The crystal structures of three primary products from the selective reduction of 2,4,6-trinitrotoluene

Article abstract of DOI:10.1039/b309792g

The crystal structures of three primary products from the selective reduction of 2,4,6-trinitrotoluene (TNT) have been determined by synchrotron X-ray powder diffraction (2-amino-4,6-dinitrotoluene) and single crystal X-ray diffraction (4-amino-2,6-dinitr

Full text of DOI:10.1039/b309792g

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P A P E R
The crystal structures of three primary products from the selective
reduction of 2,4,6-trinitrotoluene
a
a
a
a
Duncan Graham, Alan R. Kennedy,* Callum J. McHugh, W. Ewen Smith,
b
b
cd
William I. F. David, Kenneth Shankland and Norman Shankland
a
Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street,
Glasgow G1 1XL, Scotland
b
c
d
ISIS Facility, CLRC Rutherford Appleton Laboratory, Chilton, Oxfordshire OX11 0QX,
England
Department of Pharmaceutical Sciences, University of Strathclyde, 27 Taylor Street,
Glasgow G4 0NR, Scotland
CrystallografX Limited, 38 Queen Street, Glasgow G1 3DX, Scotland.
E-mail: a.r.kennedy@strath.ac.uk; Fax: 0141 552 0876; Tel: 0141 548 2016
Received (in London, UK) 14th August 2003, Accepted 20th September 2003
First published as an Advance Article on the web 22nd October 2003
The crystal structures of three primary products from the selective reduction of 2,4,6-trinitrotoluene (TNT)
have been determined by synchrotron X-ray powder diffraction (2-amino-4,6-dinitrotoluene) and single crystal
X-ray diffraction (4-amino-2,6-dinitrotoluene and 2-hydroxyamino-4,6-dinitrotoluene). The molecular structure
of 2-amino-4,6-dinitrotoluene, including rotational disorder of the 6-nitro group, was subsequently detailed to a
higher resolution by a single-crystal analysis. In contrast to the known structures of TNT, the crystal structures
of these amino species are dominated by hydrogen-bonded sheets connected via ring stacking, whilst that of 2-
hydroxyamino-4,6-dinitrotoluene is dominated by the dual hydrogen-bonding acceptor/donator role of the
hydroxyamine group.
to nitroreductase enzymes as well as to soils and metal
surfaces.
Introduction
The reduction chemistry of high explosives such as 2,4,6,-trini-
trotoluene (TNT) and 1,3,5-trinitro-1,3,5-triazacyclohexane
Experimental
(RDX) is an important area of current research, in particular
amongst groups investigating the treatment and clean-up of
Synthesis
1
land contaminated with explosive residues. Our own interest
in this chemistry is in the detection of trace levels of an explo-
sive’s vapour by Surface Enhanced Resonance Raman Scatter-
ing (SERRS). Whilst a lack of sensitivity limits the use of
normal Raman scattering in the detection of explosive vapours
or trace amounts, SERRS should enable detection of TNT at
the levels required. In order to exploit the SERRS effect, the
analyte must be adsorbed onto the SERRS metal substrate
and should contain a chromophore that absorbs visible wave-
lengths of light. As neither TNT nor RDX possesses either of
these attributes, chemical modification of the explosive is
required to obtain a coloured derivative that possesses the
functionality needed to enable strong interaction with a
SERRS metal substrate. We have recently described the devel-
2-Amino-4,6-dinitrotoluene [1]. To a vigorously stirred solu-
tion of TNT (4 g, 17.6 mmol) in glacial acetic acid (88 mL)
under argon at room temperature was added four portions
of iron powder-325 mesh (3.28 g, 58.6 mmol) over two hours,
by which time TLC (A) indicated the conversion of starting
material. To the solution was added distilled water (80 mL),
which caused the precipitation of a bright yellow flocculent
solid. The solid was collected by filtration under pressure,
washed with copious amounts of water and dried at the pump
to leave a mixture of 1 and 2 (2.6 g, 75% combined yield).
Recrystallisation of this mixture from ethanol afforded 1 (1
ꢀ1
g, 29% recrystallised yield). R
NH ), 3387 (sym NH ), 1635, 1519 (asym NO
NO ). H NMR (acetone-d ) d 2.30 (3H, s, CH ), 5.80 (2H, s,
NH ), 7.80 (2H, s, ArH). C NMR (acetone-d ) d 13.91
(CH ), 105.54 (CNH ), 111.04 (CMe), 121.89 (CH), 147.24
), 152.50 (CNO ). m/z (EI) 197.04335
:C,
f
(A) 0.71. nmax/cm 3479 (asym
2
2
2
), 1341 (sym
2
1
opment of synthetic routes to such highly coloured TNT and
2
6
3
3
RDX derivatives suitable for SERRS analysis and reported
on the optimisation of their SERRS response.
13
2
6
3
2
Herein, we report on the crystal structures of the main
amino and hydroxyamino products formed upon initial
selective reduction of TNT, 2-amino-4,6-dinitrotoluene [1],
(CH), 150.42 (CNO
2
2
þ
[C
7
H N
7 3
O
4
(M) < 1.5 ppm]. Anal. Calcd for C
H
7 7
3
N O
4
42.64; H, 3.55; N, 21.32. Found C, 42.32; H, 3.21; N, 21.34%.
4-amino-2,6-dinitrotoluene [2] and 2-hydroxyamino-4,6-dini-
trotoluene [3]. In TNT contaminated environments these
reduction products are formed by the action of bacterial
nitroreductase and, although they contribute significantly
to the toxicity of contaminated soil, they are necessary inter-
4-Amino-2,6-dinitrotoluene [2]. The general procedure was as
per compound 1. The crude mixture of 1 and 2 was extracted
repeatedly from ethanol to afford a small quantity of 2 as thick
ꢀ
1
yellow/brown needle crystals. R
(asym NH ), 3387 (sym NH ), 1635, 1519 (asym NO
). H NMR (acetone-d ) d 2.29 (3H, s, CH
(2H, s, NH ), 7.38 (2H, s, ArH). m/z (EI) 197.04362
f
(A) 0.71. nmax/cm 3479
), 1341
), 5.71
mediates en route to the non-toxic and fully reduced 2,4,
1
-triaminotoluene. The molecular recognition properties of
2
2
2
1
6
these species are thus of interest with regard to their binding
(sym NO
2
6
3
2
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 1 6 1 – 1 6 5
161

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þ
[
4
C
7
H
7
N
3
O
4
(M) < 0.2 ppm]. Anal. Calcd for C
2.64; H, 3.55; N, 21.32. Found C, 42.01; H, 3.39; N, 20.78.
7
H
7
N
3
O
4
: C,
Table 1 Crystallographic data
1
2
3
2
-Hydroxylamino-4,6-dinitrotoluene [3]. To a stirred solution
Formula
C
7
H
7
N
3
O
4
C
197.16
7
H
7
N
3
O
4
7 7 3 5
C H N O
of TNT (1.4 g, 6.16 mmol) in ethyl acetate (20 mL) was added
a slurry of stannous chloride (4.2 g, 22.22 mmol) in HCl (7.5
mL). An immediate yellow colour resulted. Stirring was con-
tinued until TLC (A) and ninhydrin development indicated
the complete conversion of starting materials. The acidic solu-
tion was made basic by addition of NaOH solution (1 M) and
then extracted with saturated potassium chloride solution
(4 ꢁ 10 mL). The organic layer was dried over sodium sulfate
and purified by column chromatography, eluting with dichlor-
omethane to afford 3 as a yellow/orange solid (0.5 g, 38%).
Crystallisation from chloroform gave 3 as fine orange needles
Formula weight
Crystal system
Space group
197.16
Monoclinic
P2 /a
213.16
Monoclinic
P2 /c
Triclinic
¯
P1
1
1
˚
a/A
6.7072(5)
16.0387(11)
8.1083(5)
8.1036(3)
8.0502(3)
15.0980(4)
3.9219(1)
16.4446(5)
˚
b/A
c/A˚
14.2752(5)
75.097(2)
74.059(2)
78.453(5)
847.35(5)
4
ꢂ
a/
ꢂ
ꢂ
b/
91.160(4)
116.586(2)
g/
V/A
˚
3
872.07(10)
4
295
870.77(4)
4
150
Z
T/K
1
(B) 0.18. H NMR (acetone-d
150
54.94
(
CH ), 8.04 (1H, s, ArH), 8.19 (1H, s, ArH), 8.39 (1H, s,
0.22 g). R
f
6
) d 2.29 (3H, s,
ꢂ
2y max./
50.04
7058
1515
0.034
0.0645
0.1835
1111
143
57.20
10574
2227
0.057
0.0417
0.1120
1628
145
3
Refl. measured
Refl. unique
13402
3812
0.036
OH), 8.42 (1H, s, NH). m/z (EI) 213.03817 [C
(
7
H N
7 3
O
M) < 1.9 ppm]. Anal. Calcd for C H N O : C, 39.43; H,
5
þ
7
7
3
5
R
R1
int
3
.28; N, 19.72. Found C, 38.02; H, 2.07; N, 18.84.
0.0611
0.1852
3221
wR2
Crystallography
Refl. observed
Parameters
GoF
271
1.122
Single crystal measurements on 1, 2 and 3 were carried out on
a Nonius Kappa CCD diffractometer using MoKa radiation,
1.100
1.042
˚
l ¼ 0.71073 A. All non-disordered, non-H-atoms for 2 and 3
were refined anisotropically and the H-atoms bonded to N
or O were refined isotropically. All other H-atoms were placed
in calculated positions and in riding modes. The structures
the SOF’s accurately, the structure was solved using different
fixed values of the SOF’s and the solution returning the best
fit to the data (Table 2, Model 4) was taken to be the most
probable solution.
A single crystal data collection on 1 was subsequently
repeated, but this time with the sample temperature held at
2
were refined against F to convergence using the SHELXL-
9
4
7 program. Specific crystallographic data and refinement
parameters are given in Table 1.y
Initial attempts to solve the structure of 1 from single crystal
data collected at 123 K failed. The problem was investigated
by collecting X-ray powder diffraction (XRPD) data from a
polycrystalline sample of 1 contained in a 1 mm capillary at
2
93 K. The structure solved and refined satisfactorily to give
SOF’s for the O-atoms of the 6-nitro group equal to
9.8(8) : 20.2(8), in good agreement with the XRPD data.
7
The solution and refinement details were as for 2 and 3, with
the O-atoms of the minor disordered component refined iso-
tropically.
5
station BM16 of the European Synchrotron Radiation Facil-
˚
ity, Grenoble (l ¼ 0.8000 A). At 105 K the sample was extre-
mely line-broadened, whereas at 293 K the pattern exhibited
acceptably sharp diffraction features (see A comparison of sin-
gle crystal and XRPD analyses of crystal structure 1, below). A
full data set was therefore collected at 293 K with a view to sol-
ving the crystal structure. An appropriate data collection
scheme similar to the one described in ref. 6 was employed
in order to increase preferentially the quality of short d-spacing
reflections and thus increase the probability of solving the
structure. The data were indexed to a monoclinic cell
Results and discussion
Molecular structures
1
As in the known structures of TNT and other nitro-aro-
0
1
1
matics, the major deviations from idealised aromatic geome-
try in the molecular structures of 1, 2 and 3 include a marked
widening of the internal ring angles at the C-atoms bonded to
˚
ꢂ
[
˚
a ¼ 6.703, b ¼ 16.031, c ¼ 8.106 A, b ¼ 91.034 , V ¼ 870.9
ꢂ
ꢂ
3
7
nitro groups, with angles ranging from 123.3(2) to 125.8(2) .
Of the other internal angles, only the angle at the C-atom
A ] using DICVOL91, with promising figures of merit,
M(23) ¼ 30, F(23) ¼ 161. The volume of the unit cell sug-
gested Z ¼ 4 and a preliminary examination of the predicted
peak positions for this cell against the measured data indicated
ꢂ
bonded to the hydroxyamine group in 3 ( ¼ 121.28(13) ) is sig-
ꢂ
nificantly greater than 120 ; the remaining angles tend to be
equal to or less than 120 , reaching a minimum of 111.6(2)
at C1 in 2 (Table 3).
ꢂ
ꢂ
that the space group was P2 /a. Diffraction data in the range
1
1.5–25.0 2y (equating to ꢃ1.8 A resolution) were fitted using
the Pawley method in space group P2 /a using DASH to give
ꢂ
˚
2
These marked distortions from the ideal sp geometry, ran-
8
1
ꢂ
ꢂ
2
ging from 111.6(2) to 125.8(2) , are in fact entirely in keeping
a profile w of 7.6, with no significant misfit in the pattern. The
crystal structure was then solved using the simulated annealing
9
procedure described previously that is now implemented in
DASH.
2
Table 2 Compound 1: profile w and correlated integrated intensities
2
w
input models with differing SOF’s for the O-atoms of the 6-nitro
values resulting from DASH structure solution runs utilising six
A satisfactory fit to the data could not be obtained with a
structural model in which all atoms occupied fully ordered
positions. However, the fit to the data improved significantly
when the 6-nitro group was treated as being disordered. Each
O-atom was allowed to occupy two separate positions with site
occupancy factors (SOF’s) constrained to sum to unity. Since
the amount of useable diffraction data was insufficient to refine
2
group. Minimum w values were achieved with Model 4
2
2
Model
SOF’s
Profile w
Intensities w
1
2
3
4
5
6
100 : 0
90 : 10
80 : 20
70 : 30
60 : 40
50 : 50
41
36
33
32
33
34
203
174
157
154
160
163
y CCDC reference numbers 220762–220764. See http://www.rsc.org/
suppdata/nj/b3/b309792g/ for crystallographic data in .cif or other
electronic format.
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
162
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 1 6 1 – 1 6 5

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1
2
with expectations based on Domenicano’s assessment of
structural substituent effects in benzene derivatives. Following
Domenicano and utilising the angular substituent parameters
between TNT polymorphs that impact upon the explosive’s
1
0
stability and use in the solid-state. In 1, 2 and 3 we have
replaced one of TNT’s weakly hydrogen-bond accepting nitro
groups with a strong hydrogen-bond donating group. The con-
sequence of this is not only to introduce a stronger hydrogen-
bonding network, but also that all three new structures display
face-to-face ring stacking not seen in TNT. Both amino com-
pounds 1 and 2 form layer structures with extensive hydro-
gen-bonding (both N–Hꢅ ꢅ ꢅO and (ar)C–Hꢅ ꢅ ꢅO interactions)
that occurs exclusively within the layers (Fig. 3). Compound
1 shows a simple sheet structure with all layers mutually paral-
lel and perpendicular to the a axis. However 2, which has two
molecular conformations A and B per asymmetric unit, has a
more complicated AABB layering with each layer approxi-
mately perpendicular to the c axis. The molecules of the neigh-
bouring A and B sheets (Fig. 3) are roughly parallel in contrast
to the anti-parallel arrangement found across the double layers
AA and BB.
1
2
for –CH
3
, –NO
2
and –NH
2
,
it can be seen that ten of the
twelve independent pairs of predicted and observed internal
ꢂ
ring angles in 1 and 2 agree to within three e.s.d’s (ꢄ1 ). The
remaining two observed angles (at C1 and C4 in 2) are both
1.4 narrower than predicted. This discrepancy may be due
ꢂ
to a ‘‘push–pull’’ effect with substituents interacting coopera-
tively through the aromatic ring, such that the overall observed
1
2,13
effect is greater than the expected sum of parts.
dictions for angular deviations in 3 are not possible as a search
Similar pre-
1
4
of the Cambridge Structural Database found no examples of
aromatic hydroxyamines. However, a useful comparison can
be made between 1 and 3. Replacing NH in 1 with NHOH
2
ꢂ
in 3 causes the internal angle at C2 to widen by 1.9 and the
ꢂ
angle at C3 to narrow by 1.6 (the other internal angles agree
to within two e.s.d’s). This suggests that the NHOH group has
1
2
considerably less electron-donating character than NH2 , as
would be expected on simple chemical grounds.
In both 1 and 2 these internally hydrogen-bonded layers are
bound to the next layer by offset face-to-face p-stacking. 3 is of
a markedly different structural type (Fig. 4). A simple transla-
tion along b gives stacks of aromatic rings with a large face-to-
Compound 2 has a non-crystallographic mirror plane run-
ning through C7C1C4N2 in Fig. 1, which is rendered to
emphasise the non-coplanarity of the nitro groups to the aro-
matic ring. In 1 and 3 (Fig. 2), the nitro groups ortho to the
methyl group are similarly twisted out of the ring plane, while
the nitro groups para to methyl are essentially coplanar with
the ring (Table 3). This difference is attributable to steric inter-
action between adjacent methyl and nitro groups. An interest-
ing consequence of the distorted geometry at C1 in 2 is the fact
that the methyl C-atom is displaced out of the ring plane by a
˚
face spacing of 3.922 A (cf. the much shorter face-to-face dis-
˚
tances (3.3–3.5 A) in 1 and 2). Adjacent stacks along the c
direction are tilted with respect to each other and are bound
into pairs of stacks by the strong O–Hꢅ ꢅ ꢅO hydrogen-bonds
that zig-zag between neighbouring hydroxy groups. The amine
H-atom forms a similarly patterned, but longer range, connec-
tion to the 4-nitro group of a second neighbouring stack.
Given the polynitro nature of TNT and its derivatives
reported herein, we expected to find evidence of nitro–nitro
˚
significant amount in each independent molecule (0.175(3) A
˚
and 0.145(3) A cf. 0.024(4) A in 1 and 0.039(2) A in 3).
˚
˚
15
Oꢅ ꢅ ꢅN contacts as described by Wozniak et al. However,
upon examination of the twenty independent nitro groups of
TNT and its derivatives, only those in 2 had Oꢅ ꢅ ꢅN contacts
shorter than (the formally repulsive) Oꢅ ꢅ ꢅO or Oꢅ ꢅ ꢅC contacts.
Intermolecular interactions
˚
The crystal packing of TNT is of considerable significance as it
is perceived to govern the subtle and complex relationships
The closest such contact occurs in 3 (O5ꢅ ꢅ ꢅO5* ¼ 2.806 A cf.
˚
16
˚
17
sum of van der Waals radii ¼ 3.04 A to 3.12 A ), but, even
Table 3 Selected angles (degrees) for 1, 2 and 3
1
2
3
C2-C1-C6
C2-C1-C7
C6-C1-C7
C1-C2-C3
C1-C2-N1
C3-C2-N1
C2-C3-C4
C3-C4-C5
C3-C4-N2
C5-C4-N2
C4-C5-C6
C5-C6-C1
C5-C6-N3
C1-C6-N3
C7C1C2N1
C7C1C6N3
C3C4N2O2
C1C2N1O1
C1C6N3O4
116.5(2)
118.3(2)
125.1(2)
119.4(2)
120.6(2)
120.0(2)
119.9(2)
123.3(2)
118.3(2)
118.4(2)
115.6(2)
125.3(2)
115.2(2)
119.5(2)
0.7(4)
111.7(2)
124.0(2)
124.1(2)
125.6(2)
120.0(2)
114.4(2)
119.8(2)
117.3(2)
121.3(2)
121.4(2)
120.1(2)
125.6(2)
114.6(2)
119.9(2)
8.5(3)
111.6(2)
124.3(2)
123.9(2)
125.7(2)
119.8(2)
114.6(2)
119.9(2)
117.2(2)
120.9(2)
121.9(2)
119.8(2)
125.8(2)
114.9(2)
119.2(2)
ꢀ9.5(4)
12.1(4)
116.1(1)
119.9(1)
124.0(1)
121.3(1)
116.6(1)
122.1(1)
118.3(1)
123.4(1)
118.3(1)
118.2(1)
115.7(1)
125.1(1)
116.2(1)
118.6(1)
1.9(2)
ꢀ2.6(5)
178.4(3)
—
ꢀ8.5(3)
—
36.3(3)
4.0(2)
—
ꢀ34.6(3)
38.2(3)
ꢀ2.9(2)
ꢀ169.7(1)
54.6(2)
a
ꢀ51.2(5)
ꢀ38.2(3)
a
SOF(O4) ¼ 79.8(8)
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 1 6 1 – 1 6 5
163

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Fig. 1 The structure of one of the crystallographically independent
molecules of 2, with ellipsoids rendered at 50% probability.
taken as a group, the formally repulsive Oꢅ ꢅ ꢅO contacts are
typically shorter than the formally attractive Nꢅ ꢅ ꢅO contacts
Fig. 3 A section of the hydrogen-bonded B layer of 2.
˚
˚
(
viour of the nitro group was recently noted by Szcz e˛ sna and
Nꢅ ꢅ ꢅO range 3.041 A to 3.102 A). This counter-intuitive beha-
1
8
Urba n´ czyk-Lipkowska, who suggested that short Oꢅ ꢅ ꢅO con-
tacts were favoured by intramolecular resonance assisted
hydrogen-bonding (RAHB). This does not seem applicable
to the structures of TNT and its derivatives, which have no
intramolecular RAHB. In these compounds, an anisotropic
van der Waals radius for nitro-O seems a plausible mechan-
ism by which to account for unexpectedly short intermolecular
Oꢅ ꢅ ꢅO contacts.
of the 6-nitro group become disordered across two sites in an
attempt to alleviate this strain.
A comparison of the XRPD and single-crystal structures
(Fig. 6) shows excellent agreement with respect to the position
and orientation of the molecule in the unit cell, and the orien-
tation of the 6-nitro group at higher occupancy. Unsurpris-
ingly, the orientation of the lower occupancy 6-nitro group is
less well determined. Subsequent structure determinations that
included a preferred orientation correction improved the over-
1
9
2
all fit to the data (with a decrease in profile w from ꢃ32 to
A comparison of single crystal and XRPD analyses of crystal
structure 1
ꢃ26), but did not alter the rank order of the disordered models
(as listed in Table 2) or improve on the orientation of the lower
occupancy 6-nitro group.
The XRPD patterns measured for 1 exhibited much broader
peak widths at 105 K than at RT, indicating greater mosiacity.
Lattice parameters measured by single crystal diffraction
Other authors have shown that the results obtained from
global optimisation can sometimes indicate the presence of
˚
20,21
21
Huq and Stephens, for exam-
between RT [a ¼ 6.703, b ¼ 16.031, c ¼ 8.106 A,
conformational disorder.
ꢂ
ꢂ
˚
b ¼ 91.034 ] and 123 K [a ¼ 6.534, b ¼ 15.939, c ¼ 8.061 A,
ple, found that two distinct conformations of ranitidine gave
equally good fits to XRPD data obtained from a polycrystal-
line sample of ranitidine hydrochloride and went on to show
that these matched the conformations found in the disordered
structure determined by single crystal diffraction. Here, we
have taken the approach that residual misfit in the diffraction
pattern derived from a fully ordered model might well arise
from disorder in the actual structure and have used global
optimisation to prove this hypothesis by simultaneously opti-
mising models that include contributions from atoms with
fractional occupancies.
b ¼ 90.195 ] tended to suggest a gradual and reversible mono-
clinic ! orthorhombic transition, with a transition tempera-
ture <123 K (123 K was the lowest sample temperature to
yield useful data). The percentage thermal contraction is great-
est in the a direction, corresponding to a decrease in the dis-
tance between the layers in 1. As the disordered 6-nitro
group projects out of the layer plane (Fig. 5), it is forced closer
to the neighbouring molecular layer at lower temperatures and
the resulting steric strain would appear to lead to increased
mosiaicity. It is also interesting to speculate that the O-atoms
Fig. 2 The structure of 3, with ellipsoids rendered at 50% probabil-
ity.
Fig. 4 Crystal packing in 3 viewed along the b axis.
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
164
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hydrogen-bond donors to TNT results in solid-state structures
with layer architectures as opposed to the herring bone motifs
seen in TNT itself. 1 and 2 form hydrogen bonded sheets con-
nected via N–H and C–H hydrogen-bond donation to nitro
acceptors. These sheets are held to each other by p-stacking
and by dipole–dipole interactions between nitro groups. The
stronger hydrogen-bonding in 3 (with its donating and accept-
ing NHOH group) gives a different structure dominated by
NHOH–NHOH dimers.
Fig. 5 Crystal structure 1, showing the disordered 6-nitro group pro-
jecting between parallel sheets of molecules.
Acknowledgements
We gratefully acknowledge the Home Office UK for financial
support for CJM, Sally Price of the UCL Centre for Theoreti-
cal and Computational Chemistry for helpful input and the
ESRF for providing a beamtime award (CH849).
Conclusions
In determining the disordered structure of 1 from XRPD data,
chemical intuition plays an essential role in identifying the dis-
ordered atoms, which can then be correctly incorporated into
the structure solution model. This approach is distinct from
the more general one of using difference Fourier maps to com-
plete a partial structure solution, the latter being problematic
when low-resolution, low quality XRPD data makes map
interpretation difficult. The combination of chemical intuition
and molecular connectivity, on the other hand, can clearly pro-
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