Cocrystallization of two tautomers: 4-(1-{[4-(dimethyl-amino)benzyl-idene]- hydrazono}eth-yl)benzene-1,3-diol and 6-[(E)-1-{[4-(dimethyl-amino)benzyl-idene] -hydrazino}ethyl-idene]-3-hy-droxy-cyclo-hexa-2,4-dien-1-one (1/1)

Article abstract of DOI:10.1107/S0108270109006696

Two different tautomeric forms of a new Schiff base, C17H19N3O2· C17H19N3O2, are present in the crystal in a 1:1 ratio, namely the enol-imine form 4-(1-{[4-(dimethyl-am-ino)benzyl-idene]-hydra-zono}-eth-yl)benzene-1,3-diol and the keto-amine form 6-[(E)-1

Full text of DOI:10.1107/S0108270109006696

organic compounds
Acta Crystallographica Section C
Crystal Structure
series of differences between (Ia) and (Ib). When the phenol–
imine tautomer is transformed into the keto–amine tautomer,
Communications
ISSN 0108-2701
Cocrystallization of two tautomers:
4-(1-{[4-(dimethylamino)benzylidene]-
hydrazono}ethyl)benzene-1,3-diol and
6-[(E)-1-{[4-(dimethylamino)benzyl-
idene]hydrazino}ethylidene]-3-hy-
droxycyclohexa-2,4-dien-1-one (1/1)
an appreciable increase in the C—N distance is observed
Zhen-Hua Wu, Jian-Ping Ma, Xiang-Wen Wu, Ru-Qi
Huang and Yu-Bin Dong*
˚
˚
[C7—N2 = 1.290 (3) A versus C24—N4 = 1.304 (3) A]. A
concomitant decrease in the C—O distance is also noted
˚
˚
[C5—O1 = 1.344 (3) A versus C22—O3 = 1.316 (2) A]. The
C7—N2 and C5—O1 distances are similar to the corres-
ponding distances in 2,20-(azinodimethylene)diphenol
College of Chemistry, Chemical Engineering and Materials Science, Shandong
Normal University, Jinan 250014, People’s Republic of China
Correspondence e-mail: yubindong@sdnu.edu.cn
0
˚
[1.285 (7) and 1.364 (8) A; Xu et al., 1994] and 2,2 -[(1,2-
ethanediyl)bis(nitrilopropylidyne)]bisphenol [1.295 (3) and
˚
1.351 (3) A; Corden et al., 1997], which both exist in the
phenol–imine tautomeric form. Likewise, the C24—N4 and
C22—O3 bond lengths are similar to the corresponding
distances in 2-{[tris(hydroxymethyl)methyl]aminomethylene}-
cyclohexa-3,5-dien-1(2H)-one [1.2952 (18) and 1.3025 (18) A,
˘
respectively; Odabas¸oglu et al., 2003] and 3-[(2-oxo-1-
naphthylidene)methylamino]benzoic acid [1.319 (3) and
1.290 (2) A; Pavlovic & Sosa, 2000], which both show the
keto–amine tautomeric form. Hence, the C—O and C—N
bond lengths verify the phenol–imine form of (Ia) and the
keto–amine form of (Ib). In addition, the degrees of planarity
for the two molecules in the asymmetric unit are different. The
maximum dihedral angle in (Ia) is 7.06 (9)ꢁ, for the dihedral
angle between the C3-containing benzene ring and the C10-
containing benzene ring, while the corresponding dihedral
angle in (Ib) is 11.62 (7)ꢁ.
Received 9 January 2009
Accepted 23 February 2009
Online 7 March 2009
Two different tautomeric forms of a new Schiff base, C17H19-
N3O2ꢀC17H19N3O2, are present in the crystal in a 1:1 ratio,
namely the enol–imine form 4-(1-{[4-(dimethylamino)benzyl-
idene]hydrazono}ethyl)benzene-1,3-diol and the keto–amine
form 6-[(E)-1-{[4-(dimethylamino)benzylidene]hydrazino}-
ethylidene]-3-hydroxycyclohexa-2,4-dien-1-one. The tauto-
mers are formed by proton transfer between the hydroxy O
atom and the imine N atom and are hydrogen bonded to each
other to form a one-dimensional zigzag chain along the
crystallographic b axis via intermolecular hydrogen bonds.
˚
˚
´
Comment
Schiff base ligands are of interest mainly because of the
existence of typical hydrogen bonds and tautomerism between
the phenol–imine and keto–amine forms (Costamagna et al.,
1992; Sridharan et al., 2004; Fita et al., 2005). Tautomerism in
o-hydroxy Schiff bases both in solution and in the solid state
has been investigated using IR (Ledbetter, 1977; Yildiz et al.,
1998), UV (Ottolenghi & McClure, 1967), 1H NMR (Dudek &
Holm, 1962; Dudek & Dudek, 1966), 13C NMR (Salman et al.,
1991) and X-ray crystallographic techniques (Gavranic et al.,
1996; Kaitner & Pavlovic, 1996).
We have synthesized a new Schiff base compound, (I)
(Fig. 1). This compound undergoes tautomerism by proton
transfer between the hydroxy O atom and the imine N atom,
forming two tautomers, (Ia) and (Ib), and the two different
tautomeric forms of the same molecule cocrystallized in a 1:1
ratio. Form (Ia) is the phenol–imine tautomer, while (Ib) is the
keto–amine tautomeric form.
Figure 1
A view of the molecules of (a) (Ia) and (b) (Ib), with displacement
ellipsoids drawn at the 30% probability level and H atoms shown as small
spheres of arbitrary radii.
The compound crystallizes in the monoclinic form in the
space group P21/c. The tautomerism of the compound causes a
o128 # 2009 International Union of Crystallography
doi:10.1107/S0108270109006696
Acta Cryst. (2009). C65, o128–o130

organic compounds
Data collection
Bruker SMART CCD area-detector
diffractometer
15831 measured reflections
5758 independent reflections
3521 reflections with I > 2ꢃ(I)
Rint = 0.042
Refinement
R[F2 > 2ꢃ(F2)] = 0.053
wR(F2) = 0.140
S = 1.02
5758 reflections
418 parameters
2 restraints
H atoms treated by a mixture of
independent and constrained
refinement
ꢂ3
˚
Áꢄmax = 0.21 e A
ꢂ3
˚
Áꢄmin = ꢂ0.18 e A
Table 1
Hydrogen-bond geometry (A, ).
ꢁ
˚
D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
Figure 2
The intra- and intermolecular hydrogen bonding in (I).
O1—H1ꢀ ꢀ ꢀN2
O2—H2Aꢀ ꢀ ꢀO3i
O4—H4ꢀ ꢀ ꢀO3ii
N4—H4Aꢀ ꢀ ꢀO3
0.864 (10)
0.97 (3)
0.85 (3)
1.709 (17)
1.71 (3)
1.86 (3)
2.507 (3)
2.668 (2)
2.674 (2)
2.558 (2)
153 (3)
169 (2)
161 (3)
146 (2)
0.922 (10)
1.739 (15)
Both intra- and intermolecular hydrogen bonds are found in
the crystal structures of the tautomers (Fig. 2). The intra-
molecular hydrogen bonds (O—Hꢀ ꢀ ꢀN and N—Hꢀ ꢀ ꢀO) of the
two tautomeric forms are rather short, as expected (Table 1).
In (Ia), the hydrogen-bonded ring is nearly coplanar with the
adjacent ring, with a dihedral angle of 1.37 (7)ꢁ, while (Ib) is
not quite as planar, with a dihedral angle of 5.46 (7)ꢁ between
the two corresponding rings. The two tautomers are connected
via intermolecular O—Hꢀ ꢀ ꢀO hydrogen bonds (Table 1) into a
one-dimensional zigzag chain extended along the crystal-
lographic b axis.
1
2
1
2
Symmetry codes: (i) x þ 1; y ꢂ 1; z; (ii) ꢂx; y ꢂ ; ꢂz þ .
H atoms attached to C atoms were idealized and included as riding
˚
atoms [C—H = 0.93 A and Uiso(H) = 1.2Ueq(C) for CH hydrogens,
˚
and C—H = 0.96 A and Uiso(H) = 1.5Ueq(C) for CH3 hydrogens]. H
atoms attached to N and O atoms were located in a difference map
and refined isotropically with O—H and N—H distance restraints of
˚
0.83 (3) and 0.96 (2) A, respectively; the refined distances are given in
Table 1. In total, two geometric restraints (DFIX) were used.
Data collection: SMART (Bruker, 1997); cell refinement: SAINT
(Bruker, 1997); data reduction: SAINT; program(s) used to solve
structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine
structure: SHELXL97 (Sheldrick, 2008); molecular graphics:
SHELXTL (Sheldrick, 2008); software used to prepare material for
publication: SHELXTL.
In conclusion, a new Schiff base has been synthesized and
characterized by X-ray diffraction analysis. Two different
tautomeric forms are found in the solid state, and these are
hydrogen bonded to one another to form an infinite chain.
We are grateful for financial support from the NSFC (grant
Nos. 20871076 and 20671060), the PhD Programs Foundation
of the Ministry of Education of China (grant No.
200804450001), the Shandong Natural Science Foundation
(grant No. JQ200803) and the Young Scientists Fund of
Shandong Province of China (grant No. 2007BS04002).
Experimental
Compound (I) was prepared according to a literature method (Diehl
et al., 1950). 2,4-Dihydroxyacetophenone (2.00 g, 13.2 mmol) and
hydrazine hydrate (4.00 g, 40 mmol) were dissolved in ethanol
(40 ml) and four drops of methanoic acid were added. The mixture
was stirred at room temperature for 5 h. A yellow powder, namely
4-(1-hydrazonoethyl)benzene-1,3-diol, was filtered off, washed with
ethanol and dried in a vacuum. 4-(1-Hydrazonoethyl)benzene-1,3-
diol (0.20 g, 1.3 mmol) and p-(dimethylamino)benzaldehyde (0.19 g,
1.3 mmol) were dissolved in ethanol (20 ml), and then four drops of
methanoic acid were added and the mixture was stirred at room
temperature for 5 h. The resulting yellow powder was filtered off,
washed several times with ethanol and then dried in a vacuum (yield
89%, m.p. 482.7–483.9 K). Well shaped crystals were obtained by slow
evaporation of an ethanol solution.
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: FN3012). Services for accessing these data are
described at the back of the journal.
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Crystal data
3
˚
C17H19N3O2ꢀC17H19N3O2
V = 3091.4 (12) A
Z = 4
Mr = 594.70
Monoclinic, P21=c
Mo Kꢁ radiation
ꢂ = 0.09 mmꢂ1
T = 298 (2) K
˚
a = 11.872 (3) A
˚
b = 9.630 (2) A
˚
c = 28.442 (6) A
ꢀ = 108.067 (8)ꢁ
0.49 ꢃ 0.40 ꢃ 0.06 mm
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Acta Cryst. (2009). C65, o128–o130
Wu et al. C17H19N3O2ꢀC17H19N3O2 o129

organic compounds
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Acta Cryst. (2009). C65, o128–o130