4-Chloroacetophenone [1-(4-methoxyphenyl)ethylidene]hydrazone

Article abstract of DOI:10.1107/S0108270199011737

The crystal structure of the title mixed azine, C₁₇H₁₇CIN₂O, contains four independent molecules, A-D, and molecule B is disordered. All four molecules have an N-N gauche conformation, with C-N-N-C torsion angles of 136.5 (4), 137.0 (4), -134.7 (4) and -134.7 (4)°, respectively. The phenyl rings are also somewhat twisted with respect to the plane defined by C_ipso and the imine bond. On average, the combined effect of these twists results in an angle of 64.7° between the best planes of the two phenyl rings. Arene-arene double T-contacts are the dominant intermolecular interaction. The methoxy-substituted phenyl ring of one azine molecule interacts to form a T-contact with the methoxy-substituted phenyl ring of an adjacent molecule and, similarly, two chloro-substituted phenyl rings of neighboring molecules interact to form another T-contact. The only exception is for molecule B, for which the disorder leads to the formation of T-contacts between methoxy- and chloro-substituted phenyl rings. The prevailing structural motif of T-contact formation between like-substituted arene rings results in a highly dipole-parallel-aligned crystal structure.

Full text of DOI:10.1107/S0108270199011737

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
azines that we have investigated [R = Me, X = OCH3, Y = Br,
CN or NO2 (Glaser et al., 1995); R = Me, X = NH2, Y = F
(Lewis et al., 1998)] have an NÐN gauche conformation about
the azine bridge. The NÐN gauche conformation, in
conjunction with a phenyl-ring twist, causes the two phenyl
rings to be nearly orthogonal and this allows for the arene±
arene double T-contact throughout the crystal structures of
the previously studied mixed azines. A T-contact describes the
edge-to-face interaction between two phenyl rings. Such
arrangements are typically characterized by distances of 3.5±
ISSN 0108-2701
4-Chloroacetophenone [1-(4-methoxy-
phenyl)ethylidene]hydrazone1
Michael Lewis, Charles L. Barnes and Rainer Glaser*
Ê
5.0 A between the midpoints of the benzene rings (Hobza et
al., 1994). A double T-contact occurs when the two phenyl
rings of one spacer-connected biphenyl system interact with
the two phenyl rings of another such molecule to form two
intermolecular arene±arene T-contacts. Scheme 2 illustrates
four types of double arene±arene contacts; I±III are all double
T-contacts and IV is a double face-to-face contact. Type I has a
planar spacer and the two phenyl rings in each molecule are
coplanar. Types II and III contain a twisted spacer and the two
phenyl rings in each molecule are twisted with respect to each
other. Note that the double T-contacts II and III are structural
isomers and differ only in the choice of the benzene edges
used in the double T-contact. The double face-to-face contact,
illustrated by IV, occurs when the two phenyl rings of each
molecule interact in a face-to-face fashion. The double
T-contacts present in all of the mixed azines that we have
prepared to date have the conformations shown in II and III,
Department of Chemistry, University of Missouri±Columbia, Columbia, Missouri
65211, USA
Correspondence e-mail: glaserr@missouri.edu
Received 23 April 1999
Accepted 14 September 1999
The crystal structure of the title mixed azine, C17H17ClN2O,
contains four independent molecules, A±D, and molecule B is
disordered. All four molecules have an NÐN gauche
conformation, with CÐNÐNÐC torsion angles of 136.5 (4),
137.0 (4), 134.7 (4) and 134.7 (4)ꢀ, respectively. The phenyl
rings are also somewhat twisted with respect to the plane
de®ned by Cipso and the imine bond. On average, the
combined effect of these twists results in an angle of 64.7ꢀ
between the best planes of the two phenyl rings. Arene±arene
double T-contacts are the dominant intermolecular inter-
action. The methoxy-substituted phenyl ring of one azine
molecule interacts to form a T-contact with the methoxy-
substituted phenyl ring of an adjacent molecule and, similarly,
two chloro-substituted phenyl rings of neighboring molecules
interact to form another T-contact. The only exception is for
molecule B, for which the disorder leads to the formation of
T-contacts between methoxy- and chloro-substituted phenyl
rings. The prevailing structural motif of T-contact formation
between like-substituted arene rings results in a highly dipole-
parallel-aligned crystal structure.
Ê
with inter-ring distances of 3.5±5.0 A.
Comment
We have been investigating the stereochemistry (Glaser et al.,
1993, 1995; Chen et al., 1995), electronics (Glaser et al., 1993;
Chen et al., 1995; Glaser & Chen, 1998) and crystal packing
We are interested in mixed azines with the structure shown
in Scheme 1 because of their promise as non-linear optical
(NLO) materials. In order for a crystal to exhibit an NLO
response, there are two necessary conditions. First, the crystals
must be non-centrosymmetric or chiral, and this is a require-
ment for all types of polar effects of crystals (NLO activity,
piezo- and pyroelectricity, ferroelectricity, ferroelasticity and
many others). Non-centrosymmetry, in fact, occurs in
approximately 20% of organic crystals (Sakamoto, 1997). The
second condition, the central issue in the aggregation of
crystals with macroscopic polarizations, is the parallel align-
ment of the dipole moments of the individual chromophores,
and this is a challenge orders of magnitude greater than the
simple quest for non-centrosymmetry. We have previously
(Glaser et al., 1993; Chen et al., 1995; Lewis et al., 1998, 1999) of
symmetric and unsymmetric azines. An azine is the conden-
sation product of two carbonyl molecules and hydrazine. The
azines that we have studied have the general structure shown
in Scheme 1 and they are called symmetric if X equals Y and
unsymmetric or mixed if X does not equal Y. All of the mixed
1 Part 11 in the series `Stereochemistry and Stereoelectronics of Azines'. For
Part 10, see Lewis et al. (1999).
ꢁ
Acta Cryst. (2000). C56, 393±396
# 2000 International Union of Crystallography
Printed in Great Britain ± all rights reserved 393

organic compounds
prepared 4-bromoacetophenone [1-(4-methoxyphenyl)ethyl-
idene]hydrazone, (2) (X = OCH3, Y = Br, R = CH3; Chen et al.,
1995). The crystal structure of (2) is highly anisotropic, with
the long axes of all of the azine molecules pointing in the same
direction, and moreover it has a high degree of dipole parallel
alignment, with all of the dipole moments also pointing in the
same direction. In this report, we discuss the crystal structure
of 4-chloroacetophenone [1-(4-methoxyphenyl)ethylidene]-
hydrazone, (1) (X = OCH3, Y = Cl, R = CH3). As in the case of
(2), azine (1) is an extremely anisotropic material, albeit with a
somewhat lower degree of dipole parallel alignment due to the
disorder of molecules B.
N1ÐN2ÐC9 are 136.5 (4), 137.0 (4),
134.7 (4) and
134.7 (4)ꢀ for molecules A±D, respectively. Our previous
electronic investigations into the NÐN gauche conformation
of mixed azines showed that the azine bridge is essentially a
conjugation stopper (Glaser & Chen, 1998). Crystallographic
and ab initio studies showed that the bond distances and
populations of one phenyl ring are virtually unaffected by the
substitution pattern on the other phenyl ring. The NÐN
gauche conformation in (1) would suggest that the azine
bridge is once again acting as a conjugation stopper. If this is
true then we would expect little contribution from resonance
form (1a) in the ground-state structure of (1).
The importance of resonance form (1a) should be manifest
through a structural comparison of mixed azine (1) with the
symmetrical azines 4-methoxyacetophenone azine, (3) (R =
CH3, X = Y = OMe; Glaser et al., 1995), and 4-chloroaceto-
phenone azine, (4) (R = CH3, X = Y = Cl; Glaser et al., 1993). If
there existed a substantial decrease in the C13ÐO1, C10ÐC9
and N2ÐN1 bond lengths and a signi®cant increase in the
C9 N2 bond length in (1) with respect to (3), then this would
Mixed azine (1) is the condensation product of a para-
methoxyacetophenone molecule, a para-chloroacetophenone
molecule and hydrazine. The bromine analog (2) was prepared
previously and its crystal structure reported by Chen et al.
(1995). The crystal structure of azine (2) is monoclinic with
ꢀ
Ê
P21 symmetry [a = 7.766, b = 31.949 and c = 6.339 A, ꢀ = 95.38
and Z = 4]. The similarity of the cell dimensions with those of
azine (1) led us to assume that (1) and (2) were isostructural.
Re®nement of (1) in P21 gave a model in which one of the two
independent molecules was disordered and the re®nement
converged to R = 13%. The merging R factor in the monoclinic
setting, however, was 10% and an unconstrained re®nement of
the cell dimensions gave ꢁ and ꢂ angles that deviated signi®-
cantly from 90ꢀ. Re®nement of the structure in the triclinic
setting in space group P1 gave an R factor of 5%. In the
triclinic structure, there are four independent molecules in the
unit cell (Fig. 1, molecules A±D) and the disorder is limited to
only one molecule (B). Because of the deviation of unit-cell
parameters from monoclinic and because the disorder is more
localized, the crystal structure of (1) is better described in the
triclinic setting.
The crystal structure of (1) is layered (Fig. 2), with mol-
ecules A and C always residing in one layer and molecules B
and D in the other. Molecule B is disordered such that in 43%
of the molecules the chloro group is pointing in the same
direction as the chloro group of molecule D. For the other
57% of the molecules, the chloro group is pointing in the
opposite direction. The layers in (1) are at an angle of
approximately 35ꢀ with respect to each other. The confor-
mation about the azine bridge in (1) (Fig. 1) is NÐN gauche
for all four independent molecules. The torsion angles C1Ð
Figure 1
ORTEPII (Johnson, 1976) drawing of molecules A±D of mixed azine (1)
with displacement ellipsoids at the 50% probability level. H atoms are
shown as spheres of arbitrary radii.
ꢁ
394 Michael Lewis et al. C17H17ClN2O
Acta Cryst. (2000). C56, 393±396

organic compounds
for the layer containing azine molecules A and C, each azine
molecule in the layer containing molecules B and D takes part
in two type-II double T-contacts and one type-III double
T-contact.
The crystal structure of (1) has a high degree of dipole
parallel alignment. Ab initio molecular orbital calculations
show that the vectors of the dipole moments of molecules A±
D are all essentially along the long axis of each azine molecule.
Furthermore, the direction of the NÐN bond in each azine is
also collinear with the long axis of the molecule and all of the
NÐN bonds are almost perfectly parallel. Thus, within the
layer containing molecules A and C, the degree of dipole
parallel alignment is essentially complete. The disorder in
molecule B detracts somewhat from the dipole parallel
alignment of the layer containing molecules B and D. After
taking into account the disorder at molecule B, the degree of
dipole parallel alignment in the crystal structure of (1) is
approximately 71.5% that of (2). The crystal structure of (1),
however, promises to be a better candidate for understanding
the electronic factors involved in dipole parallel alignment.
Why is there disorder and why is the disorder so highly
`organized' that it affects only molecules B ? Molecule B exists
in a crystal environment that is at the junction between dipole
parallel alignment and dipole antiparallel alignment, and we
are currently studying this phenomenon with ab initio mole-
cular orbital theory.
Figure 2
The crystal packing of mixed azine (1). The view is approximately down
the a axis, with the origin at the lower right, b up and c to the left.
suggest that conjugation played a role in the ground state of
(1). Likewise, a decrease in the C2ÐC1 and N1ÐN2 bond
lengths and an increase in the Cl1ÐC5 and C1 N2 bond
lengths in (1) with respect to (4) would also suggest that
conjugation plays a signi®cant role in the ground state of (1).
We compared the four pertinent bond lengths for (1) and (3)
(C13ÐO1, C9ÐN2, C9ÐC10 and N1ÐN2) and for (1) and (4)
(Cl1ÐC5, C1ÐN1, C2ÐC1 and N1ÐN2), and in all cases the
Ê
deviations are no greater than 0.02 A. Moreover, the direc-
Experimental
tions of these small changes are not consistent with contri-
bution from resonance form (1a) to the ground state of (1).
Thus, the azine bridge in (1) is operating as a conjugation
stopper. The half of azine (1) with the methoxy-substituted
phenyl ring is impervious to the substituent located on the
phenyl ring in the other half, and the same statement can be
made about the half of azine (1) with the chloro-substituted
phenyl ring.
The crystal packing of mixed azine (1) (Fig. 2) is dominated
by double T-contacts of the types described by II and III
(Scheme 2). In the layer that contains molecules A and C, in
which all of the molecules are ordered, the methoxy-substi-
tuted phenyl ring of azine molecule A is always involved in a
T-contact with a methoxy-substituted ring of an adjacent azine
molecule C. Likewise, the chloro-substituted phenyl ring of
azine molecule A is always involved in a T-contact with a
chloro-substituted phenyl ring of a neighboring azine mol-
ecule C. In this manner, each azine molecule A takes part in
two type-II double T-contacts and one type-III double
T-contact with neighboring azine C molecules. A similar motif
is found for the layer containing molecules B and D, except
that molecule B is disordered. Thus, in 43% of cases, the
methoxy-substituted phenyl ring in azine molecule B is
involved in a T-contact with the methoxy-substituted phenyl
ring of an adjacent azine molecule D. In the other 57% of
cases, it is involved in a T-contact with the chloro-substituted
phenyl ring of an adjacent azine molecule D. As was the case
Diethyl phosphite and hydrazine hydrate were reacted in a solution
of tetrachloromethane, dichloromethane and potassium carbonate
with a catalytic amount of triethylbenzylammonium chloride to give
diethyl phosphite hydrazine. The diethyl phosphite hydrazine was
then coupled with para-methoxyacetophenone in benzene to give
diethylphosphine-(4-methoxyphenylethylidene)hydrazone,
which
was then coupled with para-chloroacetophenone to yield (1). Crystals
of (1) were obtained by slow diffusion of hexane into a solution of (1)
in chloroform.
Crystal data
C17H17ClN2O
Mr = 300.78
Triclinic, P1
a = 6.3260 (3) A
b = 31.465 (2) A
Z = 4
Dx = 1.316 Mg m
Mo Kꢁ radiation
3
Ê
Ê
Ê
Cell parameters from 7704
re¯ections
c = 7.6680 (4) A
ꢃ = 1.29±27.00ꢀ
ꢄ = 0.252 mm
T = 173 (2) K
1
ꢁ = 90.264 (1)ꢀ
ꢀ = 95.891 (1)ꢀ
ꢂ = 90.154 (1)ꢀ
Prism, yellow
0.40 Â 0.25 Â 0.15 mm
3
Ê
V = 1518.21 (14) A
Data collection
Siemens SMART CCD area-
detector diffractometer
! scans
Absorption correction: empirical
(SADABS; Blessing, 1995)
Tmin = 0.81, Tmax = 0.96
7704 measured re¯ections
6600 independent re¯ections (plus
1104 Friedel-related re¯ections)
7038 re¯ections with I > 2ꢅ(I)
Rint = 0.017
ꢃmax = 27ꢀ
h = 8 ! 6
k = 40 ! 30
l = 8 ! 9
Intensity decay: <2%
ꢁ
Acta Cryst. (2000). C56, 393±396
Michael Lewis et al. C17H17ClN2O 395

organic compounds
Re®nement
Data collection: SMART-NT (Bruker, 1998); cell re®nement:
SMART-NT; data reduction: SMART-NT; program(s) used to solve
structure: SHELXS97 (Sheldrick, 1997); program(s) used to re®ne
structure: SHELXL97 (Sheldrick, 1997); molecular graphics:
ORTEPII (Johnson, 1976); software used to prepare material for
publication: SHELXL97.
R = 0.05
wR = 0.13
S = 1.108
7704 re¯ections
760 parameters
H-atom parameters constrained
w = 1/[ꢅ2(Fo2) + (0.0378P)2
+ 1.7102P]
where P = (Fo2 + 2Fc2)/3
(Á/ꢅ)max = 0.004
3
Ê
Áꢆmax = 0.32 e A
3
Ê
0.30 e A
Áꢆmin
=
Absolute structure: Flack (1983)
Flack parameter = 0.02 (7)
Table 1
Selected geometric parameters (A, ) in molecules A±D of (1).
ML thanks the Natural Sciences and Engineering Research
Council of Canada for a Postgraduate Scholarship (Type A).
ꢀ
Ê
A
B
C
D
Cl1ÐC5
O1ÐC13
N1ÐC1
N1ÐN2
N2ÐC9
C1ÐC2
C9ÐC10
1.748 (5)
1.368 (5)
1.300 (6)
1.396 (5)
1.297 (6)
1.490 (6)
1.481 (6)
1.826 (6)
1.323 (7)
1.284 (6)
1.404 (5)
1.299 (5)
1.478 (7)
1.485 (6)
1.740 (4)
1.372 (5)
1.283 (5)
1.400 (5)
1.289 (6)
1.488 (5)
1.488 (5)
1.738 (5)
1.374 (5)
1.299 (5)
1.392 (5)
1.288 (5)
1.497 (6)
1.475 (6)
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: FR1211). Services for accessing these data are
described at the back of the journal.
References
C1ÐN1ÐN2
C9ÐN2ÐN1
N1ÐC1ÐC2
N2ÐC9ÐC10
114.5 (4)
114.8 (3)
115.9 (4)
116.6 (4)
115.0 (4)
114.7 (4)
117.1 (4)
116.6 (4)
115.6 (3)
114.4 (4)
116.9 (4)
116.4 (4)
115.2 (4)
114.9 (4)
115.7 (4)
116.9 (4)
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Wisconsin, USA.
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Perkin Trans. 2, pp. 1449±1458.
C1ÐN1ÐN2ÐC9
N2ÐN1ÐC1ÐC2
N1ÐC1ÐC2ÐC3
N1ÐN2ÐC9ÐC10
N2ÐC9ÐC10ÐC15
136.5 (4)
178.4 (3)
164.7 (4)
178.0 (3)
7.9 (6)
137.0 (4)
178.0 (4)
172.4 (4)
178.3 (4)
15.2 (6)
134.7 (4)
178.2 (4)
175.6 (4)
179.5 (3)
15.4 (6)
134.7 (4)
178.1 (3)
175.2 (4)
179.0 (4)
14.4 (6)
Glaser, R., Chen, G. S. & Barnes, C. L. (1993). J. Org. Chem. 58, 7446±7455.
Hobza, P., Selzle, H. L. & Schlag, E. W. (1994). Chem. Rev. 94, 1767±1785.
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Laboratory, Tennessee, USA.
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975±978.
Sakamoto, M. (1997). Chem. Eur. J. 3, 684.
Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of
È
Gottingen, Germany.
The positional parameters of the disordered Cl and methoxy
groups were not constrained or restrained during re®nement, leading
to less than ideal geometry for these moieties. In particular, the CÐCl
bond distances are longer than those in the ordered molecules. H
Ê
atoms were placed in calculated positions with CÐH = 0.95 A (0.98 A
Ê
for methyl H) and Uiso = 1.2Ueq(C).
ꢁ
396 Michael Lewis et al. C17H17ClN2O
Acta Cryst. (2000). C56, 393±396