The zwitterion of 4-nitro-2-{(E)-[2-(piperidin-1-yl)eth-yl]imino-meth-yl}- phenol

Article abstract of DOI:10.1107/S0108270108040407

The title Schiff base compound, 4-nitro-1-oxo-2-{(E)-[2-(piperidin-1-yl) eth-yl]iminiometh-yl}cyclo-hexa-dienide, C14H19N3O3, exists as a zwitterion, with the H atom of the phenol group being transferred to the imine N atom. The C=O, CAr - CAr and C - N b

Full text of DOI:10.1107/S0108270108040407

organic compounds
the double-bond character for the imine (ꢁ at 1601 cmꢁ1) and
keto-carbonyl groups (ꢁ at 1657 cmꢁ1), respectively (Allen,
2002). Moreover, the bond lengths in the C1–C6 ring show
Acta Crystallographica Section C
Crystal Structure
Communications
ISSN 0108-2701
The zwitterion of 4-nitro-2-{(E)-[2-
(piperidin-1-yl)ethyl]iminomethyl}-
phenol
clear alternation in the delocalized C2–C6 portion. The nitro
group is tilted out of the mean plane of the adjacent ring by
ꢁ11.1 (3)ꢂ, whereas the C4—N4 distance is in the character-
istic range suggesting limited conjugation with the ring. Thus,
the whole geometry is in agreement with the predominace of
the oxocyclohexadienide–iminium zwitterion bonding scheme
(see scheme) (Krygowski & Stepien, 2005), in close agreement
with the reported configurations of p-nitrophenolates of alkali
metal cations (Butt et al., 1987).
Rocio J. Santos-Contreras,a Angel Ramos-Organillo,a
b
b
´
´
´
´
Efren V. Garcıa-Baez, Itzia I. Padilla-Martınez and
a
´
´
Francisco J. Martınez-Martınez *
a
´
´
Facultad de Ciencias Quımicas, Universidad de Colima, Carretera Coquimatlan-
Colima, Coquimatlan Colima, 28400, Mexico, and bUnidad Profesional Inter
´
´
´
disciplinaria de Biotecnologıa, Instituto Politecnico Nacional, Avenida
´
´
Acueducto s/n, Barrio La Laguna Ticoman, Mexico DF 07340, Mexico
Correspondence e-mail: fjmartin@ucol.mx
The iminium H atom (located in a difference map) is
coplanar with the oxocyclohexadienide ring and on the same
side of the molecule as the O atom of the keto group, allowing
the formation of an intramolecular N—Hꢀ ꢀ ꢀO hydrogen bond
Received 11 November 2008
Accepted 1 December 2008
Online 6 December 2008
The title Schiff base compound, 4-nitro-1-oxo-2-{(E)-[2-
(piperidin-1-yl)ethyl]iminiomethyl}cyclohexadienide, C14H19-
N3O3, exists as a zwitterion, with the H atom of the phenol
group being transferred to the imine N atom. The C O,
CAr—CAr and C—N bond lengths are in agreement with the
oxocyclohexadienide–iminium zwitterionic form. The iminium
H atom is engaged in a strong intramolecular hydrogen bond
with the O atom of the keto group (N+—Hꢀ ꢀ ꢀO) to form an
S(6) motif. Soft C—Hꢀ ꢀ ꢀO interactions in the ac plane lead to
the development of hydrogen-bonded tapes, which are ꢀ-
stacked through the oxocyclohexadienide ring and iminium
group. The significance of this study is in providing crystal-
lographic evidence, supported by NMR and IR data, of the
predominance of the oxocyclohexadienide–iminium zwit-
terion form over the noncharged canonical form in the title
Schiff base.
Figure 1
The molecular structure of (I), showing the atom-labelling scheme.
Displacement ellipsoids are drawn at the 30% probability level and H
atoms are shown as small spheres of arbitrary radii.
Comment
Aromatic imines and their derivatives are an important group
of molecules in organic chemistry, in particular those that have
aryl groups bound to N or C atoms. They have been used
successfully to study resonance-assisted hydrogen bonds
(RAHBs; Krygowski & Stepien, 2005; Sobczyk et al., 2005).
Imines substituted in the aromatic ring have offered the
opportunity to study the substituent effects in RAHBs. In this
context, the molecular structure of the title compound, (I)
(Fig. 1), is reported here.
The single-crystal structure of the title Schiff base
compound is built up by discrete molecules in the monoclinic
space group P2/c, with one molecule in the asymmetric unit. A
summary of bond lengths and angles is presented in Table 1.
The N8—C7 and O1—C1 bond lengths are in agreement with
Figure 2
Hydrogen-bonded tapes formed by N—Hꢀ ꢀ ꢀO and C—Hꢀ ꢀ ꢀO inter-
actions along the c axis. H atoms not involved in the motifs shown have
been omitted for clarity. [Symmetry codes: (i) ꢁx + 1, y, ꢁz + 32; (ii) ꢁx + 1,
y, ꢁz + 12.]
o8 # 2009 International Union of Crystallography
doi:10.1107/S0108270108040407
Acta Cryst. (2009). C65, o8–o10

organic compounds
(Table 2) in an S(6) motif (Bernstein et al., 1995), with
dimensions in agreement with the usual values (Krygowski et
al., 1997; Steiner 1998, 2002). The N8ꢀ ꢀ ꢀO1 distance has almost
described above to develop discrete centrosymmetric ribbons
which propagate along the c axis.
˚
the same value as the RAHB of 2.607 (3) A found in
Experimental
3-{[(diphenoxythiophosphoryl)hydrazine]methylidene}-3,4-
dihydro-2H-1-benzopyran-2,4-dione (Rybarczyk-Pirek et al.,
2002). The iminium H atom is also engaged in N—Hꢀ ꢀ ꢀO
hydrogen bonding with the O atom from the keto group of a
neighbouring molecule, forming dimers with an almost square
R22(4) motif (Fig. 2).
Compound (I) was synthesized by amidation of ethyl 6-nitro-2-oxo-
2H-chromene-3-carboxylate (0.5 g, 1.9 mmol), prepared according to
Santos-Contreras et al. (2007), with 1-(2-aminoethyl)piperidine
(0.26 ml, 1.9 mmol) and two drops of piperidine as catalyst in
refluxing ethanol (10 ml) for 24 h. The resulting orange solution was
treated with activated charcoal and evaporated to give 0.3 g of an
orange solid in 57% yield. Crystals suitable for X-ray analysis were
obtained by slow evaporation from a saturated ethyl acetate solution
(m.p. 413 K). IR (cmꢁ1): ꢁ (C O) 1657, (C N) 1601, (C—NO)
1535; 1H NMR (300 MHz, CDCl3): ꢂ 6.90 (d, H6, 3J = 9.0 Hz), 8.16 (dd,
H5, 3J = 9.0 and 4J = 3.0 Hz), 8.22 (d, H3, 3J = 9.0 Hz), 11.9 (b, NH),
The first dimension of the extended structure is built up by
soft C—Hꢀ ꢀ ꢀO interactions with the participation of one of the
O atoms from the nitro group, in a monocoordinative fashion
(Allen et al., 1997), as the acceptor of two hydrogen bonds
(Table 2) to form an R12(6) motif. The whole hydrogen-bonding
scheme, makes up tapes propagating along the direction of the
c axis. All C—Hꢀ ꢀ ꢀON and Cꢀ ꢀ ꢀON distances are shorter than
3
3
8.31 (s, H7), 3.74 (t, 2H, J = 6.2 Hz, –+NHCH2–), 2.64 (t, 2H, J =
6.2 Hz, –CH2N), 2.46 [m, 4H, N—(CH2)2], 1.56 (m, 4H, –CH2–),
1.46 (m, 2H, –CH2–); 13C NMR: ꢂ 173.1 (C1), 115.6 (C2), 129.7 (C3),
137.5 (C4), 129.0 (C5), 120.9 (C6), 165.3 (C7), 58.4 (C9), 53.2 (C10),
54.8 (C12), 26.2 (C13), 24.3 (C14).
˚
the mean values of 2.7 (2) and 3.5 (2) A, respectively, found in
´
a study of nitrobenzenes (Andre et al., 1997), although the C—
Hꢀ ꢀ ꢀON angles are within the accepted range [C—Hꢀ ꢀ ꢀO =
133 (20)ꢂ]. Even when C—Hꢀ ꢀ ꢀO interactions involving an
NO2 group as acceptor are half as strong as C—Hꢀ ꢀ ꢀO inter-
actions (Allen et al., 1997) involving a CO group as the
acceptor, they play a significant role in packing owing to their
co-operative action.
The second dimension is ruled by the zwitterionic nature of
(I). The anionic oxocyclohexadiene ring and the cationic
iminium group from neighbouring tapes are overlapped. The
Crystal data
3
˚
C14H19N3O3
Mr = 277.17
Monoclinic, P2=c
a = 10.5688 (17) A
V = 1484.2 (4) A
Z = 4
Mo Kꢄ radiation
ꢅ = 0.09 mmꢁ1
T = 293 (2) K
0.20 ꢃ 0.17 ꢃ 0.12 mm
˚
˚
b = 12.1887 (19) A
˚
c = 12.6816 (15) A
ꢃ = 114.696 (10)ꢂ
Data collection
Bruker APEXII area-detector
diffractometer
13954 measured reflections
2617 independent reflections
2217 reflections with I > 2ꢆ(I)
Rint = 0.039
˚
iminium N and C atoms are 3.257 (3) and 3.462 (3) A,
respectively, from the centroid of the cyclohexadienide ring at
(ꢁx + 1, ꢁy, ꢁz). These short distances strongly suggest not
only ion pairing but also a ꢀ-stacking interaction between the
iminium group, as acceptor, and the oxocyclohexadiene ring,
as the donor of electron density (Fig. 3). These ꢀ-stacking
interactions crosslink pairs of the hydrogen-bonded tapes
Table 1
Selected geometric parameters (A, ).
ꢂ
˚
O1—C1
1.257 (3)
1.227 (3)
1.230 (3)
1.442 (3)
1.285 (3)
1.454 (3)
1.449 (3)
1.451 (3)
N11—C16
C1—C2
C1—C6
C2—C3
C3—C4
C4—C5
C5—C6
C9—C10
1.455 (3)
O4A—N4
O4B—N4
N4—C4
N8—C7
N8—C9
1.447 (3)
1.435 (3)
1.395 (3)
1.372 (3)
1.406 (3)
1.357 (3)
1.514 (3)
N11—C10
N11—C12
O4A—N4—O4B
O4A—N4—C4
O4B—N4—C4
C7—N8—C9
C10—N11—C12
C10—N11—C16
C12—N11—C16
O1—C1—C6
122.9 (2)
118.4 (2)
118.7 (2)
123.6 (2)
111.9 (2)
112.7 (2)
109.9 (2)
122.3 (2)
O1—C1—C2
N4—C4—C5
N4—C4—C3
N8—C7—C2
N8—C9—C10
N11—C10—C9
N11—C12—C13
N11—C16—C15
122.0 (2)
119.6 (2)
120.0 (2)
125.0 (2)
111.0 (2)
112.2 (2)
111.1 (3)
110.9 (3)
Table 2
Hydrogen-bond geometry (A, ).
ꢂ
˚
D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
N8—H8ꢀ ꢀ ꢀO1
N8—H8ꢀ ꢀ ꢀO1i
C3—H3ꢀ ꢀ ꢀO4Bii
C7—H7ꢀ ꢀ ꢀO4Bii
0.90 (2)
0.90 (2)
0.93
2.02 (3)
2.13 (3)
2.57
2.674 (3)
2.857 (3)
3.400 (3)
3.302 (3)
129 (3)
137 (3)
149
Figure 3
0.93
2.44
155
The centrosymmetric oxocyclohexadienide–iminium ꢀ-stacked pairs of
compound (I). [Symmetry code: (iii) ꢁx + 1, ꢁy + 1, ꢁz + 1.]
3
2
1
2
Symmetry codes: (i) ꢁx þ 1; y; ꢁz þ ; (ii) ꢁx þ 1; y; ꢁz þ .
ꢄ
Acta Cryst. (2009). C65, o8–o10
Santos-Contreras et al. C14H19N3O3 o9

organic compounds
Refinement
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: GD3261). Services for accessing these data are
described at the back of the journal.
R[F2 > 2ꢆ(F2)] = 0.066
wR(F2) = 0.151
S = 1.20
Áꢇmax = 0.21 e A
ꢁ3
˚
ꢁ3
˚
Áꢇmin = ꢁ0.20 e A
2617 reflections
185 parameters
H atoms treated by a mixture of
independent and constrained
refinement
References
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˚
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˚
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This work was supported by CGIC–UC (Coordinacion
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o10 Santos-Contreras et al.
C14H19N3O3
Acta Cryst. (2009). C65, o8–o10