Spectroscopic studies and crystal structure of 3-[(2-morpholinoethylimino) methyl]benzene-1,2-diol

Article abstract of DOI:10.1007/s10870-007-9270-1

Schiff base 3-[(2-morpholinoethylimino)methyl]benzene-1,2-diol has been synthesized from the reaction of 4-(2-aminoethyl)morpholine with 2,3-dihydroxybenzaldehyde. The title compound has been characterized by elemental analysis, IR, ¹H-NMR, ¹³C-NMR and UV-visible techniques. The structure of the compound also has been examined crystallographically. For the compound exist as dominant form of enol-imines in both the solutions and solid state. The crystal structure has been solved by direct methods and refined by full-matrix least squares. The title compound crystallize in the monoclinic space group P2₁/n with a = 12.085(1), b = 8.256(1), c = 13.650(1) ?, β = 108.56(1)°, V = 1291.1(2) ?³, D _x = 1.288 g cm^-3, respectively (R ₁ = 0.0336 and wR ₂ = 0.0922 for 2117 reflections [I > 2σ(I)]. Intramolecular hydrogen bonding is important on the tautomeric properties and the type of aldehyde plays a vital role of the enol-imine and keto-amine properties of the Schiff base ligand.

Full text of DOI:10.1007/s10870-007-9270-1

J Chem Crystallogr (2008) 38:103–108
DOI 10.1007/s10870-007-9270-1
ORIGINAL PAPER
Spectroscopic Studies and Crystal Structure
of 3-[(2-morpholinoethylimino)methyl]benzene-1,2-diol
¨
Hu¨seyin Unver Æ Mustafa Yıldız Æ Nazan Ocak Æ
Tahsin Nuri Durlu
Received: 26 February 2007 / Accepted: 5 October 2007 / Published online: 17 November 2007
Ó Springer Science+Business Media, LLC 2007
Abstract Schiff base 3-[(2-morpholinoethylimino)methyl]
benzene-1,2-diol has been synthesized from the reaction of
4-(2-aminoethyl)morpholine with 2,3-dihydroxybenzalde-
hyde. Thetitlecompoundhasbeencharacterized byelemental
analysis, IR, 1H-NMR, 13C-NMR and UV–visible techniques.
The structure of the compound also has been examined
crystallographically. For the compound exist as dominant
form of enol-imines in both the solutions and solid state.
The crystal structure has been solved by direct methods and
refined by full-matrix least squares. The title compound
crystallize in the monoclinic space group P21/n with a =
bases derived from the condensation of salicylaldehyde with
aniline and with substituted aniline and naphthaldehyde with
aniline and exists as enol-imine [9–17], keto-amine [18], or
enol-imine/keto-amine form [19–23] in all solvents.
The UV–visible spectrum of ortho hydroxylated Schiff
bases which exists mainly as enol-imine structure indicate
the presence of a band at\400 nm, while compounds exists
either as keto-amine or as mixture of enol-imine/keto-amine
forms show a new band, especially in polar solvents at
[400 nm. Different methods were used to show the pres-
ence of the enol-imine and keto-amine forms, amongst them
are UV–visible, IR, MS, 1H-, 13C-, 14N-NMR spectroscopy
and X-ray crystallographically [13–20]. N-salicylideneani-
line derivatives have been shown to exist as tautomeric forms
due to intramolecular proton shifts between the phenol–
oxygen and the imine–nitrogen, via intramolecular hydrogen
bonding O–HꢀꢀꢀN or OꢀꢀꢀH–N [13, 24–34]. These prototropic
shifts in solution and in the crystal. Some crystals of such
internally hydrogen bonded Schiff bases exhibit thermo-
chromism by a thermally induced intramolecular proton shift
to the keto-amine tautomer, or photochromism, by an irra-
diation-induced proton migration [35, 36].
˚
12.085(1), b = 8.256(1), c = 13.650(1) A, b = 108.56(1)°,
3
V = 1291.1(2)A , Dx = 1.288 g cm-3, respectively (R1 =
˚
0.0336 and wR2 = 0.0922 for 2117 reflections [I[2r(I)].
Keywords Schiff base ꢀ Spectroscopy ꢀ Crystal structure ꢀ
1
FT-IR ꢀ H-NMR
Introduction
Many salicylidene anilines being relatively simple in struc-
ture and exhibiting intramolecular proton transfer, have,
therefore, attracted considerable attention from both exper-
imental [1–3] and theoretical points of view [4–8]. Schiff
In this study, we have synthesized new Schiff base and
1
investigated by using IR, H-NMR, 13C-NMR, UV–visible
and X-ray crystallographic techniques in order to study the
hydrogen bonding and tautomeric equilibrium in both the
solution and solid states (Scheme 1).
¨
H. Unver ꢀ T. N. Durlu
Department of Physics, Faculty of Science, Ankara University,
06100 Tandogan, Ankara, Turkey
M. Yıldız (&)
Experimental
Department of Chemistry, Faculty of Science and Arts,
C¸ anakkale Onsekiz Mart University, 17100 Canakkale, Turkey
e-mail: myildiz@comu.edu.tr
Reagents and Techniques
N. Ocak
Department of Physics, Faculty of Science and Arts,
Ondokuz Mayıs University, 55139 Kurupelit, Turkey
1
The H- and 13C-NMR spectra were recorded on a Bruker
AVANCE DPX NMR spectrometer operating at 400 and
123

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J Chem Crystallogr (2008) 38:103–108
933–2,872 m, mO–HꢀꢀꢀN; 2,821 m, mC=N; 1,630 s, mC=C;
1,468 s, mC–N; 1,374 m, mC–O; 1,320 m, 1,271 s, mC–O–C;
1,259 s, 1,230 s, 1,115 s, 1,071 m.
N
O
HO
O
H
N
Crystallography
The data were collected on a STOE IPDS II imaging plate
diffractometer [37] using plane graphite monochromated
MoKa radiation. Preliminary cell constants were obtained
from 165 narrow frame (frame wide = 1° in w) data. Final
cell parameters were obtained by global refinement of
reflections obtained from integration of all frame data. A
total of 331 frames were collected with a frame wide of 1°
in w and a counting time of 1 min. per frame at a crystal-
to-detector distance of 10 cm. The multiple pinhole
method of scanning was used to exclude any noise. The
collected frames were integrated using the preliminary cell
orientation matrix. The integration process yielded a total
of 16,281 reflections of which 2,527 were independent
reflections. Data collections and cell refinement were made
by using the program STOE X-AREA [37]. Data reduction
and absorption correction by integration method was car-
ried out by using STOE X-RED [37] program. The
structure was solved by direct methods using SHELXS-97
[38] and refined by full-matrix least squares using SHEL-
XL-97 [39]. All hydrogen atoms were located from a
difference Fourier map and refined isotropically. I [ 2r(I)
with weighting scheme, w = 1/[r2(Fo2) + (0.0525P)2 +
0.1413P] where P = (Fo2 + 2F2c)/3. The details of the X-ray
data collection, structure solution and structure refinements
are given in Table 1. Selected bond distances and angles
are listed in Table 2. The molecular structure with the
atom-numbering scheme is shown in Fig. 1 [40]. Crystal-
lographic data (excluding structure factors) for the
structures reported in this paper has been deposited with
the Cambridge Crystallographic Data Centre as supple-
mentary publication No. CCDC 264162 [41].
Enol-imine
N
O
HO
O
H
N
Keto-amine
Scheme 1 Tautomerisim of the title compound
101.6 MHz. The H- and 13C-NMR chemical shifts were
measured using SiMe4 as an internal standard. Infrared
absorption spectra were obtained from a Perkin Elmer BX II
spectrometer in KBr discs and were reported in cm-1 units.
The UV–visible spectra were measured using a SHIMADZU
1208 series spectrometer. Carbon, nitrogen and hydrogen
analyses were performed on a LECO CHNS-932 analyzer.
Melting points were measured on an Electro Thermal IA
9100 apparatus using a capillary tube. 4-(2-aminoethyl)
morpholine, 2,3-dihydroxybenzaldehyde, THF, CHCl3,
EtOH, benzene, DMSO were purchased from Merck
(Germany).
1
Result and Discussion
Synthesis of 3-[(2-morpholinoethylimino)methyl]
benzene-1,2-diol
1
FT-IR, H-NMR, 13C-NMR and UV–visible
Spectroscopic Studies
4-(2-aminoethyl) morpholine (1.30 g; 1 9 10-2 mol) was
added to a dry THF (100 mL) solution of 2,3-dihydroxy-
benzaldehyde (1.38 g; 1 9 10-2 mol). The mixture was
stirred and heated for 2 h. Compound was obtained from the
evaporation of THF. It was crystallized from chloroform/n-
heptane as a yellow crystal, m.p. 135 °C, 2.13 g (85 %)
yield. Found: C, 62.18; H, 7.13; N, 11.10. Calc. For
C13H18N2O3; C, 62.40; H, 7.20; N, 11.20%. IR (KBr, cm-1);
mO–H; 3,448 m, mAr–H; 3,057 w, mC–H; 2,971–2,
The IR spectra of the compounds are given in synthetic
procedures. Vibration bands with the wave numbers of 3,448
(mO–H), 3,054 cm-1 (mC–H, Ar–H), 1,630 cm-1 (mC=N),
1,468 cm-1 (mC=C), 1,374, 1,271 cm-1 (mC–O, Ar–O) and
1,259, 1,230, 1,115, 1,071 cm-1 (mC–O–C, Csp3–O–Csp3)
were observed for compound, respectively Fig. 2. The
stretching frequency observed at 2,849 and 2,821 cm-1 in
compound shows the presence of O–HꢀꢀꢀN intramolecular
123

J Chem Crystallogr (2008) 38:103–108
105
˚
Table 1 Crystal and experimental data
Table 2 Some selected bond lengths (A), bond angles (°) and torsion
angles (°)
Compound
C13H18N2O3
O1 C1
1.337(1)
1.468(1)
1.276(2)
1.461(1)
1.403(2)
1.450(2)
1.406(2)
1.357(2)
101.8(1)
119.9(1)
120.0(1)
122.1(1)
120.6(1)
122.4(1)
118.3(1)
119.2(1)
114.0(1)
119.3(1)
121.0(1)
C3 C2 C1
119.8(1)
109.5(1)
108.4(8)
107.4(8)
120.2(1)
176.9(1)
-179.5(1)
-1.3(2)
-179.7(1)
2.1(2)
Compound weight
250.29
N2 C9
N1 C8 C9
CCDC deposit No.
264162
N1 C7
N1 C8 H8A
N1 C8 H8B
C5 C4 C3
Crystal system
Monoclinic
P21/n
0.25 9 0.33 9 0.42 mm3
N1 C8
Space group
C6 C1
Crystal dimension
C6 C7
C8 N1 C7 C6
C5 C6 C7 N1
C1 C6 C7 N1
C5 C6 C1 O1
C7 C6 C1 O1
C5 C6 C1 C2
C7 C6 C1 C2
O1 C1 C2 O2
C6 C1 C2 O2
O1 C1 C2 C3
C6 C1 C2 C3
O2 C2 C3 C4
C7 N1 C8 C9
Unit cell parameters
C1 C2
˚
12.0850(10) A
a
b
c
O2 C2
˚
8.2563(5) A
C1 O1 H1
C7 N1 C8
C1 C6 C7
N1 C7 C6
N1 C7 H7
O1 C1 C6
O1 C1 C2
C6 C1 C2
C2 O2 H2
O2 C2 C3
O2 C2 C1
˚
13.6500(12) A
b
V
Z
108.564(6)°
1291.10(17) A
3
1.6(2)
˚
-176.7(1)
-1.0(2)
177.8(1)
178.7(1)
-2.5(2)
-178.6(1)
108.3(1)
4
Dc (g cm-3
l(MoKa)
F(000)
)
1.288 g cm-3
0.092 mm-1
536
2hmax
59.30°
h, k, l range
-14 B h B 14
-10 B k B 10
-16 B l B 16
0.9880 and 0.9349
Maximum and
minimum transmission
Goodness of fit on F2
No. of reflections used
Final R indices[I [ 2r (I)]
R indices (all data)
Measurement
1.069
O2
O1
C10
2527
C2
C3
C11
O3
N2
C9
R1 = 0.0336 and wR2 = 0.0922
R1 = 0.0436 and wR2 = 0.0977
STOE IPDS 2
C1
C6
N1
C13
C8
C4
C7
C12
Program system
STOE X-AREA
SHELXS-97
C5
Structure determination
Refinement: full matrix
-3
Fig. 1 The molecular structure of the title compound. Displacement
ellipsoids are plotted at the 50% probability level [40]
˚
0.178, -0.127e A
(Dq)max, (Dq)min
hydrogen bond [13, 14]. The C=N bond which is accountable
partially for the existence enol-imine form can also be
inferred from the IR spectra of compound. The compound
with strong band at 1,271 cm-1 possesses highestpercentage
of enol-imino tautomer due to the stabilization of phenolic
C–O bond [42].
compound. The phenyl protons resonate at d = 6.45–
6.72 ppm multiplet, the OCH2 protons of the compound
3
gave a triplet at d = 3.59 ppm (4H, OCH2, JHH = 5.40
Hz). The Ar–C=N–CH2– and –N–CH2CH2O– protons are
equivalent for compound. These protons are observed as
3
triplets 3.46 ppm (6H, JHH = 5.45 Hz) for compound.
1H-NMR spectra of some Schiff bases were measured in
a range of solvents, and the presence of a 3J(CHNH) coupling
between the exchangeable and the olefinic proton, con-
firmed by decoupling, was interpreted as being due to the
presence of the keto-amine tautomer. This coupling and
1J(NH) were measured in a range of solvents and, with a
good reference value for this in a non-tautomeric situation
Ar–C=N–CH2CH2–N protons of the compound gave a
3
triplet at d = 2.48 ppm (2H, JHH = 5.45 Hz).
According to the proton de-coupled 13C-NMR spectra
compound has 10 signals Fig. 3. The compound seems to
have symmetric carbon atoms (10, 100 and 11, 110) in
solution (Scheme 2). The aliphatic –ArC=N–C(8)– and
–N–C–CH2O(10 and 100) carbons are found to be equiva-
lent for compound. The C=N–C(8)– and –N–C–(10 and
100) carbons are observed at d = 58.79 ppm for compound.
The chemical shifts d ppm; 166.9 (s, 1C, C7, –CH=N–),
154.2 (s, 1C, C2, Cipso–, OH), 146.87 (s, 1C3, Cipso,
–OH), 122.31 (s, 1C6), 117.77 (s, 1C1), 117.47 (s, 1C5),
3
of 96 Hz; it is then possible to deduce a value for J(CHNH)
for pure keto-amine tautomer of 11.6 Hz [43]. The
1H-NMR data for compound show that the tautomeric
equilibrium favours the enol-imine in DMSO. The OH
and azomethine protons are observed as singlets d = 13.75
and d = 8.87 ppm, and d = 8.20 ppm, respectively for
123

106
J Chem Crystallogr (2008) 38:103–108
Fig. 2 FT-IR spectra of
compound in the solid state
(KBr)
Fig. 3 13C-NMR spectra of the compound
11
10
Fig. 4 Solvent effect on compound. DMSO ––––, Ethanol –ꢀ–ꢀ–ꢀ,
CHCl3 - - - - -, Benzene – – – –, Schiff base concentration 5 9 10-5
mol dm-3
9
N
O
H
HO
O
6
5
N
11'
10'
8
4
7
1
3
2
Scheme 2 Numerous carbon atoms of the title compound. Molecular
structure of the title compound which is numbered for 13C NMR
identification
117.12 (s, 1C4) and 66.66 (s, 2C11 and 110, –OCH2), 53.75
(s, 1C9, ArC=N–CH2C–).
The UV–visible spectra of the compound were studied in
polar (DMSO, ethanol and chloroform) and non-polar (ben-
zene) solvents both in acidic and basic media (Figs. 4–6).
The Schiff bases show absorption in the range greater than
Fig. 5 Acid effect on compound. DMSODMSO ––––, Ethanol –ꢀ–ꢀ–ꢀ,
CHCl3 - - - - -, Benzene – – – –, Schiff base concentration
5 9 10-5 mol dm-3
123

J Chem Crystallogr (2008) 38:103–108
107
In conclusion; UV–visible, 1H-NMR and 13C-NMR
results show that the compound exists in the enol-imine
form in DMSO solution.
Crystallographic Study
The title molecule is not planar. The plane through the C
atoms of the morpholine ring makes a dihedral angle of
56.98(4)° with the Schiff base moieties (O1, O2, C1, C2,
C3, C4, C5, C6, C7, and N1). The morpholine ring adopts a
chair conformation, with a total puckering amplitude of
˚
QT = 0.576(2) A [44]. In the morpholine ring, bond
Fig. 6 Base effect on compound. DMSO ––––, Ethanol –ꢀ–ꢀ–ꢀ,
CHCl3 - - - - -, Benzene – – – –, Schiff base concentration 5 9 10-5
mol dm-3
lengths and angles conform to those found previously [45].
There is a strong intramolecular hydrogen bond between
˚
O1 and N1 atom while HꢀꢀꢀN distance is 1.68(2) A. The
˚
O1ꢀꢀꢀN1 distance of 2.575(1) A is clearly indicative of
400 nm in polar and non-polar solvents [9–16]. It is pointed
out that the new band belongs to the keto-amine form of the
Schiff bases with OH group in ortho position to the imino
group in polar and non-polar solvents in both acidic and basic
media [9–16, 28]. The calculated keto-amine form is given in
Table 3. The compound showed absorption above 400 nm in
polar (DMSO, ethanol and chloroform) and non-polar
(benzene) solvents and acidic (CF3COOH, pH = 2) chloro-
form and benzene and basic ([C2H5]3N, pH = 9) DMSO,
ethanol, chloroform and benzene solutions. The band was
not observed with value greater than 400 nm in acidic
solutions of DMSO and ethanol for compound (Figs. 3–5).
The enol-imine tautomer is dominant in the all-pure solvents,
in acidic and basic solutions for compound. The keto-amine
tautomer ratio was increased by 85% and 216%, respectively
in the acidic chloroform and benzene solutions and 133%
and 96% in the basic DMSO and ethanol solutions with
respect to the pure solvent media, while it was not changed in
the basic chloroform and benzene solutions [14–16]. The
absence of keto-amine form in the acidic DMSO and ethanol
solutions may be explained by the hydrogen bonding to acid
(CF3COOH) [13].
strong intramolecular hydrogen bonding; a criterion for
hydrogen bonding between oxygen and nitrogen atoms
is considered to be that the distance OꢀꢀꢀN should be shorter
˚
than the sum, 3.07 A, of the van der Waals radii [46].
The intramolecular O1ꢀꢀꢀN1 hydrogen bond length can
be compared with N-(2-hydroxy-1-naphtylidene)4-aminomor-
˚
pholine [44] 2.573(3) A, 2-(3-methoxy0-2-hydroxyphenyl)
˚
benzimidazole [47] 2.577(6) A and 3,3 -dimethoxybenzy-
˚
dine(2-hydroxybenzal)diimine [48] 2.568(3) A.
C–HꢀꢀꢀX hydrogen bonds have been postulated to sta-
bilize the geometries of many organic compounds in the
solid state [49, 50]. The crystal structure is stabilized by a
strong intermolecular hydrogen bond between O2ꢀꢀꢀN2i
[O2ꢀꢀꢀN2i 2.849(1) A, O2–H2 0.90(2) A, H2ꢀꢀꢀN2i
˚
˚
i
˚
2.01(2) A, O2–H2ꢀꢀꢀN2 154.5(2)°; symmetry code: (i) -x,
-y + 2, -z].
X-ray structure determinations reveal that the enol tau-
tomer is favoured over the keto tautomer. This is evident
˚
from the observed O1–C1 bond distance of 1.337(1) A,
which is consistent with the O–C single bond; similarly the
˚
N1–C7 distance of 1.276(2) A is also consistent with the
N=C double bonding.
Table 3 Effect of solvent, acid, and base on the UV spectra of compound
Solvent
k, nm (e, M-1 cm-1
)
Keto-amine tautomer (%)
Solvent media
Acidic mediaa
Basic mediab
Compound
DMSO
EtOH
425(34409), 334(7180), 269(34640)
425(2360), 300(8760) 266(15760), 220(26740)
434(3080), 306(10280) 259(16780)
432(1300), 286(49320)
15
13
10
3
–
40
25
9
–
CHCl3
Benzene
17
13
3
a
CF3COOH
b
[(C2H5)3N]
123

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J Chem Crystallogr (2008) 38:103–108
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