Variable-temperature crystal structure studies of m-­nitroaniline

The crystal structure of m-nitroaniline has been examined at several temperatures over the 90–350 K range. Thermal evolution of the lattice parameters reveals a weak anomaly at 110 K and an important one at 300 K. The thermal expansion coefficients have been calculated at several temperatures and the principal axes cross-sections of the tensor were drawn. The lattice contraction along the b axis direction has been observed. The rigid-body analysis including an attached rigid group has provided the values of the translation and libration tensors at temperatures studied. The results indicate that m-nitroaniline undergoes a glass transition around 130 K arising from freezing molecular librations and translations. From above 340 K the growing plasticity of the m-nitroaniline crystal results in the loss of X-ray diffraction reflections. This is probably a second-order phase transition. It is coupled with a considerable increase in the nitro group torsion amplitude, but the NH...O hydrogen bonds are preserved. Analysis of the temperature evolution of short intermolecular distances enabled us to consider the occurrence of reorienting aggregates of hydrogen-bonded molecules in the high-temperature plastic phase.

Computing details

Data collection: Kuma KM4CCD Software; cell refinement: Kuma KM4CCD Software; data reduction: Kuma KM4CCD Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3; software used to prepare material for publication: SHELXL97.

Figures

'3-nitro-phenylamine'

Crystal data

C6H6N2O2	Dx = 1.492 Mg m^−3
Mr = 138.13	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pca21	Cell parameters from 1415 reflections
a = 18.873 (2) Å	θ = 3.4–28.2°
b = 6.5212 (9) Å	µ = 0.12 mm^−1
c = 4.9980 (7) Å	T = 110 K
V = 615.13 (14) Å^3	Plate, yellow
Z = 4	1.02 × 0.67 × 0.18 mm
F(000) = 288

Data collection

Kuma Diffraction KM4CCD diffractometer	1305 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.025
Graphite monochromator	θmax = 29.6°, θmin = 3.1°
ω scans	h = −26→25
4413 measured reflections	k = −9→8
1357 independent reflections	l = −6→5

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	Fixed
R[F^2 > 2σ(F^2)] = 0.040	w = 1/[σ^2(Fo^2) + (0.0638P)^2 + 0.1839P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.108	(Δ/σ)max = 0.001
S = 1.10	Δρmax = 0.27 e Å^−3
1357 reflections	Δρmin = −0.29 e Å^−3
92 parameters	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
1 restraint	Extinction coefficient: 0.29 (2)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack H D (1983), Acta Cryst. A39, 876-881
Secondary atom site location: difference Fourier map	Absolute structure parameter: −0.5 (15)

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
N1	0.14178 (7)	0.57722 (19)	0.2389 (3)	0.0204 (3)
O1	0.10120 (7)	0.43100 (18)	0.2081 (3)	0.0320 (3)
C1	0.12426 (8)	0.7287 (2)	0.4454 (3)	0.0177 (3)
O2	0.19549 (6)	0.60121 (19)	0.1048 (3)	0.0298 (3)
N2	0.19586 (7)	1.21243 (19)	0.7026 (3)	0.0219 (3)
H2A	0.2344	1.2261	0.6052	0.026*
H2B	0.1854	1.3049	0.8246	0.026*
C2	0.16823 (8)	0.8982 (2)	0.4699 (3)	0.0180 (3)
H2	0.2086	0.9140	0.3581	0.022*
C4	0.09147 (8)	1.0157 (2)	0.8234 (3)	0.0212 (3)
H4	0.0796	1.1147	0.9555	0.025*
C3	0.15155 (8)	1.0450 (2)	0.6637 (3)	0.0179 (3)
C6	0.06434 (8)	0.6964 (2)	0.5997 (4)	0.0212 (3)
H6	0.0352	0.5791	0.5755	0.025*
C5	0.04893 (8)	0.8435 (2)	0.7910 (4)	0.0228 (3)
H5	0.0085	0.8263	0.9021	0.027*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0227 (6)	0.0186 (5)	0.0201 (7)	0.0011 (4)	−0.0027 (6)	−0.0046 (5)
O1	0.0355 (6)	0.0247 (5)	0.0358 (8)	−0.0076 (5)	0.0016 (6)	−0.0127 (6)
C1	0.0193 (6)	0.0176 (6)	0.0161 (7)	0.0022 (5)	−0.0029 (6)	−0.0043 (5)
O2	0.0285 (6)	0.0316 (6)	0.0293 (8)	−0.0008 (5)	0.0055 (6)	−0.0130 (5)
N2	0.0227 (6)	0.0200 (5)	0.0230 (7)	−0.0014 (4)	−0.0005 (5)	−0.0074 (5)
C2	0.0176 (6)	0.0189 (6)	0.0175 (7)	−0.0001 (5)	−0.0006 (6)	−0.0029 (5)
C4	0.0210 (6)	0.0232 (7)	0.0195 (8)	0.0036 (5)	−0.0007 (6)	−0.0052 (6)
C3	0.0180 (6)	0.0190 (6)	0.0167 (8)	0.0025 (5)	−0.0046 (5)	−0.0027 (5)
C6	0.0200 (6)	0.0216 (7)	0.0220 (8)	−0.0014 (5)	−0.0013 (6)	−0.0023 (6)
C5	0.0197 (6)	0.0281 (7)	0.0205 (8)	−0.0006 (5)	0.0027 (6)	−0.0016 (6)

Geometric parameters (Å, º)

N1—O2	1.2253 (19)	C2—C3	1.398 (2)
N1—O1	1.2328 (16)	C2—H2	0.9500
N1—C1	1.4665 (19)	C4—C5	1.390 (2)
C1—C6	1.385 (2)	C4—C3	1.400 (2)
C1—C2	1.3874 (18)	C4—H4	0.9500
N2—C3	1.3892 (17)	C6—C5	1.385 (2)
N2—H2A	0.8800	C6—H6	0.9500
N2—H2B	0.8800	C5—H5	0.9500
O2—N1—O1	122.99 (14)	C5—C4—C3	120.76 (14)
O2—N1—C1	119.05 (12)	C5—C4—H4	119.6
O1—N1—C1	117.96 (13)	C3—C4—H4	119.6
C6—C1—C2	124.09 (13)	N2—C3—C2	119.98 (14)
C6—C1—N1	118.26 (12)	N2—C3—C4	120.99 (14)
C2—C1—N1	117.64 (13)	C2—C3—C4	118.98 (13)
C3—N2—H2A	120.0	C1—C6—C5	116.77 (13)
C3—N2—H2B	120.0	C1—C6—H6	121.6
H2A—N2—H2B	120.0	C5—C6—H6	121.6
C1—C2—C3	118.16 (14)	C6—C5—C4	121.24 (14)
C1—C2—H2	120.9	C6—C5—H5	119.4
C3—C2—H2	120.9	C4—C5—H5	119.4
O2—N1—C1—C6	−178.39 (15)	C1—C2—C3—C4	−0.2 (2)
O1—N1—C1—C6	1.9 (2)	C5—C4—C3—N2	−177.33 (15)
O2—N1—C1—C2	2.9 (2)	C5—C4—C3—C2	0.1 (2)
O1—N1—C1—C2	−176.83 (15)	C2—C1—C6—C5	−0.8 (2)
C6—C1—C2—C3	0.6 (2)	N1—C1—C6—C5	−179.36 (15)
N1—C1—C2—C3	179.18 (14)	C1—C6—C5—C4	0.6 (2)
C1—C2—C3—N2	177.23 (14)	C3—C4—C5—C6	−0.3 (3)