

Bruker SMART 1000 CCD diffractometer	1316 independent reflections
Radiation source: fine-focus sealed X-ray tube	1037 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.032
ϕ and ω scans with κ offsets	θmax = 32.5°, θmin = 3.0°
Absorption correction: multi-scan (SADABS; Bruker, 1997)	h = −11→11
Tmin = 0.969, Tmax = 0.979	k = −17→14
4272 measured reflections	l = −12→12

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)] = 0.043	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.113	H-atom parameters constrained
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0735P)^2] where P = (Fo^2 + 2Fc^2)/3
1316 reflections	(Δ/σ)max < 0.001
101 parameters	Δρmax = 0.25 e Å^−3
2 restraints	Δρmin = −0.26 e Å^−3

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

	x	y	z	Uiso*/Ueq
C1	0.9082 (2)	0.07296 (16)	0.7383 (2)	0.0344 (4)
C2	0.8859 (2)	−0.04640 (14)	0.71078 (18)	0.0337 (4)
C3	0.8083 (3)	−0.08360 (15)	0.5633 (2)	0.0360 (4)
C4	0.7538 (2)	−0.00392 (17)	0.44279 (18)	0.0352 (4)
C5	0.7736 (3)	0.11337 (16)	0.4687 (2)	0.0405 (4)
C6	0.8508 (3)	0.15102 (16)	0.6156 (2)	0.0399 (4)
N1	0.9814 (3)	0.11329 (15)	0.8825 (2)	0.0478 (4)
C7	0.9475 (3)	−0.13003 (19)	0.8422 (3)	0.0465 (5)
N2	0.6745 (2)	−0.04422 (15)	0.29017 (18)	0.0463 (4)
O1	0.6538 (3)	−0.14825 (15)	0.2675 (2)	0.0621 (5)
O2	0.6279 (4)	0.02700 (18)	0.1852 (2)	0.0811 (7)
H3	0.7922	−0.1618	0.5440	0.043*
H5	0.7354	0.1657	0.3883	0.049*
H6	0.8652	0.2295	0.6338	0.048*
H1A	0.9923	0.1861	0.8981	0.057*
H1B	1.0168	0.0660	0.9582	0.057*
H7A	0.9344	−0.2071	0.8015	0.070*
H7B	0.8782	−0.1206	0.9344	0.070*
H7C	1.0692	−0.1157	0.8747	0.070*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0390 (9)	0.0353 (8)	0.0284 (7)	−0.0033 (7)	−0.0018 (6)	−0.0021 (6)
C2	0.0384 (10)	0.0309 (8)	0.0310 (8)	−0.0026 (6)	−0.0023 (6)	0.0024 (5)
C3	0.0448 (9)	0.0310 (7)	0.0312 (7)	−0.0022 (7)	−0.0055 (6)	−0.0015 (6)
C4	0.0433 (9)	0.0355 (8)	0.0255 (6)	−0.0017 (6)	−0.0063 (6)	−0.0026 (5)
C5	0.0518 (11)	0.0358 (9)	0.0327 (8)	0.0002 (7)	−0.0051 (7)	0.0050 (6)
C6	0.0557 (11)	0.0299 (8)	0.0330 (8)	−0.0019 (7)	−0.0046 (7)	−0.0013 (6)
N1	0.0676 (12)	0.0397 (9)	0.0341 (8)	−0.0040 (8)	−0.0107 (7)	−0.0052 (6)
C7	0.0579 (12)	0.0408 (9)	0.0387 (9)	−0.0025 (8)	−0.0119 (8)	0.0097 (7)
N2	0.0584 (11)	0.0479 (10)	0.0304 (8)	−0.0021 (8)	−0.0121 (7)	−0.0046 (6)
O1	0.0877 (12)	0.0457 (8)	0.0497 (8)	−0.0066 (8)	−0.0182 (8)	−0.0136 (7)
O2	0.132 (2)	0.0645 (12)	0.0408 (9)	−0.0039 (12)	−0.0375 (10)	0.0062 (8)

Geometric parameters (Å, º)

C1—C2	1.415 (2)	C4—N2	1.433 (2)
C2—C3	1.381 (2)	N2—O1	1.233 (2)
C3—C4	1.398 (2)	N2—O2	1.231 (2)
C3—H3	0.9300	C2—C7	1.505 (2)
C4—C5	1.387 (3)	N1—H1A	0.8600
C5—C6	1.377 (3)	N1—H1B	0.8600
C5—H5	0.9300	C7—H7A	0.9600
C6—C1	1.405 (2)	C7—H7B	0.9600
C6—H6	0.9300	C7—H7C	0.9600
C1—N1	1.358 (2)
N1—C1—C6	119.51 (16)	C5—C6—C1	121.14 (17)
N1—C1—C2	121.04 (15)	C5—C6—H6	119.4
C6—C1—C2	119.44 (15)	C1—C6—H6	119.4
C3—C2—C1	119.13 (14)	C1—N1—H1A	120.0
C3—C2—C7	121.43 (15)	C1—N1—H1B	120.0
C1—C2—C7	119.44 (14)	H1A—N1—H1B	120.0
C2—C3—C4	120.16 (16)	C2—C7—H7A	109.5
C2—C3—H3	119.9	C2—C7—H7B	109.5
C4—C3—H3	119.9	H7A—C7—H7B	109.5
C5—C4—C3	121.28 (15)	C2—C7—H7C	109.5
C5—C4—N2	119.38 (16)	H7A—C7—H7C	109.5
C3—C4—N2	119.34 (17)	H7B—C7—H7C	109.5
C6—C5—C4	118.84 (16)	O2—N2—O1	121.80 (16)
C6—C5—H5	120.6	O2—N2—C4	118.53 (16)
C4—C5—H5	120.6	O1—N2—C4	119.67 (16)
N1—C1—C2—C3	178.99 (18)	C2—C3—C4—C5	−0.9 (3)
N1—C1—C2—C7	−1.2 (3)	C3—C4—N2—O1	0.7 (3)
C6—C1—C2—C3	0.1 (2)	C3—C4—N2—O2	−179.8 (2)
C6—C1—C2—C7	179.93 (17)	C5—C4—N2—O1	−178.79 (19)
N1—C1—C6—C5	−179.0 (2)	C5—C4—N2—O2	0.8 (3)
C2—C1—C6—C5	−0.1 (3)	N2—C4—C5—C6	−179.66 (18)
C1—C2—C3—C4	0.4 (3)	C3—C4—C5—C6	0.9 (3)
C7—C2—C3—C4	−179.40 (18)	C4—C5—C6—C1	−0.4 (3)
C2—C3—C4—N2	179.62 (16)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1^i	0.86	2.56	3.239 (3)	136
N1—H1B···O2^ii	0.86	2.27	3.117 (3)	169

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