organic compounds
Figure 4
A packing diagram for (II), viewed along the a axis, showing two adjacent
chains along the b axis and the C—Hꢀ ꢀ ꢀO interactions (dashed lines).
and the phenylenediamine (C9–C14) rings at (ꢂx + 1, y,
3
˚
ꢂz + 2) [3.759 (2) A] and (ꢂx + 1, ꢂy + 1, ꢂz + 1)
˚
[3.878 (2) A] (Fig. 3). These ꢀ–ꢀ interactions and two C—
Figure 3
Hꢀ ꢀ ꢀO interactions connect the molecules into antiparallel
stacks. The other three C—Hꢀ ꢀ ꢀO contacts connect the stacks
to neighbouring ones.
A packing diagram for (I), viewed along the b axis, showing the stacked
molecules and the C—Hꢀ ꢀ ꢀO interactions (dashed lines) between methyl
and nitro groups.
There is only one C—Hꢀ ꢀ ꢀO contact between the methyl
groups and the nitro group in (II) (Table 2). Arylic atoms C5
and C14 donate C—Hꢀ ꢀ ꢀO contacts, which are accepted by
nitro and hydroxy groups, respectively. In (II), there are ꢀ–ꢀ
stacking interactions between the phenol (C1–C6) ring and
the phenylenediamine (C9–C14) ring at (ꢂx + 2, ꢂy, ꢂz + 1)
and proved by spectroscopic methods in solution about
40 years ago (Avramovici et al., 1973). Due to the conjugated
system and the intramolecular hydrogen bond with an S(6)
graph-set motif (Bernstein et al., 1995) in the solid state, the
benzylideneamine group becomes closely planar, as demon-
strated by the torsion angles of 179.7 (4) (C5—C6—C7—N8)
and 0.9 (6)ꢁ (C1—C6—C7—N8) between the imine bond and
the phenolic ring in (I). In (II), these torsion angles are similar,
with values of ꢂ178.28 (15) and 0.9 (2)ꢁ, respectively.
˚
[centroid–centroid distance = 3.5826 (10) A], and between two
˚
phenol (C1–C6) rings [3.6267 (9) A; symmetry code for the
second ring (ꢂx + 2, ꢂy, ꢂz + 2)]. Due to the different
intermolecular interactions, the packing in (II) is different, as
can be seen in Fig. 4. Furthermore, the only C—Hꢀ ꢀ ꢀO contact
between a methyl (C17) and a nitro group is not sufficiently
strong to hold the C16—C17 ethyl group completely in one
conformation. The minor component does not show a similar
close contact.
The hydroxy H atom in both compounds was found from an
˚
electron-density map within bonding distance (ꢃ1 A) of the O
atom, before being refined at its geometrically idealized
position. Although this shows signs of the structures occurring
in the imine form, reliable determination of H-atom positions
is difficult. More evidence of the predominant imine form can
be seen from the bond distances. The O1—C1 distance in both
˚
˚
compounds [1.338 (5) A in (I) and 1.334 (2) A in (II)] is close
to normal values reported for single C—O bonds in phenols
and salicylideneamines (e.g. Ozeryanskii et al., 2006). Also, the
Experimental
A solution of N,N-dimethyl-p-phenylenediamine (0.68 g, 5 mmol)
and 2-hydroxy-5-nitrobenzaldehyde (0.83 g, 5 mmol) in ethanol
(20 ml) was refluxed for 15 min. The solid which precipitated from
the cooled reaction mixture was filtered off and recrystallized twice
from ethanol to give crystals of (I). Compound (II) was obtained in a
similar manner using N,N-diethyl-1,4-phenylenediamine (0.82 g, 5 mmol)
as the starting material.
˚
N8—C7 bond is short in both compounds [1.294 (5) A in (I)
˚
and 1.289 (2) A in (II)], strongly indicating the existence of a
conjugated C N bond, while the long C6—C7 bond
˚
˚
[1.446 (5) A in (I) and 1.457 (2) A in (II)] implies a single
bond. Based on these facts, the presence of an intramolecular
O—Hꢀ ꢀ ꢀN bond (Tables 1 and 2) and the pure E isomer in
both compounds are justified. These features are similar to
what has been observed in related 4-dimethylamino-N-
salicylideneanilines (Filipenko et al., 1983; Aldoshin et al.,
Analysis for compound (I): yield 91%; red crystals, m.p. 488–
491 K. Elemental analysis calculated for C15H15N3O3: C 63.15, H 5.30,
1
N 14.73%; found: C 63.01, H 5.49, N 14.59%. H NMR (CDCl3): ꢁ
15.19 (br s, 1H, OH/NH), 8.65 (s, 1H, H7), 8.31 (s, 1H, H5), 8.19 (d, J =
9.0 Hz, 1H, H3), 7.32 (d, J = 9.0 Hz, 2H, H10 and H14), 7.02 (d, J =
9.2 Hz, 1H, H2), 6.75 (d, J = 9.0 Hz, 2H, H11 and H13), 3.03 (s, 6H,
2 ꢄ CH3); 13C NMR (CDCl3): ꢁ 167.4 (C1), 154.5 (C7), 150.6 (C12),
139.6 (C9), 134.4 (C4), 127.5 (C5), 127.4 (C3), 122.4 (C10 and C14),
118.5 (C6), 118.2 (C2), 112.6 (C11 and C13), 40.4 (C16 and C18);
15N NMR (CDCl3/ext. CH3NO2): ꢁ ꢂ13.1 (N4), ꢂ93.8 (N8), ꢂ331.3
(N15).
¨
1984; Wozniak et al., 1995; Pizzala et al., 2000; Gul et al., 2007).
Whereas these structures, including the present ones, show
phenol–imine forms, the related 4,5-bis(dimethylamino)-1-[(2-
hydroxy-5-nitrobenzylidene)amino]naphthalene is reported
to have the enaminone form (Ozeryanskii et al., 2006).
The molecule of (I) has intermolecular C—Hꢀ ꢀ ꢀO contacts
between the methyl groups and the nitro group (Fig. 3), and
between atom C2 and the nitro group (Table 1). There are also
two different weak ꢀ–ꢀ stacking interactions, with rather long
centroid–centroid distances between the phenol (C1–C6) ring
Analysis for compound (II): yield 89%; red crystals, m.p. 441–
443 K. Elemental analysis calculated for C17H19N3O3: C 65.16, H 6.11,
1
N 13.41%; found: C 65.11, H 6.17, N 13.37%. H NMR (CDCl3): ꢁ
15.30 (br s, 1H, OH/NH), 8.63 (s, 1H, H7), 8.30 (s, 1H, H5), 8.18 (d, J =
Acta Cryst. (2012). C68, o279–o282
ꢅ
o280 Valkonen et al. C15H15N3O3 and C17H19N3O3