Salicylaldehyde thiazolyl hydrazones as ligands

Article abstract of DOI:10.1002/hc.10201

Novel bidentate Schiff base ligands, 2-(2-hydroxy-5-chloro/nitro)benzaldehyde-[4-(3-methyl-3-mesitylcyclobutyl)-1,3-t hiazol-2-yl]hydrazone, and their metal complexes have been prepared and characterized by elemental analyses, IR, ¹³C and ¹H NMR spectra, and magnetic susceptibility measurements. All the complexes were found to be mononuclear.

Full text of DOI:10.1002/hc.10201

Heteroatom Chemistry
Volume 14, Number 7, 2003
Salicylaldehyde Thiazolyl Hydrazones
as Ligands
Ibrahim Yilmaz and Alaaddin C¸ ukurovali
Chemistry Department, Faculty of Arts and Sciences, Firat University, 23119 Elazig, Turkey
Received 28 May 2003
functions in their molecules seem to be suitable
ABSTRACT: Novel bidentate Schiff base ligands, 2-
candidates for further chemical modifications and
may be pharmacologically active and useful as lig-
ands in coordination chemistry. This paper deals
(2-hydroxy-5-chloro/nitro)benzaldehyde-[4-(3-methyl-
3-mesitylcyclobutyl)-1,3-thiazol-2-yl]hydrazone, and
their metal complexes have been prepared and char-
with the preparation and characterization of the
acterized by elemental analyses, IR, 13C and H NMR
complexes formed from the Schiff base ligands L1H,
spectra, and magnetic susceptibility measurements.
L2H (Scheme 1) and cobalt(II), copper(II), nickel(II),
All the complexes were found to be mononuclear.
and zinc(II) acetates.
1
ꢀ
C
2003 Wiley Periodicals, Inc. Heteroatom Chem
14:617–621, 2003; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/hc.10201
RESULTS AND DISCUSSION
The data of 1, 2, L1H, L2H, and of the complexes
are summarized in Tables 1–3. The complexes corre-
spond to the general formula L2M: They are stable at
INTRODUCTION
Schiff bases from the condensation of salicylalde-
hyde with alkyl- and arylamines are widely used in
coordination chemistry [1]. They display biological
activity, play an important role in biological systems
[2–7], and are considered to be suitable models for
pyridoxal and, in general, B6 vitamins [8]. Adducts
of nontransition, early transition, and f-metals with
ortho-hydroxy Schiff bases [9] have been studied.
Thiazoles are of interest because of their pharma-
ceutical, phytosanitary, analytical, and industrial
applications e.g., as fungicides, anthelmintics, and
herbicides [10]. On the other hand, cyclobutane
carboxylic acids were described as L-glutamate, N-
methyl-D-aspartate (NMDA) agonist, NMDA antago-
nists, and anticonvulsive drugs [11–13]. Compounds
containing cyclobutane, thiazole, and Schiff base
room temperature and are soluble in Me2CO, DMF,
and DMSO, and sparingly soluble in CHCl3. Attempts
to crystallize the ligand complexes from different sol-
vents failed.
The IR spectra of 1 and 2 showed five different
strong and sharp peaks in the 3450–3120 cm−1 re-
gion. Two of them are from NH2, one from NH ,
and one from OH; the other one has not been iden-
tified. No C O peak is observed.
There are no C S, C O, CH2 Cl, and NH2
absorptions in the IR spectra of the ligands L1H
and L2H, which indicates the formation of the ex-
pected compounds. The strong bands observed at
3115 and 3114 cm−1, respectively for the ligands L1H
and L2H, can be attributed to the NH vibration.
In the complexes, these bands are not shifted, but
have lost intensity, and it may therefore be that the
nitrogen atom of this group is not coordinated to the
metal ion. The ligands exhibit broad medium inten-
sity bands in the 2700–2560 cm−1 range which are
Correspondence to: A. C¸ ukurovali; e-mail: acukurovali@firat.
edu.tr.
c
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2003 Wiley Periodicals, Inc.
617

618 Yilmaz and C¸ukurovali
TABLE 1 Analytical and Physical Data of the Compounds
Calc. (Found) (%)
Formula Weight
m.p.
(◦C)
µeff
(BM)
(g mol−1
)
Color
Yield (%)
C
H
N
S
1
2
229.7
240.2
White
Light yellow
94
96
290
>320
–
–
41.8 (41.7)
40.0 (39.9)
3.5 (3.5)
3.4 (3.3)
18.3 (17.9)
23.3 (23.4)
14.0 (13.8)
13.4 (13.5)
L1H
440.0
936.9
941.5
936.7
943.4
450.6
958.0
962.6
957.8
964.5
Pink
Dark brown
Green
83
65
57
81
68
81
73
64
77
69
240
>330
272
–
65.5 (65.6)
61.5 (61.6)
61.2 (61.4)
61.6 (61.5)
61.1 (61.0)
64.0 (64.1)
60.2 (60.1)
59.9 (60.0)
60.2 (60.4)
59.8 (60.0)
6.0 (6.1)
5.4 (5.3)
5.4 (5.3)
5.4 (5.5)
5.3 (5.4)
5.8 (5.7)
5.3 (5.3)
5.2 (5.3)
5.3 (5.3)
5.2 (5.4)
9.6 (9.5)
9.0 (9.1)
7.3 (7.3)
6.8 (6.9)
6.8 (7.0)
6.9 (7.0)
6.8 (7.0)
7.1 (7.2)
6.7 (6.8)
6.7 (6.8)
6.7 (6.9)
6.8 (6.4)
L12Co
L12Cu
L12Ni
L12Zn
L2H
L22Co
L22Cu
L22Ni
L22Zn
4.15
1.89
3.81
Dia
–
8.9 (9.2)
Lemon
>320
>320
222
9.0 (9.0)
Yellow
8.9 (8.7)
Yellow
12.4 (12.5)
11.7 (11.8)
11.6 (11.7)
11.7 (12.0)
11.6 (12.0)
Dark yellow
Dark brown
Lemon
>320
279
4.23
1.79
3.74
Dia
>320
299 (dec)
Yellow
TABLE 2 Characteristic IR Bands (cm−1) of the Ligands and Complexes as KBr Pellets
ν (C N)
Compound
ν (OH)
ν (N H)
ν (CH3)/ν(CH2)
Thiazole
Azomethine
ν (C O)
ν (C S)
1
2
3274
3271
3171
3180
–
–
–
–
1612
1617
1190
1080
951
964
L1H
3283
3115
3113
3113
3121
3113
3114
3114
3114
3114
3114
2978–2927
2978–2927
2978–2927
2978–2927
2978–2927
2978–2927
2978–2927
2978–2927
2978–2927
2978–2927
1567
1562
1562
1562
1573
1548
1548
1548
1554
1554
1619
1612
1606
1606
1600
1619
1606
1600
1606
1606
1157
1074
1074
1082
1074
1080
1099
1105
1099
1099
–
–
–
–
–
–
–
–
–
–
L12Co
L12 Cu
L12Ni
L12Zn
L2H
L22Co
L22Cu
L22Ni
L22Zn
–
–
–
–
3265
–
–
–
–
SCHEME 1

Salicylaldehyde Thiazolyl Hydrazones as Ligands 619
TABLE 3 1H NMR Spectral Data of the Starting Substances 1 and 2 and Schiff Base Ligands
Chemical Shift (δ, ppm)
L1H
Functional Group
1
2
L2H
NH2
8.17 (s, 2H)
8.31 (s, 1H)
–
–
8.27 (s, 2H)
8.38 (s, 1H)
–
–
–
–
N CH
8.14 (s, 1H)
8.21 (s, 1H)
❍✟CH
3.40 (q, J = 8.9, 1H)
3.43 (q, J = 8.9, 1H)
CH3
1.53 (s, 3H)
1.52 (s, 3H)
o-CH3
p-CH3
CH2
C H, thiazole
OH
–
–
–
–
–
–
–
–
2.12 (s, 6H)
2.16 (s, 3H)
2.47–2.87 (m, 4H)
6.44 (s, 1H)
10.45 (br, 1H)
12.06 (br, 1H)
6.72 (s, 2H)
6.89 (d, J = 8.7, 1H3)
7.21 (dd, Jo = 8.7;
Jm = 2.7, 1H4)
7.58 (d, 1H6)
2.15 (s, 6H)
2.18 (s, 3H)
2.47–2.61 (m, 4H)
6.45 (s, 1H)
10.22 (br, 1H)
11.44 (br, 1H)
–
6.88 (d, J = 8.8, 1H3)
7.24 (dd, Jo = 8.8;
Jm = 2.8, 1H4)
8.10 (d, J = 2.8, 1H6)
11.54 (s, 1H)
11.57 (s, 1H)
–
7.05 (d, J = 8.9, 1H3)
8.13 (dd, Jo = 8.8;
Jm = 2.9, 1H4)
8.87 (d, J = 2.9, 1H6)
12.11 (br, 1H)a
12.11 (br, 1H)a
6.71(s, 2H)
NH
Arom/mesityl
Aromatics
7.05 (d, J = 9.0, 1H3)
8.13 (dd, Jo = 9.0;
Jm = 2.9, 1H4)
8.48 (d, J = 2.9, 1H6)
a
OH and NH are seen at the same resonance.
assigned the intermolecular H-bonding vibrations
(OH· · ·N). This situation is common for aromatic
thine N. The OH and NH signals disappeared
upon addition of D2O to the solution. The detailed
1H NMR spectral data of the ligands are given in
Table 3. The Zn(II) complexes L12Zn and L22Zn showed
the same resonances as those of L1H and L2H except
for the absence of the OH resonance, and a small
shift of the azomethine proton resonance. The de-
tailed 13C NMR spectral data are given in the Exper-
imental section. Azomethine carbon atoms are ob-
served at 144.45 ppm and 141.82 ppm respectively
for L1H and L2H. The 13C NMR spectral data of the
ligands confirm the 1H spectral results. The data ob-
˜
azomethine compounds containing o-OH groups
[15]. In the complexes, these bands disappear com-
pletely. The azomethine group vibrations of the free
ligands occur at 1619 cm−1. In the IR spectra of
complexes, these bands shift to lower frequencies
and, at the same time, lose intensity. This indicates
that the azomethine groups were highly affected by
complexation. For the free ligands L1H and L2H,
the bands at 1157 and 1080 cm−1, respectively can
be attributed to the phenolic group vibration [16].
In the metal complexes, these bands are shifted to
lower frequencies (1074–1082 cm−1) for L1H and
higher frequencies (1099–1105 cm−1) for L2H, indi-
cating coordination of oxygen to the metal atoms.
In the complexes, the bands in the 586–480 and
463–434 cm−1 range can be attributed to the ν(M N)
and ν(M O) modes.
1
tained from elemental analyses, IR, and H and 13C
NMR spectra of L1H and L2H are consistent with
data expected from the formula given in Scheme 1.
As is known, magnetic susceptibility measure-
ments provide information regarding the structure
of the complexes. The magnetic moments of the com-
plexes were measured at room temperature and are
listed in Table 1. Co(II), Cu(II), and Ni(II) complexes
of both ligands are paramagnetic, while their Zn(II)
complexes are diamagnetic. The data indicate two
unpaired electrons for Ni(II) and three for Co(II).
The magnetic moments of the Co(II) complexes of
both ligands at room temperature fall in the range
4–5 BM, which is characteristic for mononuclear,
high-spin, tetrahedral Co(II) complexes. The mag-
netic moment values of the Ni(II) complexes of the
ligands are also consistent with a tetrahedral geom-
etry [19]. On the basis of the spectral and magnetic
data, the cobalt, nickel, copper, and zinc complexes
have tetrahedral geometry [20]. The suggested struc-
ture of the complexes is shown in Fig. 1.
The 1H NMR spectra of 1 and 2 demonstrate aro-
matic, N CH , NH , NH2, and OH protons.
The latter three are D2O-exchangeable. OH signals
of both compounds are broad singlets. This results
from intramolecular hydrogen bonding [17]. The 1H
NMR spectral data of 1, 2 are given in Table 3, and a
more detailed spectral investigation of a similar cy-
clobutane compound, can be found in the literature
[18]. The 13C NMR assignments of both compounds
given in the Experimental.
Very similar spectra were obtained for the lig-
ands L1H and L2H. The 1H resonance of the O H is
a broad singlet for both ligands due to the presence of
hydrogen bonding [17] between OH and the azome-

620 Yilmaz and C¸ukurovali
ethanol. Characteristic 13C NMR (DMSO-d6, TMS,
δ ppm): 128.05 (C1), 163.61 (C2), 118.23 (C3), 124.00
(C4), 142.11 (C5), 123.15 (C6), 138.63 (C7), 179.84
(C8).
Thiazolyl Hydrazones L1H and L2H
To a suspension of 10 mmol 1 (1.95 g), or 2
(2.742 g) in 30 ml absolute EtOH, a solution of
2.645 g (10 mmol) of 1-mesityl-1-methyl-3-(2-chloro-
1-oxoethyl) cyclobutane in 20 ml absolute EtOH was
added dropwise at 30–40◦C with continuous stirring.
After completing the addition, the temperature was
raised to 50–55◦C. Monitoring the carbonyl group
with IR it was easy to determine when the reaction
is complete. The solution was then made alkaline
with an aqueous solution of NH3 (5%) and pale yel-
low solids L1H or L2H separated. The precipitates
were filtered off, washed with aqueous NH3 solu-
tion several times, dried in air, and crystallized from
EtOH. 13C NMR (DMSO-d6, TMS, δ ppm) L1H: 123.82
(C1), 156.40 (C2), 119.66 (C3), 131.88 (C4), 124.94
(C5), 130.63 (C6), 144.45 (C7), 164.13 (C8), 102.69
(C9), 145.86 (C10), 40.45 (C11), 42.13 (C12), 42.55 (C13),
26.35 (C14), 136.51 (C15), 135.51 (C16), 131.38 (C17),
136.17 (C18), 22.85 (C19), 21.86 (C20). L2H: 123.27
(C1), 153.09 (C2), 123.03 (C3), 127.27 (C4), 136.43
(C5), 123.18 (C6), 141.82 (C7), 169.72 (C8), 110.41
(C9), 145.95 (C10), 40.04 (C11), 42.55 (C12), 44.54 (C13),
28.34 (C14), 136.11 (C15), 131.88 (C16), 131.67 (C17),
135.50 (C18), 22.82 (C19), 21.84 (C20).
FIGURE 1 Suggested structure of the complexes.
EXPERIMENTAL
2-Hydroxy-5-chlorobenzaldehyde,
2-hydroxy-
5-nitrobenzaldehyde, and thiosemicarbazide were
purchased from Merck (pure) and were used without
further purification. 1-Mesityl-1-methyl-3-(2-chloro-
1-oxoethyl) cyclobutane was prepared according
to the previously published procedure [14]. El-
emental analyses were determined on a LECO
CHNSO-932 auto elemental analysis apparatus. IR
spectra were recorded on a Mattson 1000 FT-IR
1
spectrometer as KBr pellets. H and 13C NMR spec-
tra were recorded on a Varian-Gemini 200 MHz at
50.34 MHz spectrometer. Magnetic susceptibilities
were determined on a Sherwood Scientific magnetic
susceptibility balance (Model MK1) at room tem-
perature (20◦C) using Hg[Co(SCN)4] as calibrant;
diamagnetic corrections were calculated from
Pascal’s constants. Melting points were determined
on a Gallenkamp apparatus; they were checked by
DSC technique and are uncorrected.
Complexes
The ligand L1H (0.2028 g, 0.50 mmol) or L2H (0.2422
g, 0.50 mmol) was dissolved in absolute ethanol (15–
20 ml). A solution of 0.25 mmol of the metal salt
Co(AcO)2·4H2O (0.0623 g), Cu(AcO)2·H2O (0.0499 g),
Ni(AcO)2·4H2O (0.0623 g), Zn(AcO)2·2H2O (0.0549 g)
in ethanol (10 ml) was added dropwise with contin-
uous stirring. In the case of Co(II) complexes, a slow
stream of nitrogen was passed through the solution.
Every mixture was refluxed for 1 h and then left to
stand overnight at room temperature. The complexes
precipitated as microcrystals, were filtered, washed
with cold ethanol and water several times, and dried
in vacuum at 60◦C (over P4O10) and stored in a des-
iccator over CaCl2. Yields, melting points, elemental
analysis results, and characteristic IR bands (NaCl
cell) are given in Tables 1 and 2.
1-(2-Hydroxy-5-chlorbenzylidene)
Thiosemicarbazide (1)
To a solution of thiosemicarbazide (0.91 g, 10 mmol)
in 50 ml absolute EtOH, a solution of 5-bromo-
salicylaldehyde (2.01 g, 10 mmol) in 20 ml absolute
EtOH was added dropwise at 60–70◦C with continu-
ous stirring. The reaction was monitored by IR spec-
troscopy. After completing the reaction, the mixture
was left overnight. The solid product was filtered off,
washed with H2O several times, dried in air, and crys-
tallized from aqueous EtOH (1:3). Characteristic 13
NMR (DMSO-d6, TMS, δ ppm): 124.11 (C1), 156.90
(C2), 119.47 (C3), 132.14 (C4), 125.22 (C5), 127.22
(C6), 139.22 (C7), 179.67 (C8).
C
1H NMR spectra of L21Zn (DMSO-d6, δ, ppm) 1.53
(s, 6H, CH3), 2.14 (s, 6H, p-CH3), 2.16 (s, 12H, o-
CH3), 2.46–2.67 (m, 8H, CH2 ), 3.42 (q, J = 8.9 Hz,
2H, ❍✟CH ), 6.44 (s, 2H, CH S), 6.72 (s, 4H, aro-
matic on mesitylene), 6.95–7.52 (m, 6H, aromatic),
1-(2-Hydroxy-5-nitrobenzylidene)
Thiosemicarbazide (2)
This compound was prepared by an analogous
procedure, using 2-hydroxy-5-nitrobenzaldehyde in

Salicylaldehyde Thiazolyl Hydrazones as Ligands 621
8.05 (s, 2H, N CH ), 11.37 (s, 2H, NH ); L22Zn
(DMSO-d6, δ, ppm) 1.51 (s, 6H, CH3), 2.15 (s, 12H, o-
CH3), 2.18 (s, 6H, p-CH3), 2.47–2.61 (m, 8H, CH2 ),
3.43 (q, J = 8.9 Hz, 2H, ❍✟CH ), 6.58 (s, 2H, CH S),
6.89 (s, 4H, aromatic on mesitylene), 7.07–8.47 (m,
6H, aromatics), 8.35 (s, 2H, N CH ), 11.47 (s, 2H,
NH ).
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