Supramolecular organization of bis(3-halo-4-dimethylaminobenzylidene) hydrazines

Article abstract of DOI:10.1016/j.molstruc.2012.09.012

Bis(3-bromo-4-dimethylaminobenzylidene)hydrazine and bis(3-chloro-4- dimethylaminobenzylidene)hydrazine have been synthesized, and their monoclinic crystal structures solved in space group P2₁/c. For the bromo derivative at 150 K, a = 10.4505(2

Full text of DOI:10.1016/j.molstruc.2012.09.012

Journal of Molecular Structure 1035 (2013) 1–5
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Supramolecular organization of bis(3-halo-4-dimethylaminobenzylidene)hydrazines
a
b
Samuel Guieu a,b, , João Rocha , Artur M.S. Silva
⇑
a University of Aveiro, CICECO, Department of Chemistry, 3810-193 Aveiro, Portugal
b University of Aveiro, QOPNA, Department of Chemistry, 3810-193 Aveiro, Portugal
h i g h l i g h t s
"
"
"
Two halogenated benzaldimines were synthesized.
Single crystal structures were determined to study the supramolecular interactions.
The synthons form one-dimensional chains through halogen–halogen bonds, and no halogen–nitrogen bonds are present.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 July 2012
Received in revised form 3 September 2012
Accepted 4 September 2012
Available online 12 September 2012
Bis(3-bromo-4-dimethylaminobenzylidene)hydrazine
and
bis(3-chloro-4-dimethylaminobenzyli-
dene)hydrazine have been synthesized, and their monoclinic crystal structures solved in space group
P21/c. For the bromo derivative at 150 K, a = 10.4505(2), b = 8.0358(2), c = 11.3208(2) Å, b = 102.56(2)°,
Z = 2, V = 927(9) Å3, Dx = 1.618 g cmꢀ3, refinement on 2217 reflections, R = 0.023. For the chloro derivative
at 150 K, a = 10.3416(8), b = 8.0605(5), c = 11.1573(8) Å, b = 102.70(8)°, Z = 2, V = 907(3) Å3,
Dx = 1.330 g cmꢀ3, refinement on 2429 reflections, R = 0.038. The molecules are close to planar, the crys-
tal packing shows Brꢁ ꢁ ꢁBr or Clꢁ ꢁ ꢁCl intermolecular halogen bonds, and some CAHꢁ ꢁ ꢁBr or Cl contacts.
There are no Clꢁ ꢁ ꢁN or Brꢁ ꢁ ꢁN interactions.
Keywords:
Imine
Halogen–halogen bond
Self-assembly
Single crystal
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
halogen–halogen supramolecular interaction becomes dominant
(Fig. 2) [7,8].
Being able to predict the organization of molecules in the solid
state is one of the main goals of crystal engineering [1]. Weak
interactions usually compete with each other, as hydrogen bonds,
stacking of aromatic rings, charges repulsion or attraction, and the
molecules arrange to minimize the energy of the crystal. When one
or more halogen atoms are present in the molecule, weak interac-
tions between them and with other functional groups may appear
in the solid state. These supramolecular interactions have recently
attracted the attention of the scientific community [2], as an alter-
native to hydrogen bonds in crystal engineering. For example, hal-
ogen bonds between bromine or iodine and carbonyl oxygen atoms
have been observed and sometimes dictate the crystal packing
orientation [3]. Halogen bonds between nitrogen and bromine or
iodine atoms have been observed in pyridine derivatives [4] and
aliphatic amines [5]. Halogen bonds with aromatic amines or imi-
nes are scarcer (Fig. 1) [6] because the Lewis base is weaker and the
In an attempt to reinforce the donor properties of the imine nitro-
gen, we have designed benzalazines with electron donor substituents.
N,N0-bis(3-bromo-4-dimethylaminobenzylidene)hydrazine and N,N0-
bis(3-chloro-4-dimethylaminobenzylidene)hydrazine have been syn-
thesized and their crystal structures determined, expecting that
halogen bonded imines would be present.
2. Experimental
2.1. 3-Bromo-4-(dimethylamino)benzaldehyde [9]
N-Bromosuccinimide (1.78 g, 10 mmol, 1 equiv.) was added to a
solution of 4-(dimethylamino)benzaldehyde (1.49 g, 10 mmol, 1
equiv.) in dichloromethane (50 mL), and the reaction mixture
was stirred at room temperature for 72 h. The solvent was then
evaporated under reduced pressure, and silica gel flash column
⇑
Corresponding author at: University of Aveiro, CICECO and QOPNA, Department
of Chemistry, 3810-193 Aveiro, Portugal.
E-mail addresses: sguieu@ua.pt (S. Guieu), rocha@ua.pt (J. Rocha), artur.sil
va@ua.pt (A.M.S. Silva).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.09.012

2
S. Guieu et al. / Journal of Molecular Structure 1035 (2013) 1–5
Scheme 1. Synthesis of compounds 1 and 2: (i) NBS or NCS, CH2Cl2, room temp. (ii)
Hydrazine hydrate, MeOH, room temperature.
Fig. 1. One-dimensional chain formed through Iꢁ ꢁ ꢁN halogen bonds [6].
44%). Slow evaporation of a concentrated solution in dichlorometh-
ane gave pale yellow crystals suitable for X-ray diffraction.
1H NMR (300 MHz, CDCl3, 25 °C): d = 8.53 (s, 2H, CHN), 8.06 (d,
chromatography (eluent: dichloromethane/petroleum ether: 1/1)
of the residue gave the product as a colorless liquid (1.62 g, 71%).
1H NMR (300 MHz, CDCl3, 25 °C): d = 9.81 (s, 1H, CHO), 8.03 (d,
4
4JHAH 1.8 Hz, 2 H, H-2), 7.67 (dd, JHAH 1.8, 3JHAH 8.4 Hz, 2 H, H-5),
3
4
3
4JHAH 1.8 Hz, 1 H, H-2), 7.73 (dd, JHAH 1.8, JHAH 8.4 Hz, 1 H, H-5),
7.08 (d, JHAH 8.4 Hz, 2 H, H-6), 2.89 (s, 12 H, CH3);
13C NMR (75 MHz, CDCl3, 25°C): d = 160.3 (C@N), 154.2 (C-4),
133.8 (C-2), 129.2 (C-1), 128.6 (C-6), 119.9 (C-3), 118.1 (C-5),
43.8 (CH3).
3
7.06 (d, JHAH 8.4 Hz, 1H, H-6), 2.95 (s, 6 H, CH3).
2.2. 3-Chloro-4-(dimethylamino)benzaldehyde [10]
2.4. Bis(3-chloro-4-dimethylaminobenzylidene)hydrazine 2
N-Chlorosuccinimide (2.67 g, 20 mmol, 2 equiv.) was added to a
solution of 4-(dimethylamino)benzaldehyde (1.49 g, 10 mmol, 1
equiv.) in dichloromethane (50 mL), and the reaction mixture
was stirred at room temperature for 72 h. The solvent was then
evaporated under reduced pressure, and silica gel flash column
chromatography (eluent: dichloromethane/petroleum ether: 1/1)
of the residue gave the product as a colorless liquid (0.98 g, 54%).
1H NMR (300 MHz, CDCl3, 25 °C): d = 9.81 (s, 1H, CHO), 7.83 (d,
Hydrazine hydrate (11 mg, 0.33 mmol, 1 equiv.) in methanol
(5 mL) was added dropwise to a solution of 3-chloro-4-(dimethyl-
amino)benzaldehyde (120 mg, 0.66 mmol, 2 equiv.) in methanol
(10 mL), and the reaction mixture was stirred at room temperature
for 4 h. The solvent was then evaporated under reduced pressure,
and silica gel flash column chromatography (eluent: dichlorometh-
ane) of the residue gave the product as a yellow solid (110 mg,
93%). Slow evaporation of a concentrated solution in dichlorometh-
ane gave pale orange crystals suitable for X-ray diffraction.
1H NMR (300 MHz, CDCl3, 25 °C): d = 8.55 (s, 2H, CHN), 7.87 (d,
4
3
4JHAH 2.1 Hz, 1 H, H-2), 7.68 (dd, JHAH 2.1, JHAH 8.4 Hz, 1H, H-5),
3
7.06 (d, JHAH 8.4 Hz, 1H, H-6), 2.97 (s, 6 H, CH3).
2.3. Bis(3-bromo-4-dimethylaminobenzylidene)hydrazine 1
4
4JHAH 2.1 Hz, 2 H, H-2), 7.64 (dd, JHAH 2.1, 3JHAH 8.4 Hz, 2 H, H-5),
3
7.08 (d, JHAH 8.4 Hz, 2 H, H-6), 2.92 (s, 12 H, CH3);
13C NMR (75 MHz, CDCl3, 25°C): d = 160.4 (C@N), 152.7 (C-4),
130.5 (C-2), 128.5 (C-1), 128.0 (C-6), 127.5 (C-3), 119.5 (C-5),
43.4 (CH3).
2.5. Single crystal X-ray analysis
Hydrazine hydrate (18 mg, 0.5 mmol, 1 equiv.) in methanol
(10 mL) was added dropwise to a solution of 3-bromo-4-(dimeth-
ylamino)benzaldehyde (228 mg, 1.0 mmol, 2 equiv.) in methanol
(10 mL), and the reaction mixture was stirred at room temperature
for 4 h. The solvent was then evaporated under reduced pressure,
and silica gel flash column chromatography (eluent: dichlorometh-
ane) of the residue gave the product as a yellow solid (100 mg,
Single-crystal X-ray diffraction data of 1 and 2 were collected at
150 K on a Nonius-based Kappa Bruker diffractrometer equipped
with a charge-coupled device (CCD) area detector and MoK
a
(k = 0.7107 Å) radiation. Absorption corrections were applied using
the multi-scan semi-empirical method implemented in SADABS
[11]. The structures were solved by direct methods using the
Fig. 2. Two different one-dimensional chains formed through Iꢁ ꢁ ꢁI halogen bonds [7,8].

S. Guieu et al. / Journal of Molecular Structure 1035 (2013) 1–5
3
Table 1
Crystal data and details of the structure determination.
Crystal Data
Bromo 1
18H20Br2N4
452.20
Monoclinic
P21/c
Chloro 2
Non-halogenated 3 [12]
Empirical formula
Formula weight
Crystal system
C
C18H20Cl2N4
363.28
Monoclinic
P21/c
C18H22N4
294.40
Monoclinic
P21/c
Space group
Unit cell dimensions
a = 10.4505(2) Å
b = 8.0358(2) Å
c = 11.3208(2) Å
a = 10.3416(8) Å
b = 8.0605(5) Å
c = 11.1573(8) Å
a = 8.232(4) Å
b = 6.065(3) Å
c = 16.710(9) Å
a
= 90.00°
a
= 90.00°
a
= 90.00°
b = 102.5620(10)°
b = 102.708(3)°
b = 97.864(6)°
c
= 90.00°
c
= 90.00°
c = 90.00°
Volume
Z
Calculated density
Absorption coefficient
F(000)
927.94(3) Å3
2
907.27(11) Å3
2
826.4(7) Å3
2
1.618 g/cm3
4.375 mmꢀ1
452
1.330 g/cm3
0.365 mmꢀ1
380
1.183 g/cm3
0.07 mmꢀ1
316
Crystal size
0.30 ꢂ 0.20 ꢂ 0.04 mm
0.22 ꢂ 0.15 ꢂ 0.05 mm
0.62 ꢂ 0.45 ꢂ 0.40 mm
Data collection
Temperature
Radiation
150(2) K
150(2) K
292(2) K
MoKa 0.71073 Å
MoKa
0.71073 Å
MoKa
0.71073 Å
h Min–max
2.00–27.89°
2.00–29.10°
2.50–27.47°
Dataset
Total, unique data, Rint
Observed data (I > 2.0 r(I))
ꢀ13/+12, ꢀ13/+10, ꢀ14/+14
7688, 2218, 0.0257
2217
ꢀ12/+14, ꢀ7/+11, ꢀ14/+15
6794, 2429, 0.0190
2429
ꢀ10/+10, ꢀ7/+4, ꢀ21/+21
1794, 1192, 0.0407
1192
Refinement
Nref, Npar
2217, 109
2429, 109
1192, 108
R, wR2, S
0.0232, 0.0630, 1.051
0.000, 0.000
ꢀ0.367, 0.469
0.0383, 0.1113, 1.025
0.000, 0.000
ꢀ0.345, 0.389
0.0650,0.1669, 1.098
0.000, 0.000
ꢀ0.14, 0.14
Max. and av. shift/error
Min. and max. resid. dens. (e Åꢀ3
)
Fig. 3. Molecular structure of: (a) bromo 1, (b) chloro 2, and (c) the non-halogenated analog 3 [13], viewed down the a axis. Ellipsoids are drawn at the 50% probability level.
Hydrogen atoms are drawn as fix-size spheres of radius 0.30 Å.

4
S. Guieu et al. / Journal of Molecular Structure 1035 (2013) 1–5
program SHELXS-97 [12] and refined by full-matrix least-square
refinement on F2 using the program SHELXL-97. All non-hydrogen
atoms were refined anisotropically. The hydrogen atoms were
placed in geometrically calculated positions and included in the fi-
nal refinement using the «riding» model with isotropic tempera-
ture factors fixed at 1.2 times that of the parent atom.
steps, for 1 and 2 respectively. The structures were confirmed by
1H and 13C NMR spectroscopy.
3.2. Crystal study
Slow evaporation of a saturated solution of 1 or 2 in dichloro-
methane gave crystals suitable for X-ray diffraction, as pale yellow
or pale orange flakes respectively. They crystallized in the mono-
clinic group P21/c, as the non-halogenated analog N,N0-bis(4-
dimethylaminobenzylidene)hydrazine 3 does [13]. Crystal data
and details of the structure determination are given in Table 1.
The molecular structures of 1, 2 and 3 are similar (Fig. 3). The
molecules possess a center of symmetry, which is expected for
symmetrical benzalazine [14], and bond lengths and angles are
in normal range. The molecules are nearly planar, the dihedral an-
gles between the phenyl ring and the imine being 6.6(3)°, 5.9(3)°
and 4.8(0)° for 1, 2 and 3 respectively, and the two imines being
coplanar for all compounds.
2.6. Powder X-ray analysis
Powder X-ray diffraction data were collected on a X’Pert MPD
Philips diffractometer (CuK
a X-radiation, l = 1.54060 Å) with a
flat-plate sample holder, in a Bragg-Brentano para-focusing optics
configuration (45 kV, 40 mA). Intensity data were collected by the
step-counting method (step 0.04° and time 40 s), in continuous
mode, in the 2h = 7–50° range, and are presented in arbitrary units.
3. Results and discussion
In order to rule out the possibility of arbitrary mono crystal
selection, we tested the uniformity of the samples using powder
X-ray diffraction. For both compounds 1 and 2, the experimental
powder XRD pattern is similar to the calculated one (Fig. 4), with
the major peaks being present at the same angles. The samples
are then composed of a single polymorph.
3.1. Synthesis of the compounds
The compounds were obtained in good yields through a two-
steps strategy (Scheme 1). para-Dimethylaminobenzaldehyde
was reacted with N-bromosuccinimide or N-chlorosuccinimide to
give the mono-halogenated precursors. Double condensation with
hydrazine gave the desired compounds in 31% and 50% over two
Intermolecular halogen bonds are present in the crystal packing
of 1, with Brꢁ ꢁ ꢁBr distances of 3.58(1) Å, shorter by ca. 8% than the
Fig. 4. Experimental (—) and calculated (---) powder XRD patterns of: (a) compound 1 and (b) compound 2. Intensities are in arbitrary units.

S. Guieu et al. / Journal of Molecular Structure 1035 (2013) 1–5
5
Fig. 5. One-dimensional chains formed through Brꢁ ꢁ ꢁBr bonds in 1.
sum of the van der Waals radii, and a CABrꢁ ꢁ ꢁBr angle of 145.5(7)°
(Fig. 5). The crystal structure of 2 shows similar organization. The
shortest distance between chlorine atoms is 3.79(8) Å, longer by
ca. 5% than the sum of the van der Waals radii, and the CAClꢁ ꢁ ꢁCl
angle is 146.3(7)°.
ganic Chemistry Research Unit (project PEst-C/QUI/UI0062/2011),
the CICECO Associate Laboratory (PEst-C/CTM/LA0011/2011) and
the Portuguese National NMR Network (RNRMN). SG also thanks
the FCT for a postdoctoral grant (SFRH/BPD/70702/2010).
Amines are able to accept halogen bonds in particular cases, but
for 1 and 2, none of the amino or imino group is halogen bonded.
The dimethylamino group forms a hydrogen bond with a neighbor-
ing molecule, characterized by a CAHꢁ ꢁ ꢁN distance of 2.55(0) Å or
2.48(7) Å, and a CAHꢁ ꢁ ꢁN angle of 170.4(0)° or 171.9(8)° in the case
of 1 or 2, respectively. We introduced dimethylamino groups,
which are strong electron donating groups, in the position para
to the hydrazine nitrogen, expecting that it would strengthen its
Lewis base properties. But the halogen atom in meta position is
an electron withdrawing group. It is probably counterbalancing
the effect of the amino group, leading to the absence of supramo-
lecular interaction between the hydrazine and any other atom.
Moreover, it may be noticed that the crystal organizations of 1
and 2 are similar to the one of 3, which is the non-halogenated
equivalent. In 3, however, there are no contacts with distances
shorter than the Van der Waals radii. The unit cell dimensions in
1 and 2 are similar, and the distances between the halogenated
carbons are almost equal (CAXꢁ ꢁ ꢁXAC, ca. 7.0 Å). Due to its attrac-
tive nature, one of the effects of the halogen–halogen bonds may
be to allow a closer packing of the molecules by balancing the
unfavorable other interactions. The nature of the halogen does
not influence the packing distances, but its size allows interpene-
tration of the van der Waals radii or not. The density of 1 in the
crystalline state is higher than 2 due to the higher mass of bromine,
and is not due to a closer packing.
Appendix A. Supplementary material
CCDC-889641 and CCDC-889642 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html (or
from the Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge CB2 1EZ, UK. Fax: C44 1223 336 033. E-mail: depos-
it@ccdc.cam.ac.uk). Supplementary data associated with this arti-
cle can be found, in the online version, at http://dx.doi.org/
10.1016/j.molstruc.2012.09.012.
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In summary, bis(3-bromo-4-dimethylaminobenzylidene)hydra-
zine and bis(3-chloro-4-dimethylaminobenzylidene)hydrazine
have been successfully synthesized and characterized. They are
isomorphous with the non-halogenated bis(4-dimethylaminoben-
zylidene)hydrazine, and their crystalline structures are stabilized
mainly through van der Waals interactions. Despite the introduc-
tion of strong electron donating groups, the imine groups do not
accept hydrogen nor halogen bonds, the predominant interaction
being the intermolecular halogen–halogen bond.
Acknowledgements
Thanks are due to the University of Aveiro and the Portuguese
Fundação para a Ciência e a Tecnologia (FCT) for funding the Or-