Solid-state intermolecular contacts involving the nitrile group in p-cyano-N-(p-cyanobenzylidene)aniline and 4,4′-(azinodimethylidyne)bis- benzonitrile

Article abstract of DOI:10.1007/s10870-010-9902-8

As part of an investigation of the solid-state intermolecular contacts in which the nitrile group participates, the crystal structures of p-cyano-N-(p-cyanobenzylideneaniline), C₁₅H₉N₃ (CN/CN) and 4,4′-(azinodimethylidyne)

Full text of DOI:10.1007/s10870-010-9902-8

J Chem Crystallogr (2011) 41:464–469
DOI 10.1007/s10870-010-9902-8
ORIGINAL PAPER
Solid-State Intermolecular Contacts Involving
the Nitrile Group in p-Cyano-N-(p-cyanobenzylidene)aniline
and 4,40-(azinodimethylidyne)bis-benzonitrile
•
Charles R. Ojala William H. Ojala
•
Doyle Britton
Received: 1 February 2010 / Accepted: 17 November 2010 / Published online: 2 December 2010
Ó Springer Science+Business Media, LLC 2010
Abstract As part of an investigation of the solid-state
intermolecular contacts in which the nitrile group participates,
the crystal structures of p-cyano-N-(p-cyanobenzylideneani-
line), C15H9N3 (CN/CN) and 4,40-(azinodimethylidyne)
bis-benzonitrile, C16H10N4 (CN//CN) have been determined
Keywords Benzylideneaniline hydrazone ꢀ Nitrile ꢀ
Disorder ꢀ Weak H-bonding
Introduction
˚
at -100 °C. Cell parameters for CN/CN: a = 4.7270(9) A,
˚
˚
b = 10.443(2) A, c = 11.943(2) A; a = 90°, b = 98.70(3)°,
c = 90°; monoclinic, space group P21/c. Cell parameters
Solid-state intermolecular interactions involving the nitrile
group play a significant role in determining molecular
packing and are therefore of particular interest from the
standpoint of crystal engineering. How the C:N group
exerts its influence has been examined in several different
contexts in solid-state investigations, reflecting the variety
of packing motifs in which it appears. The nitrile group can
serve as an H-bond acceptor in crystals, frequently
participating in relatively weak and unconventional hydro-
gen bonding and forming part of a commonly occurring
H-bonded R22(10) supramolecular synthon (Fig. 1a) [13]. As
a polar functional group, it engages in dipole-dipole inter-
actions that help determine molecular packing and that have
been the focus of recent research (Fig. 1b) [35]; exclusively
non-centrosymmetric interactions have been examined by
[20]. Yet another role played by this group in the packing of
crystalline solids is as a Lewis base capable of interacting
with Lewis acids, particularly with halogen atoms on
neighboring molecules (Fig. 1c) [11, 12, 22, 29].
˚
for CN//CN: a = 3.8008(8) A, b = 7.9627(16) A, c =
˚
˚
11.181(2) A; a = 70.23(3)°, b = 84.66(3)°, c = 81.93(3)°;
triclinic, space group P1. Both molecules occupy crystal-
lographic inversion centers, which requires that (CN/CN)
be disordered. Both molecules assume nearly planar con-
formations in the solid state. Neither (CN/CN) nor (CN//
CN) is isostructural with its halogen-nitrile substituted
analogues, although (CN/CN) is found to be isostructural
with the corresponding stilbene. Both (CN/CN) and (CN//
CN) engage in centrosymmetric H-bonding interactions
that define an R22(10) motif. This motif is also observed in
many related structures, although noteworthy exceptions
can be found.
It is primarily the role of the nitrile group as a Lewis
base in the solid state that we have examined in previous
work, reporting the packing arrangements of isomeric pairs
of p-cyano-N-(p-halobenzylidene)anilines and p-halo-
N-(p-cyanobenzylidene)anilines, where the halogen atoms
are chlorine, bromine, and iodine [26, 27]. A substantial
number of benzylideneaniline crystal structures show dis-
order of the molecules: end-for-end or about the long
molecular axis or both [2, 15–17, 26, 37]. By examining
benzylideneanilines bearing both a nitrile group and a
C. R. Ojala
Department of Chemistry, Normandale Community College,
Bloomington, MN 55431, USA
W. H. Ojala (&)
Department of Chemistry, University of St. Thomas, Mail
OSS402 2115 Summit Avenue, St. Paul, MN 55105-1079, USA
e-mail: whojala@stthomas.edu
D. Britton
Department of Chemistry, University of Minnesota,
Minneapolis, MN 55455, USA
123

J Chem Crystallogr (2011) 41:464–469
465
with each other but not with any of the other four, we found
neither disorder nor halogen-nitrile contacts, the disorder
being removed by halogen-halogen interactions. In further
studies, we reported the crystal structures of the corre-
sponding 4-cyano-40-halo-bis-benzaldehyde hydrazones
[25], (Fig. 2). In DIWGIA (X = I), DIWGEW (X = Br),
and one polymorph of DIWGAS (X = Cl), halogen-nitrile
contacts are present, while a second polymorph of
DIWGAS lacks them; regardless, all four structures show
partial disorder between the two ends of the molecule.
In the disordered structures noted above, differences in
size and shape between the halogen atom and the nitrile
group are sufficiently small so that each of these substitu-
ents can replace the other in the disordered packing
arrangement. On the other hand, replacing the halogen
atom with another nitrile group would eliminate any dif-
ferences between the two substituents entirely. Would the
resulting highly symmetrical dicyanobenzylideneaniline or
dicyano-bis-benzaldehyde hydrazone necessarily be disor-
dered, or would intermolecular interactions such as
CNꢀꢀꢀH–C contacts acting in the absence of the nitrile-
halogen interaction be sufficient to fix the molecules into
an ordered crystal structure? To answer this question,
we have synthesized the two relevant compounds, p-cyano-
N-(p-cyanobenzylideneaniline) (CN/CN) and 4,40-(azino-
dimethylidyne)bis-benzonitrile (CN//CN) (Fig. 2), and
have determined their crystal structures.
Fig. 1 Solid-state packing motifs involving the nitrile group: a cen-
trosymmetric interaction with approaches to neighboring H atoms;
b dipole–dipole interaction; c Lewis base-Lewis acid interaction with
halogen atoms
halogen substituent, we sought to determine whether or not
interactions of the Lewis acid-Lewis base type between
nitrile groups and halogen atoms on neighboring molecules
could reduce or eliminate the disorder. In several of these
structures, CNꢀꢀꢀX interactions were in fact found to be
important to the packing. In the iodine-nitrile benzylid-
eneanilines LALMEQ and LALNUH [27], (Fig. 2), close
iodine-nitrile interactions were observed; both structures
are ordered. In the bromine-substituted cyanobenzylidene
structure MUTZIK and its isostructural chlorine-substi-
tuted analogue MUTZOQ [26], (Fig. 2) disorder was found
even though halogen-nitrile contacts were found as well.
That these contacts are insufficient to eliminate the disorder
is consistent with the relative weakness of bromine and
chlorine compared to iodine with respect to strength as
Lewis acids. Similarly, it has been reported by other
workers that no evidence of bromine-nitrile interactions is
found in the crystal structure of (E)-4-(4-bromostyryl)
benzonitrile [21]. In our determination of the bromine- and
chlorine-substituted cyanoaniline structures MUTZUW
and MUVBAG [26], (Fig. 2), which are isostructural
Experimental
The preparation of the benzylideneaniline (CN/CN) was
accomplished using the common method, refluxing the
substituted benzaldehyde and substituted aniline in ethanol
for approximately 15 min and allowing the solution to cool
slowly. Recrystallization from dimethylformamide (DMF)
of the solid thus obtained yielded high-melting yellow
needles, mp = 230 °C.
The preparation of the bis-cyanobenzaldehyde hydra-
zone (CN//CN) was accomplished in two steps, the prep-
aration of 4-cyanobenzaldehyde hydrazone followed by its
condensation with 4-cyanobenzaldehyde. For the prepara-
tion of the hydrazone, a solution of 4-cyanobenzaldehyde
(0.5 g, 3.8 mmol) dissolved in approximately 10 mL of
ethanol was added dropwise with stirring to an aqueous 8%
hydrazine solution (14.25 g, 36 mmol hydrazine). The
milky reaction mixture was stirred for approximately
30 min after completion of the addition and then was
refrigerated overnight (at 4 °C). The solid hydrazone
(mp = 63 °C) was removed by filtration and used without
recrystallization. A portion of it (0.06 g, 0.40 mmol) was
added to a solution of 4-cyanobenzaldehyde (0.06 g,
0.45 mmol) dissolved in 10 mL of absolute ethanol. The
Fig. 2 Substituted benzylideneanilines and bis-benzaldehyde hydra-
zones examined in previous work and in this report
123

466
J Chem Crystallogr (2011) 41:464–469
mixture was heated (lower than 50 °C) with stirring for
approximately 1 h, cooled, and then refrigerated over-
night. The crude bis-cyanobenzaldehyde hydrazone was
recrystallized from DMF, yielding yellow needles. Like
(CN/CN), (CN//CN) proved to be a high-melting solid,
mp = 319 °C.
Table 1 Crystal data, data collection, and refinement parameters
Compound
(CN/CN)
15H9N3
(CN//CN)
Molecular formula
C
C16H10N4
CCDC deposition
number
CCDC763127
CCDC763128
Mr
231.25
Monoclinic
P21/c
258.28
Data sets for (CN/CN) and (CN//CN) were collected at
Crystal system
Space group
Triclinic
P1
-100 °C on a Bruker-AXS SMART CCD diffractometer
˚
using Mo Ka radiation (k = 0.71073 A). For the benzy-
˚
a (A)
4.7270(9)
10.443(2)
11.943(2)
90
3.8008(8)
7.9627(16)
11.181(2)
70.23(3)
84.66(3)
81.93(3)
314.93(11)
1
lideneaniline (CN/CN), the data were integrated with SAINT
[6] and corrected for absorption with SADABS [4, 31].
Structure solution and refinement were accomplished using
SHELXTL [33]. The structure was found to be disordered,
the molecules being located on crystallographic inversion
centers in P21/c with Z = 2 (Z0 = 0.5). In the refinement
cycles, C7 and N1 were constrained to have the same posi-
tion and the same anisotropic displacement parameters.
The structure determination for the bis-cyanobenzalde-
hyde hydrazone (CN//CN) was complicated by twinning.
Most of the crystals in fact appeared to be twinned, and
several that did not appear on visual inspection to be
twinned proved to be twinned nonetheless during attempts
at unit cell determination. Data for (CN//CN) were ulti-
mately collected on a non-merohedrally twinned crystal
grown from DMF. The crystal used was indexed using
CELLNOW [32]. The major twin component fitted 192
reflections; the minor twin component fitted 164 of the
overall 270 reflections used. The twin law was found to be
[100/-0.613,-1,0/0,0,-1], which corresponds to a 180°
rotation about the a axis. The data were integrated with
SAINT [6] and corrected for absorption and scaling with
TWINABS [4, 31]. The ratio of the major and minor twin
components was 0.672(3):0.328(3) based on refinement
using SHELXTL [33]. As in (CN/CN), molecules of (CN//
CN) were found to be located on crystallographic inversion
centers, giving Z = 1 (Z0 = 0.5) in space group P1.
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
98.70(3)
90
3
˚
V (A )
582.8(2)
2
Z
T (°C)
Radiation
-100(2)
Mo Ka,
k = 0.71073 A
-100(2)
Mo Ka,
k = 0.71073 A
˚
˚
Dcalc (mg/m3)
1.318
1.362
F000
l (mm-1
240
134
)
0.08
0.09
Crystal dimensions
(mm)
0.50 9 0.15 9 0.15 0.30 9 0.20 9 0.15
Abs. corr.
SADABS [4, 31]
0.94, 0.99
TWINABS [4, 31]
0.96, 0.99
Tmin, Tmax
Meas/indep/
obs(I [ 2r(I))
6558/1322/1137
5504/2521/1966
Rint
R [F2 [ 2r(F2)]
wR(F2)
0.028
0.000
0.039
0.052
0.119
0.157
S
1.07
1.00
Reflections/parameters/
restraints
1322/86/0
2521/92/0
H-atom treatment
Mixed independent Constrained
and constrained
-3
˚
Dqmax, Dqmin (e A
)
0.23, -0.18
0.26, -0.27
Hydrogen atoms, with the exception of H7 in (CN/CN),
were included in both structures at geometrically idealized
positions and constrained to ride on their parent atoms with
˚
C–H distances of 0.95 A and with Uiso(H) = 1.2 Ueq(C).
of disorder is observed in (CN//CN). The bond lengths and
angles in both molecules are normal. In both molecules the
benzene rings are tilted only slightly out of the plane of the
central bridging atoms: by 1.4(1)° in (CN/CN) and 1.1(1)° in
(CN//CN). Planarity (or near-planarity) in benzylideneani-
lines is rare but not unprecedented [1, 10, 23, 36].
H7 was allowed to refine to avoid problems arising from
the disorder.
Results and Discussion
The C:NꢀꢀꢀH–C contact geometry defining the R22(10)
motif shown in Fig. 1a and found in both (CN/CN) and
(CN//CN) is given in Table 2. In Fig. 4 are shown two
molecules of (CN/CN) at xyz and -1 - x, 2 - y, 1 - z
assembled into a ribbon parallel to the [2,-1,0] direction
through this interaction, as well as two molecules (at
-1 - x, -1/2 ? y, 1/2 - z and x, 3/2 - y, 1/2 ? z) from
Unit cell parameters and structure determination data are
listed in Table 1. The atom labeling and the anisotropic
displacement parameters for both (CN/CN) and (CN//CN)
are shown in Fig. 3. As noted previously, both (CN/CN)
and (CN//CN) lie on centers of symmetry, which for
(CN/CN) requires disorder between C7 and N1. No evidence
123

J Chem Crystallogr (2011) 41:464–469
467
Fig. 4 Two molecules of (CN/CN) assembled into a ribbon parallel
to the [2,-1,0] direction (middle of figure, molecules at xyz and
-1 - x, 2 - y, 1 - z), and molecules from two adjacent ribbons
(upper left: -1 - x, -1/2 ? y, 1/2 - z; lower right: x, 3/2 - y, 1/
2 ? z). The dashed lines show the centrosymmetric H6ꢀꢀꢀN2
Fig. 3 Above: (CN/CN). Below: (CN//CN). Only the crystallograph-
ically independent atoms are numbered. Both molecules lie on a
center of symmetry, which means that in (CN/CN) atoms C7 and N1
are disordered with respect to each other. Displacement ellipsoids are
shown at the 50% probability level and H atoms are shown as small
spheres of arbitrary radius
˚
approaches of 2.56 A within the ribbon and the H2ꢀꢀꢀN2 approaches
˚
of 2.79 A between neighboring ribbons
adjacent ribbons. Nonlinear interactions of this type
between nitrile groups and H-bond donors are commonly
observed [14]. The antiparallel C:NꢀꢀꢀC:N interactions
(as measured from the midpoints of the C:N bonds of the
centrosymmetrically related molecules at xyz and -1 - x,
˚
2 - y, 1 - z) are at a distance of 3.765(2) A, considerably
˚
larger than the 3.57 A distance considered by Lee et al.
In Fig. 5 are shown four molecules of (CN//CN)
assembled into two ribbons parallel to the [2,-1,-1]
direction, molecules within each ribbon being connected
through the R22(10) motif shown in Fig. 1a. The antiparallel
C:NꢀꢀꢀC:N interaction (as measured from the midpoints
of the C:N bonds of the centrosymmetrically related
molecules at xyz and 3 - x, -y, -z) is at a distance of
[20] to be the dipole–dipole distance limit for C:NꢀꢀꢀC:N
interactions that are not part of an R22(10) motif. The sec-
ond molecule is displaced from the mean plane of the first by
˚
3.560(2) A, which is comparable to the dipole–dipole limit
considered by Lee et al. [20]. The second molecule is
˚
displaced from the mean plan of the first by 0.62(4) A. The
˚
0.767(14) A. The ribbons assemble into layers parallel
ribbons are stacked into layers parallel to the (0,1,-1)
plane through p–p contacts; the perpendicular distance
˚
between nearest benzene rings in this layer is 3.420(2) A
to the (001) plane; the perpendicular distance between
˚
nearest benzene rings in this layer is 3.490(4) A, but the
˚
centroid–centroid separation of 4.8124(11) A precludes a
˚
with a centroid-to-centroid distance of 3.8008(8) A (the
significant interaction of the p–p type. The ribbons in the
next adjacent layer lie along the [210] direction and are
rotated 84.3(1)° with respect to the ribbons in the first
layer. The same packing motifs are found in the crystal
structure of the corresponding stilbene derivative, 1,2-bis
(4-cyanophenyl)ethylene [24], with which (CN/CN) is
isostructural. (CN/CN) is not isostructural with any of the
halogen-nitrile benzylideneanilines we described previously
(Fig. 2).
a-axis repeat distance). The ribbons in the next adjacent
layer also lie along the [2,-1,-1] direction and are parallel
to the ribbons in the first layer, being related to these by
translation. This packing involves a second HꢀꢀꢀN contact,
C:NꢀꢀꢀH5; together these contacts define a centrosym-
metric R24(10) motif also shown in Fig. 5 (and shown
schematically in Fig. 6; see Table 2 for contact parameters)
that occurs frequently in the crystal structures of nitriles
[28]. Here it occurs in (CN//CN) but not in (CN/CN),
Table 2 Intermolecular C:NꢀꢀꢀH–C contact geometry
Contacts
˚
˚
NꢀꢀꢀH (A)
NꢀꢀꢀC (A)
C:NꢀꢀꢀH (°)
NꢀꢀꢀH–C (°)
(CN/CN)
C8:N2(xyz)ꢀꢀꢀH6–C6(-1 - x, 2 - y, 1 - z)
C8:N2(xyz)ꢀꢀꢀH2–C2(-1 - x, -1/2 ? y, 1/2 - z)
(CN//CN)
2.56
2.79
3.4420 (19)
3.398 (2)
133
155
155
123
C8:N2(xyz)ꢀꢀꢀH6–C6(3 - x, -y, -z)
C8:N2(xyz)ꢀꢀꢀH5–C5(x, -1 ? y, z)
2.60
2.70
3.4662 (16)
3.591 (2)
141
131
152
157
123

468
J Chem Crystallogr (2011) 41:464–469
bridge, and the R22(10) motif is again present and located
around a crystallographic inversion center in space group
P21/n. In contrast, and especially striking in light of the
results presented here for (CN/CN), is the case of 4,40-
dicyanobiphenyl [5]. No conformation of the (CN/CN)
molecule can be centrosymmetric, yet the molecule occupies
a crystallographic inversion center by means of disorder. On
the other hand, the 4,40-dicyanobiphenyl molecule, which in
a planar conformation would be centrosymmetric and
capable of occupying an inversion center (as does the
unsubstituted biphenyl molecule: [3, 7, 8, 18, 30, 34], instead
assumes a non-centrosymmetric, twisted conformation and
occupies a general position in space group P21. In the
biphenyl structure the two C:NꢀꢀꢀC:N approaches are
Fig. 5 Four molecules of (CN//CN) at xyz; x, 1 ? y, z; -2 ? x,
1 ? y, 1 ? z; and -2 ? x, 2 ? y, 1 ? z assembled into two ribbons
parallel to the [2,-1,-1] direction; molecules within each ribbon are
connected via the R22(10) motif, and adjacent ribbons are connected
via the R24(10) motif (center of figure). The dashed lines show the
˚
crystallographically independent (3.514 and 3.610 A) rather
than related by inversion symmetry. The associated
C:NꢀꢀꢀH interactions, rather than defining centrosymmetric
dimers as in (CN/CN), instead define chains of molecules
extending through the crystal, and inversion symmetry is
absent from the packing arrangement.
˚
centrosymmetric H6ꢀꢀꢀN2 approaches of 2.60 A within the ribbons
˚
and the centrosymmetric H5ꢀꢀꢀN2 approaches of 2.70 A between
neighboring ribbons
Supplementary Material
CCDC763127 and CCDC763128 contain the supplemen-
tary crystallographic data for this paper. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
data_request/cif, or by e-mailing data_request@ccdc.cam.
ac.uk, or by contacting the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
Fax: ?44(0)1223-33603.
Fig. 6 Centrosymmetric R24(10) packing motif observed in (CN//CN)
but not in (CN/CN)
Acknowledgment The assistance of Dr. Victor G. Young,
Jr. (Director) of the X-ray Crystallographic Laboratory of the
Department of Chemistry of the University of Minnesota is gratefully
acknowledged.
where the rotation of each layer of ribbons with respect to
its neighboring layers disrupts this motif. As (CN/CN) is
not isostructural with the halogen-nitrile benzylideneani-
lines described previously, neither is (CN//CN) isostruc-
tural with the halogen-nitrile bis-benzaldehyde hydrazones
described previously (Fig. 2).
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