Triclinic and orthorhombic polymorphs of 2-iodo-4-nitroaniline: interplay of hydrogen bonds, nitro...I interactions and aromatic pi-pi-stacking interactions.

Article abstract of DOI:10.1107/S0108270101007053

In the triclinic polymorph of 2-iodo-4-nitroaniline, C(6)H(5)IN(2)O(2), space group P-1, the molecules are linked by paired N-H...O hydrogen bonds into C(8)[R(2)(2)(6)] chains of rings. These chains are linked into sheets by nitro...I interactions, and the sheets are pairwise linked by aromatic pi-pi-stacking interactions. In the orthorhombic polymorph, space group Pbca, the molecules are linked by single N-H...O hydrogen bonds into spiral C(8) chains; the chains are linked by nitro...O interactions into sheets, each of which is linked to its two immediate neighbours by aromatic pi-pi-stacking interactions, so producing a continuous three-dimensional structure.

Full text of DOI:10.1107/S0108270101007053

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
Aromatic nitro groups also form robust supramolecular
synthons with iodo-aromatics, as for example in 4-iodoaniline
(CSD refcode ZONYIK; Thalladi et al., 1996) and 4-iodo-40-
nitrobiphenyl (CSD refcode RAYCID01; Masciocchi et al.,
1998), as well as in the adducts of p-dinitrobenzene with
p-diiodobenzene (CSD refcode YESZEB; Allen et al., 1994)
and with 4-iodocinnamic acid (CSD refcode ZONYOQ;
Thalladi et al., 1996). In all of these species, the shortest IÁ Á ÁO
distances are very much less than the sum of the van der Waals
ISSN 0108-2701
Triclinic and orthorhombic poly-
morphs of 2-iodo-4-nitroaniline:
interplay of hydrogen bonds,
nitroÁ Á ÁI interactions and aromatic
p±p-stacking interactions
Ê
radii (3.50 A; Bondi, 1964), while the associated CÐIÁ Á ÁO
angles lie in the range 150±170ꢁ.
As part of a continuing study of supramolecular aggregation
in substituted nitroanilines (Wardell et al., 2000; Cannon et al.,
2001; Ferguson et al., 2001; Glidewell et al., 2001), we have now
investigated the interplay of NÐHÁ Á ÁO hydrogen bonding and
nitroÁ Á ÁI interactions in 2-iodo-4-nitroaniline (C6H5IN2O2),
where we have obtained two polymorphs, a triclinic form, (Ia),
in space group P1, and an orthorhombic form, (Ib), in space
group Pbca. Both forms have Z0 = 1 and their crystal structures
exhibit a combination of NÐHÁ Á ÁO hydrogen bonds, nitroÁ Á ÁI
interactions and aromatic ꢀ±ꢀ-stacking interactions.
Susan A. McWilliam,a Janet M. S. Skakle,a John N. Low,a
James L. Wardell,a Simon J. Garden,b Angelo C. Pinto,b
Jose C. Torresb and Christopher Glidewellc*
aDepartment of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen
b
Â
Â
Ã
AB24 3UE, Scotland, Instituto de Quõmica, Departamento de Quõmica Organica,
Universidade Federal do Rio de Janeiro, 21945-970 Rio de Janeiro, RJ, Brazil, and
cSchool of Chemistry, University of St Andrews, St Andrews, Fife KY16 9ST, Scotland
Correspondence e-mail: cg@st-andrews.ac.uk
Received 20 April 2001
Accepted 27 April 2001
In the triclinic polymorph of 2-iodo-4-nitroaniline, C6H5I-
N2O2, space group P1, the molecules are linked by paired
NÐHÁ Á ÁO hydrogen bonds into C(8)[R22(6)] chains of rings.
These chains are linked into sheets by nitroÁ Á ÁI interactions,
and the sheets are pairwise linked by aromatic ꢀ±ꢀ-stacking
interactions. In the orthorhombic polymorph, space group
Pbca, the molecules are linked by single NÐHÁ Á ÁO hydrogen
bonds into spiral C(8) chains; the chains are linked by
nitroÁ Á ÁO interactions into sheets, each of which is linked to its
two immediate neighbours by aromatic ꢀ±ꢀ-stacking inter-
In the triclinic polymorph, (Ia), the planar molecules
(Fig. 1a) are linked into chains by an uncommon synthon
comprising pairs of NÐHÁ Á ÁO hydrogen bonds. The two NÐ
H bonds in the molecule at (x, y, z) form hydrogen bonds
(Table 1) with the two O atoms in the molecule at (x, 1 + y,
1 + z), so producing by translation a C(8)[R22(6)] chain of
rings (Bernstein et al., 1995) running parallel to the [011]
direction (Fig. 2). The NÐHÁ Á ÁO hydrogen bonding in (Ia) is
thus wholly different from that normally found in 4-nitro-
anilines. In the R22(6) ring, the NÐOÁ Á ÁH angles are 111 and
110ꢁ, and the sum of the internal angles is 360ꢁ within
experimental uncertainly, so that this ring is planar. The chain
of rings can thus be regarded as a continuous sequence of
planar hexagonal rings in which the covalently bonded aryl
rings alternate with hydrogen-bonded rings of almost the same
size. In this connection, Desiraju (1995) has already drawn
attention to the importance of ring size and shape, as opposed
to ring composition, as an important factor in crystal engi-
neering and molecular recognition. There are two C(8)[R22(6)]
chains of rings passing through each unit cell, related by the
centres of inversion and thus running antiparallel to one
another. A combination of nitroÁ Á ÁI interactions and aromatic
ꢀ±ꢀ-stacking interactions links these chains into sheets and it
is convenient to consider these interactions in turn.
actions, so producing
structure.
a continuous three-dimensional
Comment
Molecules of 4-nitroanilines generally act as double donors of
hydrogen bonds and as double acceptors, such that each
molecule is linked to four other molecules by NÐHÁ Á ÁO
hydrogen bonds. Thus, for example, unsubstituted 4-nitro-
aniline itself [Cambridge Structural Database (CSD; Allen &
Kennard, 1993) refcode NANILI02 (Tonogaki et al., 1993)]
forms sheets in the form of (4,4)-nets (Batten & Robson, 1998)
built from a single type of R44(22) ring (Bernstein et al., 1995).
Similar (4,4)-nets, albeit containing successively larger rings,
are found in the structures of the extended 4-nitroaniline
analogues 4-H2NC4H4±(C C)n±C6H4NO2-40 (n = 0±3) [CSD
refcodes KEFLEM (n = 0), KEFLOW (n = 1), KEFLUC (n =
2) and KEFMAJ (n = 3); Graham et al., 1989)]. By contrast,
2-methyl-4-nitroaniline forms a continuous three-dimensional
framework, in which each molecule is again linked to four
other molecules (Ferguson et al., 2001).
There is a very short intermolecular IÁ Á ÁO contact [IÁ Á ÁO2i
3.266 (5) A, CÐIÁ Á ÁO2i 154.5 (2)ꢁ and IÁ Á ÁO2iÐN4i
Ê
154.1 (4)ꢁ; symmetry code (i) 1 + x, 1 + y, 1 + z], which
ꢀ
942 # 2001 International Union of Crystallography
Printed in Great Britain ± all rights reserved
Acta Cryst. (2001). C57, 942±945

organic compounds
serves to link parallel chains of the same polarity into two-
dimensional sheets parallel to (011), in which the R22(6) rings
described above alternate with larger rings (Fig. 2). If the
graph-set notation generally employed for hydrogen-bonded
motifs is extended to other directed but non-covalent inter-
actions (Starbuck et al., 1999), these larger rings may be
described as being of R44(20) type. The shortest intermolecular
IÁ Á ÁO distance involving the other O atom [IÁ Á ÁO1ii
Ê
3.494 (5) A; symmetry code: (ii) x, 2 y, 1 z] is not
signi®cantly shorter than the sum of the van der Waals radii,
and is thus not regarded as structurally signi®cant. Two (011)
sheets pass through each unit cell, and these sheets are
themselves linked into pairs by aromatic ꢀ±ꢀ-stacking inter-
actions. Molecules at (x, y, z) and (1 x, 2 y, 1 z) are
linked by a ꢀ±ꢀ interaction; the interplanar spacing is
3.451 (3) A and the centroid offset is 0.747 (3) A.
In the orthorhombic polymorph (Ib), (Fig. 1b), the dihedral
angle between the aryl ring and the CÐNO2 plane is 11.1 (5)ꢁ.
Figure 2
Ê
Ê
Part of the crystal structure of the triclinic polymorph, (Ia), showing
C(8)[R22(6)] chains of rings linked by nitroÁ Á ÁI interactions into a (011)
sheet. For the sake of clarity, H atoms bonded to C atoms have been
omitted. Atoms marked with an asterisk (*) or hash (#) are at the
symmetry positions (x, 1 + y, 1 + z) and ( 1 + x, 1 + y, 1 + z),
respectively.
The hydrogen bonding differs from that in (Ia) in that the
molecules of (Ib) act as single donors and as single acceptors
of hydrogen bonds, so that simple C(8) chains are formed
rather than chains of rings, as in (Ia), or the sheets commonly
found in 4-nitroanilines and their analogues. Amino N1 at (x,
y, z) acts as hydrogen-bond donor to O1 at (1 x, 12 + y,
Figure 3
Part of the crystal structure of the orthorhombic polymorph, (Ib),
showing the linking of C(8) spiral chains parallel to [010] into a (100)
sheet of R24(12) and R44(28) rings. For the sake of clarity, H atoms bonded
to C atoms have been omitted. Atoms marked with an asterisk (*) or hash
Figure 1
The asymmetric unit of 2-iodo-4-nitroaniline, showing the atom-labelling
scheme (a) in the triclinic polymorph (Ia) and (b) in the orthorhombic
polymorph (Ib). Displacement ellipsoids are drawn at the 30%
probability level.
1
3
(#) are at the symmetry positions (1 x, 12 + y,
12 + z), respectively.
z) and (x,
y,
2
2
ꢀ
Acta Cryst. (2001). C57, 942±945
Susan A. McWilliam et al.
Two polymorphs of C6H5IN2O2 943

organic compounds
1
2
z), while N1 at (1 x, 21 + y, 12 z) in turn acts as donor
Experimental
to O1 at (x, 1 + y, z); hence a C(8) spiral is generated around
the 21 screw axis along (12, y, ) (Fig. 3). Four such chains run
through each unit cell, one around each of the 21 axes parallel
to [010]; two lie in the domain 0.30 < x < 0.70, and the other
two lie in the domain 0.80 < x < 1.20.
A solution of 4-nitroaniline (20 mmol) in methanol (40 ml) was
added rapidly to an aqueous solution of K[ICl2] (60 ml,
0.67 mol dm 3) at room temperature (Larsen et al., 1956; Garden et
al., 2001). The reaction mixture was stirred at room temperature for
2 h, and then ®ltered to remove the product. The product was washed
with water and allowed to dry in air. After recrystallization from
ethanol, the product had a melting point of 385±387 K. NMR
(CDCl3): ꢁH 4.84 (2H, br s, NH2), 6.66 (1H, d, J = 9.2 Hz, H-6), 8.00
(1H, dd, J = 2.4, 8.9 Hz, H-5), 8.51 p.p.m. (d, J = 2.4 Hz, H-3); ꢁC 81.6
(C-2), 113.3 (C-6), 126.7 (C-5), 136.5 (C-3), 140.2 (C-4), 153.4 p.p.m.
(C-1). Crystals suitable for single-crystal X-ray diffraction were
obtained from an ethanol solution. Samples of the two polymorphs
were isolated manually at ambient temperature.
1
4
Within each of these domains, the chains are linked into
sheets by nitroÁ Á ÁI interactions [IÁ Á ÁO1iii 3.153 (7) A, CÐ
Ê
IÁ Á ÁO1iii 171.5 (3)ꢁ and IÁ Á ÁO1iiiÐN4iii 112.6 (5)ꢁ; symmetry
3
2
code: (iii) x,
y, 12 + z] and propagation of this interaction
generates sheets parallel to (100) built from alternating R24(12)
and R44(28) rings (Fig. 3). As in the triclinic polymorph, only
one O atom forms IÁ Á ÁO contacts shorter than the sum of the
van der Waals radii. There are two (100) sheets passing
through each unit cell, and each sheet is linked to its two
immediate neighbours by aromatic ꢀ±ꢀ-stacking interactions
(Fig. 4), so generating a continuous three-dimensional struc-
Compound (Ia)
Crystal data
C6H5IN2O2
Mr = 264.02
Triclinic, P1
a = 7.1647 (4) A
b = 7.9572 (4) A
Z = 2
Dx = 2.278 Mg m
Mo Kꢂ radiation
3
Ê
Ê
Ê
Cell parameters from 1728
re¯ections
c = 8.0489 (5) A
ꢅ = 3.1±27.5ꢁ
ꢆ = 4.11 mm
T = 150 (2) K
1
ꢂ = 67.905 (3)ꢁ
ꢃ = 86.956 (3)ꢁ
ꢄ = 65.744 (2)ꢁ
Needle, yellow
0.28 Â 0.08 Â 0.03 mm
3
Ê
V = 384.84 (4) A
Data collection
KappaCCD diffractometer
' and ! scans with ꢇ offsets
Absorption correction: multi-scan
(DENZO±SMN; Otwinowski &
Minor, 1997)
1728 independent re¯ections
1556 re¯ections with I > 2ꢈ(I)
Rint = 0.047
ꢅmax = 27.5ꢁ
h = 9 ! 9
Tmin = 0.393, Tmax = 0.887
4602 measured re¯ections
k = 10 ! 10
l = 10 ! 9
Re®nement
Re®nement on F2
R[F2 > 2ꢈ(F2)] = 0.046
wR(F2) = 0.120
w = 1/[ꢈ2(Fo2) + (0.0662P)2
+ 1.2313P]
where P = (Fo2 + 2Fc2)/3
S = 1.09
1728 re¯ections
100 parameters
H-atom parameters constrained
(Á/ꢈ)max < 0.001
3
Ê
Ê
Áꢉmax = 2.77 e A (0.96 A
from I2)
3
2.14 e A (0.83 A
Ê
Ê
Áꢉmin =
from I2)
Table 1
Hydrogen-bonding geometry (A, ) for (Ia).
ꢁ
Figure 4
Ê
Part of the crystal structure of (Ib) showing the linking of (100) sheets by
means of aromatic ꢀ±ꢀ-stacking interactions. For the sake of clarity, H
atoms bonded to C atoms have been omitted. Atoms marked with an
asterisk (*), hash (#), dollar sign ($) or ampersand (&) are at the
symmetry positions ( 12 + x, y, 21 z), (21 + x, y, 12 z), (1 x, 21 + y, 12 z)
and (1 x, 12 + y, 12 z), respectively.
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
N1ÐH11Á Á ÁO1i
0.88
0.88
2.35
2.40
2.994 (7)
3.000 (8)
130
126
N1ÐH12Á Á ÁO2i
Symmetry code: (i) x; 1 ‡ y; z 1.
ture. The aryl ring at (x, y, z) is a component of the (100) sheet
in the domain 0.30 < x < 0.70; this ring forms ꢀ±ꢀ interactions
with the rings at (21 + x, y, 21 z) and ( 21 + x, y, 21 z), which
are components of the sheets in the domains 0.80 < x < 1.20
and 0.20 < x < 0.20, respectively. These rings are not all
parallel by symmetry, but the interplanar angles are only ca
Compound (Ib)
Crystal data
C6H5IN2O2
Mr = 264.02
Mo Kꢂ radiation
Cell parameters from 2339
re¯ections
Orthorhombic, Pbca
Ê
a = 7.4215 (5) A
ꢁ
Ê
2.0 , with interplanar spacings of ca 3.56 A and centroid
ꢅ = 2.5±31.1ꢁ
ꢆ = 4.08 mm
T = 296 (2) K
1
Ê
offsets of ca 1.21 A.
The CÐI distances in (Ia) and (Ib) are 2.098 (5) and
Ê
2.087 (8) A, respectively; the other bond lengths and angles
show no unexpected features.
Ê
b = 12.6755 (9) A
Ê
c = 16.4638 (11) A
Ê
V = 1548.77 (18) A
3
Plate, yellow
0.20 Â 0.20 Â 0.03 mm
Z = 8
Dx = 2.265 Mg m
3
ꢀ
944 Susan A. McWilliam et al.
Two polymorphs of C6H5IN2O2
Acta Cryst. (2001). C57, 942±945

organic compounds
Data collection
Nonius KappaCCD diffractometer, and for (Ib) at the
University of Aberdeen using a Bruker SMART CCD
diffractometer.
Bruker SMART 1000 CCD-
detector diffractometer
'±! scans
Absorption correction: multi-scan
(SADABS; Bruker, 1997)
Tmin = 0.495, Tmax = 0.887
12391 measured re¯ections
2339 independent re¯ections
1109 re¯ections with I > 2ꢈ(I)
Rint = 0.089
ꢅ
max = 31.1ꢁ
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: SK1480). Services for accessing these data are
described at the back of the journal.
h = 10 ! 10
k = 17 ! 14
l = 22 ! 23
Re®nement
Re®nement on F2
R[F2 > 2ꢈ(F2)] = 0.063
wR(F2) = 0.180
S = 0.96
2339 re¯ections
w = 1/[ꢈ2(Fo2) + (0.0943P)2]
where P = (Fo2 + 2Fc2)/3
References
(Á/ꢈ)max = 0.001
Allen, F. H., Goud, B. S., Hoy, V. J., Howard, J. A. K. & Desiraju, G. R. (1994).
J. Chem. Soc. Chem. Commun. pp. 2729±2730.
Allen, F. H. & Kennard, O. (1993). Chem. Des. Autom. News, 8, 1, 31±37.
Batten, S. R. & Robson, R. (1998). Angew. Chem. Int. Ed. 37, 1460±1494.
Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem.
Int. Ed. Engl. 34, 1555±1573.
3
Ê
Ê
Áꢉmax = 2.20 e A (0.91 A
from I2)
3
1.21 e A (0.90 A
Ê
Ê
100 parameters
H-atom parameters constrained
Áꢉmin =
from I2)
Bondi, A. (1964). J. Chem. Phys. 68, 441±451.
Bruker (1999). SADABS, SAINT and SMART. Bruker AXS Inc., Madison,
Wisconsin, USA.
Table 2
Hydrogen-bonding geometry (A, ) for (Ib).
ꢁ
Ê
Cannon, D., Glidewell, C., Low, J. N., Quesada, A. & Wardell, J. L. (2001). Acta
Cryst. C57, 216±217.
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
Desiraju, G. R. (1995). Angew. Chem. Int. Ed. Engl. 34, 2311±2327.
Ferguson, G. (1999). PRPKAPPA. University of Guelph, Canada.
Ferguson, G., Glidewell, C., Low, J. N., Skakle, J. M. S. & Wardell, J. L. (2001).
Acta Cryst. C57, 315±316.
N1ÐH11Á Á ÁO1i
Symmetry code: (i) 1 x; y
0.86
2.31
3.085 (11)
150
1
2
1
2
;
z.
Garden, S. J., Torres, J. C., de Souza Melo, S. C., Lima, A. S., Pinto, A. C. &
Lima, E. D. S. (2001). Tetrahedron Lett. 42, 2089±2092.
Glidewell, C., Cannon, D., Quesada, A., Low, J. N., McWilliam, S. A., Skakle,
J. M. S. & Wardell, J. L. (2001). Acta Cryst. C57, 455±458.
Graham, E. M., Miskowski, V. M., Perry, J. W., Coulter, D. R., Stiegman, A. E.,
Schaefer, W. P. & Marsh, R. E. (1989). J. Am. Chem. Soc. 111, 8771±8778.
Larsen, A. A., Moore, C., Sprague, J., Cloke, B., Moss, J. & Hoppe, J. O. (1956).
J. Am. Chem. Soc. 78, 3210±3216.
Masciocchi, N., Bergamo, M. & Sironi, A. (1998). Chem. Commun. pp. 1347±
1348.
Nonius (1997). KappaCCD Server Software. Windows 3.11 Version. Nonius
BV, Delft, The Netherlands.
Otwinowski, Z. & Minor, W. (1997). Methods Enzymol. 276, 307±326.
Polymorph (Ia) is triclinic; space group P1 was chosen and
con®rmed by the successful structure solution and re®nement. Poly-
morph (Ib) is orthorhombic; space group Pbca was uniquely assigned
from the systematic absences. All H atoms were treated as riding
Ê
atoms with NÐH distances of 0.86 or 0.88 A and CÐH distances of
Ê
0.93 or 0.95 A.
Data collection: KappaCCD Server Software (Nonius, 1997) for
compound (Ia), SMART (Bruker, 1999) for compound (Ib); cell
re®nement and data reduction: DENZO±SMN (Otwinowski &
Minor, 1997) for compound (Ia), SAINT (Bruker, 1999) for
compound (Ib). For both compounds, program(s) used to solve
structure: SHELXS97 (Sheldrick, 1997); program(s) used to re®ne
structure: SHELXL97 (Sheldrick, 1997); molecular graphics:
PLATON (Spek, 2001); software used to prepare material for
publication: SHELXL97 and PRPKAPPA (Ferguson, 1999).
È
Sheldrick, G. M. (1997). SHELXL97 and SHELXS97. University of Gott-
ingen, Germany.
Spek, A. L. (2001). PLATON. University of Utrecht, The Netherlands.
Starbuck, J., Norman, N. C. & Orpen, A. G. (1999). New J. Chem. 23, 969±972.
Thalladi, V. R., Goud, B. S., Hoy, V. J., Allen, F. H., Howard, J. A. K. &
Desiraju, G. R. (1996). Chem. Commun. pp. 401±402.
Tonogaki, M., Kawata, T., Ohba, S., Iwata, Y. & Shibuya, I. (1993). Acta Cryst.
B49, 1031±1039.
X-ray data for (Ia) were collected at the EPSRC X-ray
Crystallographic Service, University of Southampton, using a
Wardell, S. M. S. V., Ward, M. F., Wardell, J. L., Low, J. N. & Glidewell, C.
(2000). Acta Cryst. C56, 865±867.
ꢀ
Acta Cryst. (2001). C57, 942±945
Susan A. McWilliam et al.
Two polymorphs of C6H5IN2O2 945