A new polymorph of 2-methyl-6-nitro­aniline

A new crystal form of 2-methyl-6-nitro­aniline, C₇H₈N₂O₂, crystallizing with Z′ = 2 in the space group P2₁/c, has been identified during screening for salts and cocrystals. The different N—H...O hydrogen-bonding synthons result in linear V-shaped chains in the new polymorph, rather than the helical chain arrangement seen in the known form where Z′ = 1. The presence of a second component during crystallization appears to have determined the resultant crystal form of 2-methyl-6-nitro­aniline.

S1. Comment

The formation of polymorphs by solution crystallization is influenced by thermodynamic and kinetic factors which control the processes of nucleation and crystal growth. The mechanisms and rate by which crystallization occurs depend on a number of factors including solubility, supersaturation and impurities. If a solution crystallization is performed, the solvent used can be a major factor in determining the polymorph formed (Buckley, 1951), as can be the concentration and temperature (Threlfall, 2000; Lahav & Leiserowitz, 2001; Rohani et al., 2005). The cooling rate can also affect polymorph selection; for example, flash cooling a melt often produces the metastable form (Kuhnert-Brandstätter, 1971). The presence of additives or impurities can also affect the polymorphic outcome through inhibiting the growth of one form, or accelerating the growth of nuclei of another (Blagden, 2004). As a consequence of these many possible contributions, the investigation of the effects of various crystallization parameters and the role of structure in determining the properties of compounds still depends extensively on experimental screening methods. Temperature and solvent are usually the first factors to be assessed. We are currently engaged in a systematic study of solid forms, including polymorphs, cocrystals and salts, produced by simple organic molecules with weakly interacting functional groups. In this paper, a crystal form of pure 2-methyl-6-nitroaniline, 2M6NA, produced unexpectedly during cocrystal screening, is reported. It should be noted that the other isomers of 2-methylnitroaniline (2-methyl-3-nitroaniline, 2-methyl-4-nitroaniline and 2-methyl-5-nitroaniline) so far only have one characterized crystal form.

The crystallization of two binary systems each containing 2M6NA resulted in two polymorphs of 2M6NA being formed. One polymorph, (I), produced by crystallization with 2-imidazolidinethione, was found to be the same form as that characterized by Jing et al. (2006). Further studies have found that (I) crystallizes from methanol, ethanol, propan-2-ol, butan-1-ol, acetone, acetonitrile and dimethylformamide. A second polymorph, (II), only formed on crystallization in the presence of benzenesulfonic acid. The crystallographic data for each structure are summarized below.

Although the room-temperature structure of the most common polymorph of 2M6NA, (I), has already been published, a structure description has not been given which is pertinent for the comparison of the two polymorphs. In (I), where Z' = 2, the two independent molecules form a dimer connected by a single and a bifurcated hydrogen bond [N1—H1A···O26B = 2.68 (2), N1—H1B···O26A = 2.30 (2) and N1—H1B···O26B = 2.66 (2) Å] between the amine and nitro groups (Fig. 3a). Although single and bifurcated N—H···O hydrogen bonds between amine and nitro groups are more commonly found separately in the Cambridge Structural Database (CSD, Version?; Allen 2002), this synthon is seen in a number of structures with similar distances between the amine and O atoms. The nitro group of molecule A then forms a single hydrogen bond with the amine group of a different molecule B [N21···O6B = 2.27 (2) Å]. This results in a helical chain arrangement, due to the orientation of the molecules [83.52 (4)° between the planes of the molecules]. The chains then fit together with weak C—H···O hydrogen bonds to the remaining O atom of the nitro group of molecule A that is not involved in any N—H···O hydrogen bonding. This results in molecules B being arranged in pairs in an offset manner where the perpendicular distance between the molecules in a pair is 3.38 Å, which is suggestive of π–π interactions (Fig. 3 b). The nitro groups are nearly coplanar with the aromatic ring, due to an intramolecular hydrogen bond in both molecules between the amine and nitro groups [N···O = 1.96 (2) Å]. The angles between the planes of the ring and the nitro group are 1.8 (1) and 6.0 (3)° for molecules A and B, respectively.

The new form of 2M6NA, (II), consists of chains of N—H···O hydrogen-bonded molecules [N1···O6B = 2.35 (2) Å]. However, the hydrogen bonds do not form rings as seen in (I). The molecules form linear V-shaped chains, with an angle of 127.8 (2)° between the planes of adjacent molecules (Fig. 4). The chains are stacked on top of each other in an offset manner, with a perpendicular distance of 3.51 Å between the molecules. Similarly to (I), the nitro group is approximately coplanar with the aromatic ring [angle between the planes of the ring and nitro group = 5.2 (2)°], due to the intramolecular hydrogen bond between the amine and nitro group [N1···O6A = 1.96 (2) Å].

Although not immediately noticeable by eye, the program XPac (Gelbrich, 2002) identifies a zero-dimensional construct that is common to both structures (Fig. 5). This consists of two molecules arranged about an inversion centre, with O6A···H4 and H5···H5 distances of 3.09 (2) and 2.58 (2) Å, respectively, in (I), and O6B···H4 and H5···H5 distances of 2.94 (2) and 2.52 (2) Å, respectively in (II).

It was noted by Rafilovich & Bernstein (2006) that a number of attempts to prepare cocrystals have led to new polymorphic forms of the intended cocrystal components due to the creation of new `crystallization media'. In the present work, the occurrence of the second polymorph fof 2M6NA may be due to the more acidic conditions instigated by the benzenesulfonic acid in the methanol solution, or the benzenesulfonic acid may have acted as an impurity, thus enabling a different polymorph to form. Both of these scenarios are evidenced in the literature. Of particular note is a study by Towler et al. (2004) concerning the role of pH and additives in the polymorphic selection of γ-glycine. They attribute the appearance of the more stable but less kinetically favourable γ form to an `impurity' effect, where the glycine ions selectively inhibit the nucleation and crystal growth of α-glycine which is kinetically more favourable. Indeed, further work by Poornachary et al. (2008) regarding the glycine polymorphs highlighted the controlling effect of pH over the charged impurities. There are a number of other studies in the literature where impurities or additives that are structurally similar to the target compound have been shown to inhibit the development of one polymorphic form or to stabilize one kinetic form over another (Gu et al., 2002; Lancaster et al., 2007; Davey et al., 1997; Mukuta et al., 2005). Other work involving structurally different impurities affecting polymorph formation attributes the selection to a change in solubility or impeding mass transport (Mohan et al., 2001), or inclusion of the impurity in the fastest growing faces (Blagden et al., 1998). Due to the small molecules used here, the mass transport theory will not be applicable, whereas hydrogen bonding between the crystallization components is a possibility. Review of the literature and the unique occurrence of the second 2M6NA polymorph suggest that benzenesulfonic acid most likely acts as an impurity during the crystallization, but further work is required to substantiate this concept.

S2. Experimental

All chemicals were purchased from Sigma–Aldrich and were used without further purification. Crystals of (I) and (II) were obtained by mixing equimolar amounts of 0.1 M methanol solutions of 2M6NA with 2-imidazolidinethione and benzenesulfonic acid hydrate, respectively. The mixtures were then left to evaporate slowly at room temperature. Solution crystallizations of 2M6NA were also prepared with methanol, ethanol, propan-2-ol, butan-1-ol, acetone, acetonitrile and dimethylformamide, and left to evaporate slowly at room temperature. These all yielded form (I).

S3. Refinement

H atoms were located in difference maps. Those bonded to C atoms were treated as riding atoms in geometrically idealized positions, with C—H = 0.95 (aromatic) or 0.98 Å (methyl), and with U_iso(H) = kU_eq(C), where k = 1.5 for the methyl groups, which were permitted to rotate but not to tilt, and 1.2 for the remainder. The coordinates of the H atoms bonded to N atoms were refined subject to an N—H distance restraint of 0.89 (2) Å. For (I), U_iso(H) was set at 1.4U_eq(N), while U_iso(H) values were refined in (II).

Computing details

Data collection: COLLECT (Nonius, 1998) for (I); COLLECT (Hooft & Nonius 1998) for (II). Cell refinement: DENZO (Otwinowski & Minor, 1997) and COLLECT (Nonius, 1998) for (I); DENZO (Otwinowski & Minor, 1997) & COLLECT (Hooft & Nonius 1998) for (II). Data reduction: DENZO (Otwinowski & Minor, 1997) and COLLECT (Nonius, 1998) for (I); DENZO (Otwinowski & Minor, 1997) & COLLECT (Hooft & Nonius 1998) for (II). For both compounds, program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008). Molecular graphics: Mercury (Macrae et al., 2006) for (I); Mercury CSD 2.2 (CCDC 2008) for (II). Software used to prepare material for publication: publCIF (Westrip, 2009) for (I); publCIF 1.9.3_c (Westrip, 2009) for (II).

Figures

	Fig. 1. The molecular structures of molecules A (left) and B (right) of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. The molecular structure of (II), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 3. (a) Hydrogen-bond interactions (dotted lines) between the molecules of (I). Molecules of (I) and (II) form different hydrogen-bond synthons, resulting in a helical chain arrangement. (b) Possible π–π interaction between the pair of highlighted B molecules, one at (1 - x, -1/2 + y, 3/2 - z) from the chain at the top and one at (-1 + x, 1/2 - y, -1/2 + z) from the chain at the bottom.
	Fig. 4. (a) The hydrogen-bonded (dotted lines) chain in (II). (b) The arrangement of the hydrogen-bonded chains in (II) into stacks (chains are viewed end-on), with no hydrogen-bonding interactions between adjacent stacks of chains.
	Fig. 5. The zero-dimensional construct identified by XPac as being common to both polymorphs is highlighted, (a) for (I) and (b) for (II). In (I), the helical chain arrangement can be seen. In both structures, the construct involves molecules from adjacent hydrogen-bonded chains.

(I) 2-methyl-6-nitroaniline

Crystal data

C7H8N2O2	F(000) = 640
Mr = 152.15	Dx = 1.426 Mg m^−3
Monoclinic, P21/c	Melting point = 364–366 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 8.9267 (5) Å	Cell parameters from 3359 reflections
b = 11.1863 (6) Å	θ = 2.9–27.5°
c = 14.6796 (4) Å	µ = 0.11 mm^−1
β = 104.788 (3)°	T = 120 K
V = 1417.30 (12) Å^3	Block, orange
Z = 8	0.10 × 0.08 × 0.04 mm

Data collection

Bruker Nonius 95mm CCD camera on κ-goniostat diffractometer	3252 independent reflections
Radiation source: Bruker Nonius FR591 rotating anode	2369 reflections with I > 2σ(I)
10cm confocal mirrors monochromator	Rint = 0.065
Detector resolution: 9.091 pixels mm^-1	θmax = 27.5°, θmin = 3.0°
ϕ and ω scans	h = −11→11
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	k = −14→14
Tmin = 0.989, Tmax = 0.996	l = −19→17
18662 measured reflections

Refinement

Refinement on F^2	4 restraints
Least-squares matrix: full	0 constraints
R[F^2 > 2σ(F^2)] = 0.049	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.117	w = 1/[σ^2(Fo^2) + (0.0445P)^2 + 0.5714P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max < 0.001
3252 reflections	Δρmax = 0.21 e Å^−3
213 parameters	Δρmin = −0.28 e Å^−3

Special details

Experimental. Single crystal X-ray diffraction analyses of (I) and (II) were performed using a Nonius Kappa CCD area-detector diffractometer mounted at the window of a rotating anode FR591 generator with a molybdenum anode (λ = 0.71073?Å) and equipped with an Oxford Cryosystems cryostream device. Crystals were mounted on the end of glass fibres and data were collected at 120?(2)?K. Melting points were obtained using a hot-stage microscope (Mettler–Toledo FP82HT hot-stage). Packing indices were calculated using PLATON (Spek 2009).

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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.

Data were processed using the Collect (Nonius 1998) package and unit-cell parameters were refined against all data. An empirical absorption correction was carried out using SADABS (Sheldrick, 2003).

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

	x	y	z	Uiso*/Ueq
C1	0.57244 (19)	0.65953 (15)	0.41748 (11)	0.0231 (4)
C2	0.54684 (19)	0.66788 (16)	0.31766 (11)	0.0237 (4)
C3	0.6365 (2)	0.60254 (16)	0.27280 (12)	0.0252 (4)
H3	0.6171	0.6079	0.2062	0.030*
C4	0.7560 (2)	0.52804 (16)	0.32220 (12)	0.0265 (4)
H4	0.8176	0.4847	0.2895	0.032*
C5	0.7830 (2)	0.51836 (16)	0.41772 (12)	0.0252 (4)
H5	0.8641	0.4684	0.4519	0.030*
C6	0.6912 (2)	0.58220 (15)	0.46524 (11)	0.0229 (4)
C7	0.4210 (2)	0.74894 (18)	0.26361 (13)	0.0326 (4)
H7A	0.4168	0.7446	0.1963	0.049*
H7B	0.4430	0.8313	0.2857	0.049*
H7C	0.3212	0.7238	0.2735	0.049*
N1	0.48139 (19)	0.72491 (16)	0.45950 (11)	0.0338 (4)
N6	0.72772 (18)	0.56744 (14)	0.56571 (10)	0.0290 (4)
O6A	0.83624 (17)	0.50241 (13)	0.60495 (9)	0.0409 (4)
O6B	0.64891 (16)	0.62087 (14)	0.61224 (9)	0.0395 (4)
H1A	0.502 (2)	0.722 (2)	0.5224 (11)	0.047*
H1B	0.423 (2)	0.7812 (18)	0.4274 (15)	0.047*
C21	0.82756 (19)	0.59564 (15)	0.89978 (11)	0.0215 (4)
C22	0.9428 (2)	0.68037 (15)	0.89127 (11)	0.0226 (4)
C23	1.0325 (2)	0.73437 (16)	0.97011 (12)	0.0259 (4)
H23	1.1086	0.7906	0.9631	0.031*
C24	1.0166 (2)	0.70995 (16)	1.06081 (12)	0.0264 (4)
H24	1.0793	0.7501	1.1140	0.032*
C25	0.9096 (2)	0.62762 (15)	1.07143 (11)	0.0243 (4)
H25	0.8987	0.6091	1.1326	0.029*
C26	0.81596 (19)	0.57050 (15)	0.99251 (11)	0.0210 (4)
C27	0.9653 (2)	0.70693 (17)	0.79535 (12)	0.0289 (4)
H27A	1.0450	0.7686	0.8006	0.043*
H27B	0.8676	0.7354	0.7541	0.043*
H27C	0.9980	0.6340	0.7688	0.043*
N21	0.73956 (19)	0.54404 (14)	0.82128 (10)	0.0284 (4)
N26	0.71130 (17)	0.48160 (13)	1.00975 (9)	0.0242 (3)
O26A	0.71380 (15)	0.45487 (11)	1.09225 (8)	0.0299 (3)
O26B	0.62105 (15)	0.43052 (12)	0.94227 (8)	0.0334 (3)
H21A	0.669 (2)	0.4905 (17)	0.8273 (15)	0.040*
H21B	0.744 (2)	0.5658 (19)	0.7643 (11)	0.040*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0219 (9)	0.0228 (9)	0.0244 (8)	−0.0023 (7)	0.0057 (7)	−0.0030 (7)
C2	0.0216 (9)	0.0242 (9)	0.0243 (9)	−0.0010 (7)	0.0042 (7)	−0.0010 (7)
C3	0.0263 (10)	0.0271 (10)	0.0220 (8)	−0.0034 (8)	0.0058 (7)	−0.0044 (7)
C4	0.0260 (9)	0.0261 (10)	0.0283 (9)	−0.0001 (8)	0.0086 (7)	−0.0061 (7)
C5	0.0238 (9)	0.0222 (9)	0.0280 (9)	0.0012 (7)	0.0036 (7)	−0.0011 (7)
C6	0.0251 (9)	0.0239 (9)	0.0187 (8)	−0.0027 (7)	0.0040 (7)	−0.0006 (6)
C7	0.0309 (10)	0.0355 (11)	0.0295 (10)	0.0062 (9)	0.0046 (8)	0.0011 (8)
N1	0.0355 (10)	0.0407 (10)	0.0265 (8)	0.0116 (8)	0.0100 (7)	−0.0026 (7)
N6	0.0327 (9)	0.0298 (9)	0.0233 (8)	−0.0014 (7)	0.0047 (6)	0.0002 (6)
O6A	0.0478 (9)	0.0413 (9)	0.0276 (7)	0.0116 (7)	−0.0014 (6)	0.0046 (6)
O6B	0.0404 (8)	0.0563 (10)	0.0240 (7)	0.0060 (7)	0.0121 (6)	−0.0015 (6)
C21	0.0235 (9)	0.0194 (9)	0.0208 (8)	0.0045 (7)	0.0041 (6)	0.0019 (6)
C22	0.0252 (9)	0.0189 (9)	0.0253 (8)	0.0045 (7)	0.0093 (7)	0.0038 (6)
C23	0.0274 (10)	0.0197 (9)	0.0317 (9)	−0.0021 (7)	0.0097 (7)	−0.0006 (7)
C24	0.0300 (10)	0.0228 (9)	0.0248 (9)	−0.0019 (8)	0.0042 (7)	−0.0043 (7)
C25	0.0291 (10)	0.0240 (9)	0.0203 (8)	0.0037 (7)	0.0072 (7)	0.0002 (7)
C26	0.0216 (9)	0.0211 (9)	0.0208 (8)	0.0013 (7)	0.0067 (6)	0.0014 (6)
C27	0.0319 (11)	0.0298 (10)	0.0276 (9)	0.0019 (8)	0.0122 (8)	0.0033 (7)
N21	0.0332 (9)	0.0325 (9)	0.0185 (7)	−0.0062 (7)	0.0045 (6)	0.0027 (6)
N26	0.0249 (8)	0.0268 (8)	0.0211 (7)	−0.0008 (6)	0.0062 (6)	0.0010 (6)
O26A	0.0351 (7)	0.0362 (8)	0.0209 (6)	−0.0036 (6)	0.0116 (5)	0.0034 (5)
O26B	0.0332 (8)	0.0407 (8)	0.0240 (6)	−0.0131 (6)	0.0032 (5)	0.0009 (5)

Geometric parameters (Å, º)

C1—N1	1.353 (2)	C21—N21	1.348 (2)
C1—C6	1.409 (2)	C21—C26	1.419 (2)
C1—C2	1.427 (2)	C21—C22	1.428 (2)
C2—C3	1.370 (2)	C22—C23	1.368 (2)
C2—C7	1.503 (2)	C22—C27	1.502 (2)
C3—C4	1.401 (2)	C23—C24	1.401 (2)
C3—H3	0.9500	C23—H23	0.9500
C4—C5	1.365 (2)	C24—C25	1.364 (3)
C4—H4	0.9500	C24—H24	0.9500
C5—C6	1.400 (2)	C25—C26	1.398 (2)
C5—H5	0.9500	C25—H25	0.9500
C6—N6	1.436 (2)	C26—N26	1.431 (2)
C7—H7A	0.9800	C27—H27A	0.9800
C7—H7B	0.9800	C27—H27B	0.9800
C7—H7C	0.9800	C27—H27C	0.9800
N1—H1A	0.894 (15)	N21—H21A	0.890 (16)
N1—H1B	0.873 (16)	N21—H21B	0.883 (15)
N6—O6A	1.231 (2)	N26—O26A	1.2421 (18)
N6—O6B	1.251 (2)	N26—O26B	1.2447 (18)
N1—C1—C6	124.64 (16)	N21—C21—C26	124.46 (16)
N1—C1—C2	118.37 (16)	N21—C21—C22	119.04 (15)
C6—C1—C2	117.00 (15)	C26—C21—C22	116.49 (15)
C3—C2—C1	119.90 (16)	C23—C22—C21	119.88 (15)
C3—C2—C7	121.17 (15)	C23—C22—C27	121.09 (16)
C1—C2—C7	118.93 (15)	C21—C22—C27	119.02 (15)
C2—C3—C4	121.96 (16)	C22—C23—C24	122.55 (17)
C2—C3—H3	119.0	C22—C23—H23	118.7
C4—C3—H3	119.0	C24—C23—H23	118.7
C5—C4—C3	119.38 (16)	C25—C24—C23	118.95 (16)
C5—C4—H4	120.3	C25—C24—H24	120.5
C3—C4—H4	120.3	C23—C24—H24	120.5
C4—C5—C6	119.92 (16)	C24—C25—C26	120.12 (15)
C4—C5—H5	120.0	C24—C25—H25	119.9
C6—C5—H5	120.0	C26—C25—H25	119.9
C5—C6—C1	121.82 (15)	C25—C26—C21	121.98 (16)
C5—C6—N6	116.41 (15)	C25—C26—N26	116.77 (14)
C1—C6—N6	121.74 (15)	C21—C26—N26	121.21 (15)
C2—C7—H7A	109.5	C22—C27—H27A	109.5
C2—C7—H7B	109.5	C22—C27—H27B	109.5
H7A—C7—H7B	109.5	H27A—C27—H27B	109.5
C2—C7—H7C	109.5	C22—C27—H27C	109.5
H7A—C7—H7C	109.5	H27A—C27—H27C	109.5
H7B—C7—H7C	109.5	H27B—C27—H27C	109.5
C1—N1—H1A	117.5 (14)	C21—N21—H21A	118.4 (14)
C1—N1—H1B	119.1 (15)	C21—N21—H21B	122.2 (14)
H1A—N1—H1B	121 (2)	H21A—N21—H21B	119.2 (19)
O6A—N6—O6B	120.81 (14)	O26A—N26—O26B	120.82 (14)
O6A—N6—C6	119.58 (15)	O26A—N26—C26	119.33 (14)
O6B—N6—C6	119.61 (15)	O26B—N26—C26	119.84 (14)
N1—C1—C2—C3	−179.73 (17)	N21—C21—C22—C23	179.51 (16)
C6—C1—C2—C3	−0.2 (2)	C26—C21—C22—C23	−1.4 (2)
N1—C1—C2—C7	0.3 (3)	N21—C21—C22—C27	−1.6 (2)
C6—C1—C2—C7	179.81 (16)	C26—C21—C22—C27	177.47 (15)
C1—C2—C3—C4	−1.0 (3)	C21—C22—C23—C24	0.1 (3)
C7—C2—C3—C4	178.92 (17)	C27—C22—C23—C24	−178.77 (16)
C2—C3—C4—C5	1.0 (3)	C22—C23—C24—C25	1.2 (3)
C3—C4—C5—C6	0.3 (3)	C23—C24—C25—C26	−1.1 (3)
C4—C5—C6—C1	−1.6 (3)	C24—C25—C26—C21	−0.3 (3)
C4—C5—C6—N6	−179.75 (16)	C24—C25—C26—N26	177.37 (16)
N1—C1—C6—C5	−179.00 (18)	N21—C21—C26—C25	−179.45 (16)
C2—C1—C6—C5	1.5 (2)	C22—C21—C26—C25	1.5 (2)
N1—C1—C6—N6	−0.9 (3)	N21—C21—C26—N26	3.0 (3)
C2—C1—C6—N6	179.60 (15)	C22—C21—C26—N26	−176.02 (15)
C5—C6—N6—O6A	0.9 (2)	C25—C26—N26—O26A	−3.8 (2)
C1—C6—N6—O6A	−177.27 (16)	C21—C26—N26—O26A	173.87 (15)
C5—C6—N6—O6B	−179.14 (16)	C25—C26—N26—O26B	177.50 (15)
C1—C6—N6—O6B	2.7 (3)	C21—C26—N26—O26B	−4.8 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O6B	0.89 (2)	1.97 (2)	2.628 (2)	130 (2)
N1—H1A···O26B^i	0.89 (2)	2.68 (2)	2.980 (2)	100 (2)
N1—H1B···O26A^i	0.87 (2)	2.28 (2)	3.091 (2)	156 (2)
N1—H1B···O26B^i	0.87 (2)	2.65 (2)	2.980 (2)	104 (2)
N21—H21A···O26B	0.89 (2)	1.96 (2)	2.616 (2)	129 (2)
N21—H21B···O6B	0.88 (2)	2.26 (2)	3.0891 (19)	156 (2)

Symmetry code: (i) −x+1, y+1/2, −z+3/2.

(II) 2-methyl-6-nitroaniline

Crystal data

C7H8N2O2	F(000) = 320
Mr = 152.15	Dx = 1.404 Mg m^−3
Monoclinic, P21/c	Melting point = 334–338 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 3.9248 (2) Å	Cell parameters from 1678 reflections
b = 12.8496 (8) Å	θ = 2.9–27.5°
c = 14.2746 (9) Å	µ = 0.11 mm^−1
β = 91.464 (4)°	T = 120 K
V = 719.66 (7) Å^3	Needle, orange
Z = 4	0.50 × 0.08 × 0.05 mm

Data collection

Bruker Nonius 95mm CCD camera on κ-goniostat diffractometer	1631 independent reflections
Radiation source: Bruker Nonius FR591 rotating anode	1089 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.034
Detector resolution: 9.091 pixels mm^-1	θmax = 27.5°, θmin = 4.3°
ϕ & ω scans	h = −4→5
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	k = −15→16
Tmin = 0.949, Tmax = 0.995	l = −18→16
8872 measured reflections

Refinement

Refinement on F^2	0 constraints
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F^2 > 2σ(F^2)] = 0.045	w = 1/[σ^2(Fo^2) + (0.0564P)^2 + 0.1081P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.125	(Δ/σ)max < 0.001
S = 1.04	Δρmax = 0.17 e Å^−3
1631 reflections	Δρmin = −0.13 e Å^−3
110 parameters	Extinction correction: SHELXL
2 restraints	Extinction coefficient: 0.081 (16)

Special details

Experimental. Single crystal X-ray diffraction analyses of (I) and (II) were performed using a Nonius Kappa CCD area-detector diffractometer mounted at the window of a rotating anode FR591 generator with a molybdenum anode (λ = 0.71073?Å) and equipped with an Oxford Cryosystems cryostream device. Crystals were mounted on the end of glass fibres and data were collected at 120?(2)?K.

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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.

Data were processed using the Collect (Nonius, 1998) package and unit-cell parameters were refined against all data. An empirical absorption correction was carried out using SADABS (Sheldrick, 2003).

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

	x	y	z	Uiso*/Ueq
C1	0.3383 (3)	0.84204 (11)	0.25832 (10)	0.0447 (4)
C2	0.1879 (4)	0.92341 (13)	0.20402 (11)	0.0527 (4)
C3	0.0633 (4)	1.01012 (13)	0.24766 (13)	0.0605 (5)
H3	−0.0398	1.0633	0.2104	0.073*
C4	0.0821 (4)	1.02305 (13)	0.34367 (13)	0.0641 (5)
H4	−0.0061	1.0841	0.3717	0.077*
C5	0.2281 (4)	0.94741 (13)	0.39741 (12)	0.0574 (5)
H5	0.2457	0.9559	0.4635	0.069*
C6	0.3526 (3)	0.85709 (11)	0.35587 (10)	0.0464 (4)
C7	0.1676 (6)	0.91331 (18)	0.09944 (12)	0.0820 (6)
H7A	0.0508	0.9742	0.0726	0.123*
H7B	0.0404	0.8502	0.0824	0.123*
H7C	0.3982	0.9090	0.0750	0.123*
N1	0.4565 (4)	0.75594 (11)	0.21480 (11)	0.0611 (4)
N6	0.5077 (4)	0.78146 (11)	0.41765 (10)	0.0608 (4)
O6A	0.5386 (4)	0.80276 (11)	0.50157 (9)	0.0909 (5)
O6B	0.6083 (4)	0.69781 (11)	0.38718 (10)	0.0876 (5)
H1B	0.553 (5)	0.7044 (13)	0.2494 (14)	0.078 (6)*
H1A	0.468 (5)	0.7543 (15)	0.1541 (11)	0.077 (6)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0461 (8)	0.0458 (8)	0.0422 (8)	−0.0079 (6)	0.0018 (6)	0.0009 (6)
C2	0.0503 (8)	0.0580 (9)	0.0495 (9)	−0.0079 (7)	−0.0024 (6)	0.0097 (7)
C3	0.0548 (9)	0.0533 (9)	0.0735 (12)	0.0005 (7)	0.0012 (8)	0.0161 (8)
C4	0.0646 (10)	0.0513 (10)	0.0767 (13)	0.0043 (7)	0.0123 (8)	−0.0035 (8)
C5	0.0643 (10)	0.0577 (10)	0.0505 (9)	−0.0026 (7)	0.0095 (7)	−0.0059 (7)
C6	0.0513 (8)	0.0457 (8)	0.0423 (8)	−0.0030 (6)	0.0026 (6)	0.0039 (6)
C7	0.0939 (14)	0.0990 (15)	0.0525 (11)	−0.0003 (11)	−0.0108 (9)	0.0168 (10)
N1	0.0817 (10)	0.0555 (9)	0.0461 (8)	0.0020 (7)	0.0018 (7)	−0.0066 (7)
N6	0.0764 (10)	0.0604 (9)	0.0456 (8)	0.0018 (7)	0.0008 (6)	0.0058 (7)
O6A	0.1401 (14)	0.0898 (11)	0.0423 (8)	0.0080 (9)	−0.0095 (7)	0.0074 (7)
O6B	0.1305 (12)	0.0675 (9)	0.0646 (9)	0.0354 (8)	−0.0007 (8)	0.0074 (7)

Geometric parameters (Å, º)

C1—N1	1.356 (2)	C5—H5	0.9500
C1—C6	1.406 (2)	C6—N6	1.437 (2)
C1—C2	1.421 (2)	C7—H7A	0.9800
C2—C3	1.373 (2)	C7—H7B	0.9800
C2—C7	1.499 (2)	C7—H7C	0.9800
C3—C4	1.381 (2)	N1—H1B	0.904 (15)
C3—H3	0.9500	N1—H1A	0.868 (15)
C4—C5	1.356 (2)	N6—O6A	1.2318 (19)
C4—H4	0.9500	N6—O6B	1.2284 (18)
C5—C6	1.397 (2)
N1—C1—C6	124.09 (14)	C5—C6—C1	121.95 (14)
N1—C1—C2	119.50 (14)	C5—C6—N6	116.65 (13)
C6—C1—C2	116.40 (13)	C1—C6—N6	121.37 (13)
C3—C2—C1	119.84 (14)	C2—C7—H7A	109.5
C3—C2—C7	120.79 (15)	C2—C7—H7B	109.5
C1—C2—C7	119.37 (15)	H7A—C7—H7B	109.5
C2—C3—C4	122.52 (15)	C2—C7—H7C	109.5
C2—C3—H3	118.7	H7A—C7—H7C	109.5
C4—C3—H3	118.7	H7B—C7—H7C	109.5
C5—C4—C3	119.10 (16)	C1—N1—H1B	119.4 (13)
C5—C4—H4	120.4	C1—N1—H1A	120.2 (13)
C3—C4—H4	120.4	H1B—N1—H1A	119.7 (19)
C4—C5—C6	120.17 (15)	O6A—N6—C6	118.44 (15)
C4—C5—H5	119.9	O6B—N6—O6A	120.94 (15)
C6—C5—H5	119.9	O6B—N6—C6	120.62 (14)
N1—C1—C2—C3	179.06 (14)	C4—C5—C6—N6	179.17 (14)
C6—C1—C2—C3	−0.7 (2)	N1—C1—C6—C5	179.83 (14)
N1—C1—C2—C7	−1.0 (2)	C2—C1—C6—C5	−0.4 (2)
C6—C1—C2—C7	179.29 (14)	N1—C1—C6—N6	2.1 (2)
C1—C2—C3—C4	1.0 (2)	C2—C1—C6—N6	−178.23 (13)
C7—C2—C3—C4	−178.95 (16)	C5—C6—N6—O6A	−4.0 (2)
C2—C3—C4—C5	−0.2 (2)	C1—C6—N6—O6A	173.94 (15)
C3—C4—C5—C6	−1.0 (2)	C5—C6—N6—O6B	176.40 (15)
C4—C5—C6—C1	1.3 (2)	C1—C6—N6—O6B	−5.7 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O6A^i	0.87 (2)	2.32 (2)	3.160 (2)	162 (2)
N1—H1B···O6B	0.90 (2)	1.98 (2)	2.625 (2)	128 (2)

Symmetry code: (i) x, −y+3/2, z−1/2.