Structure, polymorphism and thermal properties of phenyliminoisoindolines

Article abstract of DOI:10.1002/poc.793

The crystal and molecular structures of (a) 1-imino-3-phenyliminoisoindoline (2), (b) two polymorphs (3Mono and 3Tric) and a nexane solvate (3Hex) of 1,3-bis(phenylimino)isoindoline (3) and (c) 3-phenyliminoisoindolinone (4) were determined via single-crystal x-ray diffraction. The two polymorphs and solvate of 3 were all obtained by crystallization from hexane. In the solid state, 2 is found as the anti isomer of the amino tautomer, and all forms of 3 exist as either the syn,anti or anti,anti isomers of the diimino tautomer. The 3Tric and 3Mono polymorphs represent a rare example in which the phenomena of conformational polymorphism and conformational isomorphism occur for the same substance. Compound 4 crystallizes as the anti isomer of the keto form. Differential scanning calorimetry and thermogravimetric analysis were performed to characterize the thermal properties of samples of 2-4. X-ray powder diffraction studies on 2, 3 and 4 reveal that, whereas specimens of 2 are a single phase, none of the samples of 3 and 4 crystallize as single phases under the conditions of the experiments. Copyright

Full text of DOI:10.1002/poc.793

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2004; 17: 769–776
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/poc.793
Structure, polymorphism and thermal properties
of phenyliminoisoindolines
Zhi-Qin Zhang,1 Samnang Uth,1 Daniel J. Sandman1* and Bruce M. Foxman2**
1Center for Advanced Materials, Department of Chemistry, University of Massachusetts Lowell, Lowell, Massachusetts 01854-2881, USA
2Department of Chemistry, Brandeis University, Waltham, Massachusetts 02454-9110, USA
ABSTRACT: The crystal and molecular structures of (a) 1-imino-3-phenyliminoisoindoline (2), (b) two polymorphs
epoc
(3Mono and 3Tric) and a hexane solvate (3Hex) of 1,3-bis(phenylimino)isoindoline (3) and (c) 3-phenyliminoi-
soindolinone (4) were determined via single-crystal x-ray diffraction. The two polymorphs and solvate of 3 were all
obtained by crystallization from hexane. In the solid state, 2 is found as the anti isomer of the amino tautomer, and all
forms of 3 exist as either the syn,anti or anti,anti isomers of the diimino tautomer. The 3Tric and 3Mono polymorphs
represent a rare example in which the phenomena of conformational polymorphism and conformational isomorphism
occur for the same substance. Compound 4 crystallizes as the anti isomer of the keto form. Differential scanning
calorimetry and thermogravimetric analysis were performed to characterize the thermal properties of samples of 2–4.
X-ray powder diffraction studies on 2, 3 and 4 reveal that, whereas specimens of 2 are a single phase, none of the
samples of 3 and 4 crystallize as single phases under the conditions of the experiments. Copyright # 2004 John Wiley
& Sons, Ltd.
Additional material for this paper is available in Wiley Interscience
KEYWORDS: aryliminoisoindolines; crystal structure; molecular structure; tautomers
INTRODUCTION
28 attracted our attention. It was found that heating of 2 at
150 ꢀC, well below its reported8 decomposition tempera-
ture (203 ꢀC), led to decomposition, possibly initiated by
dissociation of 2 to aniline and phthalonitrile.7 This
process ultimately destroys the lattice of 2 and leads to
the formation of 3, ammonia and phthalocyanine (0.25%
yield). Following a report8 of its synthesis and thermal
decomposition, 2 has been the subject of NMR studies9
intended to deduce its preferred tautomeric structure. We
were interested in the crystal structure of 2 for insights
into the thermal decomposition process and for definitive
identification of the preferred tautomer in the solid state.
Compound 3 was initially described8 as yellow needles
with a melting-point of 129 ꢀC. Subsequently, 3 was
studied10 to learn about its preferred tautomeric structure
and possible stereoisomers associated with stereomuta-
tion of the phenylimino group. Based on model Schiff
bases,11 such isomerization should be facile in solution at
room temperature or in a liquid phase. Our observations
of the thermal properties of different specimens of 3
reported here are consistent with this perspective. In this
paper, we report the crystal structure of 2 and identify the
preferred solid-state tautomer. In the course of our isola-
tion and characterization of 3 and its solid-state reactivity,
we discovered two polymorphs of 3, one of which has
two stereoisomers of 3 in the same unit cell, whereas the
other contains only a single stereoisomer. This is a very
rare example of the occurrence of both conformational
polymorphism and conformational isomorphism for a
single substance.12
This paper reports the isolation and characterization of
the structural and thermal properties of phenyl derivatives
of diiminoisoindoline (1), namely phenyliminoisoindo-
line (2) and stereoisomers of 1,3-bis(phenylimino)isoin-
doline (3). There is a longstanding interest in isoindoline
rings owing to their presence in the phthalocyanines1 and
proposed presence2 in related linear conjugated poly-
mers. They are also of interest3 as intermediates for the
synthesis of hemiporphyrazines. The linear cyclopoly-
merization of 2-benzylidene-4, 5-dicyano-1,3-dithiole to
a related structure has been reported recently4 and Sn(II)
reagents5 and unmodified sugars6 bring about the linear
oligomerization and polymerization of phthalonitriles
and certain dicyanoalkenes to structures related to
polyisoindolines.
Pursuant to our interests in solid-state reactions, espe-
cially a suitable precursor for a solid-state polymerization
leading to a polyisoindoline,7 the solid-state reactivity of
*Correspondence to: D. J. Sandman, Center for Advanced Materials,
Department of Chemistry, University of Massachusetts Lowell,
Lowell, Massachusetts 01854-2881, USA.
E-mail: daniel_sandman@uml.edu
**Correspondence to: B. M. Foxman, Department of Chemistry,
Brandeis University, Waltham, Massachusetts 02454-9110, USA.
E-mail: mgreen@duke.poly.edu
Contract/grant sponsor: Petroleum Research Fund; Contract/grant
number: 33424-AC7.
Contract/grant sponsor: National Science Foundation; Contract/grant
number: DMR-0089257.
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 769–776

770
Z.-Q. ZHANG ET AL.
from the lattice constants for a given crystal. While we
recognize that observation of melting behavior is an
important part of the characterization of an organic
molecular compound, we will be unable to give definitive
thermal properties for each crystalline phase found in this
work. Nevertheless, we have made some noteworthy
attempts along these lines.
EXPERIMENTAL
General
Melting-points taken in a capillary tube are uncorrected.
Differential scanning calorimetry (DSC) and thermogra-
vimetric analysis (TGA) measurements were made on
DuPont DSC 2910 and TAꢁ21950 instruments, respec-
tively, at a rate of 10 ꢀC min under N2. X-ray powder
diffraction was recorded from 2ꢀ ¼ 2 to 60ꢀ using a Cu
Kꢁ source on a Phillips vertical diffractometer with a
graphite monochromator. Calculated x-ray powder pat-
terns were generated by MICRO-Dspace (Materials Data,
1
Livermore, CA, USA). H and 13C NMR spectra were
recorded on either a Bruker 250 MHz spectrometer or a
Varian 400 MHz spectrometer.
X-ray structure determinations
X-ray crystal structure analyses were performed at
Brandeis University on an Enraf-Nonius CAD-4U
diffractometer using graphite-monochromated Cu Kꢁ
radiation (2, 3Hex, 3Tric, 4) and on a CAD-4 Turbo
diffractometer using graphite-monochromated Mo Kꢁ
radiation (3Mono).13 Each structure was solved by direct
methods (SIR92).14 Full-matrix least-squares refinement
was carried out using the Oxford University Crystals for
Windows system.15 All ordered non-hydrogen atoms
were refined by using anisotropic displacement para-
meters; hydrogen atoms were fixed at calculated geo-
metric positions and updated after each least-squares
cycle. Hydrogen atoms attached to N were refined by
using isotropic displacement parameters. Drawings were
prepared using the Oxford University CAMERON pro-
gram.16 In 3Hex, the occupancy of a disordered hexane
solvate was also refined, leading to a value of 0.193(2). A
set of CIF files is available as Supplementary material
(available in Wiley Interscience).
In the course of attempting to dope 2 into phthalonitrile
in ethyl acetate solution, we isolated the known com-
pound 3-phenyliminoisoindolinone (4). Its crystal struc-
ture is reported here.
1-amino-3-phenyliminoisoindoline (2)7
A solution of 1,3-diiminoisoindoline (1) (2.5 g, 17 mmol)
and aniline (1.6 ml, 18 mmol) in ethanol (15 ml) was
refluxed for 2 h and allowed to cool to 5 ꢀC. The yellow
precipitate obtained was suction filtered, triturated with
cold ethanol and recrystallized from ethanol with a total
Using x-ray powder diffraction, we observed that, with
the exception of 2, all samples studied in this work
involve more than one crystalline phase by comparison
of the observed powder reflections with those calculated
Copyright # 2004 John Wiley & Sons, Ltd.
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STRUCTURE AND PROPERTIES OF PHENYLIMINOISOINDOLINES
771
Table 1. Crystallographic data
2
3Hex
3Mono
3Tric
4
Chemical formula
C14H11N3
C20H15N3ꢂ
0.1925 (C6H14)
311.235
Hexagonal
ꢀ
R3
294
25.475 (8)
25.475 (8)
13.610 (2)
90
90
120
7649 (4)
18
1.227
1.19 (2)
1.54178
0.572
C20H15N3
C20H15N3
C14H10N2O
Formula weight
Crystal system
Space group
221.263
Tetragonal
P41212
294
9.5328 (18)
9.5328 (18)
25.9609 (12)
90
297.361
Monoclinic
P21/c
297.361
Triclinic
ꢀ
P1
294
13.1134 (12)
14.252 (2)
18.331 (3)
79.190 (13)
73.781 (9)
75.565 (9)
3160.0 (8)
8
222.248
Monoclinic
P21/c
Temperature (K)
˚
294
294
a (A)
˚
11.3341 (4)
14.926 (1)
9.2767 (5)
90
90.431 (4)
90
1569.3 (15)
4
1.259
11.1873 (15)
5.0576 (7)
19.985 (3)
90
101.713 (11)
90
1107.2 (3)
4
1.333
1.31 (1)
1.54178
0.692
0.80–0.86
2322; 1774
0.043
0.0400
0.0527
1.03
b (A)
˚
c (A)
ꢁ ( ꢀ)
ꢃ ( ꢀ)
ꢄ ( ꢀ)
90
90
3
˚
V (A )
Z
2359.2 (6)
8
1.246
1.22 (1)
1.54178
0.605
0.76–0.92
1522; 1440
0.021
0.0366
0.0545
0.89
ꢅcalcd (g cmꢁ3
)
)
1.250
ꢅ
ꢆ (A)
obsd (g cmꢁ3
˚
0.71073
0.076
0.96–0.98
3177; 1965
0.014
0.0365
0.0421
1.10
1.54178
0.589
0.76–0.81
13293; 8914
0.010
0.0416
0.0528
1.04
ꢇ (mmꢁ1
Trans. coeff. (empirical corr.)
Unique reflections; No. obsd.
)
0.89–0.94
3589; 2818
0.024
0.0472
0.0639
1.01
Rmerge
R
Rw
SDU
yield of 2.89 g (77%); m.p. 203 ꢀC (decomp.) [lit.8 m.p.
203 ꢀC (decomp.)]. Ayellow single crystal obtained from
ethyl acetate was determined to be 2. The observed
density was 1.22 g cmꢁ3 (calc. 1.246 g cmꢁ3) determined
by neutral buoyancy in carbon tetrachloride–cyclohex-
ane. TGA: a 28.9% weight loss at 170 ꢀC, an additional
31.6% weight loss at 260 ꢀC and a further 20.3% weight
A yellow single crystal 3Mono with m.p. 122–125 ꢀC
was determined to be isomer 3c. Crystallographic data
1
are given in Table 1. The H NMR spectrum (CDCl3)
exhibited ꢂ 8.09–8.07 (m, 2H), 7.75 (m, 2H), 7.4–7.3 (m,
4H), 7.16–7.12 (m, 2H), 7.08–7.02 (m, 4H), 2.0 (s, broad,
1H). This spectrum is representative of those observed for
all specimens of 3 in the present work.
A yellow single crystal 3Tric with m.p. 128–130 ꢀC
was determined to be a mixture of isomers of 3c and 3d.
Crystallographic data are given in Table 1.
ꢀ
˚
loss at 321 C. Observed x-ray powder pattern, d (A): 9.0,
5.4, 4.8, 4.48, 4.21, 4.18, 4.07, 3.98, 3.16, 3.13, 3.09,
2.73, 2.50, 2.24 and 2.12.
Method B (catalyzed by CaCl2)17. A mixture of
phthalonitrile (1.28 g, 10 mmol), aniline (1.9 ml,
21 mmol), CaCl2 (0.11 g, 1 mmol) and n-butanol (20 ml)
was refluxed for 48 h. After evaporating the n-butanol
under reduced pressure, the residue was purified by
column chromatography [silica gel, CH3OH–CH2Cl2
(5:95)] to yield orange crystals (1.80 g, 61% yield) with
m.p. 125–127 ꢀC.
Bis(phenylimino)isoindoline (3)
Method A8. A mixture of 1 (1.51 g, 10 mmol), aniline
(2 ml, 20 mmol) and ethanol (15 ml) was refluxed for
24 h. After evaporation of the ethanol, the residue was
purified by column chromatography [silica gel, elution
with CH3OH–CH2Cl2(5:95)] to give a yellow solid
(1.80 g, 58%). Repeated recrystallizations from hexane
yielded four different kinds of crystals, yellow needles,
light-orange plates and two yellow single crystals.
The hexane-solvated single crystals 3Hex were recrys-
tallized from hexane and the structure was determined to
be isomer 3d. Crystallographic data are given in Table 1.
The observed density was 1.19 g cmꢁ3 determined by
neutral buoyancy in carbon tetrachloride–cyclohexane.
TGA: a 5% weight loss at 100 ꢀC with a further 95%
weight loss at 160 ꢀC. No DSC exotherm or endotherm
was observed. The crystal exhibited an irreversible melt.
On cooling, a yellow solid was found at ꢁ13 ꢀC. Ob-
Yellow needle crystals with m.p. 129–130.5 ꢀC are a
major product from the recrystallization. However, these
were of unsatisfactory quality and size for further study.
FT-IR (mineral oil): 3440, 1662, 1587, 1458, 1376, 1233,
1100, 690 cmꢁ1. The crystals exhibited an irreversible
melt and did not resolidify until cooled to ꢁ25 ꢀC.
˚
˚
Observed x-ray powder pattern (d, A): 17.3, 15.6, 14.7,
served x-ray powder pattern, d (A) (before melt): 15.5,
13.8, 12.3, 9.0, 7.2, 7.1, 6.8, 5.7, 5.5, 5.2, 4.9, 4.81, 4.63,
4.50, 4.33, 4.21, 3.68, 3.58, 3.50, 3.43, 3.37, 3.14.
14.2, 13.2, 12.9, 11.6, 9.1, 8.9, 8.7, 8.6, 6.3, 5.6, 5.3, 5.1,
4.3, 4.2, 4.0, 3.9, 3.8, 3.6, 3.5, 3.4, 3.3, 3.2, 3.1, 3.0, 2.92
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 769–776

772
Z.-Q. ZHANG ET AL.
˚
and 2.81. Observed x-ray powder pattern: d (A) (after
melt): 4.3 and 3.2. The observed reflections at d ¼ 15.5,
˚
14.2, 13.2, 9.1, 8.9, 8.7, 8.6, 5.3 and 5.1 A are not found in
the calculated pattern for 3Hex.
3-Phenyliminoisoindolinone (4)
Method A. Reaction of phthalonitrile and 2: a mixture
of phthalonitrile (1.54 g, 0.012 mmol),
2 (0.75 g,
0.003 mmol) and 25 ml of ethyl acetate was refluxed
overnight to yield an orange solution. After evaporation
of the ethyl acetate, the residue was triturated with hot
hexane, purified by column chromatography [silica gel,
CH3OH–CH2Cl2(1:99)] to yield an orange solid. Orange
single crystals was recrystallized from ethyl acetate–
hexane (1:3, v/v) and determined to be 3-phenyliminoi-
soindolinone and the isomeric form 4a with m.p. 162–
164 ꢀC (lit. m.p. 167–169 ꢀC18 and 170–171 ꢀC.19 Crys-
tallographic data are given in Table 1. The observed
density was 1.31 g cmꢁ3 determined by neutral buoyancy
in carbon tetrachloride–cyclohexane. IR (Nujol): 1735,
Figure 1. Molecular structure of 2. Selected bond distances:
N1---C1, 1.331(2); N1---C4, 1.395(1); C4---N2, 1.288(1);
˚
N2---C9, 1.425(2); C1---N3, 1.317(2) A
1677, 1579, 1258, 1165, 1087 cmꢁ1
.
Method B18. A solution of 3-iminoisoindolinone (0.5 g,
3.4 mmol) and aniline (1 ml, 11 mmol) in a mixture of
ethanol (20 ml) and acetic acid (0.67 ml) was heated
under reflux for 30 min to yield a yellow solution. After
cooling, the solution was poured into water (34 ml) to
give a yellow precipitate. The precipitate was filtered by
suction, dried in vacuum and recrystallized from ethanol
to give yellow crystals, 0.56 g (73%), m.p. 167–169 ꢀC
(lit.18 m.p. 167–169 ꢀC). The yellow crystals were found
to have the same crystal structure as the orange crystals
obtained by method A. The isomer form was 4a. Crystal-
lographic data are given in Table 1. The observed density
was 1.33 g cmꢁ3 determined by neutral buoyancy in
carbon tetrachloride–cyclohexane. Observed x-ray pow-
Figure 2. Hydrogen bonding in 2
tautomeric form. Bond lengths (Fig. 1) and angles are in
normal ranges, in good agreement with those of the
similar compounds 3-amino-5,6-dicyano-1-phenyli-
mino-1H-isoindole21 and 5-(1-aminoisoindol-3-ylidenea-
mino)-1,3,4-thiadiazol-2(3H)-thione dimethylformamide
solvate monohydrate.22 The C4—N2—C9—C14 tor-
sion angle is 84.1ꢀ, a likely result of packing forces.
Figure 2 shows a portion of the infinite hydrogen-bonding
˚
der pattern, d (A): 20.3, 19.8, 14.7, 10.2, 8.3, 6.8, 5.5, 5.3,
4.9, 4.44, 4.19, 3.67, 3.48, 3.34, 3.28 and 3.10. The
observed reflections at d ¼ 20.3, 19.8, 14.7, 6.8 and
˚
4.19 A are not in the calculated pattern.
RESULTS AND DISCUSSION
The stereoisomers and tautomers of 1 and its deri-
vatives have been of interest since 1945.20 Here we report
our observations from structural determinations for 2, 3
and 4.
Structural characterization of
phenyliminoisoindoline (2)
Figure 3. Molecular structure of 3Mono. Selected bond
distances: N1---C1, 1.395(2); N1---C4, 1.393(2); C4---N2,
1.276(2); N2---C9, 1.415(2); C1---N3, 1.270(2); N3---C15,
As shown in Fig. 1, 2, which can exist in several isomeric
forms, crystallizes as the anti isomer 2a of the amino
˚
1.420(2) A
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STRUCTURE AND PROPERTIES OF PHENYLIMINOISOINDOLINES
773
solution NMR study in the literature.10 If the solid-state
decomposition of 27,8 to aniline and phthalonitrile is an
intramolecular process, it cannot proceed through the
observed tautomer.
Structural characterization of
bis(phenylimino)isoindoline (3)
The specimens obtained from synthetic methods A or B
given in the Experimental Section are a mixture of phases
as revealed by x-ray powder diffraction, and single
crystals were selected from the mixtures. Three different
single crystals, 3Mono, 3Tric and 3Hex, were obtained
by modifying the literature procedures and recrystallizing
the products from hexane. During various attempts, two
or more polymorphs and/or solvates crystallized conco-
mitantly,24 without strong reproducibility.
After melting, all specimens of 3 remain viscous
liquids when cooled to ambient temperature. As stated
in the Experimental section, they do not resolidify until
cooled significantly below 0 ꢀC. These resolidified mate-
rials are not homogeneous crystalline phases and have
significant amorphous character, as revealed by x-ray
powder diffraction. This melting behavior of the various
forms of 3 is a likely consequence of the low barrier to
stereomutation11 of the phenylimino groups. The result is
a mixture of stereoisomers that does not crystallize
readily upon cooling to ambient temperature.
Figure 4. Molecular structure of 3Hex. Selected bond
distances: N1---C1, 1.378(2); N1---C4, 1.397(2); C4---N2,
1.265(2); N2---C9, 1.412(2); C1---N3, 1.276(2); N3---C15,
˚
1.424(2) A
network. One hydrogen bond, N3—H1ꢂ ꢂ ꢂN1(1 þ y,
ꢀ
˚
x ꢁ 1, ꢁ z; Nꢂ ꢂ ꢂN, 2.96 A; N—Hꢂ ꢂ ꢂN, 156 ) forms an
R22ð8Þ ring, whereas the other, N3—H2ꢂ ꢂ ꢂN2(12 þ y,
1
1
ꢀ
˚
ꢁ x, z ꢁ ; Nꢂ ꢂ ꢂN, 2.95 A; N—Hꢂ ꢂ ꢂN, 166 ), is part
2
4
of an infinite chain, C(6).23 Tautomer 2 was indicated in a
Figure 5. Packing diagram of 3Hex projected down the c-axis; the hexagonal motifs represent disordered hexane with average
S6 symmetry
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774
Z.-Q. ZHANG ET AL.
1
1
152ꢀ) and C20—H201ꢂ ꢂ ꢂN2(x, ꢁ y, þ z; Cꢂ ꢂ ꢂN,
2
2
ꢀ
˚
3.50 A; C—Hꢂ ꢂ ꢂN, 138 ). The lack of N—H hydrogen
bonding is confirmed in the FT-IR spectrum of 3Mono,
which exhibits a sharp peak at 3446 cmꢁ1, an appropriate
frequency for a NH group not involved in hydrogen
bonding. The 1H NMR spectrum of the sample obtained
from isolated crystals of 3Mono (see Experimental sec-
tion) is similar to that obtained in an earlier NMR study
(at 263 K),9 which suggested that a mixture of both
stereoisomers 3c and 3d was observed in CDCl3.
Crystal 3Hex is a solvate, and contains ꢃ0.2 mol of
hexane per mole of syn,anti stereoisomer 3d (Fig. 4). The
results from the x-ray structure determination (5.3%
hexane) are consistent with TGA analysis, which re-
vealed an initial 5% weight loss. Crystalline 3Hex has
an irreversible melt; after resolidification, some of the
original peaks reappeared, but additional peaks and
evidence for an amorphous component were also present.
Bond lengths (Fig. 4) and angles are again in good
agreement with the structures discussed above. The
C4—N2—C9—C10 and C1—N3—C15—C16 torsion
angles are 86.2 and 65.8ꢀ, respectively, probably a
reflection of packing forces. Compound 3Hex crystal-
Figure 6. Hydrogen bonding C(4) chain in 3Hex
The crystal structure of 3Mono (Fig. 3) reveals it to be
the anti,anti isomer 3c. Bond lengths and angles are in
good agreement with the structures discussed above, and
also that of 2-trimethylsilyl-1,3-bis(trimethylsilylimino)-
1,3-dihydroisoindole.25 The C4—N2—C9—C14 and
C1—N3—C15—C20 torsion angles are 61.0 and
59.5ꢀ, respectively, which isolates the NH group
and precludes intermolecular hydrogen bonding. There
are therefore no N—Hꢂ ꢂ ꢂN hydrogen bonds; inspection
of the crystal structure reveals only two weak inter-
molecular C—Hꢂ ꢂ ꢂN interactions (not shown), C5—
ꢀ
lizes in the high-symmetry trigonal space group R3;
inspection of a packing diagram projected down the c-
axis reveals the disordered hexane molecules in a site
1
1
˚
ꢀ
of crystallographic 3(S6) symmetry (Fig. 5). A single
H51ꢂ ꢂ ꢂN3(1 ꢁ x, 2 þ y, 2 ꢁ z; Cꢂ ꢂ ꢂN, 3.65 A; C—Hꢂ ꢂ ꢂN,
Figure 7. Asymmetric unit (four molecules) of 3Tric
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STRUCTURE AND PROPERTIES OF PHENYLIMINOISOINDOLINES
775
Figure 9. Molecular structure of 4. Selected bond distances:
N1---C1, 1.367(2); N1---C4, 1.402(2); C4---N2, 1.271(2);
˚
N2---C9, 1.419(2); C1---O1, 1.224(2) A
Figure 8. Discrete D(4) hydrogen bonding in 3Tric
hydrogen bond, N1—H1ꢂ ꢂ ꢂN3 (43 ꢁ y; x ꢁ y ꢁ ; z ꢁ ;
1
1
3
3
ꢀ
˚
Nꢂ ꢂ ꢂN, 3.01 A; N—Hꢂ ꢂ ꢂN, 154 ), is part of an infinite
chain, C(4), as shown in Fig. 6.
Crystal 3Tric, a second polymorph in the series, is a
3:1 mixture of the anti,anti and anti,syn stereoisomers 3c
and 3d (Fig. 7). This is an example of conformational
isomorphism (presence of different conformers in the
same crystal). The 3Tric and 3Mono polymorphs repre-
sent another rare example12 in which the phenomena of
conformational polymorphism (presence of different con-
formers in different polymorphs) and conformational
isomorphism (presence of different conformers in the
same crystal) occur for the same substance. The density
of 3Mono is only slightly greater than that for 3Tric
(1.259 and 1.250 g cmꢁ3, respectively), which suggests
similar packing efficiencies. For 3Tric, the bond lengths
and angles are again in normal ranges, in good agreement
with the structures discussed above. The analogous C—
N—C—C torsion angles, reflecting, as above, the twist
angle between the phenyl and phthalic imidine molecular
planes, lie in the narrow range 55.1–68.3ꢀ. As suggested
by the crystal structure of the anti,anti isomer 3Mono,
hydrogen bonding may be expected to play only a minor
role in the overall packing of the molecules. Figure 8
shows only a discrete N—Hꢂ ꢂ ꢂN hydrogen bond, of graph
set type D(4), N101–H101ꢂ ꢂ ꢂN402(ꢁx; 1 ꢁ y; 2 ꢁ z;
Figure 10. Hydrogen bonding in 4 [R22ð8Þ ring shown]
N2—C9—C10 torsion angle is again typical at 57.4ꢀ.
The crystal structure of 4 contains only an R22ð8Þ hydro-
gen bond (Fig. 10), N1—H1ꢂ ꢂ ꢂO1 (1 ꢁ x; 1 ꢁ y; 1 ꢁ z;
ꢀ
˚
Nꢂ ꢂ ꢂO, 2.88 A, N—Hꢂ ꢂ ꢂO, 170 ).
Both yellow and orange crystals of 4 were obtained as
described in the Experimental section. The yellow crys-
tals had a slightly higher melting-point than the orange
crystals, but both have the same unit cell constants within
experimental error. A calculated powder x-ray pattern,
using the unit cell data for 4, did not correspond to the
observed powder pattern from the bulk material, which
therefore must not be a single phase.
ꢀ
˚
Nꢂ ꢂ ꢂN, 3.10 A; N—Hꢂ ꢂ ꢂN, 158 ).
Structural characterization of
3-phenyliminoisoindolinone (4)
CONCLUSIONS
Earlier studies17,26 indicated that two isomers of 4 have
been observed in CD3OD whereby the anti isomer is the
predominant structure in solution. An x-ray structure
determination of a single crystal of 4 (Fig. 9) showed
only the anti isomer to be present; the bond lengths
(Fig. 9) and angles lie in normal ranges. The C4—
The crystal structures of 1-imino-3-phenyliminoisoindo-
line (2), three forms of bis(phenylimino)isoindoline (3)
and 3-phenyliminoisoindolinone (4) have been solved.
TGA and DSC were used to characterize their thermal
properties. The 3Tric and 3Mono polymorphs represent a
rare example in which the phenomena of conformational
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 769–776

776
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The work at the University of Massachusetts Lowell was
supported in part by the Petroleum Research Fund,
administered by the American Chemical Society, under
Grant 33424-AC7. The work at Brandeis University was
supported in part by the National Science Foundation
(Grant DMR-0089257). Samnang Uth was a student at
Lowell High School during this research, supported in
part by the US Army Research and Engineering Appren-
tice Program via a grant from the Academy of Applied
Sciences, Concord, NH. The authors thank M. J. Downey
for furnishing x-ray powder patterns.
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