The structures of some ortho-hydroxy Schiff base ligands

Article abstract of DOI:10.1016/S0022-2860(00)00915-7

Nine ortho-hydroxy Schiff base ligands, (1)-(9), were synthesized and characterized by chemical analysis, mass spectrometry, ¹H and ¹³C NMR spectroscopy. The crystal and molecular structures of compounds (1), (3), (5), (7), (8) and (

Full text of DOI:10.1016/S0022-2860(00)00915-7

Journal of Molecular Structure 561 (2001) 197±207
www.elsevier.nl/locate/molstruc
The structures of some ortho-hydroxy Schiff base ligands
a,
J.M. Fernandez-G , F. del Rio-Portilla , B. Quiroz-Garcõa , R.A. Toscano , R. Salcedo
a
a
a
b
*
Â
Â
a
Â
Instituto de Quõmica, UNAM, Circuito Exterior Cd. Universitaria, Coyoacan 04510, Mexico DF, Mexico
Â
Instituto de Investigacion en Materiales, Circuito Exterior Cd. Universitaria, Coyoacan 04510, Mexico DF, Mexico
b
Received 21 September 2000; accepted 16 November 2000
Abstract
Nine ortho-hydroxy Schiff base ligands, (1)±(9), were synthesized and characterized by chemical analysis, mass spectro-
1
metry, H and 13C NMR spectroscopy. The crystal and molecular structures of compounds (1), (3), (5), (7), (8) and (9) were
determined. The solid state X-ray diffraction studies show that compounds (5) and (8) are in the keto±amine tautomeric form,
1
while (1), (3), (7) and (9) are found as phenol±imine tautomers. Moreover, studies in the solution phase by H and 13C NMR
spectroscopy indicate that compounds (2), (5) and (8) are found as keto±amine tautomers, while (1), (3), (4), (6), (7) and (9) are
found as phenol±imine tautomers. Furthermore, ab initio calculations at the HF/6-31Gp level with full optimization of
geometry, performed for both tautomers of (1) and (5), agree with the observed behavior in solution and solid state of these
compounds. q 2001 Elsevier Science B.V. All rights reserved.
1
Keywords: Crystal structure of o-hydroxy Schiff base ligands; H and 13C NMR studies of o-hydroxy Schiff bases; Tautomerism in o-hydroxy
Schiff bases; Ab initio calculations of o-hydroxy Schiff bases; Synthesis of Schiff bases
1. Introduction
2-hydroxy-1-naphthaldehyde and 3-hydroxy-2-napht-
haldehyde, where there are intrinsic aromaticity
differences that could be re¯ected in some structural
features of these ligands. Therefore, the structures of
this kind of Schiff bases, which are widely used as
chelating agents, are relevant due to the possibility
of ®nding them in the solid state and/or in solution
as keto±amine or phenol±imine tautomers, and their
connections with photochromism and thermo-
chromism. Furthermore, there are only a small
number of structures determined by X-ray crystal-
lography for 1,2-naphthalenic Schiff bases [7±13]
and an even smaller number for 2,3-naphthalenic
Schiff bases [14].
There has been considerable interest in some Schiff
bases derived from salicylaldehyde because they
show thermochromism and photochromism in the
solid state [1±3]. It has been proposed that molecules
showing thermochromism are planar, while those
showing photochromism are non-planar [4,5], both
phenomena being associated with a proton transfer
[5,6]. Consequently, it is evident that a closely related
phenomenon of interest is the possibility of
tautomeric isomerism in ortho-hydroxy Schiff bases.
In particular, we are interested in comparing those
derived from salicylaldehyde with those from
In this paper, we report the characterization of
several Schiff base ligands resulting from the
condensation of: salicylaldehyde, 2-hydroxy-1-
naphthaldehyde and 3-hydroxy-2-naphthaldehyde
with 1-adamantanamine, cyclohexylamine and
* Corresponding author. Tel.: 1525-622-4506; fax: 1525-616-
2203/2217.
E-mail address: jmanuel@servidor.unam.mx
Â
(J.M. Fernandez-G).
0022-2860/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(00)00915-7

Â
J.M. Fernandez-G et al. / Journal of Molecular Structure 561 (2001) 197±207
198
1-adamantanemethylamine, respectively, i.e. N-
(1-adamantyl)-salicylaldamine (1) [15], 1-[(1-adam-
and the C atom of the lateral chain gives an interesting
resonant form to the molecule in such a way that the
energy of both tautomers would be very close.
antylamino)-methylene]2-(1H)-naphthalenone
(2)
[15], whose crystal structure has already been studied
[7], 2-[(1-adamantyl)iminomethyl]-3-naphthol (3)
[15], N-(cyclohexyl)-salicylaldamine (4), 1-[(cyclo-
2. Experimental
hexylamino)methylene]-2-(1H)-naphthalenone
(5)
[16], 2-[(cyclohexyl)iminomethyl]-3-naphthol (6)
[16], N-(1-adamantanemethyl)-salicylaldamine (7),
1-[(1-adamantanemethylamino)methylene]-2-(1H)-
naphthalenone (8) and 2-[1-(adamantanemethyl)-
iminomethyl]-3-naphthol (9). The crystal and
molecular structure of compounds (1), (3), (5), (7),
(8) and (9) were determined. Although some 1H
NMR spectroscopic characteristics of compounds
(1), (2), (3), (5) and (6) have already been reported
[15,16], this study allow us to make a more correct
assignment of their NMR signals and their structures
in solution.
While it has been reported that in the solid state
some Schiff bases derived from 2-hydroxy-1-
naphthaldehyde and n-propyl- and n-butylamine,
respectively [8,9], are found as phenol±imine
tautomers, the data obtained here suggest that in the
crystalline state as well as in solution, the keto±amine
tautomer prevails in Schiff bases resulting from the
condensation of 2-hydroxy-1-naphthaldehyde and
alkylamines, while those Schiff bases derived from
salicylaldehyde or 3-hydroxy-2-naphthaldehyde and
alkylamines are mainly found as phenol±imine
tautomers.
In relation to the theoretical calculations, it has been
found that the keto tautomer is the preferred one by
almost 48 kJ/mol for acetone [17], but, there are certain
cases where the enolformcan bestabilized [18]. Indeed,
the presence of aromaticity against a quinoid form
allows the equilibrium to be shifted to the side of the
enol. This is the case where an MP2/6-31Gp//RHF-6-
31Gp result shows a DGT of 70.61 kJ/mol [19], for the
equilibrium from phenol to 2,5-cyclohexadienone and
72.5 kJ/mol from phenol to 2,4-cyclohexadienone.
However, in the case of substituted 2-naphthols, when
there is an imine group at position 1 of the naphthalene
ring, the tautomeric equilibrium between the keto form
and the enol form seems to be more constricted than
other aryl±enolcasesbecause inbothtautomers a strong
hydrogen bond is present, and in the keto±amine isomer
the double bond formed between the C1 atom of the ring
2.1. Reagents and techniques
Cyclohexylamine, 1-(aminomethyl)adamantane, 1-
adamantanamine, 2-hydroxy-1-naphthaldehyde and
salicylaldehyde were obtained from Aldrich Chemical
Co. Inc., and were used without further puri®cation; 3-
hydroxy-2-naphthaldehyde was prepared from
naphthol AS (Aldrich) as described [20]. Melting
points were determined in a Fisher±Jones apparatus
and are uncorrected; mass spectra were obtained using
a JEOL Mod. JMS-SX-102A mass spectrometer oper-
ated at 70 eV ionizing potential. All the NMR data
were acquired on a Varian UNITY 300 spectrometer
equipped with a four-channel nucleus probe or/and a
Varian Unity 500 spectrometer equipped with a two-
nucleus inverse detection probe operating at 300 K.
Samples of 60 mg were dissolved in ca. 0.7 ml of
CDCl3 in a 5 mm tube using CDCl3 and TMS as
internal standard. COSY [21], absolute intensity
spectra were recorded for a 1H spectral width of
2600 Hz with 1024 data points (zero-®lled to 2048),
256 increments and 16 transients per increment. Zero-
®lled to 512 and Gaussian weighting were used in
both dimensions. For NOESY spectra [22], the same
spectral width and processing parameters as for the
COSY spectra were used with mixing times of 1.2 s.
HETCOR spectra [23,24] had identical 1H
parameters, while the 13C window was 10,700 Hz
and 128 time increments were collected (128 transi-
ents per increment). Gaussian weighting was applied
in both dimensions.
1
Spectral widths of 2600 Hz were used for H, while
13,250 Hz for 13C spectral width. 128 time increments
(with 256 transients per increment)intheseconddimen-
sion and linear predicted to 256 increments for the
FLOCK spectra [25] were used. Gaussian weighting
functions were applied in the latter. All assignments
shown in Table 3 were performed using 1H, 13C,
DEPT, HETCOR, FLOCK and NOESY spectra.
Elemental analyses were performed by Galbraith
Laboratories, Inc. Knoxville, TN, USA.

Table 1
Crystallographic data for compounds (1), (3), (5), (7), (8) and (9)
Compound
(1)
(3)
(5)
(7)
(8)
(9)
Empirical formula
Color, habit
C17H21NO
Yellow, lamina
255.35
C21H23NO
Yellow, block
305.41
C17H19NO C18H23NO
Orange, irregular Yellow, prism
C22H25NO
Yellow, prism
319.43
C22H25NO
Orange, prism
319.43
Formula weight
Temperature (K)
253.33
293(2)
269.37
293(2)
293(2)
293(2)
293(2)
293(2)
Ê
Wavelength (A)
0.71073 (MoKa) 0.71073 (MoKa) 0.71073 (MoKa) 1.54178 (CuKa)
Orthorhombic
0.71073 (MoKa)
Monoclinic
P21/c
1.54178 (CuKa)
Monoclinic
P21/n
Crystal system
Space group
Triclinic
Orthorhombic
Monoclinic
P 2 1
Pna21
P212121
P21/n
Ê
Ê
Ê
Ê
Ê
Ê
Unit cell dimensions
a ˆ 6.5090(1) A
a ˆ 30.482(6) A a ˆ 8.485(2) A
a ˆ 6.502(1) A
a ˆ 6.784(1) A
a ˆ 6.452(1) A
Ê
Ê
Ê
Ê
Ê
Ê
b ˆ 9.4780(1) A
b ˆ 17.217(4) A b ˆ 12.037(3) A b ˆ 21.900(4) A
b ˆ 15.429(1) A
b ˆ 11.380(2) A
Ê
Ê
Ê
Ê
Ê
Ê
c ˆ 12.3690(1) A c ˆ 6.431(3) A
c ˆ 13.827(3) A c ˆ 10.508(2) A
c ˆ 16.344(2) A
c ˆ 23.300(5) A
a ˆ 94.400(1)8
a ˆ 908
a ˆ 908
b ˆ 908
g ˆ 908
1412.2(6)
4
a ˆ 908
b ˆ 91.71(3)8
g ˆ 908
1495.6(5)
4
a ˆ 908
b ˆ 98.98(1)8
g ˆ 908
1689.8(3)
4
a ˆ 908
b ˆ 97.89(3)8
g ˆ 908
1694.6(5)
4
b ˆ 103.290(1)8 b ˆ 908
g ˆ 104.070(1)8
713.21(14)
2
g ˆ 908
3375.0(19)
8
Ê 3
Volume (A )
Z
Density (calcd) (Mg m23
Absorption coef®cient
F(000)
)
1.189
0.073 mm21
1.202
0.073 mm21
1.192
0.073 mm21
1.196
0.564 mm21
1.256
0.076 mm21
1.252
0.583 mm21
276
1312
544
584
688
688
Crystal size (mm)
Diffractometer
0.8 £ 0.44 £ 0.36 0.44 £ 0.4 £ 0.28 0.6 £ 0.4 £ 0.24
0.6 £ 0.44 £ 0.26
Siemens P3/F
1.5±55
0.4 £ 0.24 £ 0.22
Siemens P4
1.5±27.5
v
0.4 £ 0.16 £ 0.1
Siemens P3/F
1.5±55
Siemens P4
Siemens P4
1.5±25
Siemens P4
1.5±27.5
u/2u
u Range for data collection 1.5±25
Scan type
u/2u
u/2u
u/2u
u/2u
Index ranges
0 # h # 7
211 # k # 10
214 # l # 14
N/A
21 # h # 36
220 # k # 1
21 # l # 7
N/A
0 # h # 11
0 # k # 15
217 # l # 17
N/A
0 # h # 6
0 # k # 23
2 11 # l # 11
N/A
0 # h # 8
0 # k # 20
221 # l # 20
N/A
0 # h # 6
0 # k # 12
224 # l # 24
N/A
Absorption correction
Re¯ections collected
Independent re¯ections
R(int)
2735
2495
4266
3840
3581
3228
2067
1875
4193
3873
2361
2129
0.0428
0.0410
0.0802
0.0846
0.0243
0.0412
Data/restraints/parameters 2495/0/176
Goodness-of-®t on F2
1.165
3840/1/422
1.030
3228/0/176
1.005
1875/0/185
1.066
3873/0/221
1.001
2129/0/221
1.027
Final R indices [I . 2s(I)] R1 ˆ 0.058,
R1 ˆ 0.071,
wR2 ˆ 0.1663
R1 ˆ 0.066,
wR2 ˆ 0.1276
0.122 and
20.134
R1 ˆ 0.0395, wR2 ˆ 0.1032 R1 ˆ 0.0634, wR2 ˆ 0.1234 R1 ˆ 0.0432, wR2 ˆ 0.099
wR2 ˆ 0.1792
Largest diff. peak and hole 1.34 and 20.152 0.305 and
Ê 23
0.125 and 20.131 0.186 and 20.162 0.120 and 20.140
(eA
)
20.193

Â
J.M. Fernandez-G et al. / Journal of Molecular Structure 561 (2001) 197±207
200
2.2. Synthetic procedures
82.64; H, 7.85; N, 4.37%. Calcd for C22H25NO: C,
82.70; H, 7.89; N, 4.39%.
The Schiff base ligands (1)±(9), were prepared by a
literature method [26]. The general method is as
follows:
To a solution of aldehyde (0.004 mol) in ethanol
(100 ml) was added a solution of amine (0.004 mol)
in ethanol (75 ml). The resulting solution was boiled
under re¯ux for ca. 4 h, then concentrated and cooled
in an ice bath until crystallization was observed. The
yellow solid was suction ®ltered, dried and recrystal-
lized from dichloromethane±methanol.
2-[1-Adamantanemethyl)iminomethyl]-3-naphthol
(9). Yellow crystals, m.p. 172±1748C; M1 319 m/z
(base peak 319 m/z). Found: C, 82.72; H, 7.85; N,
4.40%. Calcd for C22H25NO: C, 82.76; H, 7.89; N,
4.39%.
2.3. Crystallography
Good-quality crystals suitable for the X-ray diffrac-
tion study were obtained by slow layer diffusion of
methanol into a saturated dichloromethane solution of
compounds (1), (3), (5), (7), (8) and (9) at room
temperature.
N-(1-Adamantyl)-salicylaldamine (1) [15]. Yellow
crystals, m.p. 82±848C; M1 255 m/z (base peak 135
m/z). Found: C, 79.84; H, 8.24; N, 5.53%. Calcd for
C17H21NO: C, 79.96; H, 8.30; N, 5.49%.
2.3.1. Data collection and processing
1-[(1-Adamantylamino)methylene]-2-(1H)-
naphthalenone (2) [15]. Yellow crystals, m.p. 165±
1668C; M1 305 m/z (base peak 305 m/z). Found: C,
82.47; H, 7.62; N, 4.56%. Calcd for C21H23NO: C,
82.57; H, 7.59; N, 4.59%.
2-[(1-Adamantyl)iminomethyl]-3-naphthol (3)
[15]. Yellow crystals, m.p. 155±1568C; M1 305 m/z
(base peak 305 m/z). Found: C, 82.49; H, 7.56; N,
4.55%. Calcd for C21H23NO: C, 82.57; H, 7.59; N,
4.59%.
N-(Cyclohexyl)-salicylaldamine (4). Pale yellow
liquid, b.p. 858C (1 mmHg); M1 203 m/z (base
peak 203 m/z). Found: C, 76.82; H, 8.50; N,
6.95%. Calcd for C13H17NO: C, 76.79; H, 8.43;
N, 6.89%.
1-[(Cyclohexylamino)methylene]-2-(1H)-
naphthalenone (5) [16]. Yellow crystals, m.p. 68±
708C; M1 253 m/z (base peak 170 m/z). Found: C,
80.51; H, 7.61; N, 5.56%. Calcd for C17H19NO: C,
80.58; H, 7.56; N, 5.53%.
2-[Cyclohexyliminomethyl]-3-naphthol (6) [16].
Pale yellow crystals, m.p. 126±1288C; M1 253 m/z
(base peak 253 m/z). Found: C, 80.61; H, 7.54; N,
5.55%. Calcd for C17H19NO: C, 80.58; H, 7.56; N,
5.53%.
N-(1-Adamantanemethyl)-salicylaldamine (7).
Yellow crystals, m.p. 91±928C; M1 269 m/z (base
peak 135 m/z). Found: C, 80.15; H, 8.53; N, 5.17%.
Calcd for C18H23NO: C, 80.24; H, 8.61; N, 5.20%.
1-[(1-Adamantanemethylamino)methylene]-2-
(1H)-naphthalenone (8). Yellow crystals, m.p. 200±
2018C; M1 319 m/z (base peak 319 m/z). Found: C,
All crystals were mounted on glass ®bers. Pre-
liminary examinations and data collection for (1),
(3), (5), and (8) were performed on a Siemens P4/
PC diffractometer (MoKa radiation, oriented graphite
monochromator), and for (7) and (9) on a Siemens P3/
F diffractometer (CuKa radiation, oriented graphite
monochromator) at 293(2) K. Cell parameters were
calculated from the least-squares ®tting for 25 high-
angle re¯ections. Omega scans for several intense
re¯ections indicated acceptable crystal quality. Data
were collected for 3.00±50.008 using a two-theta scan
mode at 293(2) K with a variable scan rate. Three
standards were collected for every 97 re¯ections
showing no signi®cant trends. Background measure-
ments were done by stationary crystal and stationary
counter techniques at the beginning and the end of
each scan for half the total scan time. Lorentz and
polarization corrections were applied to the data set
and only unique re¯ections were used in further calcu-
lations (see Table 1).
2.3.2. Structure solution and re®nement
The structures were solved by Direct Methods [27].
Anisotropic full-matrix least-squares re®nement [28]
on F2 was done for all non-Hydrogen atoms.
Weighted R-factors, wR, and all goodnesses of ®t S
are based on F2, conventional R-factors R are based on
F, with F set to zero for negative F2. The observed
criterion of F2 . 2s(F2) are used only for calculating
R factors. Hydrogen atoms attached to C atoms were
placed in idealized positions with isotropic thermal

Â
J.M. Fernandez-G et al. / Journal of Molecular Structure 561 (2001) 197±207
201
Table 2 (continued)
Table 2
Ê
Selected bond lengths (A) and angles (8) for compounds (1), (3), (5),
(7), (8) and (9)
Compound (1)
C(3)±C(4)
1.370(3)
1.458(3)
1.358(2)
1.274(3)
1.468(3)
C(11)±N(1)±C(12)
O(1)±C(3)±C(4)
C(1)±C(2)±C(3)
C(2)±C(3)±C(4)
C(3)±C(2)±C(11)
121.5(2)
C(2)±C(11)
O(1)±C(3)
119.7(2)
118.5(2)
120.0(2)
120.6(2)
Compound (1)
C(1)±C(2)
C(2)±C(3)
C(3)±C(4)
C(1)±C(7)
O(1)±C(2)
N(1)±C(7)
N(1)±C(8)
1.401(4)
1.390(4)
1.369(5)
1.460(4)
1.352(4)
1.269(3)
1.473(3)
N(1)±C(7)±C(1)
O(1)±C(2)±C(1)
C(7)±N(1)±C(8)
O(1)±C(2)±C(3)
C(1)±C(2)±C(3)
C(2)±C(3)±C(4)
C(2)±C(1)±C(7)
121.8(3)
121.0(3)
122.9(2)
119.4(3)
119.6(3)
119.8(3)
121.5(3)
N(1)±C(11)
N(1)±C(12)
parameters ®xed 1.2 times the value of the attached
atom. The H atoms attached to N or O atoms were
located on a difference Fourier map at an advanced
stage of re®nement and their positional parameters
re®ned. Neutral atom scattering factors and anoma-
lous scattering factors were taken from the Interna-
tional Tables for X-ray Crystallography [29].
Theoretical calculations were carried out using the
Gaussian-94 program [30] at the HF/6-31Gp level
with full optimization of geometry. The initial geom-
etries were built using the Universal 1.01 Molecular
Mechanics software [31]. Both methods mentioned
above are included in the Cerius package.1
Compound (3)
C(1a)±C(2a)
C(2a)±C(3a)
C(3a)±C(4a)
1.356(10) N(1a)±C(11a)±C(2a)
1.427(11) O(1a)±C(3a)±C(2a)
1.373(10) C(11a)±N(1a)±C(12a) 124.3(7)
121.9(8)
121.6(7)
C(2a)±C(11a) 1.472(10) O(1a)±C(3a)±C(4a)
118.8(8)
119.2(7)
119.6(7)
120.7(7)
121.9(8)
119.5(8)
O(1a)±C(3a)
1.358(9)
C(1a)±C(2a)±C(3a)
C(2a)±C(3a)±C(4a)
C(3a)±C(2a)±C(11a)
N(1a)±C(11a) 1.270(9)
N(1a)±C(12a) 1.461(9)
C(1b)±C(2b)
C(2b)±C(3b)
C(3b)±C(4b)
1.372(11) N(1b)±C(11b)±C(2b)
1.436(12) O(1b)±C(3b)±C(2b)
1.370(11) C(11b)±N(1b)±C(12b) 121.8(7)
C(2b)±C(11b) 1.478(10) O(1b)±C(3b)±C(4b)
O(1b)±C(3b) 1.364(10) C(1b)±C(2b)±C(3b)
122.1(9)
119.6(8)
118.4(8)
121.8(8)
N(1b)±C(11b) 1.296(10) C(2b)±C(3b)±C(4b)
N(1b)±C(12b) 1.470(10) C(3b)±C(2b)±C(11b)
3. Results and discussion
Compound (5)
C(1)±C(2)
C(2)±C(3)
C(3)±C(4)
C(1)±C(11)
O(1)±C(2)
N(1)±C(11)
N(1)±C(12)
1.435(5)
1.445(5)
1.339(5)
1.403(4)
1.263(4)
1.310(5)
1.474(4)
N(1)±C(11)±C(1)
O(1)±C(2)±C(1)
C(11)±N(1)±C(12)
O(1)±C(2)±C(3)
C(1)±C(2)±C(3)
C(2)±C(3)±C(4)
C(2)±C(1)±C(11)
124.1(3)
122.9(3)
123.4(3)
120.4(3)
116.6(3)
122.1(3)
118.9(3)
3.1. Crystal study
Crystal data, additional data collection parameters
and re®nement details are given in Table 1. A selec-
tion of bond lengths and angles is given in Table 2.
The molecular structures of (1), (3), (5), (7), (8) and
(9), including atom-numbering schemes, are illu-
strated in Figs. 1±6.
In the unit cell of compound (3), there are two
crystallographically independent but structurally
very similar molecules, (3a) and (3b), differing only
in the rotational orientation of the 1-adamantyl group
in relation to the rest of the molecule.
Compound (7)
C(1)±C(2)
C(2)±C(3)
C(3)±C(4)
C(1)±C(7)
O(1)±C(2)
N(1)±C(7)
N(1)±C(8)
1.402(2)
1.392(2)
1.375(3)
1.454(2)
1.350(2)
1.270(2)
1.458(2)
N(1)±C(7)±C(1)
O(1)±C(2)±C(1)
C(7)±N(1)±C(8)
O(1)±C(2)±C(3)
C(1)±C(2)±C(3)
C(2)±C(3)±C(4)
C(2)±C(1)±C(7)
122.87(14)
121.33(15)
119.22(14)
119.02(15)
119.64(16)
119.99(17)
121.00(14)
Compound (8)
C(1)±C(2)
C(2)±C(3)
C(3)±C(4)
C(1)±C(11)
O(1)±C(2)
N(1)±C(11)
N(1)±C(12)
Compounds (1), (3a), (3b), (7) and (9) crystallize in
the solid state into the phenol±imine tautomeric form
with O±H distances of 0.86(4), 0.86(9), 0.97(10),
Ê
0.94(2), and 1.03(2) A, respectively. Strong intra-
molecular hydrogen bonds occur between the O1
and N1 atoms, with N´´´H distances of 1.79(4),
1.423(4)
1.440(4)
1.347(4)
1.410(4)
1.285(3)
1.303(3)
1.459(3)
N(1)±C(11)±C(1)
O(1)±C(2)±C(1)
C(11)±N(1)±C(12)
O(1)±C(2)±C(3)
C(1)±C(2)±C(3)
C(2)±C(3)±C(4)
C(2)±C(1)±C(11)
123.5(3)
122.9(3)
124.5(3)
122.9(3)
118.2(3)
121.1(3)
118.3(2)
Ê
1.82(10), 1.76(11), 1.74(2) and 1.62(2) A,
Compound (9)
C(1)±C(2)
1
1.372(3)
1.428(3)
N(1)±C(11)±C(2)
O(1)±C(3)±C(2)
121.5(2)
120.3(2)
The results published were generated using the program
cerius2e, developed by Molecular Simulations Inc.
C(2)±C(3)

Â
J.M. Fernandez-G et al. / Journal of Molecular Structure 561 (2001) 197±207
202
Fig. 1. Molecular structure of compound (1) in the solid state with the atom numbering scheme. Thermal ellipsoids are drawn at 50% of
probability.
Ê
1.478(10) A) correspond to conjugated CyN groups
respectively, while N´´´O distances are 2.594(3),
Ê
2.618(9), 2.618(10), 2.6041(18)and 2.563(2) A, respec-
tively; the values for the O±H´´´N angles are 155(4),
153(9), 147(9), 151(2) and 151(2)8, respectively.
The range of C±O bond lengths (1.352(4)±
Ê
Ê
(1.279 A) and Car±CyN± bond lengths (1.476(14) A)
[32], respectively.
In contrast, for compounds (5) and (8), which are
structurally very similar, the tautomeric keto±amine
isomer is observed with N±H distances of 0.92(4) and
Ê
1.364(10) A) correspond to the value described for
Ê
the C±O bond in phenols (1.362 A) [32], while the
Ê
0.89(3) A, respectively. Strong intramolecular
Ê
ranges for CyN bonds (1.270(9)±1.296(10) A) and
the bond lengths between the C1 atom of the aromatic
rings and the C atom of the imine groups (1.454(2)±
hydrogen bonds are found between the N1 and O1
atoms with O´´´H distances of 1.84(4) and
Ê
1.76(3) A, respectively, while N´´´O distances are
Fig. 2. Molecular structure of the two molecules of compound (3) in the solid state with the atom numbering scheme. Thermal ellipsoids are
drawn at 50% of probability.

Â
J.M. Fernandez-G et al. / Journal of Molecular Structure 561 (2001) 197±207
203
Fig. 3. Molecular structure of compound (5) in the solid state with
the atom numbering scheme. Thermal ellipsoids are drawn at 50%
of probability.
Ê
2.587(4) and 2.540(3) A, respectively; the values for the
N±H´´´O angles are 136(3) and 146(3)8, respectively.
The bond lengths of the fragment N1±C11±C1±C2±
O1 suggest an electronic delocalization, i.e. the C2±O1
Ê
bondlengths, 1.266(4) and 1.285(3) A, are similar to the
values observed for conjugated CyO bonds. The C1±
C2 bond length values are slightly larger than the values
found for the corresponding bond in the phenol±imine
tautomers, the C1yC11 bond lengths are between
Csp2±Csp2 in a,b-unsaturated carbonyls and Car±
Fig. 4. Molecular structure of compound (7) in the solid state with
the atom numbering scheme. Thermal ellipsoids are drawn at 50%
of probability.
Ê
CyN± values(1.476(14)and1.340(13) A, respectively)
[32]. Finally, C11yN1 bond lengths show values
similar Schiff bases already reported [8,9] (the n-
propyl- and n-butyl-1,2-naphthalenic analogs, respec-
tively), it is dif®cult to determine whether, as they
claimed, they actually synthesized, isolated and char-
acterized the phenol±imine tautomers of those Schiff
bases or maybe they misassigned their structures.
However, they report unexpectedly short C2±O
Ê
bond lengths (1.254(8) and 1.23(1) A, respectively),
and the C11±N bond length of the 1,2-Schiff base
with n-propyl substituent is of the same order
Ê
(1.310(5) and 1.303(3) A, respectively) corresponding
Ê
to conjugated CyN groups (1.279(8) A) [32]. The short
Ê
C3yC4 bonds, i.e. 1.339(5) and 1.347(4) A, respec-
tively, also con®rm the quinonoid character of both
compounds [7,10,13,33]. Furthermore, compound (2)
shows the same features, and in the crystalline state,
was also found as the keto±amine tautomer [7].
Although the molecules of (1), (3), (5), (7), (8) and
(9) show strong intramolecular hydrogen bonds that
ªlockº planar their corresponding salicylaldimino or
naphthaldimino moieties, due to the non-aromatic
nature of the substituent at the imino nitrogen, the
molecules as whole are not planar.
Ê
(1.313(8) A) than the corresponding bond in (5) and
(8) (the reported value for the n-butyl derivative is not
Ê
very good, i.e. 1.31(2) A).
3.2. NMR spectroscopy
On the other hand, because of the lack of precise
localization of the hydrogen atom bonded to oxygen
or nitrogen atoms in other X-ray crystal structures of
1
The solution structures of (1)±(9), and the H and
13C NMR spectral assignments were con®rmed by a

Â
J.M. Fernandez-G et al. / Journal of Molecular Structure 561 (2001) 197±207
204
[34,35]. For (2), (5) and (8), the crucial observation
was provided by the chemical shift of the C2 atom
(178.6, 177.1 and 178.0 ppm, respectively) and the
scalar coupling constant magnitude between H11
and H±N is given as 12.5 Hz, which characterizes
the keto±amine structure. The JHN±H11 measured at
room temperature are very similar with those
measured at 183 K. Coupling constants immersed in
the linewidth of HN signals were measured by the J
doubling method [36], which are in complete agree-
ment with those measured in the H11 signals. Broad
lines of HN signals are a consequence of the fast
exchange rate of these protons [37]. Whereas, for
compounds (1), (3), (4), (6), (7) and (9), the chemical
shift of the corresponding C2 or C3 atoms are
observed at higher ®elds (162.2, 157.3, 161.3, 157.0,
161.5 and 157.1 ppm, respectively), and there is
absence of any H±HN coupling [35]. All data for
both sets of compounds are in complete agreement
with the X-ray structures and theoretical calculations.
Because under normal experimental conditions
it was not possible to observe both tautomeric
species for any compound, the 1H and 13C NMR
spectra for compound (8) were obtained between
323 and 183 K in D6-acetone and D2-dichloro-
methane, to determine any possible isomers.
However, no considerable changes were observed.
This strongly suggests for this series of Schiff
bases, that for all 1,2-naphthaldamines the keto±
amine isomer form is the most stable, which is in
good agreement with a low interchangeable activation
energy between those isomers [38]. Meanwhile for the
salicylaldamines and 2,3-naphthaldamines the
Fig. 5. Molecular structure of compound (8) in the solid state with
the atom numbering scheme. Thermal ellipsoids are drawn at 50%
of probability.
series of one-dimensional (1H and 13C, DEPT) and
two-dimensional (COSY, HETCOR, FLOCK and
NOESY) NMR experiments. The experiments were
carried out in CDCl3. Spectral assignments are
summarized in Table 3. All assigned chemical shifts
for the naphthalene and benzene rings are in agree-
ment with similar compounds reported in literature
Fig. 6. Molecular structure of compound (9) in the solid state with the atom numbering scheme. Thermal ellipsoids are drawn at 50% of
probability.

Table 3
1
Assigned H and 13C chemical shifts [in ppm relative to internal Si(CH3)4] for compounds (1)±(9)
Compound
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
Carbon dC
1
dH
±
dC
105.48
178.62
dH
±
dC
dH
dC
132.58 7.70(s) 118.67
dH
±
dC
105.85
177.11
dH
±
dC
132.45 7.63(s) 118.64
dH
dC
dH
±
dC
106.03
177.97
dH
±
dC dH
132.61 7.75(s)
118.79
162.22
2
±
±
121.44
±
±
161.27
±
±
121.29
±
±
161.55
±
±
121.16
±
±
3
117.26 6.91(dd) 125.93 6.86(d) 157.30
116.70 6.92(dd) 125.10 6.89(d) 157.03
116.92 6.94(dd) 125.56 6.90(d) 157.09
4
131.80 7.25(ddd) 137.09 7.59(d) 110.61 7.23(s) 131.62 7.23(ddd) 136.82 7.59(d) 110.65 7.24(s) 131.86 7.26(ddd) 137.31 7.65(d) 110.80 7.26(s)
117.81 6.81(ddd) 128.82 7.51(d) 126.03 7.63(dd) 117.96 6.80(ddd) 128.76 7.51(dd) 126.12 7.63(dd) 118.12 6.82(ddd) 129.13 7.57(dd) 126.24 7.67(dd)
131.16 7.21(dd) 121.90 7.14(dd) 127.59 7.39(m) 130.85 7.17(dd) 122.03 7.14(ddd) 127.75 7.39(ddd) 130.97 7.20(dd) 122.39 7.19(ddd) 127.90 7.44(m)
159.09 8.30(s) 127.47 7.36(dd) 122.95 7.23(m) 162.04 8.26(s) 127.47 7.34(ddd) 123.10 7.23(m) 164.72 8.20(s) 127.80 7.39(ddd) 123.26 7.27(m)
5
6
7
8
56.94
±
117.04 7.78(d) 128.15 7.70(dd) 66.97 3.14(m) 117.29 7.78(dd) 128.21 7.68(dd) 72.14 3.20(s) 117.44 7.80(dd) 128.27 7.74(m)
9
42.82 1.81(d) 134.02
29.26 2.15(bs) 125.44
±
±
127.13
135.46
±
±
33.97 1.62(m) 133.68
24.00 1.45(m) 125.56
±
±
127.16
135.59
±
±
33.94
±
133.93
±
±
127.25
135.71
±
±
10
11
12
13
14
15
16
17
18
19
20
21
22
OH
NH
40.67 1.54(s) 125.87
36.18 1.70(dd) 151.24 8.64(d) 159.05 8.42(s) 25.23 1.38(m) 154.97 8.68(d) 162.10 8.37(s)
29.26 2.15(bs) 54.33 57.53 24.00 1.45(m) 60.14 3.28(m) 67.74 3.18(m) 36.83 1.66(dd) 65.12 3.17(dd) 72.85 3.27(s)
36.18 1.70(dd) 42.55 1.90(s) 42.71 1.80(s) 33.97 1.62(m) 33.36 1.66(m) 34.09 1.65(m) 28.28 1.96(dd) 33.85 34.22
28.28 1.96(dd) 157.86 8.53(d) 164.75 8.40(s)
±
±
±
±
29.26 2.15(bs) 28.86 2.14(s) 29.23 2.14(s)
±
±
±
±
±
±
±
±
±
±
±
±
23.79 1.52(m) 24.19 1.55(m) 40.67 1.54(s)
24.75 1.36(m) 25.39 1.44(m) 40.67 1.54(s)
40.03 1.55(s)
28.06 1.98(s)
40.89 1.59(s)
28.40 1.99(s)
42.82 1.81(d)
42.82 1.81(d)
35.45 1.67(dd) 36.15 1.69(dd)
28.86 2.14(s) 29.23 2.14(s)
±
±
23.79 1.52(m) 24.19 1.55(m) 36.83 1.66(dd) 36.59 1.66(dd) 36.95 1.69(dd)
33.36 1.66(m) 34.09 1.65(m) 36.83 1.66(dd) 28.06 1.98(s) 28.40 1.99(s)
28.28 1.96(dd) 36.59 1.66(dd) 36.95 1.69(dd)
36.18 1.70(dd) 35.45 1.67(dd) 36.15 1.69(dd)
±
±
±
±
±
±
±
±
±
28.86 2.14(s) 29.23 2.14(s)
42.55 1.90(s) 42.71 1.80(s)
42.55 1.90(s) 42.71 1.80(s)
35.45 1.67(dd) 36.15 1.69(dd)
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
28.06 1.98(s)
40.03 1.55(s)
40.03 1.55(s)
28.40 1.99(s)
40.89 1.59(s)
40.89 1.59(s)
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
36.59 1.66(dd) 36.95 1.69(dd)
14.43(b)
±
±
13.82(b)
±
13.73(b)
±
±
13.24(b)
±
13.84(b)
±
±
±
±
±
±
13.25(b)
±
14.67(b)
14.52(b)
14.50(b)

Â
J.M. Fernandez-G et al. / Journal of Molecular Structure 561 (2001) 197±207
206
Fig. 7. Frontier orbitals, HOMO±LUMO, of: (a,b) phenol±imine and (c,d) keto±amine tautomers of compound (5).
phenol±imine isomer form is the preferred structure
in deuterochloroform solution.
U ˆ 22058800:451 kJ=mol for the phenol±imine
form. A small preference for the keto tautomer with
a DG ˆ 1:246 kJ=mol was found, which is in agree-
ment with the value obtained by NMR spectroscopy
for the p-methylaniline Schiff base adduct of 2-
hydroxy-1-naphthaldehyde [35]. Fig. 7 shows the
frontier orbitals, HOMO±LUMO, of both keto±
amine and phenol±imine tautomers of compound (5)
resulting from the calculations.
Hence, all data analyzed here suggest that all the 2-
hydroxy-1-naphthaldehyde Schiff base adducts of
alkyl- or cycloalkylamines are always found in the
solid state as well in solution as the keto±amine
tautomer. Furthermore, the non-planarity of the
compounds analyzed by X-ray crystallography
suggest a photochromic behavior [5] in the crystalline
state, nevertheless, this feature should to be demon-
strated.
3.3. Ab initio calculations
Theoretical calculations show that in the case of
compound (1), the keto±amine form has an energy
U ˆ 22061816:691 kJ=mol; very close to that of the
phenol±imine form U ˆ 22061820:900 kJ=mol: The
value of DG for the equilibrium between the keto±
amine and phenol±imine forms is 24.17 kJ/mol,
which suggest that both isomers could be found in
solution; however, in a deuterochloform solution
only the phenol±imine isomer was observed, and in
the solid state the X-ray study also shows that only the
phenol±imine form was isolated.
A similar analysis was carried out for the 1,2-
naphthalenic compound (5), where a cyclohexyl
substiuent is bonded to the nitrogen of the imine
group. The calculations show an energy U ˆ
22058798:918 kJ=mol for the keto±amine form and
Supplementary material has been deposited with
the British Library Document Supply Centre as
Supplementary Publication No. SUP 26654.

Â
J.M. Fernandez-G et al. / Journal of Molecular Structure 561 (2001) 197±207
207
[19] T.A. Gadosy, R.A. McClellad, J. Mol. Struct. (THEOCHEM)
369 (1996) 1.
Acknowledgements
[20] M.L. Khorana, S.Y. Pandit, Indian J. Chem. Soc. 40 (1963)
789.
We thank Prof. W.F. Reynolds for helpful sugges-
Â
tions and G. Espinosa-Perez for technical assistance.
[21] W.P. Aue, E. Bartholdi, R.R. Ernst, J. Chem. Phys. 64 (1976)
2229.
[22] O.W. Sorensen, M. Rance, R.R. Ernst, J. Magn. Reson. 56
(1984) 527.
References
[23] G. Bodenhausen, J. Ruben, Chem. Phys. Lett. 69 (1980)
185.
[1] M.D. Cohen, G.M.J. Schmidt, S. Flavian, J. Chem. Soc.
(1964) 2041.
[24] L. Muller, J. Am. Chem. Soc. 101 (1979) 4481.
[25] W.F. Reynolds, S. McLean, M. Perpick-Dumont, R.G. Enri-
quez, Magn. Res. Chem. 27 (1989) 162.
[2] J. Bregman, L. Leiserowitz, K. Osaki, J. Chem. Soc. (1964)
2086.
[3] E. Hadjoudis, M. Vittorakis, I. Moustakali, I. Mavridis, Mol.
Cryst. Liq. Cryst. 137 (1986) 1.
[26] S. Patai, The Chemistry of the Carbon±Nitrogen Double
Bond, Wiley/Interscience, London, 1970 (pp. 64±65).
[27] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi,
M.C. Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr.
27 (1994) 435.
[4] I. Moustakali, I. Mavridis, E. Hadjoudis, A. Mavridis, Acta
Crystallogr. B 34 (1978) 3709.
[5] E. Hadjoudis, M. Vittorakis, I. Moustakali, I. Mavridis, Tetra-
hedron 43 (1987) 1345.
[28] G.M. Sheldrick, SHELXL93, Program for Re®nement of
Crystal Structures, University of Gottingen, Germany,
1993.
[6] D. Higelin, H. Sixl, Chem. Phys. 77 (1983) 391.
Â
[7] E. Acevedo-Arauz, J.M. Fernandez-G, M.J. Rosalez-Hoz,
R.A. Toscano, Acta Crystallogr. C 48 (1992) 115.
È
[29] International Tables for X-ray Crystallography, vol. C.
[30] M.J. Frish, G.W. Trucks, M. Head-Gordon, P.M.W. Gill,
M.W. Wong, J.B. Foresman, B.J. Johnson, H.B. Schlegel,
M.A. Robb, E.S. Repogle, R. Gomperts, J.L. Andress,
È
È
[8] T. Hokelek, N. Gunduz, Z. Hayvali, Z. Kilic, Acta Crystallogr.
C 51 (1995) 880.
È
È
[9] T. Hokelek, N. Gunduz, Z. Hayvali, Z. Kilic, J. Chem. Crys-
È
tallogr. 25 (1995) 831.
Â
Ï
[10] M. Gavranic, B. Kaitner, E. Mevtrovic, J. Chem. Crystallogr.
Â
K. Raghavachari, J.S. Binkley, C. Gonzalez, R.L. Martin,
D.J. Fox, D.J. DeFrees, J. Baler, J.J.P. Stewart, J.A. Pople,
Gaussian Inc., Pittsburgh, PA, 1995.
Â
[31] A.K. Rappe, C.J. Casewit, K.S. Colwell, W.A. Goddard,
26 (1996) 23.
[11] Y. Elerman, M. Kabak, A. Elmali, I. Svoboda, Acta Crystal-
logr. C 54 (1998) 128.
W.M. Skiff, J. Am. Chem. Soc. 114 (1992) 10024.
[32] F.H. Allen, O. Kennard, D.G. Watson, L. Brammer, A.G.
Orpen, J. Chem. Soc. Perkin Trans. 2 (1987) S1.
[12] A. Elmali, Y. Elerman, E. Kendi, Acta Crystallogr. C 54
(1998) 1137.
È
[13] T. Hokelek, Z. Kilic, M. Isiklan, M. Toy, J. Mol. Struct. 523
È È È È È È È È
[33] M. Nasakkala, H. Saarinen, J. Korvenranta, E. Nasakkala,
(2000) 61.
 Â
[14] J.M. Fernandez-G, A. Rodrõguez-Romero, K. Paneerselvam,
Acta Chem. Scand. Ser. A 31 (1977) 469.
[34] G. Razniewska-Lazecka, A. Dambska, A. Janowski, Magn.
Res. Chem. 24 (1986) 365.
Â
M. Soriano-Garcõa, Acta Crystallogr. C 51 (1995) 1643.
 Â
[15] J.M. Fernandez-G, E. Acevedo-Arauz, R. Cetina-Rosado,
[35] S.R. Salman, R.D. Farrant, J.C. Lindon, Spectrosc. Lett. 24
(1991) 1071.
 Â
R.A. Toscano, N.R. Macõas-Ruvalcaba, M. Aguilar-Martõnez,
Transition Met. Chem. 24 (1999) 18.
[36] G.O. Dudek, J. Am. Chem. Soc. 85 (1963) 694.
[37] F. del Rio-Portilla, V. Blechta, R. Freeman, J. Magn. Res. A
111 (1994) 132.
Â
[16] J.M. Fernandez-G, M.R. PatinÄo-Maya, R.A. Toscano,
 Â
L. Velasco, M. Otero-Lopez, M. Aguilar-Martõnez, Poly-
hedron 16 (1997) 4371.
[38] O. Michinori, in: A.P. Marchand (Ed.), Applications of
Dynamic NMR Spectroscopy to Organic Chemistry, Methods
in Stereochemistry Analysis, vol. 4, VCH, Florida, 1985.
[17] J. March, Advanced Organic Chemistry, Reactions,
Mechanism and Structure, 4th ed., Wiley, New York, 1992.
[18] A. Kresge, Acc. Chem. Res. 23 (1990) 43.