Interplay of hydrogen bonds, iodo nitro interactions and aromatic π...π stacking interactions in iodo-nitroanilines

Article abstract of DOI:10.1107/S0108768102007978

Molecules of 2-iodo-5-nitroaniline (I) are linked by N-H...O hydrogen bonds into centrosymmetric dimers and by asymmetric three-centre iodo...nitro interactions into chains, so forming chains of fused centrosymmetric rings: these chains are linked by aromatic π...π stacking interactions to form a three-dimensional structure. In the isomeric 4-iodo-2-nitro-aniline (II), each of the two independent molecules forms hydrogen-bonded chains that are linked by two-centre iodo...nitro interactions into sheets of two types, each containing only a single type of molecule: π...π stacking interactions are absent. In 2,4-diiodo-3-nitroaniline (III), where the nitro group is almost orthogonal to the aryl ring, a combination of N - H...O hydrogen bonds and two distinct two-centre iodo...nitro interactions links the molecules into a three-dimensional framework that is reinforced by aromatic π...π stacking interactions. Bond lengths and conformations are discussed and comparisons are drawn with related compounds.

Full text of DOI:10.1107/S0108768102007978

research papers
Acta Crystallographica Section B
Structural
Science
Interplay of hydrogen bonds, iodoÁ Á Ánitro
interactions and aromatic pÁ Á Áp stacking
ISSN 0108-7681
interactions in iodo-nitroanilines
Simon J. Garden,a Silvia P.
Fontes,a James L. Wardell,b
Janet M. S. Skakle,c John N.
Lowc² and Christopher
Glidewelld*
Molecules of 2-iodo-5-nitroaniline (I) are linked by NÐHÁ Á ÁO
hydrogen bonds into centrosymmetric dimers and by asym-
metric three-centre iodoÁ Á Ánitro interactions into chains, so
forming chains of fused centrosymmetric rings: these chains
are linked by aromatic ꢀÁ Á Áꢀ stacking interactions to form a
three-dimensional structure. In the isomeric 4-iodo-2-nitro-
aniline (II), each of the two independent molecules forms
hydrogen-bonded chains that are linked by two-centre
iodoÁ Á Ánitro interactions into sheets of two types, each
containing only a single type of molecule: ꢀÁ Á Áꢀ stacking
interactions are absent. In 2,4-diiodo-3-nitroaniline (III),
where the nitro group is almost orthogonal to the aryl ring,
a combination of NÐHÁ Á ÁO hydrogen bonds and two distinct
two-centre iodoÁ Á Ánitro interactions links the molecules into a
three-dimensional framework that is reinforced by aromatic
ꢀÁ Á Áꢀ stacking interactions. Bond lengths and conformations
are discussed and comparisons are drawn with related
compounds.
Received 12 April 2002
Accepted 30 April 2002
a
Â
Instituto de Quõmica, Departamento de
Â
Ã
Quõmica Organica, Universidade Federal do Rio
de Janeiro, CP 68563, 21945-970 Rio de Janeiro
b
Â
RJ, Brazil, Instituto de Quõmica, Departamento
Â
Ã
de Quõmica Inorganica, Universidade Federal
do Rio de Janeiro, CP 68563, 21945-970 Rio de
Janeiro RJ, Brazil, cDepartment of Chemistry,
University of Aberdeen, Meston Walk, Old
Aberdeen AB24 3UE, UK, and dSchool of
Chemistry, University of St Andrews, St
Andrews, Fife KY16 9ST, UK
² Present Address: School of Engineering,
University of Dundee, Dundee DD1 4HN, UK
1. Introduction
Correspondence e-mail: cg@st-andrews.ac.uk
In simple nitroanilines, the supramolecular structures are
generally dominated by the effects of NÐHÁ Á ÁO hydrogen
bonds, although the detailed supramolecular arrangement
may be subtly in¯uenced by the presence of other substituents,
even those as modest as C-methyl groups (Ploug-Sùrensen &
Andersen, 1986; Tonogaki et al., 1993; Ellena et al., 1999;
Cannon et al., 2001; Ferguson et al., 2001). Likewise, the
supramolecular structures of the extended 4-nitroaniline
analogues 4-H2NC6H4-(C C)n-C6H4NO2-40 (for n = 0±3) are
controlled by the NÐHÁ Á ÁO hydrogen bonds (Graham et al.,
1989). When nitro groups are present with I atoms in benze-
noid compounds, the resulting intermolecular iodoÁ Á Ánitro
interactions can play an important role in the supramolecular
aggregation (Allen et al., 1994; Thalladi et al., 1996;
Masciocchi et al., 1998; Ranganathan & Pedireddi, 1998;
McWilliam et al., 2001; Kelly et al., 2002). Finally, aromatic
molecules of this type may engage in aromatic ꢀÁ Á Áꢀ stacking
interactions.
Substituted iodo-nitroanilines thus provide very compact
molecular systems within which to investigate the interplay of
NÐHÁ Á ÁO (and possibly CÐHÁ Á ÁO) hydrogen bonding,
iodoÁ Á Ánitro interactions (which may be of two-centre and/or
three-centre type) and ꢀÁ Á Áꢀ stacking interactions. To this end,
we have now investigated three carefully selected examples:
2-iodo-5-nitroaniline (I), 4-iodo-2-nitroaniline (II) and
2,4-diiodo-3-nitroaniline (III), having in (I) an isolated nitro
group with no ring neighbours other than H, in (II) a similarly
isolated I substituent and in (III) a nitro group sandwiched
# 2002 International Union of Crystallography
Printed in Great Britain ± all rights reserved
ꢀ
Acta Cryst. (2002). B58, 701±709
Simon J. Garden et al.
Interactions in iodo-nitroanilines 701

research papers
Table 1
Experimental details.
between two I substituents. We compare the
resulting patterns of supramolecular aggregation
with those of the closely related compounds 4-
(I)
(II)
(III)
iodo-2-methyl-5-nitroaniline
(IV)
(Garden,
Crystal data
Chemical formula
Chemical formula
weight
Cell setting, space
group
Ê
a, b, c (A)
Glidewell et al., 2001) and 2-iodo-4-nitroaniline
(V) (McWilliam et al., 2001): it may be noted here
that compounds (I), (II) and (V) are isomeric.
C6H5IN2O2
264.02
C6H5IN2O2
264.02
C6H4I2N2O2
389.91
Triclinic, P1
Monoclinic, C2=c
Monoclinic, P21=c
6.4236 (15), 7.4979
(18), 8.293 (2)
71.422 (4), 85.285
(4), 86.125 (4)
376.98 (16)
2
26.5541 (9), 7.0445
(2), 16.4416 (5)
90, 101.1548 (16), 90 90, 106.6693 (16), 90
7.6069 (3), 12.5917
(4), 10.2546 (3)
ꢁ, ꢃ, ꢄ ꢁꢂ†
3
Ê
V (A )
3017.47 (16)
16
2.325
Mo Kꢁ
3426
940.95 (6)
4
2.752
Mo Kꢁ
2144
Z
Dx (Mg mꢃ3
Radiation type
)
2.326
Mo Kꢁ
No. of re¯ections for 1674
cell parameters
ꢅ range (ꢂ)
ꢆ (mmꢃ1
Temperature (K)
2.60±28.44
4.195
120 (2)
3.0±27.48
4.192
3.23±27.46
6.647
)
120 (2)
Plate, orange
0.25 Â 0.20 Â 0.05
120 (2)
Plate, colourless
0.28 Â 0.24 Â 0.08
Crystal form, colour Plate, orange
Crystal size (mm)
0.24 Â 0.12 Â 0.04
Data collection
Diffractometer
Data collection
method
Absorption correc-
tion
Tmin
KappaCCD
KappaCCD
KappaCCD
' scans, and ! scans ' scans, and ! scans ' scans, and ! scans
with ꢇ offsets
Multi-scan
with ꢇ offsets
Multi-scan
with ꢇ offsets
Multi-scan
0.434
0.850
2274, 1674, 1620
0.380
0.811
10470, 3426, 2696
0.180
0.618
8456, 2144, 1950
Tmax
No. of measured,
independent and
observed re¯ec-
tions
2. Experimental
2.1. Synthesis
Criterion for
observed re¯ec-
tions
Rint
ꢅmax (ꢂ)
Range of h, k, l
I > 2ꢈꢁI†
I > 2ꢈꢁI†
I > 2ꢈꢁI†
Compounds (I)±(III) were prepared by iodina-
tion of the appropriate nitroaniline using K[ICl2]
in methanol (Larsen et al., 1956; Garden, Torres et
al., 2001). Iodination of 2-nitroaniline gave (II),
m.p. 395±396 K. Iodination of 3-nitroaniline gave
a mixture of (I) and (III) (m.p. 429±431 K and
391±392 K, respectively), separated by thin-layer
chromatography using chloroform and light
petroleum as eluants; in addition, a third product
was formed in this reaction in very low yield, but
so far this has not been puri®ed suf®ciently for
de®nitive identi®cation. Crystals of (I)±(III)
suitable for single-crystal X-ray diffraction were
grown by slow evaporation of solutions in ethanol.
0.0248
28.44
ꢃ8 ! h ! 7
ꢃ10 ! k ! 9
ꢃ10 ! l ! 10
0.0556
27.48
ꢃ34 ! h ! 33
ꢃ8 ! k ! 9
ꢃ21 ! l ! 21
0.1038
27.46
ꢃ9 ! h ! 8
ꢃ14 ! k ! 16
ꢃ13 ! l ! 13
Re®nement
Re®nement on
R‰F2 > 2ꢈꢁF2†Š,
wRꢁF2†, S
F2
0.0375, 0.1022, 1.069 0.0322, 0.0815, 1.046 0.0445, 0.1215, 1.131
F2
F2
No. of re¯ections
and parameters
used in re®ne-
ment
1674, 100
3426, 193
2144, 110
H-atom treatment
H-atom parameters
constrained
H-atom parameters
constrained
H-atom parameters
constrained
Weighting scheme
w = 1/[ꢈ2(Fo2) +
(0.0823P)2 +
0.6322P] where P
w = 1/[ꢈ2(Fo2) +
(0.0372P)2 +
3.2146P] where P
w = 1/[ꢈ2(Fo2) +
(0.0534P)2 +
3.8878P] where P
2.2. Data collection, structure solution and
refinement
2
2
2
= (Fo + 2Fc2)/3
= (Fo + 2Fc2)/3
= (Fo + 2Fc2)/3
ꢁÁ=ꢈ†
0.001
1.291, ꢃ1.864
0.001
1.222, ꢃ1.551
0.001
2.356, ꢃ2.261
max
Áꢉmax, Áꢉmin (e
Diffraction data for compounds (I)±(III) were
collected at 150 (2) K, using a Bruker SMART-100
CCD for (I) and Nonius KappaCCD for (II) and
(III), diffractometers with graphite-mono-
Ê ꢃ3
A
)
Extinction method
Extinction coef®-
cient
None
0
None
0
SHELXL
0.0044 (5)
Ê
chromated Mo Kꢁ radiation (ꢂ = 0.71073 A).
Computer programs used: SMART (Bruker, 1997), SHELXTL (Bruker, 1997), SHELXS97 (Sheldrick,
1997b), SHELXL97 (Sheldrick, 1997a), PRPKAPPA (Ferguson, 1999), KappaCCD server software
(Nonius, 1997), DENZO±SMN (Otwinowski & Minor, 1997).
Other details of cell data, data collection and
re®nement are summarized in Table 1, together
with details of the software employed (Bruker,
1997; Ferguson, 1999; Nonius, 1997; Otwinowski &
Minor, 1997; Sheldrick, 1997a,b).
ꢀ
Compound (I) is triclinic: space group P1 was selected and
con®rmed by the analysis. For compound (II), the systematic
ꢀ
702 Simon J. Garden et al.
Interactions in iodo-nitroanilines
Acta Cryst. (2002). B58, 701±709

research papers
Table 3
Hydrogen-bonding parameters (A, ).
Table 2
Selected geometric parameters.
ꢂ
Ê
Ê
Intramolecular distances (A)
DÐHÁ Á ÁA
HÁ Á ÁA DÁ Á ÁA
DÐHÁ Á ÁA Motif
Direction
±
Compound (I)
Compound (II)
Compound (III)
Compound (I)
N1ÐH1BÁ Á ÁO51i
2.51
3.311 (6) 152
R22(14)
n = nil
n = 1
n = 2
n = nil
Compound (II)
Cn1ÐCn2
Cn2ÐCn3
Cn3ÐCn4
Cn4ÐCn5
Cn5ÐCn6
Cn6ÐCn1
Cn2ÐIn2
Cn4ÐIn4
Cn1ÐNn1
CnmÐNnm²
1.406 (6)
1.392 (6)
1.387 (7)
1.389 (6)
1.372 (6)
1.415 (6)
2.099 (4)
±
1.421 (5)
1.399 (5)
1.370 (5)
1.398 (5)
1.366 (5)
1.405 (5)
±
2.095 (4)
1.343 (5)
1.433 (5)
1.404 (4)
1.409 (5)
1.357 (5)
1.397 (5)
1.366 (5)
1.417 (6)
±
2.099 (4)
1.344 (5)
1.426 (5)
1.404 (10)
1.394 (8)
1.380 (8)
1.398 (9)
1.370 (9)
1.409 (9)
2.099 (6)
2.089 (6)
1.380 (8)
1.484 (8)
N11ÐH11AÁ Á ÁO11ii
N11ÐH11BÁ Á ÁO12
N21ÐH21AÁ Á ÁO21ii
N21ÐH21BÁ Á ÁO22
C15ÐH15Á Á ÁO12iii
C25ÐH25Á Á ÁO22iv
2.24
2.01
2.19
2.00
2.63
2.55
3.005 (5) 146
C(6)
S(6)
C(6)
S(6)
C(7)
C(7)
[010]
±
[010]
±
[001]
[001]
2.642 (4) 128
2.979 (5) 149
2.626 (4) 127
3.524 (4) 157
3.495 (4) 172
Compound (III)
N1ÐH1BÁ Á ÁO132v
1.361 (6)
1.469 (6)
2.46
3.128 (8) 133
C(7)
[201]
Symmetry codes: (i) ꢃx, 1 ꢃ y, 1 ꢃ z; (ii) x, 1 + y, z; (iii) x, ꢃy, 12 + z; (iv) x, ꢃy, ꢃ + z; (v)
1
2
3
2
1 + x, ꢃ y, 12 + z.
Bond angles (ꢂ)
Compound (I)
N1ÐC1ÐC2
N1ÐC1ÐC6
C2ÐC1ÐC6
I2ÐC2ÐC1
I2ÐC2ÐC3
122.8 (4)
N5ÐC5ÐC4
118.7 (4)
117.3 (4)
124.0 (4)
121.9 (4)
Table 4
120.4 (4)
116.7 (4)
119.0 (3)
119.1 (3)
N5ÐC5ÐC6
C4ÐC5ÐC6
C1ÐC2ÐC3
ꢂ
Ê
Geometric parameters for IÁ Á ÁO interactions (A, ).
CÐIÁ Á ÁOÐX
IÁ Á ÁO
CÐIÁ Á ÁO
IÁ Á ÁOÐX
Compound (I)
Compound (II)
N11ÐC11ÐC12
N11ÐC11ÐC16
C12ÐC11ÐC16
N12ÐC12ÐC11
N12ÐC12ÐC13
C11ÐC12ÐC13
I14ÐC14ÐC13
I14ÐC14ÐC15
C13ÐC14ÐC15
C2ÐI2Á Á ÁO51iÐN5i
3.521 (4)
3.239 (4)
154.0 (2)
167.6 (2)
93.2 (3)
107.2 (3)
124.2 (4)
120.0 (4)
115.8 (3)
121.6 (3)
116.8 (3)
121.6 (3)
119.4 (3)
121.0 (3)
119.6 (3)
N21ÐC21ÐC22
N21ÐC21ÐC26
C22ÐC21ÐC26
N22ÐC22ÐC21
N22ÐC22ÐC23
C21ÐC22ÐC23
C23ÐC24ÐC25
I24ÐC24ÐC23
I24ÐC24ÐC25
124.9 (4)
119.3 (4)
115.8 (3)
121.5 (3)
116.6 (3)
121.9 (3)
119.0 (3)
120.3 (3)
120.7 (3)
C2ÐI2Á Á ÁO52iÐN5i
Compound (II)
C14ÐI14Á Á ÁO11iiÐN12ii
3.177 (3)
3.161 (3)
167.6 (2)
166.9 (2)
122.7 (2)
119.9 (2)
C24ÐI24Á Á ÁO21iiiÐN22iii
Compound (III)
C2ÐI2Á Á ÁO132ivÐN3iv
3.165 (5)
3.382 (5)
176.4 (2)
155.2 (2)
115.0 (4)
116.9 (4)
C4ÐI4Á Á ÁO132vÐN3v
Compound (III)
N1ÐC1ÐC2
N1ÐC1ÐC6
C2ÐC1ÐC6
N3ÐC3ÐC2
N3ÐC3ÐC4
C2ÐC3ÐC4
In (I)
In (III)
O51iÁ Á ÁI2Á Á ÁO52i
I2viÁ Á ÁO132Á Á ÁI4v
36.92 (9)
91.3 (2)
123.4 (6)
119.8 (6)
116.7 (6)
118.0 (5)
119.0 (5)
122.9 (6)
I2ÐC2ÐC1
I2ÐC2ÐC3
C1ÐC2ÐC3
IÐC4ÐC3
I4ÐC4ÐC5
C3ÐC4ÐC5
119.1 (4)
121.4 (5)
119.5 (6)
123.4 (5)
118.9 (4)
117.7 (5)
² Symmetry codes: (i) 1 + x, y, ꢃ1 + z; (ii) x, ꢃ1 ꢃ y, 12 + z; (iii) x, ꢃ1 ꢃ y, ꢃ + z; (iv) x,
1
2
3
2
1
2
ꢃ y, 12 + z; (v) 1 ꢃ x, 1 ꢃ y, 1 ꢃ z; (vi) x, 32 ꢃ y, ꢃ + z.
hydrogen-bonding geometry and IÁ Á ÁO interactions are given
in Tables 2, 3 and 4, respectively. The diagrams were prepared
with the aid of PLATON (Spek, 2002). Figs. 1, 2 and 3 show
the molecules (I)±(III) with the atom-labelling schemes, and
Figs. 4±10 show aspects of the supramolecular structures.
Lists of atomic coordinates, anisotropic displacement
parameters, geometric parameters and structure factors have
been deposited with the IUCr.1
Torsional angles (ꢂ)
Compound (I)
C4ÐC5ÐN5ÐO51
C4ÐC5ÐN5ÐO52
Compound (II)
ꢃ176.1 (5)
C11ÐC12ÐN12ÐO11
C11ÐC12ÐN12ÐO12
C21ÐC22ÐN22ÐO21
C21ÐC22ÐN22ÐO22
170.8 (4)
ꢃ9.3 (6)
ꢃ178.0 (4)
2.2 (6)
3.2 (7)
Compound (III)
C2ÐC3ÐN3ÐO131
C2ÐC3ÐN3ÐO132
ꢃ100.3 (6)
80.4 (7)
² For N of nitro group, in compound (I), m = 5; in (II), m = 2; in (III), m = 3.
3. Results and discussion
absences permitted C2/c and Cc as possible space groups: C2/c
was selected and con®rmed by the analysis. For compound
(III), the space group P21/c was uniquely assigned from the
systematic absences. The structures were solved by direct
methods and re®ned with all data on F2. A weighting scheme
based on P = [Fo2 ‡ Fc2]/3 was employed in order to reduce
statistical bias (Wilson, 1976). All H atoms were located from
difference maps and included in the re®nements as riding
3.1. Molecular dimensions and conformations
In compound (I) (Fig. 1), where the amino and nitro groups
are meta to one another, the C1ÐN1 and C5ÐN5 distances
(Table 2) are, within experimental uncertainty, identical to the
Ê
Ê
mean values (1.355 A and 1.468 A, respectively) for
C(ar)ÐNH2 and C(ar)ÐNO2 distances (Allen et al., 1987): at
the same time, there is no evidence for any signi®cant bond
Ê
Ê
atoms with NÐH = 0.88 A and CÐH = 0.95 A.
Supramolecular analyses were made with the aid of
PLATON (Spek, 2002). Details of molecular dimensions,
1 Supplementary data for this paper are available from the IUCr electronic
archives (Reference: NA0135). Services for accessing these data are described
at the back of the journal.
ꢀ
Acta Cryst. (2002). B58, 701±709
Simon J. Garden et al.
Interactions in iodo-nitroanilines 703

research papers
®xation in the aryl ring, so the ring-delocalized form (I) is an
adequate representation of the molecular-electronic structure.
By contrast, the Cn1ÐNn1 and Cn2ÐNn2 distances (n = 1 or
2 for the two independent molecules) in (II) (Fig. 2), where the
amino and nitro groups are mutually ortho, are both short for
their types, while amongst the ring CÐC bonds Cn3ÐCn4 and
Cn5ÐCn6 are systematically much shorter than the
remainder, pointing to the importance of the charge-separated
quinonoid form (IIa) as a signi®cant contributor.
whereas in (III), where the nitro group lies between two I
substituents, the nitro group is almost perpendicular to the
Compound (III) (Fig. 3) is similar to (I) in having the amino
and nitro substituents in meta positions, but differs from (I) in
that there is an I substituent interposed between the amino
and nitro groups. There is again no bond ®xation within the
ring, as judged by the CÐC distances, but both of the CÐN
distances are rather long and indeed both are just above the
Ê
Ê
upper quartile values for their types, 1.372 A and 1.476 A,
respectively (Allen et al., 1987). Closely associated with these
long CÐN bonds is the overall conformation of (III), which
differs markedly from those observed in (I) and (II). It has
been clearly demonstrated (Domenicano et al., 1990) that
while the coplanar conformation of a nitro group bonded to a
benzenoid ring represents an energy minimum, the barrier to
rotation about a C(ar)ÐNO2 bond is rather small (probably
no more than 15 kJ molꢃ1). A contributory factor to the
stabilization of the planar conformation may be the attractive
interaction between the negatively polarized O atoms of the
nitro group and the positively polarized H atoms ortho to the
nitro group. Thus, in both (I) and (II) the twist of the nitro
groups away from the ring plane is very modest (Table 2),
Figure 2
The two independent molecules of (II) showing the atom-labelling
scheme. Displacement ellipsoids are drawn at the 30% probability level.
Figure 1
A molecule of (I) showing the atom-labelling scheme. Displacement
ellipsoids are drawn at the 30% probability level.
Figure 3
A molecule of (III) showing the atom-labelling scheme. Displacement
ellipsoids are drawn at the 30% probability level.
ꢀ
704 Simon J. Garden et al.
Interactions in iodo-nitroanilines
Acta Cryst. (2002). B58, 701±709

research papers
3.2.2. IodoÁ Á Ánitro interactions. The iodoÁ Á Ánitro interac-
tions in compounds (I)±(III) display a wide variety of struc-
tural types, with an asymmetric three-centre interaction in (I)
where the longer component is perhaps at the margin of
signi®cance, two similar two-centre interactions in (II), one for
each independent molecule, and an unusual type of three-
centre interaction in (III) involving two different I atoms
linked to the same O atom, which is the same O that acts as the
acceptor in the NÐHÁ Á ÁO hydrogen bond in (III). The IÁ Á ÁO
distances in two-centre IÁ Á Ánitro interactions are, in general,
shorter than those in three-centre systems of IÁ Á Á(O)2 type, as
ring plane. We have noted previously (Garden, Glidewell et
al., 2001) that intramolecular interactions between mutually
ortho I and nitro substituents on aryl rings appear to be
repulsive, although intermolecular IÁ Á Ánitro interactions are
generally attractive. The twist of the nitro group in (III), as
well as those in (IV) and 2,4,6-trinitroiodobenzene (VI)
[Cambridge Structural Database (CSD; Allen & Kennard,
1993) refcode ITNOBE01 (Weiss et al., 1999)], indicates
repulsion between ortho I and nitro. It is interesting to note
that in ITNOBE01 the CÐN distances for the 2-nitro and
4-nitro groups (the molecules lie on twofold rotation axes in
Ê
Ê
deduced not only from
a
study of iodo-nitro-
space group P43212) are 1.476 (9) A and 1.451 (8) A asso-
ciated with nitro-group twist angles of 75.2 (9)ꢂ and 7.8 (8)ꢂ,
respectively.
arenesulfonamides (Kelly et al., 2002) but also from an analysis
of iodoÁ Á Ánitro interactions in compounds retrieved from the
CSD (Allen & Kennard, 1993). The IÁ Á ÁO distances in
compounds (I) and (II) (Table 4) certainly conform to this
pattern, while the two distances in the (I)2Á Á ÁO system of
compound (III) differ signi®cantly from one another.
Further evidence of repulsive interactions between adjacent
substituents can be gleaned from the bond angles at the ipso C
atoms, although here it is necessary also to take into consid-
eration the well established effects of substituent electro-
negativity on the internal CÐCÐC angle at the ipso C atoms
(Domenicano & Murray-Rust, 1979). From the values in
Table 2 and those in other iodo-nitroanilines and related
compounds (Weiss et al., 1999; Garden, Glidewell et al., 2001;
McWilliam et al., 2001), the following general comments can
be made:
(i) The internal CÐCÐC angle ipso to an amino group is
always small, regardless of other substituents, consistent with
the electron-donor characteristics of this substituent.
(ii) The internal CÐCÐC angle ipso to a nitro group is
large, consistent with the electron-withdrawing behaviour of
this substituent, provided only that there are no ortho
substituents.
3.3. Supramolecular structures
The supramolecular structures of compounds (I)±(III) are
characterized by a combination of NÐHÁ Á ÁO hydrogen bonds,
two-centre and three-centre iodoÁ Á Ánitro interactions and
aromatic ꢀÁ Á Áꢀ stacking interactions (Tables 3 and 4);
however, structurally signi®cant CÐHÁ Á ÁO hydrogen bonds
are generally absent. To codify the hydrogen-bonding motifs
we employ the now-familiar graph-set notation (Etter, 1990;
Bernstein et al., 1995; Motherwell et al., 1999), and for the
iodoÁ Á Ánitro interactions we employ the recently described
(Starbuck et al., 1999) extension of this notation to encompass
secondary bonding, wherein we regard the negatively polar-
ized O atoms of the nitro group as `donors' and the positively
polarized I atoms as `acceptors'.
(iii) The internal CÐCÐC angle ipso to I is close to 120ꢂ;
mutually ortho amino and nitro groups are repulsive, as
indicated here by the angles Nn1ÐCn1ÐCn2 and
Nn2ÐCn2ÐCn3 in compound (II).
(iv) Mutually ortho I and nitro substituents are repulsive, as
indicated here by the I4ÐC4ÐC3 angle in (III) and by the
nitro conformation.
While no indications can be drawn from the present data
concerning mutually ortho I and amino substituents, it is
unfortunate that there appear to be no structures in the CSD
for simple iodoanilines having no further substituents.
3.3.1. Compound (I). The supramolecular structure of
compound (I) (Fig. 1) is characterized by hard hydrogen bonds
of the NÐHÁ Á ÁO type, asymmetric three-centre IÁ Á ÁNO2
interactions and weak aromatic ꢀÁ Á Áꢀ stacking interactions.
The absence of intermolecular CÐHÁ Á ÁO hydrogen bonds
may be ascribed ®rstly to the adequacy of the hard-hydrogen-
bond donors, since there are equal numbers of NÐH bonds
and of nitro O acceptors, and secondly to the involvement of
both O atoms in the iodoÁ Á Ánitro interaction. The hydrogen
bonds and the iodoÁ Á Ánitro interactions together produce a
chain of fused rings, while adjacent chains are linked by the
ꢀÁ Á Áꢀ stacking interactions.
3.2. Supramolecular dimensions
3.2.1. Hydrogen bonds. It is noteworthy that in compound
(II), where the charge-separated form (IIa) is signi®cant, the
intermolecular NÐHÁ Á ÁO hydrogen bonds are characterized
by shorter HÁ Á ÁO and NÁ Á ÁO distances (Table 3) than those in
compounds (I) and (III), where the development of compar-
able charge-separated forms is not possible. This is consistent
with and supportive of the general concept of resonance-
enhanced hydrogen bonding (Gilli et al., 1994). Likewise, it is
only in compound (II) that there is a CÐHÁ Á ÁO hydrogen
bond, albeit a comparatively weak example as judged by the
HÁ Á ÁO and CÁ Á ÁO distances.
Atom I2 in the molecule at (x, y, z) is linked to both O51
and O52 in the molecule at (1 + x, y, ꢃ1 + z), so generating by
ꢀ
translation a chain parallel to [101], and pairs of these chains
are linked by a single NÐHÁ Á ÁO hydrogen bond. Atom N1 at
(x, y, z) acts as hydrogen-bond donor, via H1B, to O51 at (ꢃx,
1 ꢃ y, 1 ꢃ z). Propagation of the hydrogen bond in combi-
nation with the IÁ Á Ánitro interactions generates a chain of
fused centrosymmetric rings (Fig. 4) in which hydrogen-
bonded R22(14) rings are centred at (n, 0.5, 0.5 ꢃ n) (n = zero
or integer) and twelve-membered rings built from a combi-
ꢀ
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Simon J. Garden et al.
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research papers
nation of hydrogen bonds and IÁ Á ÁO interactions are centred
at (0.5 ꢃ n, 0.5, n) (n = zero or integer).
molecule contains I24) forms an independent two-dimensional
substructure built from a combination of NÐHÁ Á ÁO hydrogen
bonds and two-centre IÁ Á ÁO interactions, but there are no
direction-speci®c interactions between molecules of different
types. Each type of molecule forms an intramolecular
NÐHÁ Á ÁO hydrogen bond, producing an S(6) motif, and the
sheets formed by the two types of molecule are broadly
similar, so we discuss in detail only that formed by the type 1
molecule.
The aryl ring of the molecule at (x, y, z) participates in
aromatic ꢀÁ Á Áꢀ stacking interactions with the strictly parallel
rings in molecules both at (1 ꢃ x, 1 ꢃ y, 1 ꢃ z) and at
(1 ꢃ x, ꢃy, 1 ꢃ z) (Fig. 5); the corresponding interplanar
Ê
Ê
spacings are 3.410 (3) A and 3.567 (3) A, respectively, asso-
Ê
ciated with ring-centroid offsets of 1.413 (3) A and
Ê
1.430 (3) A. In this way, the molecule at (ꢃx, 1 ꢃ y, 1 ꢃ z),
ꢀ
which forms part of the reference [101] chain, is linked to that
Atom N11 in the type 1 molecule at (x, y, z) acts as
hydrogen-bond donor via H11A to nitro O11 in the type 1
molecule at (x, 1 + y, z), so generating by translation a C(6)
chain running parallel to the [010] direction. Eight chains of
type 1 molecules run through each unit cell, with two in each
of the domains 0.17 < x < 0.20, 0.30 < x < 0.33, 0.67 < x < 0.70
and 0.80 < x < 0.83, and the chains within each domain of x are
linked into sheets by means of two-centre iodoÁ Á Ánitro inter-
actions. Atom I14 in the type 1 molecule at (x, y, z) forms a
short IÁ Á ÁO contact with nitro O11 at (x, ꢃ1 ꢃ y, 12 + z), while
I14 at (x, ꢃ1 ꢃ y, 12 + z) in turn forms a similar contact with
O11 at (x, y, 1 + z), so producing a chain running parallel to
at (ꢃ1 + x, y, z), so generating a chain parallel to [100], and to
ꢀ
that at (ꢃ1 + x, 1 + y, z), so producing a chain parallel to [110].
ꢀ
The combination of chain motifs along [100] and [110] and
propagation of these two interactions by translation and
ꢀ
inversion serves to link all of the [101] chains into a single
three-dimensional continuum.
3.3.2. Compound (II). Compound (II) crystallizes with
Z0 = 2 in space group C2/c. Each of the two molecular types
(Fig. 2; the type 1 molecule contains I14 and the type 2
1
2
[001] and generated by the c-glide plane at y = ꢃ . The
combination of the [010] and [001] chains generates a (100)
sheet built from 20-membered rings (Fig. 6): if the notations
for hydrogen bonds and for IÁ Á ÁO interactions are combined,
these rings are of R44(20) type. The molecules of type 2 form a
very similar type of sheet (Fig. 7), and for each type of sheet
there is also a single weak and possibly adventitious
CÐHÁ Á ÁO hydrogen bond within the sheet (Table 3). The
sheets formed by the type 2 molecules lie in the domains
0.05 < x < 0.07,
0.43 < x < 0.45,
0.55 < x < 0.57
and
Figure 4
Part of the crystal structure of (I) showing formation of a chain of fused
ꢀ
rings along [101]. For the sake of clarity, H atoms bonded to C are
Figure 5
Part of the crystal structure of (I) showing the ꢀÁ Á Áꢀ stacking interactions.
The atoms marked with (*) or (#) are at the symmetry positions (1 ꢃ x,
1 ꢃ y, 1 ꢃ z) and (1 ꢃ x, ꢃy, 1 ꢃ z), respectively.
omitted. Atoms marked with (*), (#) or (&) are at the symmetry positions
(1 + x, y, ꢃ1 + z), (ꢃx, 1 ꢃ y, 1 ꢃ z) and (ꢃ1 + x, y, 1 + z), respectively.
ꢀ
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0.93 < x < 0.95. Hence, the sheets of type 1 and type 2 mole-
cules are stacked in pairs parallel to (100) thus,
. . . 11221122 . . ., with adjacent sheets of a given type related
within a pair by centres of inversion.
3.3.3. Compound (III). In compound (III) (Fig. 3), one of
the nitro O atoms, O132, not only acts as acceptor in an
intermolecular NÐHÁ Á ÁO hydrogen bond, but also partici-
pates in two intermolecular iodoÁ Á Ánitro interactions involving
I atoms from two different molecules. By contrast, O131 plays
no role whatsoever in the intermolecular aggregation. Also
unexpected is the non-participation of amino H1A in the
intermolecular hydrogen bonding (Table 3). These three
intermolecular interactions, one hydrogen bond and two
distinct two-centre IÁ Á ÁO interactions, together generate a
three-dimensional framework structure, which is readily
analyzed using the substructure approach (Gregson et al.,
2000).
Figure 6
Part of the crystal structure of (II) showing the formation of a (100) sheet
built from type 1 molecules only. For the sake of clarity, H atoms bonded
to C are omitted. Atoms marked with (*), (#), ($), (&) or (@) are at the
symmetry positions (x, ꢃy, 21 + z), (x, 1 + y, z), (x, ꢃ1 ꢃ y, ꢃ + z),
1
2
Atom I4 in the molecule at (x, y, z) forms an IÁ Á ÁO inter-
action with O132 at (1 ꢃ x, 1 ꢃ y, 1 ꢃ z), so generating a
centrosymmetric R22(10) dimeric unit centred at (12, 21, 12), and it
is convenient to treat this zero-dimensional substructural
`dimer' as the core building unit of the structure. The second
IÁ Á ÁO interactions, which involves I2 rather than I4, generates
a two-dimensional substructure. The atoms I2 in the reference
(x, ꢃ1 ꢃ y, 12 + z) and (x, ꢃy, ꢃ + z), respectively.
1
2
1
1
dimer centred at (12, , ) are at (x, y, z) and (1 ꢃ x, 1 ꢃ y,
2
2
1 ꢃ z), and these two atoms are involved in short IÁ Á ÁO
interactions with the O132 atoms at (x, 32 ꢃ y, 21 + z) and (1 ꢃ x,
1
ꢃ + y, 12 ꢃ z), respectively, which themselves lie in the dimeric
2
units centred at (12, 1, 1) and (12, 0, 0), respectively. The two
1
1
O132 atoms in the dimer centred at (12, , ), at (x, y, z) and
2
2
(1 ꢃ x, 1 ꢃ y, 1 ꢃ z), are in turn involved in IÁ Á ÁO interactions
with atoms I2 at (x, ꢃ y, ꢃ + z) and (1 ꢃ x, ꢃ + y, ꢃ z),
3
1
1
3
2
2
2
2
respectively, and these I atoms are components of the dimers
centred at (12, 1, 0) and (21, 0, 1). Thus, each R22(10) dimeric unit
is linked via the various I2Á Á ÁO132 interactions to four other
dimers, and propagation of these interactions generates a
continuous sheet parallel to (100) (Fig. 8) in which the R22(10)
rings alternate in checkerboard fashion with R64(22) rings,
where the four negatively charged nitro O atoms are regarded
as the donors and the six positively charged I as the acceptors.
A second sheet results from the action of the hydrogen
bonds: each dimer unit accepts two NÐHÁ Á ÁO hydrogen
bonds and contains the donors in two
Figure 7
Part of the crystal structure of (II) showing the formation of a (100) sheet
built from type 2 molecules only. For the sake of clarity, H atoms bonded
to C are omitted. Atoms marked with (*), (#), ($), (&) or (@) are at the
symmetry positions (x, ꢃy, ꢃ + z), (x, 1 + y, z), (x, ꢃ1 ꢃ y, 12 + z),
1
2
(x, ꢃ1 ꢃ y, ꢃ + z) and (x, ꢃy, 12 + z), respectively.
1
2
other such bonds. The amino N-atoms
at (x, y, z) and (1 ꢃ x, 1 ꢃ y, 1 ꢃ z) both
1
1
lie in the dimer centred at (12, , ), and
they act as hydrogen-bond donors, via
2
2
3
H1B, to atoms O132 at (1 + x, ꢃ y,
2
12 + z) and (ꢃx, ꢃ + y, ꢃ z), respec-
1
2
1
2
tively, which are components of the
dimeric units centred at (32, 1, 1) and (ꢃ ,
1
2
0, 0), respectively. Similarly, the atoms
O132 at (x, y, z) and (1 ꢃ x, 1 ꢃ y,
1 ꢃ z) accept hydrogen bonds from
3
2
amino N atoms at (ꢃ1 + x, ꢃ y,
Figure 8
ꢃ + z) and (2 ꢃ x, ꢃ + y, 32 ꢃ z), which
1
2
1
2
Stereoview of part of the crystal structure of (III) showing formation of a (100) sheet of R22(10) and
R64(22) rings built from IÁ Á ÁO interactions only.
1
2
lie in the dimers centred at (ꢃ , 1, 0) and
ꢀ
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Simon J. Garden et al.
Interactions in iodo-nitroanilines 707

research papers
the supramolecular structures of
compounds (I)±(III), in order to
compare these with the two related
compounds (IV) and (V).
The hydrogen bond in (I) generates
a ®nite (zero-dimensional) dimer, while
the iodoÁ Á Ánitro interaction generates
single chains: the combined effect of
these two interactions is the formation
of a strictly one-dimensional substruc-
ture (Fig. 4), while the ꢀÁ Á Áꢀ stacking
interaction links the one-dimensional
fragments into a three-dimensional
whole. In (II) and in both polymorphs
of (V), a compound which is isomeric
Figure 9
Part of the crystal structure of (III) showing the formation of a (102) sheet of R2(10) and R6(30)
2
6
ꢀ
rings. The atoms marked with (*), (#), ($) or (&) are at the symmetry positions (1 ꢃ x, 1 ꢃ y, 1 ꢃ z),
with both (I) and (II), the NÐHÁ Á ÁO
1
2
3
2
1
2
(1 + x, 32 ꢃ y, 12 + z), (2 ꢃ x, ꢃ + y, 32 ꢃ z) and (ꢃ1 + x, ꢃ y, ꢃ + z), respectively.
hydrogen bonds and the iodoÁ Á Ánitro
interactions individually form chains,
and in combination they form sheets, but in each of these three
structures the effects of the ꢀÁ Á Áꢀ stacking interactions are
different. In the orthorhombic modi®cation of (V), the
stacking interactions link the sheets into a single three-
dimensional framework; in the triclinic polymorph of (V), the
sheets are pairwise linked by the stacking interactions forming
bi-layers; in (II), there are no ꢀÁ Á Áꢀ stacking interactions and
the structure is based on isolated sheets. One of the
iodoÁ Á Ánitro interactions in (III) generates a ®nite dimer, and
these units are linked into sheets of different type and direc-
tion by the second iodoÁ Á Ánitro interaction and by the
hydrogen bond, so that a three-dimensional structure results
from these interactions alone. This is simply reinforced by the
ꢀÁ Á Áꢀ stacking interactions.
Figure 10
Part of the crystal structure of (III), showing the ꢀÁ Á Áꢀ stacking
interaction. The atoms marked with (*) are at the symmetry position
(2 ꢃ x, 1 ꢃ y, 2 ꢃ z).
(32, 0, 1), respectively. Propagation of the hydrogen bond in
4. Concluding comments
combination with the IÁ Á ÁO interaction that generates the
The structures discussed here show that even in simple
isomeric series, such as compounds (I), (II) and (V), the
patterns of supramolecular aggregation and even the nature of
the interactions involved may differ substantially. In effect, the
aggregation pattern for any one compound is not readily
predicted from knowledge of the patterns in the others, even
those of its isomers. Contrasts of this kind provide continuing
challenges to attempts to predict from ®rst principles the
crystal structures of comparatively simple molecular
compounds (Lommerse et al., 2000).
ꢀ
dimer produces a sheet parallel to (102) (Fig. 9), in which the
R22(10) rings alternate in checkerboard fashion with centro-
symmetric R66(30) rings incorporating hydrogen bonds and
IÁ Á ÁO interactions. It may also be noted that the NÐHÁ Á ÁO
hydrogen bond alone produces a one-dimensional substruc-
ture in the form of a C(7) chain running parallel to the [201]
direction, generated by the glide plane at y = 0.75. If in both
2
ꢀ
the (100) sheet and the (102) sheet the R2(10) dimers are
regarded as the nodes of the resulting nets, then these nets are
both of (4,4) type (Batten & Robson, 1998). The combination
ꢀ
of the (100) and (102) sheets is suf®cient to generate a
continuous three-dimensional framework.
X-ray data were collected at the EPSRC X-ray Crystal-
lographic Service, University of Southampton, UK. The
authors thank the staff of the service for all their help and
advice. JNL thanks NCR Self-Service, Dundee, for grants that
have provided computing facilities for this work. SJG, SPF and
JLW thank CNPq and FAPERJ for ®nancial support.
This framework is further reinforced by aromatic ꢀÁ Á Áꢀ
stacking interactions between molecules at (x, y, z) and
(2 ꢃ x, 1 ꢃ y, 2 ꢃ z), where the interplanar spacing and the
Ê
Ê
centroid separation are 3.503 (3) A and 3.636 (3) A, respec-
Ê
tively, corresponding to a centroid offset of only 0.902 (3) A
(Fig. 10): the mutual disposition of the stacked rings neatly
accommodates the nearly orthogonal nitro groups.
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