Isomers and polymorphs of (E,E)-1,4-bis(nitrophenyl)-2,3-diaza-1,3-butadienes

Article abstract of DOI:10.1107/S010876810601439X

The structures of five of the possible six isomers of (E,E)-1,4-bis(nitrophenyl)-2,3-diaza-1,3-butadiene are reported, including two polymorphs of one of the isomers. (E,E)-1,4-Bis(2-nitrophenyl)-2,3-diaza-1,3-butadiene, C₁₄H ₁₀N₄O₄ (I), crystallizes in two polymorphic forms (Ia) and (Ib) in which the molecules lie across centres of inversion in space groups P2₁/n and P2₁/c, respectively: the molecules in (Ia) and (Ib) are linked into chains by aromatic π...π stacking interactions and C-H...π(arene) hydrogen bonds, respectively. Molecules of (E,E)-1-(2-nitrophenyl)-4-(3-nitrophenyl)-2,3-diaza-1,3-butadiene (II) are linked into sheets by two independent C-H...O hydrogen bonds. The molecules of (E,E)-1,4-bis(3-nitrophenyl)-2,3-diaza-1,3-butadiene (III) lie across inversion centres in the space group P2₁/n, and a combination of a C-H...O hydrogen bond and a π...π stacking interaction links the molecules into sheets. A total of four independent C-H...O hydrogen bonds link the molecules of (E,E)-1-(3-nitrophenyl)-4-(4-nitrophenyl)-2,3-diaza-1,3-butadiene (IV) into sheets. In (E,E)-1,4-bis(4-nitrophenyl)-2,3-diaza-1,3-butadiene (V) the molecules, which lie across centres of inversion in the space group P2 ₁/n, are linked by just two independent C-H...O hydrogen bonds into a three-dimensional framework.

Full text of DOI:10.1107/S010876810601439X

research papers
Acta Crystallographica Section B
Structural
Isomers and polymorphs of (E,E)-1,4-bis(nitro-
Science
phenyl)-2,3-diaza-1,3-butadienes
ISSN 0108-7681
Christopher Glidewell,a* John N.
Low,b Janet M. S. Skakleb and
James L. Wardellc
The structures of five of the possible six isomers of (E,E)-
1,4-bis(nitrophenyl)-2,3-diaza-1,3-butadiene are reported,
including two polymorphs of one of the isomers. (E,E)-1,4-
Bis(2-nitrophenyl)-2,3-diaza-1,3-butadiene, C14H10N4O4 (I),
crystallizes in two polymorphic forms (Ia) and (Ib) in which
the molecules lie across centres of inversion in space groups
P21/n and P21/c, respectively: the molecules in (Ia) and (Ib)
are linked into chains by aromatic ꢀꢀ ꢀ ꢀꢀ stacking interactions
and C—Hꢀ ꢀ ꢀꢀ(arene) hydrogen bonds, respectively. Mole-
cules of (E,E)-1-(2-nitrophenyl)-4-(3-nitrophenyl)-2,3-diaza-
1,3-butadiene (II) are linked into sheets by two independent
C—Hꢀ ꢀ ꢀO hydrogen bonds. The molecules of (E,E)-1,4-bis(3-
nitrophenyl)-2,3-diaza-1,3-butadiene (III) lie across inversion
centres in the space group P21/n, and a combination of a C—
Hꢀ ꢀ ꢀO hydrogen bond and a ꢀꢀ ꢀ ꢀꢀ stacking interaction links
the molecules into sheets. A total of four independent C—
Hꢀ ꢀ ꢀO hydrogen bonds link the molecules of (E,E)-1-(3-
nitrophenyl)-4-(4-nitrophenyl)-2,3-diaza-1,3-butadiene (IV)
into sheets. In (E,E)-1,4-bis(4-nitrophenyl)-2,3-diaza-1,3-buta-
diene (V) the molecules, which lie across centres of inversion
in the space group P21/n, are linked by just two independent
C—Hꢀ ꢀ ꢀO hydrogen bonds into a three-dimensional frame-
work.
Received 28 February 2006
Accepted 20 April 2006
aSchool of Chemistry, University of St Andrews,
St Andrews, Fife KY16 9ST, Scotland,
bDepartment of Chemistry, University of
Aberdeen, Meston Walk, Old Aberdeen
AB24 3UE, Scotland, and cInstituto de Quımica,
´
´
ˆ
Departamento de Quımica Inorganica, Univer-
sidade Federal do Rio de Janeiro, CP 68563,
21945-970 Rio de Janeiro-RJ, Brazil
Correspondence e-mail: cg@st-andrews.ac.uk
1. Introduction
We have recently reported the supramolecular structures of
the three isomeric (E,E)-1-(2-iodophenyl)-4-(nitrophenyl)-
2,3-diaza-1,3-butadienes (Glidewell, Low, Skakle & Wardell,
2005). In this series, the 2-nitro isomer forms chains, the 3-
nitro isomer forms a three-dimensional framework structure,
while the 4-nitro isomer forms a sheet structure. In each
isomer, a different array of direction-specific intermolecular
interactions is manifest: an iodoꢀ ꢀ ꢀnitro interaction in the 2-
nitro isomer, C—Hꢀ ꢀ ꢀO and C—Hꢀ ꢀ ꢀI hydrogen bonds and
aromatic ꢀꢀ ꢀ ꢀꢀ stacking interactions in the 3-nitro isomer, and
a C—Hꢀ ꢀ ꢀO hydrogen bond and an iodoꢀ ꢀ ꢀnitro interaction in
the 4-nitro isomer. Intrigued by the changes in intermolecular
interactions and the corresponding structural changes conse-
quent upon a simple positional change of a single substituent,
we have developed the earlier study to an even simpler
series of positional isomers, namely the isomeric (E,E)-
1,4-bis(nitrophenyl)-2,3-diaza-1,3-butadienes, O2NC6H4CH
N—N CHC6H4NO2, and again we observe wide structural
variation. We report here the molecular and supramolecular
structures of five of the possible six isomeric 1,4-bis(nitro-
phenyl)-2,3-diaza-1,3-butadienes, compounds (I)–(V) (see
Scheme, and Figs. 1–6) and, in addition, we have identified two
polymorphs of 1,4-bis(2-nitrophenyl)-2,3-diazabutadiene (I)
(Figs. 1 and 2), but we have consistently failed in attempts
# 2006 International Union of Crystallography
Printed in Great Britain – all rights reserved
666 doi:10.1107/S010876810601439X
Acta Cryst. (2006). B62, 666–675

research papers
to synthesize the sixth isomer 1-(2-nitrophenyl)-4-(4-nitro-
phenyl)-2,3-diaza-1,3-butadiene (VI). Both polymorphs of (I)
are monoclinic, but their b-axis vectors differ by a factor of
more than two: we denote the polymorph with the shorter b
axis as (Ia) and that with the longer b axis as (Ib). The
structure of the polymorph denoted here as (Ia) was deter-
mined some years ago (Hsu et al., 1993) using ambient-
temperature diffraction data: however, no discussion of the
supramolecular aggregation was given; in particular, the
occurrence of the ꢀꢀ ꢀ ꢀꢀ stacking interactions (see x3.2.1) went
unreported.
Figure 1
The molecule of polymorph (Ia) showing the atom-labelling scheme.
Displacement ellipsoids are drawn at the 30% probability level, and the
atoms marked with ‘a’ are at the symmetry position (1
ꢂ
x,
1 ꢂ y, 1 ꢂ z).
Figure 2
The molecule of polymorph (Ib) showing the atom-labelling scheme.
Displacement ellipsoids are drawn at the 30% probability level, and the
atoms marked with ‘a’ are at the symmetry position (1
ꢂ
x,
1 ꢂ y, 1 ꢂ z).
benzaldehyde hydrazone with 2-nitro- or 4-nitrobenzaldehyde
yielded isomers (II) and (IV); (II) was recrystallized from
methanol, m.p. 471–473 K after partial liquifaction at 421–
423 K; (IV) was recrystallized from 1,2-dichloroethane, m.p.
480–483 K. Polymorph (Ib) was isolated by recrystallization,
from 1,2-dichloroethane, of the initial product obtained by
reaction of 2-nitrobenzaldehyde hydrazone and 2-iodobenz-
aldehyde, m.p. 443–446 K, following loss of crystallinity at
423 K. Despite the reasonably straightforward preparations of
the 2,30 and 3,40 isomers (II) and (IV), numerous attempts to
prepare a sample of the 2,40 isomer (VI) (see Scheme) have
consistently proved fruitless: using either the reaction of 2-
nitrobenzaldehyde with 4-nitrobenzaldehyde hydrazone, or
2. Experimental
2.1. Synthesis
Isomers (Ia), (III) and (V) were obtained by heating under
reflux a mixture of the appropriate nitrobenzaldehyde
(3 mmol) and hydrazine hydrate (1.5 mmol) in methanol
(20 cm3) for 30 min, and then leaving the reaction solution at
room temperature for 24 h. The products were collected and
recrystallized from 1,2-dichloroethane: m.p.s (Ia) 483–486 K,
(III) 475–477 K, (V) >500 K. Similar reactions of 3-nitro-
ꢁ
Acta Cryst. (2006). B62, 666–675
Christopher Glidewell et al.
(E,E)-1,4-Bis(nitrophenyl)-2,3-diaza-1,3-butadienes 667

research papers
Figure 5
The molecule of isomer (IV) showing the atom-labelling scheme.
Displacement ellipsoids are drawn at the 30% probability level.
Figure 3
The molecule of isomer (II) showing the atom-labelling scheme.
Displacement ellipsoids are drawn at the 30% probability level.
Figure 6
The molecule of isomer (V) showing the atom-labelling scheme.
Displacement ellipsoids are drawn at the 30% probability level, and
the atoms marked with ‘a’ are at the symmetry position (1 ꢂ x, 1 ꢂ y, 1 ꢂ
z).
For each of (Ia), (III) and (V), the space group P21/n was
uniquely assigned from the systematic absences; likewise the
space group P21/c was uniquely assigned for (Ib). For isomer
(II) the systematic absences permitted P21 and P21/m as
possible space groups: from a consideration of the unit-cell
volume and the likely value of Z0, the space group P21 was
selected and subsequently confirmed by the structure analysis.
For isomer (IV), the systematic absences permitted Cc and
C2/c as possible space groups: C2/c was selected and subse-
quently confirmed by the structure analysis.
The structures were solved by direct methods and refined
with all data on F2. A weighting scheme based upon P = [Fo2 +
2Fc2]/3 was employed in order to reduce statistical bias
(Wilson, 1976). All H atoms were located from difference
maps and then treated as riding atoms with C—H distances of
Figure 4
The molecule of isomer (III) showing the atom-labelling scheme.
Displacement ellipsoids are drawn at the 30% probability level, and
the atoms marked with ‘a’ are at the symmetry position (1 ꢂ x, 1 ꢂ y, 1 ꢂ
z).
that of 4-nitrobenzaldehyde with 2-nitrobenzaldehyde hydra-
zone, the only crystalline products obtained were the
symmetrical isomers (I) and (V). The reasons for this beha-
viour, so different from that in the preparations of isomers (II)
and (IV), are entirely unclear.
˚
0.95 A and with Uiso(H) = 1.2Ueq(C). In the absence of
2.2. Data collection, structure solution and refinement
significant anomalous dispersion, the Flack parameter (Flack,
1983) for (II) was inconclusive (Flack & Bernardinelli, 2000):
hence the Friedel-equivalent reflections were merged prior to
the final refinements and it was not possible to determine the
correct orientation of the structure relative to the polar-axis
direction (Jones, 1986). In isomer (Ib), the maximum residual
Diffraction data for compounds (I)–(III) and (V) were
collected at 120 (2) K using a Nonius–Kappa CCD diffract-
ometer; in all these cases graphite-monochromated Mo Kꢁ
˚
radiation (ꢂ = 0.71073 A) was employed. Data for (IV) were
collected at 120 (2) K using a Bruker SMART APEX2
ꢂ3
˚
˚
˚
density, 1.438 e A , is located 0.93 A from the C4 atom, lying
almost equidistant from H4 and H5, while the largest hole,
diffractometer and synchrotron radiation (ꢂ = 0.6778 A).
Other details of cell data, data collection and refinement are
summarized in Table 1, together with details of the software
employed.
ꢂ3
˚
˚
ꢂ0.306 e A , is located 0.62 A from N2: no plausible disorder
model can be developed to take account of these extrema.
ꢁ
668 Christopher Glidewell et al.
(E,E)-1,4-Bis(nitrophenyl)-2,3-diaza-1,3-butadienes
Acta Cryst. (2006). B62, 666–675

research papers
Table 1
Experimental table.
(Ia)
(Ib)
(II)
Crystal data
Chemical formula
Mr
C14H10N4O4
298.26
C14H10N4O4
298.26
C14H10N4O4
298.26
Cell setting, space group
Temperature (K)
Monoclinic, P21/n
120 (2)
9.1379 (4), 6.1776 (3), 11.7682 (4)
93.853 (3)
662.82 (5)
2
1.494
Mo Kꢁ
1511
Monoclinic, P21/c
120 (2)
7.7809 (2), 14.7825 (6), 6.2196 (2)
113.106 (2)
658.00 (4)
2
1.505
Mo Kꢁ
1503
Monoclinic, P21
120 (2)
7.8036 (2), 7.0914 (3), 12.3424 (4)
101.742 (2)
668.72 (4)
2
1.481
Mo Kꢁ
1653
˚
a, b, c (A)
ꢃ (ꢃ)
3
˚
V (A )
Z
Dx (Mg mꢂ3
)
Radiation type
No. of reflections for cell
parameters
ꢄ range (ꢃ)
3.5–27.5
0.11
3.2–27.5
0.11
3.3–27.5
0.11
ꢅ (mmꢂ1
)
Crystal form, colour
Crystal size (mm)
Block, yellow
0.46 ꢄ 0.34 ꢄ 0.18
Block, yellow
0.48 ꢄ 0.22 ꢄ 0.08
Blade, orange
0.50 ꢄ 0.32 ꢄ 0.12
Data collection
Diffractometer
Bruker–Nonius 95 mm CCD
camera on ꢆ-goniostat
’ and ! scans
Multi-scan
Bruker–Nonius 95 mm CCD
camera on ꢆ-goniostat
’ and ! scans
Multi-scan
Bruker–Nonius 95 mm CCD
camera on ꢆ-goniostat
’ and ! scans
Multi-scan
Data collection method
Absorption correction
Tmin
Tmax
0.967
0.980
8093, 1511, 1232
0.957
0.991
10 780, 1503, 1222
0.936
0.987
7771, 1653, 1519
No. of measured, independent and
observed reflections
Criterion for observed reflections
Rint
I > 2ꢇ(I)
0.034
27.5
I > 2ꢇ(I)
0.043
27.5
I > 2ꢇ(I)
0.031
27.5
ꢄmax (ꢃ)
Range of h, k, l
ꢂ10 ) h ) 11
ꢂ7 ) k ) 8
ꢂ15 ) l ) 15
ꢂ9 ) h ) 10
ꢂ19 ) k ) 19
ꢂ8 ) l ) 8
ꢂ10 ) h ) 10
ꢂ8 ) k ) 9
ꢂ15 ) l ) 14
Refinement
Refinement on
F2
F2
0.060, 0.160, 1.02
1503
100
Constrained to parent site
w = 1/[ꢇ2(Fo2) + (0.0754P)2 +
0.8974P], where P = (Fo2 + 2Fc2)/3
<0.0001
F2
0.040, 0.107, 1.25
1653
199
Constrained to parent site
w = 1/[ꢇ2(Fo2) + (0.0658P)2 +
0.0096P], where P = (Fo2 + 2Fc2)/3
<0.0001
R[F2 > 2ꢇ(F2)], wR(F2), S
No. of reflections
No. of parameters
H-atom treatment
Weighting scheme
0.039, 0.124, 1.00
1511
100
Constrained to parent site
w = 1/[ꢇ2(Fo2) + (0.093P)2 +
0.0092P], where P = (Fo2 + 2Fc2)/3
<0.0001
(Á/ꢇ)max
Áꢈmax, Áꢈmin (e A
ꢂ3
˚
)
0.23, ꢂ0.29
1.44, ꢂ0.31
0.27, ꢂ0.31
(III)
(IV)
(V)
Crystal data
Chemical formula
Mr
C14H10N4O4
298.26
C14H10N4O4
298.26
C14H10N4O4
298.26
Cell setting, space group
Temperature (K)
Monoclinic, P21/n
120 (2)
7.0128 (4), 7.6318 (5), 12.8037 (5)
105.825 (3)
659.29 (6)
2
1.502
Mo Kꢁ
1507
Monoclinic, C2/c
120 (2)
30.865 (3), 4.7660 (5), 21.736 (2)
123.926 (2)
2653.1 (5)
8
1.493
Synchrotron
2789
Monoclinic, P21/n
120 (2)
3.7318 (2), 7.2442 (3), 23.9367 (10)
94.053 (2)
645.48 (5)
2
1.535
Mo Kꢁ
1479
˚
a, b, c (A)
ꢃ (ꢃ)
3
˚
V (A )
Z
Dx (Mg mꢂ3
)
Radiation type
No. of reflections for cell
parameters
ꢄ range (ꢃ)
3.1–27.6
0.11
3.0–28.8
0.11
2.9–27.6
0.12
ꢅ (mmꢂ1
)
Crystal form, colour
Crystal size (mm)
Plate, yellow
0.43 ꢄ 0.30 ꢄ 0.08
Lath, yellow
0.10 ꢄ 0.06 ꢄ 0.01
Lath, yellow
0.40 ꢄ 0.10 ꢄ 0.01
Data collection
Diffractometer
Bruker–Nonius 95 mm CCD
camera on ꢆ goniostat
’ and ! scans
Bruker SMART APEX2 CCD
diffractometer
Fine-slice ! scans
Multi-scan
Bruker–Nonius 95 mm CCD
camera on ꢆ goniostat
’ and ! scans
Data collection method
Absorption correction
Multi-scan
Multi-scan
ꢁ
Acta Cryst. (2006). B62, 666–675
Christopher Glidewell et al.
(E,E)-1,4-Bis(nitrophenyl)-2,3-diaza-1,3-butadienes 669

research papers
Table 1 (continued)
(III)
(IV)
(V)
Tmin
Tmax
0.969
0.991
7854, 1507, 1095
0.980
0.999
14 589, 3961, 2817
0.949
0.999
6443, 1479, 1239
No. of measured, independent and
observed reflections
Criterion for observed reflections
Rint
I > 2ꢇ(I)
0.061
27.6
I > 2ꢇ(I)
0.034
29.0
I > 2ꢇ(I)
0.049
27.6
ꢄmax (ꢃ)
Range of h, k, l
ꢂ9 ) h ) 9
ꢂ9 ) k ) 9
ꢂ16 ) l ) 14
ꢂ43 ) h ) 44
ꢂ6 ) k ) 6
ꢂ30 ) l ) 30
ꢂ4 ) h ) 4
ꢂ9 ) k ) 9
ꢂ30 ) l ) 31
Refinement
Refinement on
F2
F2
0.057, 0.170, 1.09
3961
199
Constrained to parent site
w = 1/[ꢇ2(Fo2) + (0.095P)2 +
1.033P], where P = (Fo2 + 2Fc2)/3
0.001
F2
0.041, 0.110, 1.06
1479
100
Constrained to parent site
w = 1/[ꢇ2(Fo2) + (0.0454P)2 +
0.3185P], where P = (Fo2 + 2Fc2)/3
0.001
R[F2> 2ꢇ(F2)], wR(F2), S
No. of reflections
No. of parameters
H-atom treatment
Weighting scheme
0.044, 0.122, 1.04
1507
100
Constrained to parent site
w = 1/[ꢇ2(Fo2) + (0.068P)2 +
0.1014P], where P = (Fo2 + 2Fc2)/3
<0.0001
(Á/ꢇ)max
Áꢈmax, Áꢈmin (e A )
–3
˚
0.20, ꢂ0.35
0.44, ꢂ0.26
0.24, ꢂ0.24
Computer programs used: COLLECT (Hooft, 1999), APEX2 (Bruker AXS Inc., 2004), DENZO (Otwinowski & Minor, 1997), SAINT (Bruker AXS Inc., 2004), OSCAIL (McArdle,
2003), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), PLATON (Spek, 2003), PRPKAPPA (Ferguson, 1999), SADABS (Sheldrick, 2003).
Table 2
Table 3
Selected hydrogen-bond parameters (A, ).
o
Selected torsional angles (ꢃ).
˚
(a) Centrosymmetric isomers
Parameter
D—Hꢀ ꢀ ꢀA
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
(Ia)
(Ib)
(III)
(V)
(Ib)
C3—H3ꢀ ꢀ ꢀCg1i†
N1i—N1—C7—C1 ꢂ176.75 (11) ꢂ176.8 (2) ꢂ179.28 (14) 179.48 (13)
2.89
3.568 (2)
129
N1—C7—C1—C2
C1—C2—N2—O21
C2—C3—N3—O31
C3—C4—N4—O41
ꢂ146.55 (12) ꢂ149.4 (2)
ꢂ3.0 (2)
178.82 (13)
–
19.17 (15)
21.2 (3)
–
(II)
C14—H14ꢀ ꢀ ꢀO232ii
–
–
–
–
ꢂ3.83 (19)
–
9.71 (19)
2.45
2.51
3.178 (3)
3.289 (3)
134
139
–
C22—H22ꢀ ꢀ ꢀO231iii
(III)
C4—H4ꢀ ꢀ ꢀO32iv
(b) Non-centrosymmetric isomers
Parameter
2.50
3.448 (2)
176
(II)
(IV)
C17—N11—N21—C27
N21—N11—C17—C11
N11—C17—C11—C12
N11—N21—C27—C21
N21—C27—C21—C22
C11—C12—N12—O121
C22—C23—N23—O231
C12—C13—N13—O131
C23—C24—N24—O241
175.13 (18)
ꢂ179.66 (18)
ꢂ159.7 (2)
179.39 (17
165.11 (19)
25.1 (3)
ꢂ172.53 (14)
ꢂ179.43 (13)
6.4 (2)
ꢂ178.92 (14)
ꢂ175.28 (15)
–
(IV)
C14—H14ꢀ ꢀ ꢀO132v
C17—H17ꢀ ꢀ ꢀO242vi
C22—H22ꢀ ꢀ ꢀO131vii
C27—H27ꢀ ꢀ ꢀO131vii
2.44
2.42
2.51
2.53
3.309 (3)
3.262 (2)
3.363 (3)
3.383 (2)
151
147
149
149
ꢂ3.9 (3)
–
(V)
C3—H3ꢀ ꢀ ꢀO41viii
–
–
ꢂ1.5 (2)
2.50
2.47
3.186 (2)
3.343 (2)
129
152
C7—H7ꢀ ꢀ ꢀO42ix
ꢂ0.1 (2)
1
2
Symmetry codes: (i) x; 32 ꢂ y; ꢂ þ z; (ii) 1 þ x; 2 þ y; z; (iii) 1 ꢂ x; 12 þ y; 1 ꢂ z; (iv)
Symmetry code: (i) 1 ꢂ x, 1 ꢂ y, 1 ꢂ z.
3
2
ꢂ1 ꢂ x; ꢂy; 1 ꢂ z;
(v)
1 ꢂ x; ꢂ2 ꢂ y; 1 ꢂ z;
(vi)
ꢂ x; 32 ꢂ y; 1 ꢂ z;
(vii)
1 ꢂ x; 1 þ y; 12 ꢂ z; (viii) ꢂ x; ꢂ þ y; 32 ꢂ z; (ix) 1 þ x; ꢂ1 þ y; z. † Cg1 is the
3
1
2
2
centroid of ring C1–C6.
Supramolecular analyses were made and the diagrams were
prepared with the aid of PLATON (Spek, 2003). Details of
molecular conformations are given in Table 2, and details of
hydrogen-bond dimensions are given in Table 3.1
isomers the central C—C N—N C—C fragment has an all-
transoid conformation and it is essentially planar, as shown by
the leading torsional angles (Table 2). In both polymorphs of
(I), where there is a 2-nitro substituent, the aryl rings are
significantly twisted out of the plane of the central spacer unit,
and the molecular conformations are very similar, as shown by
the leading torsional angles (Table 2). However, in isomers
(III) and (V), containing 3-nitro and 4-nitro substituents,
respectively, the aryl rings are almost coplanar with the spacer
unit. In (III) the nitro group is on the edge of the molecule
remote from the methine C—H bond, whereas in both poly-
morphs of (I) the two groups are on the same edge (Table 2;
3. Results and discussion
3.1. Molecular conformations
In the symmetrically substituted isomers (I), (III) and (V),
the molecules lie across centres of inversion, and in all of the
1 Supplementary data for this paper are available from the IUCr electronic
archives (Reference: BM5032). Services for accessing these data are described
at the back of the journal.
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Figs. 1, 2 and 4). In isomer (II) both of the independent nitro
groups are on the same edges of the molecules as the nearest
methine C—H bond, whereas the 3-nitro group in isomer (IV)
is remote from the corresponding C—H bond (Table 2; Figs. 3
and 5). In all of compounds (I)–(V), the bond lengths and
angles present no unusual features.
each unit cell, but there are no direction-specific interactions
between adjacent chains.
3.2.2. Isomer (II), 1-(2-nitrophenyl)-4-(3-nitrophenyl)-2,3-
diaza-1,3-butadiene. In contrast to the dimorphism observed
for (I), only a single polymorph has been observed for the
isomeric 1-(2-nitrophenyl)-4-(3-nitrophenyl)-2,3-diazabutadi-
ene (II) (Fig. 3). In this isomer the molecules lie in general
positions in the non-centrosymmetric space group P21, but the
molecular skeleton apart from the nitro groups is nearly
centrosymmetric, as shown by the principal torsional angles
(Table 2).
The two-dimensional supramolecular structure of isomer
(II) is built from two independent C—Hꢀ ꢀ ꢀO hydrogen bonds
(Table 3), augmented by a ꢀꢀ ꢀ ꢀꢀ stacking interaction: C—
Hꢀ ꢀ ꢀꢀ(arene) hydrogen bonds are absent, however. The aryl
C22 atom in the molecule at (x, y, z) acts as a hydrogen-bond
donor to the nitro O231 atom in the molecule at (1 ꢂ x, 12 + y, 1
3.2. Supramolecular aggregation
3.2.1. Polymorphs of isomer (I), 1,4-bis(2-nitrophenyl)-2,3-
diaza-1,3-butadiene. The supramolecular aggregation of the
two polymorphs (Ia) and (Ib) of isomer (I) differs signifi-
cantly: the supramolecular aggregation is determined in (Ia)
by an aromatic ꢀꢀ ꢀ ꢀꢀ stacking interaction and in (Ib) by a C—
Hꢀ ꢀ ꢀꢀ(arene) hydrogen bond: ꢀꢀ ꢀ ꢀꢀ stacking interactions are
absent from the structure of (Ib).
The aryl rings in (Ia) at (x, y, z) and (ꢂx, 2 ꢂ y, 1 ꢂ z) are
components of the molecules across the inversion centres at
(0.5, 0.5, 0.5) and (ꢂ0.5, 1.5, 0.5), respectively. These two rings
˚
are strictly parallel with an interplanar spacing of 3.569 (2) A;
˚
the ring–centroid separation is 3.887 (2) A, corresponding to a
˚
nearly ideal centroid offset of 1.539 (2) A. Propagation by
inversion of this interaction then leads to the formation of a ꢀ-
stacked chain of centrosymmetric molecules running parallel
ꢀ
to the [110] direction (Fig. 7).
In polymorph (Ib) the chain structure is generated by a
single C—Hꢀ ꢀ ꢀꢀ(arene) hydrogen bond (Table 3). The aryl C3
atom in the ring at (x, y, z) is part of the molecule centred
across (12, 21, 12): this atom acts as a hydrogen-bond donor to the
aryl ring at (x, 32 ꢂ y, ꢂ + z), which forms part of the molecule
1
2
centred across (12, 1, 0). Propagation of this hydrogen bond
Figure 8
Stereoview of part of the crystal structure of polymorph (Ib) showing the
ꢀ
then forms a zigzag chain running parallel to the [011] direc-
ꢀ
formation of a hydrogen-bonded chain along [011]. For the sake of clarity
the H atoms not involved in the motif shown have been omitted.
tion and generated by the c-glide plane at y = 0.75 (Fig. 8). In
the structures of both (Ia) and (Ib) two chains pass through
Figure 7
Stereoview of part of the crystal structure of polymorph (Ia) showing the
formation of a ꢀ-stacked chain along [110]. For the sake of clarity the H
atoms have all been omitted.
Figure 9
Stereoview of part of the crystal structure of isomer (II) showing the
formation of a hydrogen-bonded C(5) chain along [010]. For the sake of
clarity the H atoms not involved in the motif shown have been omitted.
ꢀ
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ꢂ z), so forming a spiral C(5) chain (Bernstein et al., 1995)
running parallel to the [010] direction and generated by the 21
screw axis along (12, y, 21) (Fig. 9). At the same time, the aryl C14
atom in the molecule at (x, y, z) acts as a hydrogen-bond
donor to the nitro O232 atom in the molecule at (1 + x, 2 + y,
z), so generating by translation a C(14) chain running parallel
to the [120] direction (Fig. 10). It is notable that the two O
acceptor atoms in (II) belong to the same nitro group: the
second nitro group containing the N12 atom plays no part in
the hydrogen bonding. The combination of the [101] and [120]
chains generates a (001) sheet, which is reinforced by the
ꢀꢀ ꢀ ꢀꢀ stacking interaction.
The aryl rings at (x, y, z) and (ꢂx, ꢂy, 1 ꢂ z), which form
1 1
parts of the molecules of (III) centred at (12, 21, 21) and (ꢂ , ꢂ , 21),
2
2
respectively, are strictly parallel with an interplanar spacing of
˚
3.344 (2) A; the ring–centroid separation is 3.784 (2) A,
˚
˚
corresponding to a ring offset of 1.770 (2) A. Propagation by
inversion of this ꢀ-stacking interaction then generates a chain
running parallel to the [110] direction (Fig. 13). The combi-
nation of [110] and [210] chains generates a (001) sheet, but
there are no direction-specific interactions between adjacent
sheets.
3.2.4. Isomer (IV), 1-(3-nitrophenyl)-4-(4-nitrophenyl)-2,3-
diaza-1,3-butadiene. Although the molecules of the 3,40
The aryl rings C11–C16 and C21–C26 in the molecules at
(x, y, z) and (1 + x, 1 + y, z), respectively, make a dihedral
angle of only 1.1 (2)ꢃ. The ring–centroid separation is
˚
˚
3.722 (2) A and the interplanar spacing is ca 3.42 A, corre-
˚
sponding to a centroid offset of ca 1.48 A. In this manner a
[110] chain is produced (Fig. 11), which lies wholly within the
hydrogen-bonded (001) sheet. There are no direction-specific
interactions between adjacent sheets.
3.2.3. Isomer (III), 1,4-bis(3-nitrophenyl)-2,3-diaza-1,3-
butadiene. The molecules of the 3,30 isomer (III) (Fig. 4) lie
across centres of inversion in the space group P21/n with the
1
1
reference molecule selected as that lying across (12, , ). The
2
2
molecules are effectively planar, and they are linked into
chains of rings by a single C—Hꢀ ꢀ ꢀO hydrogen bond (Table 3),
and the chains are further linked into sheets by a single ꢀꢀ ꢀ ꢀꢀ
stacking interaction. The aryl C4 atom at (x, y, z), which lies in
the molecule centred at (21, 21, 12), acts as a hydrogen-bond donor
to the nitro O32 atom at (ꢂ1 ꢂ x, ꢂy, 1 ꢂ z), which lies in the
3
2
1 1
2 2
molecule centred at (ꢂ , ꢂ , ): propagation by inversion of
Figure 11
this single hydrogen bond then generates a C(14)[R22(10)]
chain of rings running parallel to the [210] direction (Fig. 12).
Stereoview of part of the crystal structure of isomer (II) showing the
formation of a ꢀ-stacked chain along [110]. For the sake of clarity the H
atoms have all been omitted.
Figure 10
Figure 12
Stereoview of part of the crystal structure of isomer (II) showing the
formation of a hydrogen-bonded C(14) chain along [120]. For the sake of
clarity the H atoms not involved in the motif shown have been omitted.
Stereoview of part of the crystal structure of isomer (III) showing the
formation of a hydrogen-bonded chain of rings along [210]. For the sake
of clarity the H atoms not involved in the motif shown have been omitted.
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672 Christopher Glidewell et al.
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research papers
isomer (IV) (Fig. 5) have no crystallographic symmetry,
nonetheless they are very nearly planar. The two-dimensional
aggregation is determined by four C—Hꢀ ꢀ ꢀO hydrogen bonds
(Table 3), but it can readily be analysed in terms of two one-
dimensional substructures. In the first of these substructures,
the aryl C14 atom in the molecule at (x, y, z) acts as a
hydrogen-bond donor to the nitro O132 atom in the molecule
at (1 ꢂ x, ꢂ2 ꢂ y, 1 ꢂ z), thereby forming an R22(10) ring
centred at (12, ꢂ1, 12): similarly, the methine C17 atom at (x, y, z)
acts as a donor to the nitro O242 atom in the molecule at (32 ꢂ
generates a C22(22)[R22(10)][R22(22)] chain of rings running
parallel to the [170] direction (Fig. 14). In the second
substructure, atoms C22 and C27 in the molecule at (x, y, z)
both act as donors to the nitro O131 atom in the molecule at
(1 ꢂ x, 1 + y, 12 ꢂ z), while C22 and C27 at (1 ꢂ x, 1 + y, 12 ꢂ z)
in turn act as donors to O131 at (x, 2 + y, z). In this way a pair
of C(10)C(12)[R12(6)] chains of rings (Fig. 15) is generated by
the twofold rotation axis along (12, y, 41), forming a double helix
running parallel to the [010] direction (Fig. 16). The combi-
nation of the [170] and [010] chains generates a (001) sheet.
3.2.5. Isomer (V), 1,4-bis(4-nitrophenyl)-2,3-diaza-1,3-
butadiene. The molecules of the 4,40 isomer (V) (Fig. 6) lie
across centres of inversion in the space group P21/n with the
3
2
3 1
4 2
x, ꢂ y, 1 ꢂ z), so forming an R22(22) ring centred at (43, , ).
Propagation by inversion of these two interactions then
1
1
reference molecule selected as that lying across (12, , ). With
2
2
the exception of the nitro groups, the molecules are effectively
planar (Table 2). The supramolecular aggregation in (V) is
dominated by two C—Hꢀ ꢀ ꢀO hydrogen bonds, one much
stronger than the other (Table 3). The overall effect of these
Figure 13
Stereoview of part of the crystal structure of isomer (III) showing the
formation of a ꢀ-stacked chain along [110]. For the sake of clarity the H
atoms have been omitted.
Figure 15
Part of the crystal structure of isomer (IV) showing the formation of a
[010] chain of rings along [010]. For the sake of clarity the H atoms not
involved in the motif shown have been omitted. The atoms marked with
an asterisk (*) or a hash (#) are at the symmetry positions (1 ꢂ x, 1 + y,
1
2
ꢂ z) and (x, 2 + y, z), respectively.
Figure 14
Stereoview of part of the crystal structure of isomer (IV) showing the
formation of a chain along [170] containing R22(10) and R22(22) rings. For
the sake of clarity the H atoms not involved in the motif shown have been
omitted.
Figure 16
Stereoview of part of the crystal structure of isomer (IV), showing the
formation of a hydrogen-bonded double helix along [010]. For the sake of
clarity the H atoms not involved in the motif shown have been omitted.
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interactions is to link the molecules into a three-dimensional
framework, and the formation of this framework is most
readily analysed in terms of two substructures, each generated
by a single hydrogen bond. In the stronger interaction, the
methine C7 atom at (x, y, z) acts as a hydrogen-bond donor to
the nitro O41 atom at (1 + x, ꢂ1 + y, z): propagation of this
interaction by translation and inversion then leads to the
formation of a chain of edge-fused centrosymmetric R22(22)
tuted isomers and then the non-symmetric forms. The supra-
molecular structures of the two polymorphs (Ia) and (Ib) of
the 2,20-isomer are both one-dimensional (Figs. 7 and 8), but
they depend upon different intermolecular interactions, ꢀꢀ ꢀ ꢀꢀ
stacking in (Ia) and a C—Hꢀ ꢀ ꢀꢀ(arene) hydrogen bond in (Ib).
In the 3,30-isomer (III) the supramolecular structure is two-
dimensional, utilizing a C—Hꢀ ꢀ ꢀO hydrogen bond and a ꢀꢀ ꢀ ꢀꢀ
stacking interaction, while in the 4,40-isomer (V) the only
direction-specific intermolecular interactions are two inde-
pendent C—Hꢀ ꢀ ꢀO hydrogen bonds which generate a three-
dimensional structure. Thus, these symmetrical isomers can
form supramolecular structures which are one-, two- or three-
dimensional, and in which no two exhibit the same types of
intermolecular interaction.
Amongst the three non-symmetrically substituted isomers,
the 2,30-isomer (II) forms a two-dimensional supramolecular
structure dominated by two C—Hꢀ ꢀ ꢀO hydrogen bonds, and
the structure of the 3,40-isomer (IV) is again two-dimensional
but here determined by four independent C—Hꢀ ꢀ ꢀO
hydrogen bonds.
Within the two- and three-dimensional structures a wide
variety of low-dimensional substructures can be discerned,
including simple chains in the 2,30-isomer (II) (Figs. 9 and 10),
chains of rings in both the 3,30-isomer (III) and the 3,40-isomer
(IV), including a double-helical chain in (IV) (Figs. 12, 14, 15
and 16), and both chains of edge-fused rings and sheets of
R44(38) rings in the 4,40-isomer (V) (Figs. 17 and 18).
These supramolecular structures are built from C—Hꢀ ꢀ ꢀO
and C—Hꢀ ꢀ ꢀꢀ(arene) hydrogen bonds and aromatic ꢀꢀ ꢀ ꢀꢀ
stacking interactions although, perhaps surprisingly, C—
Hꢀ ꢀ ꢀN hydrogen bonds are absent. All of these interactions
are comparatively weak; accordingly, the computational
modelling and prediction of crystal structures in which inter-
actions of this type are the only direction-specific inter-
molecular interactions present, is fraught with difficulty.
Despite considerable effort in recent years, reliable predictive
methods for such structures remain elusive: extended series of
isomeric compounds, such as those whose structures are
described here, will provide a keen test of computational
methods for structure prediction.
ꢀ
rings running parallel to the [110] direction (Fig. 17).
In contrast to the stronger hydrogen bond, which generates
a one-dimensional substructure, the weaker interaction
generates a substructure which is two-dimensional. The aryl
atoms C3 at (x, y, z) and (1 ꢂ x, 1 ꢂ y, 1 ꢂ z), which both form
part of the molecule centred at (12, 21, 21), act as hydrogen-bond
1
donors, respectively, to the nitro O41 atoms at (32 ꢂ x, ꢂ + y,
2
ꢂ z) and (ꢂ + x, 32 ꢂ y, ꢂ + z), which themselves lie in the
3
2
1
2
1
2
molecules centred at (1, 0, 1) and (0, 1, 0), respectively.
Similarly, the O41 atoms at (x, y, z) and (1 ꢂ x,
1 ꢂ y, 1 ꢂ z) accept hydrogen bonds from C3 atoms at (32 ꢂ x,
12 + y, 32 ꢂ z) and (ꢂ + x, 12 ꢂ y, ꢂ + z), respectively, which are
1
2
1
2
components of the molecules centred at (1, 1, 1) and (0, 0, 0),
respectively. Propagation of this hydrogen bond then gener-
ꢀ
ates a (101) sheet in the form of a (4, 4) net (Batten & Robson,
1998) built from a single type of R44(38) ring (Fig. 18). The
ꢀ
ꢀ
combination of the [110] chains and (101) sheets suffices to
link all of the molecules into a single framework, from which
C—Hꢀ ꢀ ꢀꢀ(arene) hydrogen bonds and aromatic ꢀꢀ ꢀ ꢀꢀ
stacking interactions are, however, both absent.
3.2.6. General discussion of the structures. In making
comparisons between the supramolecular aggregation
patterns of the various forms of bis(nitrobenzaldehyde)azine,
it is convenient to consider firstly the symmetrically substi-
Figure 17
Part of the crystal structure of isomer (V) showing the formation of a
2
ꢀ
chain of edge-fused R2(22) rings along [110]. For the sake of clarity the H
atoms not involved in the motif shown have been omitted. The atoms
marked with an asterisk (*), a hash (#) or a dollar sign ($) are at the
symmetry positions (1 ꢂ x, 1 ꢂ y, 1 ꢂ z), (1 + x, ꢂ1 + y, z) and (2 ꢂ x, ꢂy,
1 ꢂ z), respectively.
Figure 18
Stereoview of part of the crystal structure of isomer (V) showing the
ꢀ
formation of a sheet of R4(38) rings parallel to (101). For the sake of
clarity the H atoms not involved in the motif shown have been omitted.
4
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674 Christopher Glidewell et al.
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Acta Cryst. (2006). B62, 666–675

research papers
Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew.
Chem. Int. Ed. Engl. 34, 1555–1573.
Bruker AXS Inc. (2004). APEX2 and SAINT, Version 6.02. Bruker
AXS Inc., Madison, Wisconsin, USA.
Ferguson, G. (1999). PRPKAPPA – a WordPerfect-5.1 Macro to
Formulate and Polish CIF Format Files from the SHELXL-97
Refinement of Kappa-CCD Data. University of Guelph, Canada.
Ferguson, G., Glidewell, C., Low, J. N., Skakle, J. M. S. & Wardell, J. L.
(2005). Acta Cryst. C61, o445–o449.
Flack, H. D. (1983). Acta Cryst. A39, 876–881.
Flack, H. D. & Bernardinelli, G. (2000). J. Appl. Cryst. 33, 1143–
1148.
Glidewell, C., Howie, R. A., Low, J. N., Skakle, J. M. S., Wardell,
S. M. S. V. & Wardell, J. L. (2002). Acta Cryst. B58, 864–
876.
Glidewell, C., Low, J. N., Skakle, J. M. S. & Wardell, J. L. (2005). Acta
Cryst. C61, o312–o316.
Glidewell, C., Low, J. N., Skakle, J. M. S., Wardell, S. M. S. V. &
Wardell, J. L. (2002). Acta Cryst. C58, o487–o490.
Glidewell, C., Low, J. N., Skakle, J. M. S., Wardell, S. M. S. V. &
Wardell, J. L. (2005). Acta Cryst. B61, 227–237.
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4. Concluding remarks
The supramolecular structures of (Ia), (Ib) and (II)–(V) all
exhibit different combinations of direction-specific inter-
molecular interactions, and different overall patterns of
supramolecular aggregation. Accordingly it is not possible to
make a reliable prediction of the supramolecular molecular
structure of isomer (VI). To the extent that no one structure in
this series can be predicted, even with knowledge of all the
others, the series under study here neatly mimics the beha-
viour of other extended series of simple positional isomers
which we have studied recently, including iodo-arene-
nitroarenesulfonamides (Kelly et al., 2002), nitrobenzylidene-
iodoanilines, where solvent-dependent polymorphism occurs
(Glidewell, Howie et al., 2002; Ferguson et al., 2005), iodo-
N-(nitrobenzyl)anilines (Glidewell, Low et al., 2002) and
N-iodophenyl)nitrophthalimides (Glidewell, Low, Skakle,
Wardell & Wardell, 2005). In each of these series, every isomer
manifests a distinct pattern of intermolecular interactions such
that predictions on further isomers become merely spec-
ulative. The occurrence of polymorphism in two of these series
adds to the overall complexity, which presents a keen chal-
lenge to computational methods for crystal structure predic-
tion.
Jones, P. G. (1986). Acta Cryst. A42, 57.
Kelly, C. J., Skakle, J. M. S., Wardell, J. L., Wardell, S. M. S. V., Low,
J. N. & Glidewell, C. (2002). Acta Cryst. B58, 94–108.
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lography Centre, Chemistry Department, NUI Galway,
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Otwinowski, Z. & Minor, W (1997). Methods in Enzymology, Vol.
276, Macromolecular Crystallography, Part A, edited by C. W.
Carter Jr & R. M. Sweet, pp. 307–326. New York: Academic
Press.
X-ray data were collected at the EPSRC X-ray Crystal-
lographic Service, University of Southampton, UK, and at the
Daresbury SRS station 9.8: the authors thank the staff of these
facilities for all their help and advice. JLW thanks CNPq and
FAPERJ for financial support.
Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of
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Christopher Glidewell et al.
(E,E)-1,4-Bis(nitrophenyl)-2,3-diaza-1,3-butadienes 675