4-Dimethylamino-β-nitrostyrene and 4-dimethylamino-β-ethyl- β-nitro-styrene at 100 K

Article abstract of DOI:10.1107/S0108270106025819

The structures of 4-dimethylamino-β-nitrostyrene (DANS), C ₁₀H₁₂N₂O₂, and 4-dimethylamino- β-ethyl-β-nitrostyrene (DAENS), C₁₂H₁₆N ₂O₂, have been solved at T = 100 K.

Full text of DOI:10.1107/S0108270106025819

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
obtained with relatively long conjugated molecules containing
strongly interacting donor±acceptor groups. For 4-dimethyl-
amino-ꢀ-nitrostyrene, denoted DANS, the NLO properties
found for dilute solutions are very close to those for 4-
dimethylamino-40-nitrostilbene, usually quoted as an example
of a conjugated molecule which exhibits very large non-
linearities (Chemla & Zyss, 1987; Cheng, Tam, Stevenson et al.,
1991). However, a strong steric effect of the methyl substituent
was observed in a series of ꢀ-methyl-ꢀ-nitrostyrene deriva-
tives (Cho et al., 1996). In particular, the distortion from
planarity caused by steric repulsion is able to reduce the
optical non-linearities to nearly zero.
ISSN 0108-2701
4-Dimethylamino-b-nitrostyrene and
4-dimethylamino-b-ethyl-b-nitro-
styrene at 100 K
Lamine Hamdellou,a Olivier Hernandezb and Jean
Meinnelb*
a
Â
Â
Laboratoire de Cristallographie, Departement de Physique, Universite Mentouri
b
Â
Constantine, 25000 Constantine, Algeria, and UMR 6226 CNRS, Universite de
Â
Rennes 1 `Sciences Chimiques de Rennes', Equipe `Materiaux Inorganiques, Chimie
Â
Â
Ã
 Â
Douce et Reactivite', Batiment 10B, Campus de Beaulieu, 263 Avenue du General
Leclerc, F-35042 Rennes, France
Correspondence e-mail: jean.meinnel@univ-rennes1.fr
We present here the structure of DANS in order to establish
the in¯uence of charge transfer upon the molecular geometry,
which affects the strength of the NLO properties. In parallel,
in order to analyse the importance of steric effects upon
conjugation, we also report the structure of 4-dimethylamino-
ꢀ-ethyl-ꢀ-nitrostyrene, denoted DAENS (Pianka, 1963). For
both compounds, data collection at 100 K has allowed an
Received 2 June 2006
Accepted 4 July 2006
Online 11 August 2006
The structures of 4-dimethylamino-ꢀ-nitrostyrene (DANS),
C10H12N2O2, and 4-dimethylamino-ꢀ-ethyl-ꢀ-nitrostyrene
(DAENS), C12H16N2O2, have been solved at T = 100 K. The
structure solution for DANS was complicated by the presence
of a static disorder, characterized by a misorientation of 17%
of the molecules. The molecule of DANS is almost planar,
indicating signi®cant conjugation, with a push±pull effect
through the styrene skeleton extending up to the terminal
substituents and enhancing the dipole moment. As a
consequence of this conjugation, the hexagonal ring displays
Ê
a quinoidal character; the lengths of the CÐN [1.3595 (15) A]
Ê
and CÐC [1.448 (2) A] bonds adjacent to the benzene ring are
shorter than single bonds. The molecules are stacked in dimers
with antiparallel dipoles. In contrast, the molecule of DAENS
is not planar. The ethyl substituent pushes the nitropropene
group out of the benzene plane, with a torsion angle of
21.9 (3). Nevertheless, the molecule remains conjugated,
with a shortening of the same bonds as in DANS.
Figure 1
A composite view of the disordered molecule of DANS at 100 K, showing
the atom-labelling scheme. Displacement ellipsoids are drawn at the 50%
probability level and H atoms are represented by circles of arbitrary radii.
The labels of the H atoms have been omitted for clarity.
Comment
A large number of conjugated organic compounds have been
studied experimentally and theoretically in order to establish
the structure±property relationships inducing large non-linear
optical (NLO) properties. Among these, ꢀ-nitrostyrene deri-
vatives have been very attractive (Oudar, 1977; Zyss, 1979,
Dulcic et al., 1981; Cheng, Tam, Marder et al., 1991; Keshari et
al., 1993). Such work has tried to determine the role and
importance of the number of conjugated double bonds, the
electronic biasing strengths of various donor and acceptor
groups, charge-transfer enhancement, and the pattern and
polarity of multiple substituents. The results of these studies
reveal that very large second-order non-linearities can be
Figure 2
A view of the molecular unit of DAENS at 100 K, showing the atom-
labelling scheme. Displacement ellipsoids are drawn at the 50%
probability level and H atoms are represented by circles of arbitrary radii.
Acta Cryst. (2006). C62, o557±o560
DOI: 10.1107/S0108270106025819
# 2006 International Union of Crystallography o557

organic compounds
increase up to an acceptable level of the ratio of the number of
independent observable re¯ections to the number of least-
squares parameters, compared with the data collection at
293 K. Furthermore, for DANS it appears that the structure is
disordered. The static disorder consists of a 180ꢀ rotation of
17% of the molecules around their long axis and is similar to
that found in trans-stilbene and trans-azobenzene (Brown,
1966a,b; Bouwstra et al., 1983; Finder et al., 1974). In this
paper, we report the molecular geometry and crystal packing
of DANS, obviously only with regard to the molecule with the
most probable orientation, for which atomic displacement
parameters have been re®ned anisotropically.
The molecular structure of DANS is shown in Fig. 1, while
selected geometric parameters are given in Table 1. The
molecule is almost planar, indicating a high degree of conju-
gation, with a strong push±pull effect between the nitro and
dimethylamine groups through the styrene skeleton.
Excluding the dimethylamine group (atom N1 has slightly
pyramidal bonds), the highest mean square deviation from the
which is yellow, not red like DANS. Nevertheless, a noticeable
conjugation remains, evidenced by the shortening of several
Ê
bonds [C2ÐC3 = 1.383 (2) A, C5ÐC6 = 1.391 (3) A, N1Ð
Ê
Ê
Ê
C1 = 1.369 (2) A and C4ÐC7 = 1.450 (2) A]. The conjugation
also explains why the N atom of the dimethylamine moiety has
lost all pyramidal character [the sum of the bond angles
around atom N1 is 359.02 (5)ꢀ].
The aforementioned steric hindrance of the ethyl group on
the molecular planarity of DAENS must be compared with
that of the methyl group in ꢀ-methyl-ꢀ-nitrostyrene
compounds substituted by donors of various strengths on the
benzene ring. The value of the torsion angle between the
benzene and nitropropene groups in 4-dimethylamino-
ꢀ-methyl-ꢀ-nitrostyrene, with the same donor as in DAENS,
is only 1.6 (8)ꢀ (Brito et al., 1991), while it is 27.1ꢀ in the
4-methoxy analogue (Boys et al., 1993) and 23.7ꢀ in the
4-hydroxy-3-methoxy (Zabel et al., 1980) analogue. These
values illustrate how molecular conjugation, or in other words
the planarity of the molecule, is counter-balanced between
steric effects and the strength of donors.
Ê
calculated mean plane is 0.014 (2) A. The dihedral angle
between the mean planes of these two parts of the molecule is
1.4 (2)ꢀ. The sum of the bond angles around N1 is 359.2 (3)ꢀ,
close to 360ꢀ, revealing the delocalization of the lone pair
In the crystal structure, molecules of DANS are stacked as
dimers, interacting in an antiferroelectric manner, and
consequently no second-order NLO effect is observed in the
solid state. The distance between the mean planes of the dimer
Ê
toward the N1ÐC1 bond, which is too short [1.3595 (15) A]
for a single NÐC bond. Conjugation through the styrene
Ê
is 3.276 (2) A, while the smallest distance is between atoms C1
Ê
and N21 of 3.322 (2) A. The dimers are organized in chains
induces the quinoidal character of the hexagonal ring; the
Ê
Ê
C21ÐC31 [1.390 (2) A] and C51ÐC61 [1.373 (2) A] bond
lengths, roughly parallel to the molecular dipole, are signi®-
along the c axis (Fig. 3) via CÐHÁ Á ÁO interactions between
donor and acceptor groups (Table 2). Each chain of dimers is
symmetrically surrounded by four other chains, within which
the molecular planes are almost perpendicular to the mol-
ecular plane of the central chain.
Ê
cantly shorter than C1ÐC21 [1.418 (2) A], C1ÐC61
Ê
[1.423 (2) A], C31ÐC41 [1.4045 (17) A] and C41ÐC51
Ê
Ê
[1.4057 (19) A]. For the same reason, the C41ÐC71 bond
Ê
[1.448 (2) A] is shorter than a single bond.
The packing of molecules of (II) in the crystal structure
displays short contacts between O atoms and methyl groups
(see Table 4 and Fig. 4). The asymmetric interactions of the O
atoms with the methyl groups of the dimethylamine group
explain the difference between torsion angles C2ÐC1ÐN1Ð
C9 [10.4 (3)ꢀ] and C6ÐC1ÐN1ÐC10 [ 1.4 (3)ꢀ]. Unfortu-
nately in this non-centrosymmetric structure, the non-
planarity of the molecules does not allow an ef®cient NLO
effect.
A perspective view of DAENS is shown in Fig. 2 and
selected geometric parameters are given in Table 3. Several
differences from the conformation of DANS are found. The
most striking feature is the C5ÐC4ÐC7ÐC8 torsion angle of
21.9 (3)ꢀ, which pushes the nitro and ethyl substituent
groups out of the benzene ring plane. The main consequence
of this torsion is to decrease the conjugation between the
C7 C8 double bond and the dimethylaminobenzene moiety,
and hence explains the hypsochromic effect for DAENS,
Figure 3
A crystal packing diagram of part of DANS at 100 K, along the [321]
direction, showing the formation of a chain of dimers surrounded by half
a chain of two neighbours. CÐHÁ Á ÁO contacts are represented by dotted
lines. For the sake of clarity, the molecule with 17% of the disorder and H
atoms not involved in hydrogen bonding have been omitted.
Figure 4
A crystal packing diagram of DAENS at 100 K, viewed along [100] and
slightly rotated around the c axis, showing asymmetric CÐHÁ Á ÁO
hydrogen-bond interactions (dotted lines). For the sake of clarity, H
atoms not involved in the hydrogen bonds shown have been omitted.
ꢁ
o558 Hamdellou et al. C10H12N2O2 and C12H16N2O2
Acta Cryst. (2006). C62, o557±o560

organic compounds
Table 2
Short-contact geometry (A, ) for (I).
Experimental
ꢀ
Ê
The syntheses of both materials consists of the condensation of
4-dimethylaminobenzaldehyde (DABA) with a nitroole®n. To obtain
DANS, a mixture of DABA (0.01 mol) and nitromethane (0.03 mol)
was used at 373 K, with a few drops of butylamine. For DAENS, the
synthesis begins with the condensation of DABA with butylamine to
obtain the 4-dimethylaminobenzylidene butylamine. After separa-
tion, this butylamine reacts with nitromethane in the presence of
acetic acid to give the nitrostyrene. Single crystals of DANS were
grown by slow evaporation of a solution in toluene. Single crystals of
DAENS were obtained from a saturated solution in ethanol prepared
at room temparature and slowly evaporated in a refrigerator [m.p.
390 K for DANS and 361 K for DAENS].
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
C9ÐH91Á Á ÁO21i
C9ÐH93Á Á ÁO11ii
C10ÐH101Á Á ÁO11iii
1.00
1.00
1.00
2.55
2.78
2.79
3.534 (2)
3.419 (2)
3.503 (2)
169
122
129
Symmetry codes: (i) x; y ‡ 32; z ‡ 21; (ii) x ‡ 21; y ‡ 23; z ‡ 1; (iii) x ‡ 21, y ‡ 1,
1
2
z
.
DAENS
Crystal data
C12H16N2O2
Mr = 220.27
Z = 4
Dx = 1.255 Mg m
Mo Kꢁ radiation
ꢂ = 0.09 mm
T = 100 (1) K
Plate, yellow
0.45 Â 0.34 Â 0.28 mm
3
DANS
Orthorhombic, P212121
Ê
1
Crystal data
a = 5.9641 (1) A
Ê
b = 8.4492 (1) A
C10H12N2O2
Mr = 192.22
Orthorhombic, Pbca
Ê
a = 10.1460 (2) A
Ê
b = 7.3091 (2) A
Z = 8
Dx = 1.368 Mg m
Mo Kꢁ radiation
ꢂ = 0.10 mm
T = 100 (1) K
Plate, dark red
0.26 Â 0.18 Â 0.16 mm
Ê
3
c = 23.1400 (4) A
Ê
V = 1166.07 (3) A
3
1
Data collection
Ê
Nonius KappaCCD area-detector
diffractometer
CCD scans
Absorption correction: multi-scan
(SADABS; Sheldrick, 2002)
Tmin = 0.962, Tmax = 0.976
14807 measured re¯ections
5077 independent re¯ections
2017 re¯ections with I > 3ꢃ(I)
Rint = 0.04
c = 25.1662 (7) A
Ê
V = 1866.28 (8) A
3
Data collection
ꢄmax = 35.0ꢀ
Bruker APEX-II diffractometer
CCD scans
Absorption correction: multi-scan
(SADABS; Sheldrick, 2002)
Tmin = 0.975, Tmax = 0.985
20691 measured re¯ections
2137 independent re¯ections
1488 re¯ections with I > 2ꢃ(I)
Rint = 0.032
Re®nement
ꢄmax = 27.5ꢀ
Re®nement on F
R[F2 > 2ꢃ(F2)] = 0.038
wR(F2) = 0.039
S = 1.14
2017 re¯ections
Prince (1982) modi®ed Chebychev
polynomial with three parameters
(Watkin, 1994): 3.54, 1.10, 3.21
(Á/ꢃ)max = 0.001
Re®nement
Re®nement on F
R[F2 > 2ꢃ(F2)] = 0.033
wR(F2) = 0.037
S = 1.17
1488 re¯ections
Prince (1982) modi®ed Chebychev
polynomial with ®ve parameters
(Watkin, 1994): 1.34, 1.99, 1.39
0.636 0.244
3
Ê
Áꢅmax = 0.28 e A
3
Ê
0.22 e A
148 parameters
H-atom parameters constrained
Áꢅmin
=
Absolute structure: Flack (1983),
with 3060 Friedel pairs
Flack parameter: 0.7 (14)
(Á/ꢃ)max = 0.001
3
Ê
161 parameters
H-atom parameters constrained
Áꢅmax = 0.22 e A
3
Ê
0.21 e A
Áꢅmin
=
Table 3
Selected geometric parameters (A, ) for (II).
ꢀ
Ê
Table 1
Selected geometric parameters (A, ) for (I).
O1ÐN2
O2ÐN2
N1ÐC1
N1ÐC9
N1ÐC10
N2ÐC8
C1ÐC2
C1ÐC6
1.232 (2)
1.231 (2)
1.369 (2)
1.454 (2)
1.453 (2)
1.468 (2)
1.421 (2)
1.408 (2)
C2ÐC3
C3ÐC4
C4ÐC5
C4ÐC7
C5ÐC6
C7ÐC8
C8ÐC11
C11ÐC12
1.383 (2)
1.395 (2)
1.410 (2)
1.450 (2)
1.391 (3)
1.345 (3)
1.502 (2)
1.527 (3)
ꢀ
Ê
O11ÐN21
O21ÐN21
N1ÐC1
1.2394 (19)
1.240 (2)
C1ÐC61
1.423 (2)
1.390 (2)
1.4045 (17)
1.4057 (19)
1.448 (2)
1.373 (2)
1.336 (2)
C21ÐC31
C31ÐC41
C41ÐC51
C41ÐC71
C51ÐC61
C71ÐC81
1.3595 (15)
1.4554 (15)
1.4554 (15)
1.4313 (19)
1.418 (2)
N1ÐC9
N1ÐC10
N21ÐC81
C1ÐC21
C1ÐN1ÐC9
C1ÐN1ÐC10
C9ÐN1ÐC10
O1ÐN2ÐO2
O1ÐN2ÐC8
O2ÐN2ÐC8
N1ÐC1ÐC2
N1ÐC1ÐC6
C2ÐC1ÐC6
C1ÐC2ÐC3
C2ÐC3ÐC4
121.12 (15)
120.01 (15)
117.89 (15)
122.23 (16)
117.74 (15)
120.01 (15)
120.82 (15)
121.69 (15)
117.50 (15)
120.11 (16)
123.06 (15)
C3ÐC4ÐC5
C3ÐC4ÐC7
C5ÐC4ÐC7
C4ÐC5ÐC6
C1ÐC6ÐC5
C4ÐC7ÐC8
N2ÐC8ÐC7
N2ÐC8ÐC11
C7ÐC8ÐC11
C8ÐC11ÐC12
116.54 (16)
117.66 (15)
125.68 (16)
121.70 (16)
121.05 (15)
130.66 (16)
115.37 (16)
114.77 (16)
129.85 (16)
112.52 (14)
C1ÐN1ÐC9
120.35 (10)
120.11 (10)
118.73 (10)
122.53 (15)
119.86 (16)
117.61 (16)
119.90 (11)
123.75 (11)
116.34 (12)
C1ÐC21ÐC31
C21ÐC31ÐC41
C31ÐC41ÐC51
C31ÐC41ÐC71
C51ÐC41ÐC71
C41ÐC51ÐC61
C1ÐC61ÐC51
C41ÐC71ÐC81
N21ÐC81ÐC71
120.75 (13)
122.46 (13)
116.55 (12)
119.10 (13)
124.35 (13)
121.93 (13)
121.91 (13)
126.72 (14)
120.71 (14)
C1ÐN1ÐC10
C9ÐN1ÐC10
O21ÐN21ÐO11
O21ÐN21ÐC81
O11ÐN21ÐC81
N1ÐC1ÐC21
N1ÐC1ÐC61
C21ÐC1ÐC61
C5ÐC4ÐC7ÐC8
C3ÐC4ÐC7ÐC8
C4ÐC7ÐC8ÐN2
C7ÐC8ÐN2ÐO1
21.9 (3)
C7ÐC8ÐN2ÐO2
C2ÐC1ÐN1ÐC9
C6ÐC1ÐN1ÐC10
C4ÐC7ÐC8ÐC11
7.0 (3)
10.4 (3)
1.4 (3)
3.3 (3)
C51ÐC41ÐC71ÐC81
C31ÐC41ÐC71ÐC81
C41ÐC71ÐC81ÐN21
C71ÐC81ÐN21ÐO11
1.148
179.887
179.863
179.363
C71ÐC81ÐN21ÐO21
C21ÐC1ÐN1ÐC9
C61ÐC1ÐN1ÐC10
0.427
6.750
4.305
162.26 (19)
178.23 (17)
174.21 (17)
ꢁ
Acta Cryst. (2006). C62, o557±o560
Hamdellou et al. C10H12N2O2 and C12H16N2O2 o559

organic compounds
Table 4
Short-contact geometry (A, ) for (II).
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: HJ3016). Services for accessing these data are
described at the back of the journal.
ꢀ
Ê
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
C10ÐH101Á Á ÁO1i
C12ÐH121Á Á ÁO1ii
C9ÐH92Á Á ÁO2iii
C10ÐH102Á Á ÁO2iii
C11ÐH112Á Á ÁO2iv
1.00
1.00
1.00
1.00
1.00
2.47
2.50
2.77
2.82
2.58
3.401 (2)
3.499 (2)
3.283 (2)
3.310 (2)
3.539 (2)
154
175
112
111
161
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ꢁ
o560 Hamdellou et al. C10H12N2O2 and C12H16N2O2
Acta Cryst. (2006). C62, o557±o560