Isostructuralism among 'bridge-flipped' isomeric benzylideneanilines and phenylhydrazones

Article abstract of DOI:10.1107/S0108768107018034

'Bridge-flipped' isomers may be defined as pairs of molecules related by a reversal of a bridge of atoms connecting two major parts of the individual molecules. This kind of isomerism is commonly found among benzylideneanilines and phenylhydrazones. Isost

Full text of DOI:10.1107/S0108768107018034

research papers
Acta Crystallographica Section B
Structural
Science
Isostructuralism among ‘bridge-flipped’ isomeric
benzylideneanilines and phenylhydrazones
ISSN 0108-7681
William H. Ojala,a* Jonathan M.
Smieja,a Jill M. Spude,a Trina M.
Arola,a Marika K. Kuspa,a Nell
Herreraa and Charles R. Ojalab
‘Bridge-flipped’ isomers may be defined as pairs of molecules
related by a reversal of a bridge of atoms connecting two
Received 4 January 2007
Accepted 11 April 2007
major parts of the individual molecules. This kind of
isomerism is commonly found among benzylideneanilines
and phenylhydrazones. Isostructural pairs might be suitable
for co-crystallization and are thus useful in the preparation of
new solid materials. Although most of the examples of bridge-
flipped isomeric benzylideneanilines and phenylhydrazones in
the crystallographic literature are not isostructural, a small
number of isostructural pairs have been reported by previous
workers. This paper describes the molecular and crystal
structures of four pairs of bridge-flipped isomers: two
isostructural phenylhydrazones, (E)-2-bromobenzaldehyde 4-
cyanophenylhydrazone (I) and (E)-4-cyanobenzaldehyde 2-
bromophenylhydrazone (II); two pairs of isostructural benzyl-
ideneanilines, N-(2-trifluoromethylbenzylidene)-2-methylani-
line (III) and N-(2-methylbenzylidene)-2-trifluoromethyl-
aniline (IV), and N-(2-bromobenzylidene)-2-methylaniline
(V) and N-(2-methylbenzylidene)-2-bromoaniline (VI); and
a pair of benzylideneanilines with closely similar unit-cell
dimensions but different packing arrangements, N-(4-methyl-
benzylidene)-4-cyanoaniline (VII) and N-(4-cyanobenzyli-
dene)-4-methylaniline (VIII). The structure of (V) is
disordered. The packing arrangement of (VIII) resembles
that of the chloro-/methyl-substituted benzylideneanilines
MBZCLA/MBZCLB [N-(4-methylbenzylidene)-4-chloroani-
line and N-(4-chlorobenzylidene)-4-methylaniline]. Although
intermolecular hydrogen bonding plays a part in the
isostructuralism of the two phenylhydrazones, the other
examples of isostructuralism occur in the absence of similar,
relatively strong intermolecular interactions.
aDepartment of Chemistry, University of St
Thomas, St Paul, Minnesota 55105, USA, and
bDepartment of Chemistry, Normandale
Community College, Bloomington, Minnesota
55431, USA
Correspondence e-mail: whojala@stthomas.edu
1. Introduction
Among the benzylideneaniline and phenylhydrazone families
of organic compounds are found pairs of isomeric molecules
related by a reversal of the orientation of the bridge of atoms
Figure 1
Bridge-flipped isomeric benzylideneanilines (upper) and phenylhydra-
zones (lower).
# 2007 International Union of Crystallography
Printed in Singapore – all rights reserved
Acta Cryst. (2007). B63, 485–496
doi:10.1107/S0108768107018034 485

research papers
Figure 2
Non-isostructural ‘bridge-flipped’ benzylideneanilines and phenylhydrazones.
ꢀ
486 William H. Ojala et al.
Isomeric benzylideneanilines and phenylhydrazones
Acta Cryst. (2007). B63, 485–496

research papers
that links the aryl groups (Fig. 1). We have been examining the
solid-state structures of these compounds to determine
whether such pairs of ‘bridge-flipped’ isomers can assume
similar packing arrangements. We are doing so with the goal of
eventually using these isomers to prepare new solid materials.
Pairs of bridge-flipped isomers, in particular those that form
isostructural crystals, might be capable of co-crystallization
from a suitable solvent, yielding materials with properties that
can be systematically modified by co-crystallization of various
proportions of the pure components. The color, melting point
or conductivity of the new solid solution might be adjustable
to any desired degree or extent for bridge-flipped isomers that
are mutually soluble in the solid state. Recent work in both
pharmaceutics (He et al., 2001) and materials chemistry
(Morimoto et al., 2003) has demonstrated the usefulness of co-
crystallization leading to solid-solution formation as a method
of modifying solid-state properties such as transition
temperature and photochromism. The exchange of the
—CH group for —NH— or —N is a familiar strategy in
drug development, in which these groups serve as bioisosteric
replacements for each other (Silverman, 2004; Patani &
LaVoie, 1996). The space-filling requirements of —CH and
—N are sufficiently similar to allow isostructuralism and
mixed-crystal formation between (for example) trans-stilbene
and azobenzene (Bouwstra et al., 1985).
arrangement in their respective crystals might appear doubtful
in light of their record in the crystallographic literature. In
Figs. 2 and 3 are listed the structures and refcodes of pairs of
bridge-flipped isomeric benzylideneanilines and phenylhy-
drazones we have located in the Cambridge Structural Data-
base (CSD Version 5.27 including updates through August
2006; Allen, 2002). Although our search has been done simply
by surveying the CSD and not by means of a search algorithm
that would ensure retrieval of every pair, we have made an
effort to locate as many as do exist. Most of these pairs (those
listed in Fig. 2) are not isostructural. Although the members of
each pair have their own (potentially complex) set of reasons
for assuming different packing arrangements, upon examining
these structures it is possible to identify several common
structural features that can differentiate the packing
arrangements of bridge-flipped isomers from each other in
general. Although the sheer number of non-isostructural pairs
may seem discouraging for the prospects of isostructuralism
and mutual solid-state solubility, an understanding of the
features that differentiate these structures could be useful in
efforts to design isostructural pairs.
A major structure-differentiating feature common particu-
larly among benzylideneanilines is the difference in confor-
mation that can exist between bridge-flipped isomers as a
result of the difference in position of the bridge hydrogen
atom. Steric interaction between this H atom and the aniline
ring H atom ortho to the bridge can result in the twisting of the
aniline ring further than the benzylidene ring out of copla-
narity with the bridge atoms. The resulting difference in
conformation between the two isomers contributes to their
difference in crystal structure and is commonly found among
the nonisostructural pairs listed in Fig. 2. Yet, at the same time,
it is difficult to claim that this feature is the reason for the
difference in packing arrangement between benzylideneani-
line pairs in which one or both molecules are very nearly
planar, as is true of NBZMAA, TEKMOL, RONKIO and
RONKOU. In some cases the authors of these studies have
identified other reasons for the structural differences, such as a
preference for a particular type of intermolecular contact over
another (e.g. Nꢁ ꢁ ꢁhalogen versus Hꢁ ꢁ ꢁhalogen interactions;
Navon & Bernstein, 1997) that for reasons of molecular
geometry or connectivity is accessible to only one of the two
isomers.
On the other hand, whether a significant number of bridge-
flipped isomeric pairs might be co-crystallized especially
readily because they assume the same molecular packing
Another differentiating feature is the change in position
within the bridge of a hydrogen-bond donor or hydrogen-
bond acceptor from one isomer to the other. In the case of the
benzylideneanilines, the bridge N atom can serve as a
hydrogen-bond acceptor in those derivatives that are substi-
tuted with hydrogen-bond donors on the rings. Changing the
position of this acceptor within the bridge presumably
contributes to the difference in crystal structure between
QQQAJM/QQQAJM01 and ZZZGMO/ZZZGMO01, and
also between VUKDEK and MXBYAP, as the hydroxyl group
intermolecularly hydrogen bonds to the bridge N atom in all
four structures. The role of hydrogen bonding in differ-
entiating the structure in the BZANPC series from the
structure QQQAJJ has yet to be determined, as only the cell
Figure 3
Isostructural benzylideneanilines and phenylhydrazones.
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Acta Cryst. (2007). B63, 485–496
William H. Ojala et al.
Isomeric benzylideneanilines and phenylhydrazones 487

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constants of QQQAJJ have been published thus far. The
BZANPC series features the familiar centrosymmetric
hydrogen-bonding interaction between carboxyl groups; the
possible occurrence of this solid-state motif also in QQQAJJ
should actually favor isostructuralism, in contrast to the
previous examples. In the case of the phenylhydrazones, the
bridging N—H group is a strong hydrogen-bond donor, and a
difference in its bridge position in two isomers in which it
participates in hydrogen bonding can cause differences in
molecular packing between the two crystal structures. This
effect is seen in the pair YUJGIT/YUJGIT01 and DAHLAZ,
in which a two-pronged intermolecular contact involving the
nitro group is shifted from its location in one isomer to a
different location in the other (Fig. 4), a change in the inter-
molecular hydrogen-bonding motif that contributes to the
difference in crystal structure between these isomers. In both
structures the strongly hydrogen-bonding N—H group parti-
cipates in the two-pronged hydrogen-bonding contact with the
nitro group of a neighboring molecule as part of an R22ð8Þ
interaction, but in YUJGIT/YUJGIT01 this interaction is
completed by a contact with the bridging C—H, whereas in
DAHLAZ this contact is with a ring C—H ortho to the bridge,
a C—H with enhanced hydrogen-bonding capability owing to
the presence of the electron-withdrawing nitro group on the
same ring. [That this change in the N—H position need not
disrupt the solid-state hydrogen-bonding pattern in every case
is demonstrated by the phenylhydrazones LAWJAV and
LAWCOC (Ferguson et al., 2005) in Fig. 3, and by the pair of
isostructural phenylhydrazones we describe in this report.]
Hydrogen bonding as a structure-differentiating influence
also occurs intramolecularly. A structural feature that contri-
butes to differences in molecular packing between salicylide-
neanilines such as SANYIP/SANYIP01, SALAMP/
SALAMP01, the BADDAL series, BADDEP/BADDEP10
and the BANGOM series on one hand and their ortho-
aminophenol-based counterparts on the other is an intramo-
lecular hydrogen bond to the bridge N atom that enforces a
difference in molecular conformation (shown for the isomeric
pair BANGOM02 and HUTXUP in Fig. 5) that can be
expected to favor a difference in molecular-packing arrange-
ment. The particular molecular conformation that allows this
intramolecular hydrogen bond is found in every ortho-
hydroxylated structure in Fig. 2. That this conformation is
different for the two bridge-flipped isomers is a major obstacle
to isostructuralism between the salicylideneanilines and the N-
benzylidene-o-hydroxyanilines.
In spite of the variety of factors that discourage isostruc-
turalism between bridge-flipped isomers, a few pairs have
been found to be isostructural nonetheless. Fig. 3 shows the
isostructural examples we have identified thus far in the
crystallographic literature. A feature of particular significance
in the 4-chloro-4-methyl benzylideneaniline pair MBZCLA/
MBZCLB is their disorder, which involves an end-for-end flip
of the molecule as well as a rotation of the molecule about the
long molecular axis, resulting in the possibility of multiple
orientations of the bridge. Disorder in the positions of
benzylideneaniline bridge atoms is frequently observed (Bar
& Bernstein, 1987; Zamir & Bernstein, 1993; Haller et al.,
1995; Ojala et al., 2001; Harada et al., 2004a,b), which suggests
to us that if multiple orientations of the bridge can co-exist in a
single crystal of a given benzylideneaniline, then it should be
possible for crystals of bridge-flipped isomeric benzylidenea-
nilines to differ in the orientation of the bridge and yet be
structurally similar otherwise. (Disorder also exchanges the
C—H and N—H positions within the bridge of isostructural
phenylhydrazones; Ferguson et al., 2005; Wardell et al., 2005.)
Co-crystallization of ordered, isostructural benzylideneani-
lines or phenylhydrazones would thus yield crystals disordered
at the bridge atoms by design. Another isostructural pair is
found among the polymorphs of the 4-methyl-4-nitro benzyl-
ideneanilines. The MBZPNA series includes three poly-
morphs, one orthorhombic and two monoclinic; the
NMBYAN series includes two polymorphs, one triclinic and
one monoclinic. The Pc polymorph of MBZPNA (structure
MBZPNA11) is isostructural with the Pc polymorph of
NMBYAN (structures NMBYAN01, NMBYAN02 and
NMBYAN22). Neither the chloro–methyl isostructural pair
nor the methyl–nitro isostructural pair shows any conforma-
tional differentiation owing to the interaction described above
involving the aniline ring’s ortho H atom and the bridging H
atom; in both pairs the torsional angles defining the twist of
the benzylidene and aniline rings out of the plane of the bridge
atoms are similar. The molecules in MBZCLA/MBZCLB are
located on crystallographic inversion centers and the mole-
cules in the Pc polymorphs of MBZPNA/NMBYAN are
nearly planar. In the pair of isostructural phenylhydrazones
LAWJAV and LAWCOC, the structure-differentiating effect
Figure 5
Conformations assumed by BANGOM02 (left) and HUTXUP (right) in
the solid state. Both conformations facilitate intramolecular hydrogen
bonding; at the same time they promote differences in molecular packing
between the two structures.
Figure 4
Intermolecular hydrogen-bonding interactions involving the nitro group
in YUJGIT/YUJGIT01 (left) and DAHLAZ (right).
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488 William H. Ojala et al.
Isomeric benzylideneanilines and phenylhydrazones
Acta Cryst. (2007). B63, 485–496

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Table 1
Experimental details, cell parameters and refinement results.
(I)
(II)
(III)
(IV)
(V)
Crystal data
Chemical formula
Mr
C14H10BrN3
300.16
Monoclinic, Cc
C14H10BrN3
300.16
Monoclinic, Cc
C15H12F3N
263.26
Monoclinic, P21/c
C15H12F3N
263.26
Monoclinic, P21/c
C14H12BrN
274.16
Orthorhombic, Pbcn
Cell setting, space
group
Temperature (K)
173 (2)
173 (2)
173 (2)
4.2021 (3), 21.0409 (13), 4.4902 (4), 19.9376 (17), 9.6046 (6), 7.7953 (5),
173 (2)
173 (2)
13.4669 (10), 11.7471 (9),
14.9271 (11)
90.00
2361.4 (3)
8
1.542
Mo Kꢁ
3.45
˚
a, b, c (A)
9.7556 (6), 7.8003 (5),
16.8794 (11)
102.647 (1)
1253.30 (14)
4
1.395
Mo Kꢁ
0.11
14.3803 (9)
96.248 (1)
1263.90 (14)
4
1.577
Mo Kꢁ
3.24
14.3182 (12)
92.884 (1)
1280.20 (19)
4
1.557
Mo Kꢁ
3.20
17.2756 (11)
104.316 (1)
1253.27 (14)
4
1.395
Mo Kꢁ
0.11
ꢀ (ꢂ)
3
˚
V (A )
Z
Dx (Mg mꢃ3
Radiation type
)
ꢂ (mmꢃ1
)
Crystal form, colour
Crystal size (mm)
Needle, yellow
0.50 ꢄ 0.20 ꢄ 0.20
Needle, yellow
0.50 ꢄ 0.15 ꢄ 0.15
Prism, yellow
0.50 ꢄ 0.50 ꢄ 0.18
Prism, yellow
0.50 ꢄ 0.35 ꢄ 0.10
Prism, yellow
0.50 ꢄ 0.50 ꢄ 0.08
Data collection
Diffractometer
Bruker SMART Plat-
form CCD
Siemens SMART Plat-
form CCD
Siemens SMART Plat-
form CCD
Siemens SMART Plat-
form CCD
Siemens SMART Plat-
form CCD
Data collection
method
Absorption correction
Area detector, ! scans
per ’
Multi-scan (based on
symmetry-related
measurements)
0.462
Area detector, ! scans
per ’
Multi-scan (based on
symmetry-related
measurements)
0.565
Area detector, ! scans
per ’
Multi-scan (based on
symmetry-related
measurements)
0.942
Area detector, ! scans
per ’
Multi-scan (based on
symmetry-related
measurements)
0.951
Area detector, ! scans
per ’
Multi-scan (based on
symmetry-related
measurements)
0.194
Tmin
Tmax
0.521
6085, 2202, 2082
0.616
6162, 2226, 2132
0.977
11 890, 2226, 2044
0.986
10 706, 2205, 1947
0.756
21 446, 2088, 1788
No. of measured, inde-
pendent and
observed reflections
Criterion for observed
reflections
I > 2ꢃ(I)
I > 2ꢃ(I)
I > 2ꢃ(I)
I > 2ꢃ(I)
I > 2ꢃ(I)
Rint
ꢄmax (ꢂ)
0.023
25.0
0.024
25.0
0.018
25.1
0.018
25.1
0.034
25.1
Refinement
Refinement on
R[F2 > 2ꢃ(F2)],
wR(F2), S
F2
0.026, 0.061, 1.04
F2
0.024, 0.053, 1.06
F2
0.032, 0.084, 1.05
F2
0.028, 0.075, 1.04
F2
0.027, 0.063, 1.10
No. of reflections
No. of parameters
H-atom treatment
2202
167
2226
167
2226
173
2205
173
2088
196
Mixture of independent Mixture of independent Constrained to parent
site
Constrained to parent
site
Constrained to parent
site
and constrained
refinement
and constrained
refinement
Weighting scheme
w = 1/[ꢃ2(Fo2) +
(0.0102P)2 + 1.0482P],
where P = (Fo2 + 2Fc2)/3
0.001
w = 1/[ꢃ2(Fo2) +
(0.0003P)2 + 0.4653P],
where P = (Fo2 + 2Fc2)/3
0.002
w = 1/[ꢃ2(Fo2) +
(0.0424P)2 + 0.3704P],
where P = (Fo2 + 2Fc2)/3
< 0.0001
w = 1/[ꢃ2(Fo2) +
(0.0344P)2 + 0.3477P],
where P = (Fo2 + 2Fc2)/3
< 0.0001
w = 1/[ꢃ2(Fo2) +
(0.0232P)2 + 1.5024P],
where P = (Fo2 + 2Fc2)/3
0.001
(Á/ꢃ)max
Áꢅmax, Áꢅmin (e A
Absolute structure
ꢃ3
˚
)
0.55, ꢃ0.52
0.29, ꢃ0.34
0.16, ꢃ0.24
0.17, ꢃ0.20
0.26, ꢃ0.22
Flack (1983), 1087
Friedel pairs
0.036 (10)
Flack (1983), 1085
Friedel pairs
0.030 (9)
–
–
–
Flack parameter
–
–
–
(VI)
(VII)
(VIII)
Crystal data
Chemical formula
Mr
C14H12BrN
274.16
C15H12N2
220.27
C15H12N2
220.27
Cell setting, space group
Temperature (K)
˚
a, b, c (A)
Orthorhombic, Pbcn
173 (2)
13.3550 (12), 11.6667 (11), 14.9529
Monoclinic, P21/n
173 (2)
6.1535 (9), 7.1990 (10), 26.253 (4)
Monoclinic, P21/n
173 (2)
6.1878 (12), 7.3785 (15), 25.895 (5)
(14)
90.00
ꢀ (ꢂ)
V (A )
92.285 (2)
1162.1 (3)
4
94.635 (3)
1178.4 (4)
4
3
˚
2329.8 (4)
8
1.563
Mo Kꢁ
3.50
Z
Dx (Mg mꢃ3
Radiation type
)
1.259
Mo Kꢁ
0.08
1.242
Mo Kꢁ
0.07
ꢂ (mmꢃ1
)
Crystal form, colour
Crystal size (mm)
Prism, yellow
0.45 ꢄ 0.30 ꢄ 0.15
Plate, yellow
0.50 ꢄ 0.48 ꢄ 0.05
Prism, yellow
0.43 ꢄ 0.30 ꢄ 0.30
ꢀ
Acta Cryst. (2007). B63, 485–496
William H. Ojala et al.
Isomeric benzylideneanilines and phenylhydrazones 489

research papers
Table 1 (continued)
(VI)
(VII)
(VIII)
Data collection
Diffractometer
Data collection method
Absorption correction
Siemens SMART Platform CCD
Area detector, ! scans per ’
Multi-scan (based on symmetry-
related measurements)
0.293
Siemens SMART Platform CCD
Area detector, ! scans per ’
Multi-scan (based on symmetry-
related measurements)
0.960
Siemens SMART Platform CCD
Area detector, ! scans per ’
Multi-scan (based on symmetry-
related measurements)
0.971
Tmin
Tmax
0.589
21 202, 2059, 1865
0.993
10 066, 2062, 1727
0.975
2677, 2677, 2218
No. of measured, independent and
observed reflections
Criterion for observed reflections
Rint
I > 2ꢃ(I)
0.031
25.0
I > 2ꢃ(I)
0.023
25.0
I > 2ꢃ(I)
–
27.6
ꢄmax (ꢂ)
Refinement
Refinement on
F2
0.029, 0.067, 1.13
2059
146
F2
0.037, 0.093, 1.06
2062
155
F2
0.065, 0.186, 1.07
2677
155
R[F2 > 2ꢃ(F2)], wR(F2), S
No. of reflections
No. of parameters
H-atom treatment
Weighting scheme
Constrained to parent site
Constrained to parent site
Constrained to parent site
w = 1/[ꢃ2(Fo2) + (0.0269P)2 + 2.7709P], w = 1/[ꢃ2(Fo2) + (0.0412P)2 + 0.2659P], w = 1/[ꢃ2(Fo2) + (0.091P)2 + 0.6802P],
where P = (Fo2 + 2Fc2)/3
0.001
0.38, ꢃ0.35
where P = (Fo2 + 2Fc2)/3
<0.0001
0.11, ꢃ0.14
where P = (Fo2 + 2Fc2)/3
0.013
0.31, ꢃ0.26
(Á/ꢃ)max
Áꢅmax, Áꢅmin (e A
ꢃ3
˚
)
Computer programs used: SMART (Bruker, 2001), SAINT (Bruker, 2003), SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), PLATON (Spek, 2003).
of moving the strongly hydrogen-bonding N—H group to a
different position in the bridge is mitigated by a multi-point
intermolecular hydrogen-bonding interaction in which the
bridge N—H and the bridge C—H are both in contact with the
same O atom from the nitro group of a neighboring molecule.
Exchanging the positions of the C—H and N—H moieties
does not disrupt this R12ð6Þ hydrogen-bonding motif. In an
additional, intramolecular interaction, the N—H group in
Figure 7
Close intermolecular contacts involving the cyano group in the packing
arrangement of (I). Anisotropic displacement ellipsoids are shown at the
50% probability level. For clarity, the outline of the unit cell has been
Figure 6
Bridge-flipped isomeric phenylhydrazones and benzylideneanilines
described in this paper.
omitted. Symmetry-equivalent molecules shown in addition to the xyz
3
1
molecule (labeled) are 32 þ x; 23 ꢃ y; 21 þ z (top) and ꢃ þ x; 32 ꢃ y; ꢃ þ z
2
2
(right).
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490 William H. Ojala et al.
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Acta Cryst. (2007). B63, 485–496

research papers
Table 2
Angles (ꢂ) between least-squares planes in (I) and (II).
A / B
C / B
(I)
(II)
9.70 (0.32)
4.82 (0.33)
5.71 (0.34)
6.37 (0.32)
A = plane defined by ring atoms C1–C6; B = plane defined by bridge atoms N1, N2 and
C13; C = plane defined by ring atoms C7–C12.
LAWJAV and the C—H group in LAWCOC are in close
contact with the nitro group located ortho to them by virtue of
their proximity to it; the C—H group assumes the same
structural role as the N—H group, and the exchange of one
group for the other causes no disruption to the packing
arrangement common to LAWJAV and LAWCOC.
Figure 9
Molecular structure of (III), showing the atom numbering. Anisotropic
displacement ellipsoids are shown at the 50% probability level.
In attempting to make our own pursuit of isostructural
bridge-flipped isomers systematic, we have been guided in part
by results we obtained in our analysis of the non-isostructural
pair of iodo-/cyano-substituted benzylideneanilines LALNUH
and LALMEQ (Ojala et al., 1999). In both structures a close
contact of the Lewis acid–Lewis base type exists in the solid
state between the I atom of a given molecule and the nitrile N
atom of an adjacent molecule. This contact links molecules in
the two crystal structures into similar chains. The structures
differ in how layers of these molecular chains are stacked;
nonetheless, the fact that the Lewis acid–Lewis base contact
helps enforce packing similarity on at least one level of
structure has encouraged us to examine additional halogen-
nitrile compounds among both the benzylideneanilines and
the phenylhydrazones. Here we describe the molecular
packing arrangement we have found to be common to (E)-2-
bromobenzaldehyde 4-cyanophenylhydrazone (I) and (E)-4-
cyanobenzaldehyde 2-bromophenylhydrazone (II) (Fig. 6).
We have also examined compounds in which the halogen or
nitrile has been replaced by a group of similar size and shape
in order to determine both the effect of disrupting any Lewis
acid–Lewis base contacts and the possibility of further
isostructuralism. We report here two additional isostructural
pairs we have identified in this manner: N-(2-trifluoro-
methylbenzylidene)-2-methylaniline (III) and N-(2-methyl-
benzylidene)-2-trifluoromethylaniline (IV); N-(2-bromo-
benzylidene)-2-methylaniline
(V)
and
N-(2-methyl-
benzylidene)-2-bromoaniline (VI). We also describe here the
crystal structures of N-(4-methylbenzylidene)-4-cyanoaniline
(VII) and N-(4-cyanobenzylidene)-4-methylaniline (VIII),
which although closely similar in unit-cell dimensions proved
not to be identical in molecular-packing arrangement and thus
qualified in our investigation as a ‘near miss’. We did, however,
find the packing arrangement of (VIII) to be similar to that of
the chloro-methyl benzylideneanilines MBZCLA/MBZCLB.
2. Experimental
Compounds (I)–(VIII) were prepared from the corresponding
substituted aldehydes and anilines using a standard method (a
mixture composed of approximately 0.5 g of each reactant
refluxed in ethanol for usually 15–30 min) and were crystal-
lized from ethanol, unless otherwise noted. Melting points
were determined using a Gallenkamp melting point apparatus
and are uncorrected. Both (I) and (II) were obtained as yellow
needles with broad melting points; the onset of melting
occurred for (I) at 473 K with gradual melting/decomposition
continuing past 503 K, while the onset of melting occurred for
(II) at 431 K and continued past 493 K. Both (III) and (IV)
Figure 8
Close intermolecular contacts involving the cyano group in the packing
arrangement of (II). Anisotropic displacement ellipsoids are shown at the
50% probability level. For clarity, the outline of the unit cell has been
omitted. Symmetry-equivalent molecules shown in addition to the xyz
molecule (labeled) are 32 þ x; 23 ꢃ y; 21 þ z (top) and ꢃ þ x; 32 ꢃ y; ꢃ þ z
3
2
1
2
(right).
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William H. Ojala et al.
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Table 3
Hydrogen-bond parameters (A, ).
ꢂ
˚
D—Hꢁ ꢁ ꢁA
D—H
Hꢁ ꢁ ꢁA
Dꢁ ꢁ ꢁA
D—Hꢁ ꢁ ꢁA
(I)
N2—H1Nꢁ ꢁ ꢁN3
0.78 (3)
2.35 (3)
3.108 (4)
164 (3)
(II)
N2—H1Nꢁ ꢁ ꢁN3
N2—H1Nꢁ ꢁ ꢁBr1
0.75 (3)
0.75 (3)
2.64 (3)
2.72 (3)
3.341 (4)
3.095 (2)
155 (3)
113 (2)
Table 4
Angles (ꢂ) between least-squares planes in (III)–(VIII).
A / B
C / B
Figure 10
Molecular structure of (IV), showing the atom numbering. Anisotropic
displacement ellipsoids are shown at the 50% probability level.
(III)
(IV)
5.26 (0.08)
44.85 (0.08)
8.70 (1.60)
4.98 (2.68)
39.47 (0.15)
6.59 (0.12)
17.53 (0.22)
48.84 (0.08)
12.24 (0.12)
40.12 (0.87)
32.67 (1.89)
6.66 (0.24)
48.73 (0.07)
10.67 (0.25)
(V) (major component)
(V) (minor component)
(VI)
(VII)
(VIII)
were obtained as greenish-yellow prisms, (III) melting at 326–
329 K and (IV) melting at 345–347 K. The isomeric pair (V)
and (VI) showed a greater difference in appearance than pairs
(I):(II) and (III):(IV), with (V) crystallizing from ethyl acetate
as greenish-yellow prisms melting at 351–353 K and (VI)
crystallizing from ethanol as orange–yellow prisms melting at
352–355 K. Like (V) and (VI), the pair (VII) and (VIII)
differed in color; (VII) was obtained as orange–yellow plates
melting at 402–404 K, while (VIII) was obtained as greenish-
yellow prisms melting at 417–419 K.
Data sets were collected at 173 K using either a Siemens or
Bruker AXS SMART system (Bruker, 2001) with Mo Kꢁ
radiation. Cell refinement and data reduction were accom-
plished using SAINT-Plus (Bruker, 2003). Absorption
corrections were applied to all data sets using SADABS
(Blessing, 1995; Bruker, 2000). The structures were solved and
refined using the SHELXTL software package (Bruker, 2000);
the experimental details are listed in Table 1.1 In all eight
structures, H atoms bonded to C atoms were placed in
calculated positions and refined as riding. In (I) and (II), the H
atoms bonded to N atoms were located in difference maps and
their positions were refined. Graphics were prepared using
PLATON (Spek, 2003).
A = plane defined by ring atoms C1–C6; B = plane defined by atoms C1, C7, C13 and N1;
C = plane defined by ring atoms C7–C12.
atom and the bridging N—H hydrogen atom [Brꢁ ꢁ ꢁH =
˚
2.72 (3), Brꢁ ꢁ ꢁN 3.095 (2), N—H distance 0.75 (3) A, N—
Hꢁ ꢁ ꢁBr = 114 (2)ꢂ].
Also shown in Figs. 7 and 8 are close intermolecular inter-
actions involving the nitrile groups of (I) and (II). No close
approaches of the Lewis acid–base type between the Br atoms
3. Results
3.1. Isostructural phenylhydrazones (I) and (II)
Atom-numbering schemes for (I) and (II) are shown in Figs.
7 and 8, respectively. Bond lengths and angles are normal.
Both molecules have the E configuration with respect to the
C
N bond and both molecules are nearly planar, with the
rings tilted only a few degrees out of the plane of the three
non-hydrogen bridge atoms (Table 2). The bromine-substi-
tuted ring of (I) is tilted further out of the plane of these
bridge atoms than the bromine-substituted ring of (II), in
which a close intramolecular contact occurs between the Br
1 Supplementary data for this paper are available from the IUCr electronic
archives (Reference: GP5015). Services for accessing these data are described
at the back of the journal.
Figure 11
Packing arrangement assumed by both (III) and (IV) [shown here for
(III)]. For clarity, the ring H atoms have been omitted.
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492 William H. Ojala et al.
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research papers
and nitrile groups occur; instead, the nitrile group participates
in hydrogen bonding. In the previously reported isostructural
phenylhydrazone pair LAWJAV and LAWCOC (Ferguson et
al., 2005), chains of molecules are formed in which one of the
linking interactions is a bifurcated hydrogen bond between an
(acceptor) O atom of a nitro group of a given molecule and the
two hydrogen-bond donor groups (N—H and C—H) of the
bridge of a neighboring molecule, an R12ð6Þ motif. A similar
motif occurs in (I) and (II), where the nitrile N atom of a given
molecule interacts with both hydrogen-bond donors of the
bridge of a neighboring molecule and likewise links the
molecules into chains (Table 3); however, these chains are
more irregular in shape than those in LAWJAV and
LAWCOC. In the LAWJAV and LAWCOC structures, two
additional hydrogen bonds, both of the C—Hꢁ ꢁ ꢁO type, link
each molecule to its neighbor within the chain, with the result
that the molecules are effectively pinned into a position in
which their long molecular axes are approximately parallel.
Molecules within the chain are related by translation. In
contrast, (I) and (II) lack additional hydrogen-bonding groups
that would serve this function. In (I) and (II), where the only
link between molecules within the chain is the R12ð6Þ interac-
tion, the long axes of neighboring molecules are nearly
perpendicular to each other rather than parallel to each other
as in LAWJAV and LAWCOC, giving the chain an irregular,
zigzag appearance. Molecules within the chain are related by
the glide operation.
3.2. Isostructural benzylideneanilines (III) and (IV)
Atom-numbering schemes for (III) and (IV) appear in Figs.
9 and 10, respectively. Molecules of both (III) and (IV) are
definitely nonplanar (Table 4). In both structures, the aniline
ring is tilted farther than the benzylidene ring out of copla-
narity with the bridge, in accordance with the conformational
tendency ascribed to steric interaction with the bridging H
atom noted in x1. The packing arrangement assumed by (III)
[and also by (IV)] is shown in Fig. 11. A contact between an F
atom of each molecule and a ring H atom of its translationally
related neighbor [F3ꢁ ꢁ ꢁC4 (x; ꢃ1 þ y; z) approach of
˚
˚
3.2338 (15) A in (III) and 3.2553 (14) A in (IV)] links the
molecules into chains extending parallel to the b axis. There
are no close intermolecular contacts, in particular none
involving the bridging atoms, that would serve to differentiate
the packing arrangements of the two isomers from each other
upon reversal of the bridge orientation.
Figure 12
Molecular structure of disordered (V). Atom labels ending in ‘A’
designate the minor component. The ratio between the two components
is 65:35%. For both components, 50% probability ellipsoids are shown.
Figure 14
Packing arrangement assumed by both (V) and (VI) [shown here for
(VI)]. For clarity, ring H atoms have been omitted.
Figure 15
Figure 13
Molecular structure of (VI), showing the atom numbering. Anisotropic
displacement ellipsoids are shown at the 50% probability level.
Molecular structure of (VII), showing the atom numbering. Anisotropic
displacement ellipsoids are shown at the 50% probability level. One
orientation of the disordered methyl group is shown.
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research papers
3.3. Isostructural benzylideneanilines (V) and (VI)
peaks corresponding to the Br atom and the methyl C atom
suggested that the disorder could be modeled satisfactorily by
an end-for-end flip of the molecule, which would involve the
near-superposition of the Br atom and the methyl group in the
electron density map. The two orientations of the molecule of
(V) in this disorder model are shown in Fig. 12. The two
components were refined anisotropically. Distances between
ring C atoms and their bromine and methyl substituents were
Views of the molecules (V) and (VI) are shown in Figs. 12
and 13, respectively. Unlike that of the previous isomeric pairs
(I):(II) and (III):(IV), the isostructuralism of the pair (V) and
(VI) is associated with disorder, particularly in (V). Attempts
to refine (V) conventionally failed to yield a final R1 value less
than roughly 0.15. Disorder in benzylideneaniline structures is
a common occurrence, often involving four possible orienta-
tions of the molecule: two in which the molecule is flipped end-
for-end and two in which the molecule is rotated about its long
axis (Haller et al., 1995; Harada et al., 2004a,b). The absence of
any significant peaks located just off the midpoint of the
bridging C N bond and the anomalous intensities of the
˚
constrained to values of 1.902 and 1.504 A, respectively, and
corresponding angles were also constrained to target values.
Anisotropic displacement parameters for those atoms from
separate components that were located close to each other in
the model were constrained to be equal and the overall
geometries of the two components were restrained to be
equal. Refinement of this model yielded a final R1 = 0.027 and
wR2 = 0.063, the populations of the two orientations refining to
0.6457 (7) and 0.3543 (7). The resulting bridge C N bond
˚
length of 1.271 (5) A in (V) is consistent with values found in
models of other disordered benzylideneanilines (Harada et al.,
2004a). In contrast, although the presence of small peaks near
the methyl C atom and the bridge N atom of (VI) suggested a
small percentage of end-for-end disorder similar to that found
in (V), refinement of an ordered model for (VI) proved
satisfactory. The orientation of (VI) in its unit cell corresponds
to that of the minor component of disordered (V). A
comparison of the molecular conformations appears in Table
Figure 16
Molecular structure of (VIII), showing the atom numbering. Anisotropic
displacement ellipsoids are shown at the 50% probability level.
Figure 18
Packing arrangement of (VIII) viewed along the b axis. For clarity, ring H
atoms have been omitted. Despite the close resemblance between (VII)
and (VIII) in cell constants, the packing arrangements are not identical
(compare Fig. 17).
Figure 17
Packing arrangement of (VII) viewed along the b axis. For clarity, ring H
atoms have been omitted.
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Acta Cryst. (2007). B63, 485–496

research papers
4. A view of the packing arrangement assumed by (VI) [and
also in disordered fashion by (V)] appears in Fig. 14. Contacts
to the Br atoms are all of the Brꢁ ꢁ ꢁH—C type in which the C
atom is either a ring carbon or a methyl carbon. There are no
close Brꢁ ꢁ ꢁBr or Brꢁ ꢁ ꢁN contacts.
not assume the same packing arrangement thus has a
reasonable structural basis, our study so far, although
successful in increasing the number of known examples of
isostructural bridge-flipped isomers, has not yet given us the
ability to predict which pairs of isomers will assume the same
packing arrangement or even to suggest substituents or
substitution patterns that will facilitate this occurrence. Given
the variety of factors that can prevent bridge-flipped isomers
from forming isostructural crystals, perhaps our most
surprising result thus far is that even this many of them do.
3.4. Benzylideneanilines (VII) and (VIII)
Atom-numbering schemes and molecular conformations for
(VII) and (VIII) are shown in Figs. 15 and 16, respectively.
Angles between selected molecular planes are given in Table
4. Residual electron density in the difference map of (VII) in
the region of the methyl-group H atoms led to the modeling of
that group as disordered. The refinement of (VIII) resulted in
a rather high value of R, perhaps the result of some end-for-
end disorder of the molecular position similar to that shown by
(V), as suggested in the difference map by a small peak
located near the bridge N atom in a location corresponding to
the disordered position of the bridge H atom. Attempts to
model this disorder were unsuccessful, so given the fact that
Acknowledgment is made to the Donors of the American
Chemical Society Petroleum Research Fund for support of
this research. The authors express their thanks to Dr Victor G.
Young Jr (Director) and Benjamin E. Kucera of the X-ray
Crystallographic Laboratory of the Department of Chemistry,
University of Minnesota, Minneapolis, MN, and to Professor
¨
Carl Henrik Gorbitz of the University of Oslo, Norway, for
their assistance. We are grateful to Dr William B. Gleason of
the Department of Laboratory Medicine and Pathology of the
University of Minnesota, Minneapolis, MN, Dr Doyle Britton
of the Department of Chemistry of the University of Minne-
sota, Minneapolis, MN, Dr Ilia A. Guzei of the Department of
Chemistry of the University of Wisconsin, Madison, WI, and
Dr Kenneth Haller of the School of Chemistry, Suranaree
University of Technology, Nakhon Ratchasima, Thailand, for
helpful discussions.
bond lengths and bond angles (notably the bridge C
N
distance and the nitrile C N distance) were reasonable, a
disordered model was not pursued further. In spite of the
general similarity in space-filling requirements between the
methyl group and the halogens (especially chlorine and
bromine), neither (VII) nor (VIII) is isostructural with the
chloro-cyano, bromo-cyano or iodo-cyano 4,40-disubstituted
benzylideneanilines we have examined previously (Ojala et al.,
1999; Ojala et al., 2001). Moreover, in spite of their close
similarity in cell constants and space-group symmetry, (VII)
and (VIII) are not isostructural with each other (Figs. 17 and
18). On the other hand, the packing arrangement of (VIII)
resembles that of the chloro-methyl benzylideneanilines
MBZCLA/MBZCLB (compare Fig. 18 to Fig. 3 in Haller et al.,
1995).
References
Adamson, A. J., Archambeau, Y., Banks, R. E., Beagley, B., Helliwell,
M., Pritchard, R. G. & Tipping, A. E. (1994). Acta Cryst. C50, 967–
971.
Allaway, C. L., Daly, M., Nieuwenhuyzen, M. & Saunders, G. C.
(2002). J. Fluorine Chem. 115, 91–99.
Allen, F. H. (2002). Acta Cryst. B58, 380–388.
Bar, I. & Bernstein, J. (1983). Acta Cryst. B39, 266–272.
Bar, I. & Bernstein, J. (1987). Tetrahedron, 43, 1299–1305.
Bernstein, J. & Bar, I. (1980). Eur. Cryst. Meet. 6, 21.
Blessing, R. H. (1995). Acta Cryst. A51, 33–38.
Bouwstra, J. A., Schouten, A., Kroon, J. & Helmholdt, R. B. (1985).
Acta Cryst. C41, 420–426.
Bryan, R. F., Forcier, P. & Miller, R. W. (1978). J. Chem. Soc. Perkin
Trans. 2, pp. 368–372.
Bruker (2000). SADABS, Version 2.03, and SHELXTL, Version 6.12.
Bruker Analytical X-ray Instruments, Madison, Wisconsin, USA.
Bruker (2001). SMART, Version 5.054. Bruker Analytical X-ray
Instruments, Madison, Wisconsin, USA.
4. Conclusions
We began this work with the assumption that solid-state
intermolecular interactions such as classical hydrogen bonding
and Lewis acid–Lewis base contacts, interactions of at least
moderate strength, might favor isostructuralism between these
bridge-flipped isomers by organizing molecules in crystals of
different isomers into similar packing motifs. We have found
this to be true for (I) and (II), but other examples of
isostructuralism we have found, both in the literature and in
our own crystallographic studies, occur in cases in which
interactions of this type are absent. When they are present,
they often prove to play a differentiating role by organizing
molecules into different packing motifs. For pairs of isomers in
which these intermolecular interactions involve the bridging
atoms, switching the bridging-atom positions renders
isostructuralism unlikely. Such interactions operating intra-
molecularly (such as intramolecular hydrogen bonding in
salicylideneanilines and their bridge-flipped isomers) discou-
rage isostructuralism by enforcing differences in molecular
conformation. Although predicting which pairs of isomers will
Bruker (2003). SAINT-Plus, Version 6.45. Bruker Analytical X-ray
Instruments, Madison, Wisconsin, USA.
¨
Burgi, H. B. & Dunitz, J. D. (1970). Helv. Chim. Acta, 53, 1747–1764.
¨
¨
Burgi, H. B., Dunitz, J. D. & Zust, C. (1968). Acta Cryst. B24, 463–464.
Chakraborty, S., Laye, R. H., Paul, R. L., Gonnade, R. G., Puranik,
V. G., Ward, M. D. & Lahiri, G. K. (2002). J. Chem. Soc. Dalton
Trans. pp. 1172–1179.
Clegg, W., Elsegood, M. R. J., Heath, S. L., Houlton, A. & Shipman,
M. A. (1996). Acta Cryst. C52, 2548–2552.
Cole, J. M., Howard, J. A. K. & McIntyre, G. J. (2001). Acta Cryst.
B57, 410–414.
Ferguson, G., Glidewell, C., Low, J. N., Skakle, J. M. S. & Wardell, J. L.
(2005). Acta Cryst. C61, o613–o616.
ꢀ
Acta Cryst. (2007). B63, 485–496
William H. Ojala et al.
Isomeric benzylideneanilines and phenylhydrazones 495

research papers
Filipenko, O. S., Ponomarev, V. I. & Atovmyan, L. O. (1976). Dokl.
Akad. Nauk SSSR, 229, 1113–1116.
Moustakali-Mavridis, I., Hadjoudis, E. & Mavridis, A. (1978). Acta
Cryst. B34, 3709–3715.
Filipenko, O. S., Shigorin, V. D., Ponomarev, V. I., Atovmyan, L. O.,
Safina, Z. Sh. & Tarnopol’skii, B. L. (1977). Kristallografiya, 22,
534–541.
Flack, H. D. (1983). Acta Cryst. A39, 876–881.
Glidewell, C., Howie, R. A., Low, J. N., Skakle, J. M. S., Wardell,
S. M. S. V. & Wardell, J. L. (2002). Acta Cryst. B58, 864–876.
Haller, K. J., Rae, A. D., Heerdegen, A. P., Hockless, D. C. R. &
Welberry, T. R. (1995). Acta Cryst. B51, 187–197.
Harada, J., Harakawa, M. & Ogawa, K. (2004a). Acta Cryst. B60, 578–
588.
Harada, J., Harakawa, M. & Ogawa, K. (2004b). Acta Cryst. B60, 589–
597.
He, X., Stowell, J. G., Morris, K. R., Pfeiffer, R. R., Li, H., Stahly, G. P.
& Byrn, S. R. (2001). Cryst. Growth Des. 1, 305–312.
Hoshino, N., Inabe, T., Mitani, T. & Maruyama, Y. (1988). Bull. Chem.
Soc. Jpn, 61, 4207–4214.
Nakai, H., Ezumi, K. & Shiro, M. (1981). Acta Cryst. B37, 193–
197.
Nakai, H., Shiro, M., Ezumi, K., Sakata, S. & Kubota, T. (1976). Acta
Cryst. B32, 1827–1833.
Navon, O. & Bernstein, J. (1997). Struct. Chem. 8, 3–11.
Ojala, C. R., Ojala, W. H., Gleason, W. B. & Britton, D. (1999). J.
Chem. Cryst. 29, 27–32.
Ojala, C. R., Ojala, W. H., Gleason, W. B. & Britton, D. (2001). J.
Chem. Cryst. 31, 377–386.
Orr, L. B., Jr, Parsons, E. J. & Pennington, W. T. (1992). Acta Cryst.
C48, 2042–2043.
Patani, G. A. & LaVoie, E. J. (1996). Chem. Rev. 96, 3147–3176.
Ponomarev, V. I., Filipenko, O. S., Atovmyan, L. O., Grazhulene, S. S.,
Lempert, S. A. & Shigorin, V. D. (1977). Kristallografiya (Russ.)
(Crystallogr. Rep.) 22, 394–396.
Shan, S., Wang, X.-J., Hu, W.-X. & Xu, D.-J. (2004). Acta Cryst. E60,
o1954–o1956.
Sheldrick, G. M. (1990). Acta Cryst. A46, 467–473.
Sheldrick, G. M. (1997). SHELXL97 and SHELXS97. University of
Hursthouse, M. B. & Karaulov, A. (2003). Private communication.
Inabe, T., Hoshino, N., Mitani, T. & Maruyama, Y. (1989). Bull. Chem.
Soc. Jpn, 62, 2245–2251.
¨
Jiao, Y.-H., Zhang, Q. & Ng, S. W. (2006). Acta Cryst. E62, o3614–
o3615.
Kamwaya, M. E. & Khoo, L. E. (1985). J. Fiz. Malays. 6, 135–140.
Karakas, A., Elmali, A., Unver, H. & Svoboda, I. (2004). J. Mol.
Struct. 702, 103–110.
Li, A., Bin, X., Zhu, S.-Z., Huang, Q.-C. & Liu, J.-S. (1994). J. Fluorine
Chem. 68, 145–148.
Lindeman, S. V., Andrianov, V. G., Kravcheni, S. G., Potapov, V. M.,
Potekhin, K. A. & Struchkov, Y. T. (1981). Zh. Strukt. Khim. 22,
123–131.
Gottingen, Germany.
Silverman, R. B. (2004). The Organic Chemistry of Drug Design and
Drug Action, 2nd ed. pp. 29–34. New York: Elsevier, Inc.
Spek, A. L. (2003). J. Appl. Cryst. 36, 7–13.
Tanaka, M., Imai, T., Goto, T., Taka, J.-I., Akamatsu, M., Kashino, S.
& Mogi, K. (1998). Bull. Chem. Soc. Jpn, 71, 2561–2571.
Tunc, T., Tezcan, H., Sari, M., Buyukgungor, O. & Yagbasan, R.
(2003). Acta Cryst. C59, o528–o529.
Velavan, R., Sivakumar, K. & Anbu, M. (1995). Acta Cryst. C51,
1227–1229.
Lindeman, S. V., Shklover, V. E. & Struchkov, Y. T. (1981). Acta Cryst.
A37, C87.
Vickery, B., Willey, G. R. & Drew, M. G. B. (1985). Acta Cryst. C41,
1072–1075.
Lindeman, S. V., Shklover, V. E., Struchkov, Y. T., Kravcheni, S. G. &
Potapov, V. M. (1982a). Cryst. Struct. Commun. 11, 43–47.
Lindeman, S. V., Shklover, V. E., Struchkov, Y. T., Kravcheni, S. G. &
Potapov, V. M. (1982b). Cryst. Struct. Commun. 11, 49–52.
Meunier-Piret, J., Germain, G., Declercq, J. P. & van Meerssche, M.
(1982a). Bull Soc. Chim. Belg. 91, 89–90.
Wardell, J. L., Skakle, J. M. S., Low, J. N. & Glidewell, C. (2005). Acta
Cryst. C61, o10–o14.
Wardell, J. L., Wardell, S. M. S. V., Skakle, J. M. S., Low, J. N. &
Glidewell, C. (2002). Acta Cryst. C58, o428–o430.
Welberry, T. R., Butler, B. D. & Heerdegen, A. P. (1993). Acta Chim.
Hung. 130, 327–345.
Meunier-Piret, J., Germain, G., Declercq, J. P. & van Meerssche, M.
(1982b). Bull. Soc. Chim. Belg. 91, 93–94.
Meunier-Piret, J., Piret, P., Germain, G. & van Meerssche, M. (1972).
Bull. Soc. Chim. Belg. 81, 533–538.
Morimoto, M., Kobatake, S. & Irie, M. (2003). J. Am. Chem. Soc. 125,
11080–11087.
Whitney, J. F. & Corvin, I. (1949). Anal. Chem. 21, 306–307.
Yeap, G.-Y., Fun, H.-K., Teoh, S.-G., Teo, S.-B., Chinnakali, K. & Yip,
B.-C. (1992). Acta Cryst. C48, 2257–2258.
Yin, Z.-G., Qian, H.-Y., Jia, J., Zhou, N. & Feng, L.-Q. Acta Cryst. E62,
o4913–o4914.
Zamir, S. & Bernstein, J. (1993). Acta Chim. Hung. 130, 301–325.
ꢀ
496 William H. Ojala et al.
Isomeric benzylideneanilines and phenylhydrazones
Acta Cryst. (2007). B63, 485–496