Preparation and characterization of a new SNO ligand derived from ethanebis(thioamide) and 2-hydroxybenzaldehyde, and its Cu(II), Co(II), and Rh(III) metal complexes

Article abstract of DOI:10.1007/s11164-012-0772-x

A new Schiff base N-[(E)-(2-hydroxyphenyl)methylidene]-N'-[(Z)-(2- hydroxyphenyl)methylidene]ethanebis(thioamide) (L_C) containing sulfur, nitrogen, and oxygen atoms has been synthesized by condensation of ethanebis(thioamide) with 2-hydroxybenzaldehyde. Metal complexes were synthesized by reaction of the new ligand with copper(II) and cobalt(II) as nitrate salts and with rhodium(III) as chloride salt, using hot absolute ethanol as solvent. All the new compounds were characterized by use of different physicochemical techniques including UV-visible spectroscopy, magnetic susceptibility, IR spectroscopy, molar conductance, and determination of metal content. It is proposed the paramagnetic copper and cobalt complexes adopt octahedral geometry whereas the diamagnetic rhodium complex has octahedral geometry.

Full text of DOI:10.1007/s11164-012-0772-x

Res Chem Intermed (2013) 39:2463–2471
DOI 10.1007/s11164-012-0772-x
Preparation and characterization of a new SNO
ligand derived from ethanebis(thioamide)
and 2-hydroxybenzaldehyde, and its Cu(II), Co(II),
and Rh(III) metal complexes
•
Eman Turky Shamkhy Isam Hussain T. Al-Karkhi
Emad A. Jaffar Al-Mulla
•
Received: 29 July 2012 / Accepted: 16 August 2012 / Published online: 4 September 2012
Ó Springer Science+Business Media B.V. 2012
Abstract A new Schiff base N-[(E)-(2-hydroxyphenyl)methylidene]-N’-[(Z)-(2-
hydroxyphenyl)methylidene]ethanebis(thioamide) (LC) containing sulfur, nitrogen,
and oxygen atoms has been synthesized by condensation of ethanebis(thioamide)
with 2-hydroxybenzaldehyde. Metal complexes were synthesized by reaction of the
new ligand with copper(II) and cobalt(II) as nitrate salts and with rhodium(III) as
chloride salt, using hot absolute ethanol as solvent. All the new compounds were
characterized by use of different physicochemical techniques including UV–visible
spectroscopy, magnetic susceptibility, IR spectroscopy, molar conductance, and
determination of metal content. It is proposed the paramagnetic copper and cobalt
complexes adopt octahedral geometry whereas the diamagnetic rhodium complex
has octahedral geometry.
Keywords Fusion Á Salicylaldehyde Á Dithiooxamide Á Metal complexes
Introduction
Ligands containing sulfur and nitrogen as donor atoms and their metal complexes
were reviewed in 1965 [1]. More recently reviews have appeared on reac-
tions involving metal complexes of sulfur ligands [2], and on specific types of
E. T. Shamkhy (&) Á I. H. T. Al-Karkhi
Basic Science Department, College of Dentistry, University of Baghdad,
Bab Al-Moazam, Baghdad, Iraq
e-mail: bluesky_832000@yahoo.com
I. H. T. Al-Karkhi
e-mail: isamhtk@hotmail.com
E. A. Jaffar Al-Mulla
Department of Chemistry, College of Science, University of Kufa, P.O. Box 21,
An-Najaf 54001, Iraq
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E. T. Shamkhy et al.
sulfur–sulfur, sulfur–oxygen, and sulfur–nitrogen chelate complexes [3–5]. A recent
review [6] deals with ligands capable of coordinating via either sulfur or nitrogen.
However, there seems to be no review devoted exclusively to metal chelates of
sulfur–nitrogen ligands.
There is increasing interest in the preparation, reactivity, and structure of Schiff
bases, because of their widespread and potential applications in catalysis, ligand
modeling, and material chemistry, and because of their biological activity [7–9].
Schiff bases are also widely used as ligands in coordination with metal ions because
of their electron-donor and chelating ability [10–17].
The new Schiff base N-[(E)-(2-hydroxyphenyl)methylidene]-N’-[(Z)-(2-hydroxy-
phenyl)methylidene]ethanebis(thioamide) (LC) has been synthesized by condensa-
tion of ethanebis(thioamide) with salicylaldehyde (2-hydroxybenzaldehyde), and
three metal complexes have been prepared by reaction of LC with copper(II) and
cobalt(II) as the nitrate salts and with rhodium(III) as the chloride salt.
Materials and methods
Materials
All chemicals were of analytical grade and were used as supplied without any
further purification. Salicylaldehyde (2-hydroxybenzaldehyde), ethanebis(thioam-
ide) (BDH), copper(II) nitrate trihydrate (BDH), cobalt(II) nitrate hexahydrate,
rhodium(III) trichloride hydrate (BDH), absolute ethanol (99.99 %,), dimethyl
sulfoxide (DMSO) (99 %), diethyl ether, glacial acetic acid (BDH), and diethyl
ether were from Fluka, Germany.
Physical measurements
Infrared spectra of the prepared compounds were acquired by use of a Shimadzu
FT-IR-8300; the samples were measured as KBr discs in the wavelength range
4,000–400 cm-1. Carbon, hydrogen, nitrogen, and sulfur analysis was performed by
use of a Leco CHNS-932 analyzer. Electronic spectra of the prepared compounds
were acquired by use of a Shimadzu UV–Vis-160A spectrophotometer, using a
1.0 cm quartz cell at room temperature in the wavelength range 200–1,100 nm. All
prepared compounds were dissolved in DMSO at 10-3 M. The magnetic
susceptibility values of the prepared complexes were obtained at room temperature
by use of Johnson Matthey Catalytic System Division magnetic susceptibility
balance. The metal content of the complexes was measured by use of a Perkin–
Elmer 5000 flame atomic absorption sectrophotometer at 324.8 and 240.7 nm for
the Cu(II) and Co(II) ions, respectively, and by use of a GBC-933 Flame Plus
atomic absorption spectrophotometer for the Rh(III) ion at 343.5 nm. Molar
conductivity was measured at 25 °C, at a concentration of 10-3 M. All complexes
were dissolved in DMSO by using a Wissenschaftlich-Technisch Werkstatten 8120
Weilheim I.O.B, Drucker-Printer. A Gallenkamp M.F.B. 600.01 was used to
measure the melting points of all prepared compounds.
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Preparation and characterization of a new SNO ligand
2465
Preparation of the N-[(E)-(2-hydroxyphenyl)methylidene]-N’-[(Z)-
(2-hydroxyphenyl)methylidene]ethanebis(thioamide) LC ligand
A mixture of salicylaldehyde (20 mmol) and dithiooxamide (10 mmol) was
dissolved in 30 ml absolute ethanol. A few drops of glacial acetic acid were then
added as catalyst. The resulting mixture was heated under reflux for 48 h. The
precipitate obtained was isolated by filtration, washed with diethyl ether,
recrystallized, then dried under vacuum at 40 °C for 2 days. The yield was 62 %.
Preparation of the metal complexes of LC
An ethanolic solution of 0.301 mmol of the metal salt Cu(NO3)2Á3H2O (0.0728 g),
Co(NO3)2Á6H2O (0.0877 g), or RhCl3ÁH2O (0.0685 g) was added to an ethanolic
solution of LC (0.301 mmol, 0.1 g). The mixture was warmed for 5 min then heated
under reflux for 3 h; several drops of pH 9 buffer were then added to complete the
reaction. Fine crystalline powders of different color, depending on the metal salt,
were obtained. These were filtered, washed with diethyl ether, recrystallized, then
dried under vacuum at 40 °C for 2 days. The yields were 75, 78, and 72 % for
LCCu(II), LcCo(II), and LCRh(III), respectively [18, 19].
Results and discussion
A new Schiff base, N-[(E)-(2-hydroxyphenyl)methylidene]-N’-[(Z)-(2-hydroxy-
phenyl)methylidene]ethanebis(thioamide) (LC), has been synthesized and charac-
terized successfully. Different metal complexes were prepared by reacting metal ion
salts of Cu(II), Co(II), or Rh(III) with the new ligand. Scheme 1 shows the
condensation reaction for synthesis of LC. Table 1 shows physical properties of the
synthesized compounds (Lc, LCCu(II)Á3H2O, LcCo(II), and LCRh(III)).
Fourier-transform infrared spectroscopy (FT-IR)
The FT-IR spectrum of LC contained a broad band at 3,450 cm-1 which was
assigned to the stretching vibration of the hydrogen-bonded OH group in the ligand.
A band at 651 cm-1 was assigned to the hydrogen-bonded out-of the plane (O–H)
bending vibration [20]. A strong band at 1,622 cm-1 arises from the azomethine
group m C=N stretching frequency, and bands at 1,566–1,475 cm-1 are m C=C
aromatic ring bands [21]. The thioamide band appeared at approximately
1,463–1,468 cm-1 in the free ligand whereas in its metal complexes it appeared
at 1,178 cm-1, because the m C=S stretching frequency was shifted to higher
frequency on complex formation [22] A band at 705 cm-1 was ascribed to m C–S
[23] in the free ligand and a band at approximately 908 cm-1 was attributed to the
N–C–S group [24, 25] in the free ligand. The m C–H of the aromatic moiety
appeared at approximately 3,056 cm-1 in the free ligand [26]. A band at
1,278 cm-1 was assigned to the phenolic C–O [27] stretching mode. A sharp
strong band at 752 cm-1 is because of the ortho substitution [28].
123

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E. T. Shamkhy et al.
S
N
NH2
S
O
H2N
S
+
OH
OH
S
NH2
2-hydroxybenzaldehyde
ethanebis(thioamide)
O
OH
S
S
N
N
HO
HO
Scheme 1 Condensation reaction for LC Schiff base
In the FT-IR spectra of the metal complexes the azomethine m C=N band shifted
to lower frequency and appeared at 1,604–1,610 cm-1 [29] indicating coordination
through the azomethine-nitrogen with the metal. The m C–O frequency was changed
from 1,278 to 1355, 1325, and 1348 cm-1 after complexation with the central metal
ion [30, 31] because of displacement by the metal ion of the phenol hydrogen, which
is indicative of coordination of the oxygen with the central metal ion [32, 33]. The
presence of new weak bands at 557, 565 and 520 cm-1, were assigned to m M–N,
and bands at 457, 460, and 460 cm-1 were assigned to m M–O [34].
Medium bands which appeared at 622, 630, and 667 cm-1 indicate the presence
of H2O coordinated with the metal in the lattice of complexes [35] whereas broad
bands which appeared at 3396, 3218, and 3355 cm-1 are indicative of the presence
of water molecules outside the coordination sphere of the metal in the complex [36].
Table 2 shows the most characteristic bands of the ligand and metal complexes.
Molar conductance and magnetic susceptibility results
Molar conductivities were determined for solutions of the metal complexes at a
concentration of 10-3 M in DMSO at room temperature (Table 3). The conduc-
tivities were in the range 15.9–19.7 X-1 cm2 mole-1, indicating that all the
complexes are non-electrolytes. Furthermore, the non-electrolytic nature of the
complexes proves that the Schiff bases are coordinated to the metal ion [37]. The
magnetic susceptibility measurements of all metal complexes at room temperature
are tabulated in Table 3. Complexes without unpaired electrons are classified as
diamagnetic, because they tend to move out of a magnetic field. Paramagnetic
123

Preparation and characterization of a new SNO ligand
2467
123

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E. T. Shamkhy et al.
Table 2 The most significant bands in the FT-IR spectra of the ligand and its metal complexes
Symbol
m C=N
m C=S
m C–S
m C–O
m M–N
m M–O
LC
1,622
1,604
1,600
1,610
1,463
1,467
1,465
1,468
705
703
706
707
1,278
1,355
1,325
1,348
_
557
565
520
_
457
460
460
LCCu(II)
LCCo(II)
LCRh(III)
Table 3 Magnetic moments, conductivity, and suggested structures of the complexes of LC (10-3 M) in
DMSO as solvent
Complex
Magnetic moment, leff (BM)
Conductivity (ls cm-1
)
Suggested structure
LCCu(II)
LCCo(II)
LCRh(III)
1.92
16.5
19.7
15.9
Octahedral
Octahedral
Octahedral
4.97
Diamagnetic
complexes are those with unpaired electrons which tend to move into a magnetic
field [38].
Structures were suggested for the prepared complexes on the basis of the position of
the bands in the infra-red spectra, the electronic absorption bands, atomic absorption,
magnetic properties, and electric conductivity measured for these complexes.
Electronic spectra analysis
The electronic spectrum of the Schiff base ligand in the UV–visible region, in DMSO
as solvent, at 10-3 M, contained three main bands. The first absorption band, which
appeared 322 nm, can be attributed to the p ? p* transition for the aromatic system.
The second absorption band, which appeared at 359 nm, was attributed to the p ? p*
transition of the imine group [38]. This band was not significantly affected by
chelation. The third absorption band, which appeared at 415 nm in the spectrum of the
S
S
N
OH 2
Cu
N
. 2 H O
2
O
O
OH 2
Scheme 2 Expected structure of the copper(II) complex
123

Preparation and characterization of a new SNO ligand
2469
Table 4 Electronic spectra of the compounds in DMSO at 10-3
M
Compound
LC
kmax (log e) (nm)
Transition
415 (3.1)
n ? p*
359 (3.3)
p ? p* (imino)
322 (3.5)
p ? p* (aromatic)
2Eg ? 2T2g
m42T1g (F) ? 4A2g (F)
m43T1g (F) ? 4T2g (P)
LCCu(II)
LCCo(II)
762 (0.001)
690 (0.08)
395 (0.42)
449 (0.005)
335 (0.008)
LCRh(III)
m11A1g
m12A1g
?
?
1T1g
1T2g
ligand, was assigned to the n ? p* transition [39]. This is shifted to a longer
wavelength (red shift) upon formation of the complexes, possibly because of donation
of the lone pairs of the nitrogen atoms of the Schiff base to the metal ion N: ? M [35].
Details of the electronic spectra of the synthesized compounds (Lc, LCCu(II),
LcCo(II), and LCRh(III)) in DMSO at 10-3 M are listed in Table 4.
The electronic spectrum of Cu(II) nitrate contains a single broad absorption band
in the region 909–625 nm [1]. The free ion ground 2D term is expected to split in a
crystal field [36]. In this work, the deep brown color of the LCCu(II) complex
suggests a strong-field complex and the broad band at 762 nm is indicative of
2
2
distorted octahedral geometry which can be assigned to the Eg ? T2g transition
[1, 38]. The value of leff measured for the LCCu(II) complex was 1.92 BM; this
value is in the range for mononuclear octahedral geometry [35, 39]. According to
results from analysis of the FT-IR and electronic spectra, octahedral geometry
around the Cu(II) ion can be suggested, as illustrated in Scheme 2.
The spectral behavior of cobalt(II) nitrate was identical with that of LCCo(II);
both contained two bands at 690 and 395 nm which were assigned to the transitions
4
4
m2 4T1g (F) ? A2g (F) and m34T1g (F) ? T1g (P), respectively. The value of m1 was
calculated using the Tanabe–Sugano diagram for the d7 system. It was found to be at
8,988 cm-1 and was assigned to the 4T1g (F) ? T2g (F) transition. The 10Dq value
4
was also calculated from the diagram and found to be 10,930 cm-1 indicative of a
weak field state. The magnetic moment of the LCCo(II) complex was 4.97 BM. That
shows the complex is paramagnetic and has three unpaired electrons indicating a
high-spin octahedral configuration [37, 39]. The formula was further confirmed to
be non-ionic by conductivity measurement. From these results octahedral geometry
around the Co(II) ion can be suggested, as illustrated in Scheme 3.
The electronic spectrum of the deep brown of LCRh(III) complex contains two
absorption bands, one at 449 nm and the other at 335 nm; these can be assigned to
1
1
1
the m1 A1g ? T1g, and m12A1g ? T2g transitions, respectively. These transitions
are indicative of a low spin crystal-field and octahedral geometry for this complex
[37, 40]. The rhodium(III) complex is diamagnetic which is indicative of a strong
field. Conductivity measurements show that the complex is non-ionic. According to
results from analysis of FT-IR and electronic spectra, the suggested structure is
illustrated in Scheme 4.
123

2470
E. T. Shamkhy et al.
S
S
N
OH 2
Co
N
. 6H O
2
O
O
OH 2
Scheme 3 Expected structure of the cobalt(II) complex
S
S
N
Cl
N
.4 H2O
Rh
O
O
OH2
Scheme 4 Expected structure of the rhodium(III) complex
References
1. S.E. Livingstone, Quart. Rev. Chem. Sot. 19, 386 (1965)
2. L.F. Lindoy, Coord. Chem. Rev. 4, 4I (1969)
3. J.A. McCIeverty, Prog. Inorg. Chem. 10, 49 (1968)
4. D. Coucouvanis, Prog. Inorg. Chem. 11, 233 (1969)
5. R. Eisenberg, Prog. Inorg. Chem. 12, 295 (1970)
6. B.P. Kennedy, A.B.P. Lever, Can. J. Chem. 50, 3488 (1972)
7. R.D. Jones, D.A. Summerville, F. Basolo, Chem. Rev. 17, 139 (1972)
8. E. Hadjoudis, I.M. Mavridis, Chem. Soc. Rev. 2004(33), 579 (2004)
9. K. Bhat, K.J. Chang, M.D. Aggarwal, W.S. Wang, B.G. Penn, D.O. Frazier, Mater. Chem. Phys. 44,
261 (1996)
¨
10. O. Celik, M. Ulusoy, E. Tas, S. Ide, Anal. Sci. 23, x185 (2007)
123

Preparation and characterization of a new SNO ligand
2471
11. E.A.J. Al-Mulla, J. Oleo Sci. 60, 41 (2011)
12. M.R. Mahmoud, S.A. El-Gyar, A.A. Mousrafa, A. Shaker, Polyhedron 6, 1017 (1987)
13. H. Qing-Yu, M. Zheng-Hua, Z. Ya-Me, J. Coord. Chem. 21, 199 (1990)
14. P.G. Cozzi, Chem. Soc. Rev. 33, 410 (2004)
15. M.T.H. Tarafder, K.T. Jin, K.A. Crouse, A.M. Ali, B.M. Yamin, H.-K. Fun, Polyhedron 21, 2547
(2002)
16. E.A.J. Al-Mulla, N.A.B. Ibrahim, K. Shameli, M.B. Ahmad, W.M.Z.W. Yunus, Res. Chem. Inter-
med. (2012) doi:10.1007/s11164-012-0687-6 (online first article)
17. P. Sengupta, R. Dinda, S. Ghosh, Trans. Metal. Chem. 27, 665 (2002)
18. E.A.J. Al-Mulla, K.W.S. Al-Janabi, Chin. Chem. Lett. 22, 469 (2011)
19. C. Celik, M. Tu¨mer, S. Serin, J. Coord. Chem. 32, 1839 (2002)
20. P. Toyssie, J. Charette, J. Spectrochim. Acta. 19, 1407 (1963)
21. M.M. Abd-Elzaher, J. Chin. Chem. Soc. 48, 153 (2001)
22. M.I. Farah, H. AL-Samraiy, R.J. Ayad, J. Bahjat, Eur. Res. 19, 38 (2007)
23. C.A. Tsolerides, N.A. Rodies, J. Hetrocyclic Chem. 31, 1593 (1999)
24. B. Sing, K.P. Thakur, J. Inorg. Nucl. Chem. 36, 1735 (1974)
25. R.C. Agrawal, R.B.S. Yadava, Trans. Met. Chem. 1, 39 (1976)
26. L.T. Yildirim, O. Atakol, Cryst. Res. Technol. 37, 1352 (2002)
27. J.N.R. Ruddick, J.R. Sams, J. Organomet. Chem. 60, 233 (1973)
28. I.F. Scheinmann (Pergamon press 2, New York, 1973)
29. S. Carla, F. Cristina, C. de Baltazar, Molecules 8, 894 (2003)
30. M. Joseph, A. Sreekanth, V. Suni, M.R.P. Kurup, Spectrochim. Acta A Mol. Biomol. Spectrosc. 64,
637 (2006)
31. A.Z. El-Sonbati, A.A. El-Bindary, J. Polish Chem. 74, 621 (2000)
32. R. Zolfaghar, R.A. Leili, N. Kamellia, M.S. Seyed, Acta Chem. Slov. 51, 675 (2004)
33. T. Xishi, Y. Xianhong, C. Qiang, T. Minyu, Molecules 8, 439 (2003)
34. A.D. Garnovski, A.L. Ninorozhkin, V.I. Minkin, Coord. Chem. Rev. 126, 1 (1993)
35. S. Chandra, R. Kumar, Spectrochim. Acta A 61, 437 (2005)
36. E.T. Shamkhy, I.H. Al-Karkhi, Orient. J. Chem. 27, 1403 (2011)
37. L. Antonov, M. Vladimirova, E. Stanoeva, W.F. Fabian, L. Ballester, J. Incl. phenom. Mol. Recog.
Chem. 40, 23 (2001)
38. E.W. Ainsceugh, A.M. Brodie, W.A. Denny, G.J. Finlay, J.D. Renford, J. Inorg. Biochem. 77, 125
(1999)
39. E.W.A. Insco, A.M. Brodie, W.A. Denny, G.J. Finlay, J.D. Ranford, J. Indian Biochem. 70, 175
(1998)
40. V.K. Sharma, S. Srivastava, A. Srivastava, Bioinorg. Chem. Appl. 2007, 68374 (2007)
123