5-Iodobenzofurazan 1-oxide: Polymorphs, pseudosymmetry and disorder

Article abstract of DOI:10.1107/S0108270108003776

5-Iodo-benzofurazan 1-oxide (systematic name: 5-iodo-benzo-1,2,5-oxadiazole 1-oxide), C6H3IN2O2, occurs in two polymorphic forms, both monoclinic in P21/c with Z′ = 2. The inter-molecular inter-actions in the two polymorphs are quite different. In polymorph (I), there are strong inter-molecular I...O inter-actions, with I...O distances of 3.114 (8) and 3.045 (8) A. In polymorph (II), there are strong inter-mol-ecular I...N inter-actions, with I...N distances of 3.163 (4) and 3.175 (5) A. In (I), there is about 15% disorder in one mol-ecule and about 5% in the other. In both polymorphs, there are pseudosymmetric relationships between the crystal-log-raphically independent mol-ecules.

Full text of DOI:10.1107/S0108270108003776

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
ISSN 0108-2701
5-Iodobenzofurazan 1-oxide: poly-
morphs, pseudosymmetry and disorder
Doyle Britton,* Wayland E. Noland and Christopher M.
Clark
Department of Chemistry, University of Minnesota, Minneapolis, MN 55455-0431,
USA
Correspondence e-mail: britton@chem.umn.edu
Received 26 December 2007
Accepted 4 February 2008
Online 8 March 2008
Figure 1
A view of polymorph (I), showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 50% probability level and H
atoms are shown as small spheres of arbitrary radii. The minor
components of the disorder are shown with open bonds.
5
-Iodobenzofurazan 1-oxide (systematic name: 5-iodobenzo-
,2,5-oxadiazole 1-oxide), C H IN O , occurs in two poly-
1
morphic forms, both monoclinic in P2 /c with Z = 2. The
6
3
2
2
0
1
intermolecular interactions in the two polymorphs are quite
different. In polymorph (I), there are strong intermolecular
chains grow together in irregular sheets parallel to the (101)
ꢁ
Iꢀ ꢀ ꢀO interactions, with Iꢀ ꢀ ꢀO distances of 3.114 (8) and
plane, with molecule A tilted by 11.2 (1) and molecule B
ꢁ
˚
.045 (8) A. In polymorph (II), there are strong intermol-
3
tilted by 10.8 (1) with respect to the sheet; the molecules are
ꢁ
ecular Iꢀ ꢀ ꢀN interactions, with Iꢀ ꢀ ꢀN distances of 3.163 (4) and
2.5 (1) away from being parallel to one another. There are
˚
.175 (5) A. In (I), there is about 15% disorder in one
3
Hꢀ ꢀ ꢀO interactions between adjacent chains. The geometric
data for the H-atom interactions are given in Table 2; only
contacts with distances less than the sum of the van der Waals
radii (Bondi, 1964; Rowland & Taylor, 1996) are included. See
Desiraju & Steiner (1999) for a discussion of C—Hꢀ ꢀ ꢀX
hydrogen bonds. The sheets stack so that columns occur
parallel to the [001] direction, with each molecule A in contact
molecule and about 5% in the other. In both polymorphs,
there are pseudosymmetric relationships between the crystal-
lographically independent molecules.
Comment
The structure of 5-iodobenzofurazan 1-oxide was originally
determined at room temperature (Gehrz & Britton, 1972).
Diffractometer data were used, but no measurable data were
ꢁ
found above ꢀ = 18 (Mo Kꢁ radiation). The limited number
of intensity measurements, combined with the dominance of
the I atoms, led to large errors in the light-atom parameters.
This structure, polymorph (I), has been redetermined to
improve the accuracy. In the course of the redetermination a
second polymorph, (II), was discovered, the structure of which
is also reported.
Both molecules in polymorph (I) are disordered (Fig. 1),
but there is no disorder in polymorph (II) (Fig. 2). All of the
bond distances and angles are normal.
Molecules of (I) form chains parallel to [010] held together
by intermolecular Iꢀ ꢀ ꢀO interactions (Fig. 3). Each chain
involves one or other of the two independent molecules. The
geometric data for these interactions are given in Table 1. The
Figure 2
A view of polymorph (II), showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 50% probability level and H
atoms are shown as small spheres of arbitrary radii.
Acta Cryst. (2008). C64, o187–o190
doi:10.1107/S0108270108003776
# 2008 International Union of Crystallography o187

organic compounds
Figure 4
The packing of polymorph (II), showing one layer viewed normal to the
(001) plane. Molecules in each horizontal row are crystallographically
equivalent. Iꢀ ꢀ ꢀN and Hꢀ ꢀ ꢀO contacts are shown as dashed lines. Atom
Figure 3
The packing of polymorph (I), showing one layer viewed normal to the
0
I1A is related to atom I1A by the symmetry code (x, 1 + y, z) and atom
I1B is related to atom I1B by the symmetry code (x, ꢂ1 + y, z).
0
(101) plane. Molecules in each vertical column are crystallographically
equivalent. Iꢀ ꢀ ꢀO and Hꢀ ꢀ ꢀX contacts are shown as dashed lines. Atom
0
1
2
3
2
I1A is related to atom I1A by the symmetry code (2 ꢂ x, ꢂ + y, ꢂ z)
1
2
0
1
2
and atom I1B is related to atom I1B by the symmetry code (1 ꢂ x, ꢂ + y,
The pseudosymmetry in (I) can be seen in Fig. 3. Molecule
A is converted to molecule B by a pseudo-translation (all non-
H atoms weighted equally)
ꢂ z).
with two other A molecules and each B molecule with two
ꢁ
x ¼ ꢂ0:489 ð3Þ þ x ;
B
A
other B molecules. The A molecules are tilted by 16.3 (1) and
ꢁ
y ¼ 0:258 ð1Þ þ y ;
the B molecules by 16.9 (1) with respect to the direction of
the stacks. The perpendicular distances between molecules
˚
alternate between 3.59 (3) and 3.62 (3) A in both stacks.
In the preceding discussion of the packing, only the major
components of the disorder were considered. The disorder
appears to arise from both kinds of chains shifting half a unit-
cell length in the b direction. This seems a reasonable model,
although all that can be said from the X-ray data is that there
is disorder in the individual molecules.
B
A
z ¼ ꢂ0:490 ð12Þ þ z :
B
A
It can be converted to the other three molecules in Wyckoff
position e of molecule B by a pseudo-center
x ¼ 1:489 ð3Þ ꢂ x ;
B
A
y ¼ 0:742 ð1Þ ꢂ y ;
B
A
z ¼ 1:490 ð12Þ ꢂ z ;
B
A
Molecules of (II) form zigzag chains parallel to [100] (Fig. 4),
held together by intermolecular Iꢀ ꢀ ꢀN interactions. Each chain
involves, alternately, the two kinds of independent molecules.
The geometric data for these interactions are given in Table 1.
a pseudo-twofold screw axis
x ¼ 1:489 ð3Þ ꢂ x ;
B
A
y ¼ 0:758 ð1Þ þ y ;
B
A
The chains grow together in irregular sheets parallel to the
ꢁ
z ¼ 0:990 ð12Þ ꢂ z
B
A
(001) plane, with molecule A tilted by 18.6 (1) and molecule
B tilted by 19.3 (1) with respect to the sheet; the two mol-
and a pseudo-a-glide
ꢁ
ꢁ
ecules are 27.7 (1) away from being parallel to each other.
There are Hꢀ ꢀ ꢀO interactions between adjacent chains
x ¼ ꢂ0:489 ð3Þ þ x ;
B
A
y ¼ 0:242 ð1Þ ꢂ y ;
B
A
(Table 2). The sheets stack so that columns occur parallel to
z ¼ 0:010 ð12Þ þ z :
B
A
the [101] direction, with each molecule A in contact with one
A molecule and one B molecule, and vice versa. The A mol-
Similar relationships hold for the other molecules in the
Wyckoff position e of molecule A. As a measure of the
precision of the pseudosymmetry, if molecules A and B are
matched as well as possible using OFIT in SHELXTL (Shel-
drick, 2008), the r.m.s. devation between the atoms is 0.028 A.
˚
If the translation above is used, the r.m.s. deviation is 0.079 A,
ꢁ
ꢁ
ecules are tilted by 22.0 (1) and the B molecules by 20.5 (1)
with respect to the direction of the stack. The perpendicular
˚
distances between molecules are: Aꢀ ꢀ ꢀA= 3.736 (7) A, Aꢀ ꢀ ꢀB=
˚
˚
˚
3
.53 (3) A and Bꢀ ꢀ ꢀB = 3.770 (6) A.
There are no Iꢀ ꢀ ꢀI contacts in either structure shorter than
˚
.4 A. The expected van der Waals distance (Bondi, 1964;
4
Rowland & Taylor, 1996) is 3.96 A.
and if an idealized translation of ꢂa/2, b/4, ꢂc/2 is used, the
˚
˚
r.m.s. deviation is 0.218 A.
ꢃ
o188 Britton et al. Two polymorphs of C
6 3 2
H IN O
2
Acta Cryst. (2008). C64, o187–o190

organic compounds
The pseudosymmetry in (II) can be seen in Fig. 4. Molecule
A is converted to molecule B by a pseudo-a-glide
1969)] was dissolved in boiling glacial acetic acid (50 ml) and then
cooled to 298 K. A solution of NaNO
concentrated H SO (20 ml) was stirred into the acetic acid solution
and the mixture was poured over crushed ice (150 g). An aqueous
solution of NaN (0.227 M) was added slowly until the evolution of
ceased, giving a light-yellow precipitate, which was crystallized
2
(0.575 g, 8.33 mmol) in
2
4
x ¼ 0:506 ð4Þ þ x ;
B
A
y ¼ 0:411 ð10Þ ꢂ y ;
3
B
A
N
2
z ¼ 0:015 ð7Þ þ z :
B
A
i
from PrOH–H
.24 mmol, 96%) [m.p. 345.5 K, cf. 345.2 K (Deorha et al., 1962)].
Compound (2) (1.00 g, 3.45 mmol) was dissolved in toluene (50 ml)
and the solution was refluxed until the evolution of N ceased. The
2
O (ꢄ1:1 v/v) giving (2) as light-yellow needles (2.10 g,
7
It can be converted to the other three molecules in the
Wyckoff position e of molecule B by a pseudo-center
2
x ¼ 0:494 ð4Þ ꢂ x ;
B
A
solvent was removed in a rotating evaporator, leaving (3) as a light-
yellow precipitate (0.90 g, 3.4 mmol, 100%). Crystallization from
y ¼ 0:911 ð10Þ ꢂ y ;
B
A
i
PrOH–H
2
O (ꢄ1:1 v/v) gave light-yellow needles (0.85 g, 3.2 mmol,
z ¼ 0:485 ð7Þ ꢂ z ;
ꢂ1
B
A
9
7
7
4%). IR (KBr, cm ): 3089, 1604, 1517, 1466, 1267, 1194, 1123, 1018,
1
85, 613, 574, 545; H NMR (acetone-d
.45 (bs, 4H). Recrystallization from benzene gave polymorph (I),
6
): ꢂ 8.20 (bs, 7H), 765 (bs, 6H),
a pseudo-translation
x ¼ 0:506 ð4Þ þ x ;
B
A
previously obtained by sublimation (Gehrz & Britton, 1972).
Recrystallization from acetone, chloroform, carbon tetrachloride or
y ¼ 0:089 ð10Þ þ y ;
B
A
i
PrOH–H
2
O (ꢄ1:1 v/v) gave polymorph (II). Polymorph (I) melts at
z ¼ 0:515 ð7Þ þ z
B
A
348.5–348.8 K, while polymorph (II) turns opaque at 346.8 K and
melts at 348.5 K; presumably, the opacity at 346.8 K indicates the
transition from (II) to (I).
and a pseudo-twofold axis
x ¼ 0:494 ð4Þ ꢂ x ;
B
A
y ¼ 0:589 ð10Þ þ y ;
B
A
Polymorph (I)
z ¼ 0:985 ð7Þ ꢂ z :
B
A
Crystal data
Similar relationships hold for the other molecules in the
Wyckoff position e of molecule A. Again, as a measure of the
precision of the pseudosymmetry, if molecules A and B are
matched as well as possible using OFIT in SHELXTL, the
3
˚
V = 1495.1 (7) A
C
M = 262.00
Monoclinic, P2 =c
6
H
3
IN
2
O
2
r
Z = 8
Mo Kꢁ radiation
1
˚
ꢂ1
a = 10.344 (3) A
ꢄ = 4.23 mm
T = 174 (2) K
˚
b = 19.804 (6) A
˚
˚
c = 7.489 (2) A
r.m.s. deviation between the atoms is 0.008 A; if the translation
0.35 ꢅ 0.08 ꢅ 0.04 mm
ꢁ
˚
above is used, the r.m.s. deviation is 0.123 A. In this case, there
ꢃ = 102.950 (10)
is no idealized translation; although the a and c translations
1
Data collection
can both be idealized as , the translation in y is not close to
any rational fraction.
2
Siemens SMART 1K CCD area-
detector diffractometer
Absorption correction: multi-scan
15378 measured reflections
2929 independent reflections
2078 reflections with I > 2ꢅ(I)
Polymorph (II) is isomorphous with the low-temperature
form of 5-bromobenzofurazan 1-oxide (Pink & Britton, 2002).
The pseudosymmetry relationships above are virtually iden-
tical to those for the bromo analog, except that the translation
in y of 0.089 (10) in the iodo compound is 0.114 (7) in the
bromo compound, marginally different.
Although both polymorphs have the same four super-
symmetry relationships, namely translation, inversion, screw
and glide, there are significant differences between the two. In
(
SADABS; Sheldrick, 1996;
Blessing, 1995)
min = 0.68, Tmax = 0.84
Rint = 0.071
T
Refinement
2
2
R[F > 2ꢅ(F )] = 0.049
wR(F ) = 0.087
S = 0.99
58 restraints
H-atom parameters constrained
2
˚
ꢂ3
Áꢆmax = 0.77 e A
Áꢆmin = ꢂ0.80 e A˚
ꢂ3
2929 reflections
270 parameters
(I), the two types of molecules in a layer are related alter-
nately by a pseudo-translation and a pseudo-screw. In (II), the
two types of molecules are all related by a pseudo-glide.
Supersymmetry has been discussed extensively by Zorky and
co-workers (see Zorky, 1996, and references therein).
Table 1
˚
ꢁ
Geometry of the C—Iꢀ ꢀ ꢀX—Y contacts (A, ).
The Iꢀ ꢀ ꢀX distances should be compared with the van der Waals distances
˚
˚
(Bondi, 1964; Rowland & Taylor, 1996) of Iꢀ ꢀ ꢀO = 3.50 A and Iꢀ ꢀ ꢀN = 3.53 A.
I
X—Y
C—Iꢀ ꢀ ꢀX
Iꢀ ꢀ ꢀX
Iꢀ ꢀ ꢀX—Y
Experimental
Polymorph (I)
i
A sample of 4-iodo-2-nitroaniline, (1), from the chemical collection of
W. E. Noland, was converted to 4-iodo-2-nitrophenyl azide, (2),
according to the method of Deorha et al. (1962). Compound (2) was
then converted to the title compound, (3). Compound (1) (2.00 g,
I1A
I1B
O1A—N1A
O1B—N1B
169.5 (5)
172.3 (5)
3.114 (8)
3.045 (8)
116.9 (5)
121.5 (5)
ii
Polymorph (II)
I1A
I1B
iii
iv
N2B—O2B
174.0 (2)
167.1 (2)
3.163 (5)
3.175 (5)
119.2 (2)
110.8 (2)
7.57 mmol) [m.p. 396.6 K, cf. 396.2 (Deorha et al., 1962; Brenans,
914a,b), 395–396 (Garden et al., 2002), 395.2 (Bradfield et al., 1928;
N2A—O2A
1
Michael & Norton, 1878) and 394.6–395.2 K (Kavalek et al., 1967,
1
3
1
2
1
2
Symmetry codes: (i) 2 ꢂ x; þ y; ꢂ z; (ii) 1 ꢂ x; þ y; ꢂ z; (iii) ꢂ1 þ x; ꢂ1 þ y; z; (iv)
2
2
x; 1 þ y; z.
ꢃ
Acta Cryst. (2008). C64, o187–o190
Britton et al.
Two polymorphs of C H IN
6 3 2
O
2
o189

organic compounds
Table 2
constrained to be the same as in the major components, with identical
isotropic displacement parameters for the atoms of the minor
˚
ꢁ
Geometry of the the C—Hꢀ ꢀ ꢀX—Y contacts (A, ).
˚
All C—H distances are 0.95 A.
2
components, led to R = 0.049 and wR = 0.087. Occupancies for the
major components were 0.849 (3) for molecule A and 0.944 (4) for
molecule B. Similar refinement of the first data set led to corres-
ponding occupancies of 0.829 (3) and 0.920 (4). A reasonable model
for the disorder would be one in which entire chains of molecules
(Fig. 3) are shifted one molecule along in the chain direction,
although this cannot be determined from the diffraction data. The
minor components of the disorder have been ignored in the discus-
sion of the packing. H atoms were placed in geometrically idealized
positions and constrained to ride on their parent atoms, with C—H =
H
X—Y
C—Hꢀ ꢀ ꢀX Hꢀ ꢀ ꢀX Hꢀ ꢀ ꢀX—Y Cꢀ ꢀ ꢀX
Polymorph (I)
H5A
H5B
N2B—C2B
O1A—N1A
160
126
2.59
2.55
161
122
3.503 (10)
3.201 (10)
i
Polymorph(II)
H5A
H6A†
ii
i
O2B—N1B
O1B—N1B
138
132
2.52
2.55
110
135
3.282 (5)
3.261 (5)
†
1
This contact is between layers and is not shown in Fig. 4. Symmetry codes: (i)
1
1
2
0.95 A and Uiso(H) = 1.2Ueq(C).
˚
ꢂ x; þ y; ꢂ z; (ii) ꢂ1 þ x; y; z.
2
For both polymorphs, data collection: SMART (Siemens, 1995);
cell refinement: SAINT (Siemens, 1995); data reduction: SAINT;
program(s) used to solve structure: SHELXTL (Sheldrick, 2008);
program(s) used to refine structure: SHELXTL; molecular graphics:
SHELXTL; software used to prepare material for publication:
SHELXTL.
Polymorph (II)
Crystal data
˚
3
C
6
3 2
H IN O
2
V = 1505.4 (7) A
Z = 8
M
r
= 262.00
Monoclinic, P2 =c
Mo Kꢁ radiation
ꢄ = 4.20 mm
T = 174 (2) K
0.50 ꢅ 0.10 ꢅ 0.05 mm
1
˚
a = 14.392 (4) A
ꢂ1
˚
b = 7.640 (2) A
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: GD3185). Services for accessing these data are
described at the back of the journal.
˚
c = 15.284 (4) A
ꢃ = 116.390 (10)
ꢁ
Data collection
References
Siemens SMART 1K CCD area-
detector diffractometer
Absorption correction: multi-scan
17038 measured reflections
3437 independent reflections
2916 reflections with I > 2ꢅ(I)
Blessing, R. H. (1995). Acta Cryst. A51, 33–38.
Bondi, A. (1964). J. Phys. Chem. 68, 441–451.
(
SADABS; Sheldrick, 1996;
Blessing, 1995)
min = 0.63, Tmax = 0.81
R
int = 0.034
Bradfield, A. E., Orton, K. J. P. & Roberts, I. C. (1928). J. Chem. Soc. pp. 783–
785.
Brenans, P. (1914a). C. R. Acad. Sci. 158, 717–720.
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Deorha, D. S., Joshi, S. S. & Mahesh, V. K. (1962). J. Indian Chem. Soc. 39, 534–
T
Refinement
2
R[F > 2ꢅ(F )] = 0.031
wR(F ) = 0.065
S = 1.09
3437 reflections
536.
2
200 parameters
H-atom parameters constrained
Desiraju, G. R. & Steiner, T. (1999). The Weak Hydrogen Bond. Oxford
University Press.
Garden, S. J., Fontes, S. P., Wardell, J. L., Skakle, J. M. S., Low, J. N. &
Glidewell, C. (2002). Acta Cryst. B58, 701–709.
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Pink, M. & Britton, D. (2002). Acta Cryst. B58, 116–124.
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Sheldrick, G. M. (1996). SADABS. University of G o¨ ttingen, Germany.
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.
2
˚
ꢂ3
Áꢆmax = 1.29 e A
Áꢆmin = ꢂ0.95 e A˚
ꢂ3
The first crystal of polymorph (I), after refinement as an ordered
ꢂ3
˚
structure, showed peaks in the final difference map of 10 and 5 e A
near the I atom. To make sure this was real, a second data set was
collected, with the same results. At this point, the two large peaks
were considered as a disordered I atom. The ordered structure had R
= 0.095 and wR
reduced R to 0.052 and wR
2
= 0.169. Considering only the I atom to be disordered
to 0.093. After consideration of various
2
Siemens (1995). SMART and SAINT. Siemens Analytical X-ray Instruments
Inc., Madison, Wisconsin, USA.
Zorky, P. M. (1996). J. Mol. Struct. 374, 9–28.
models, the arrangement shown in Fig. 1 seemed most reasonable,
and refinement with the geometry in the minor components
ꢃ
o190 Britton et al. Two polymorphs of C
6 3 2
H IN O
2
Acta Cryst. (2008). C64, o187–o190