SYNTHESIS OF SOME BINUCLEAR METAL COMPLEXES
169
For the zone size interpretations were used recommendations of cherichia coli. The results are presented in Table 4. It was found
national committee clinical laboratory standards (NCCLs).
that anti-S. aureus activity of free ligands is better than that of
related complexes. Also, among Schiff bases, compound 4d was
found to be more potent against Staphylococcus aureus.
RESULTS AND DISCUSSION
Diazo compounds 2a-e were prepared by reaction of salicyl
aldehyde and corresponding substituted aniline 1a-e. Addition
of these azo compounds to 2-aminophenol in the presence of
catalytic amount of Cu(NO3)2, 6H2O at room temperature gave
related Schiff bases 4a-e.[19,20] The reaction of these novel Schiff
bases with transition metal salts of Cu(II) and Zn(II) in reflux-
ing EtOH/DMF afforded the related complexes 5 and 6a-e as
presented in Scheme 1.
REFERENCES
1. Taggi, A.E.; Hafez, A.M.; Wack, H.; Young, B.; Ferraris, D.; Lectka, T.
The development of the first catalysed reaction of ketenes and imines:
catalytic asymmetric synthesis of β-lactams. J. Am. Chem. Soc. 2002, 124,
6626–6635.
2. Naeimi, H.; Safari, J.; Heidarnezhad, A. Synthesis of Schiff base ligands
derived from condensation of salicylaldehyde derivatives and synthetic di-
amine. Dyes and Pigments 2007, 73, 251–253.
3. Wang, Y.; Yang, Z.Y. Crystal structure of Ni(II) complex and fluorescence
properties of Zn(II) complex with the Schiff base derived from diethenetri-
amine and PMBP. J. Lumin. 2008, 128, 373–376.
4. Colak, M.; Demirel, N. Enantioselective nitroaldol (Henry) reaction cat-
alyzed by chiral Schiff-base ligands. Tetrahedron-Asymmetr. 2008, 19,
635–639.
5. Johnson, C.P.; Atwood, J.L.; Bauer, C.B.; Rogers, R.D. Transition metal
complexes of p-sulfonatocalix[5]arene. Inorg. Chem. 1996, 35, 2602–2610.
6. Casellato, U.; Vigato, P.A. Transition metal complexes with binucleating
ligands. Coord. Chem. Rev. 1977, 23, 31–117.
7. Tumer, M.; Koksal, H.; Senser, M.K.; Serin, S. Antimicrobial activity stud-
ies of the binuclear metal complexes derived from tridentate Schiff base
ligands. Trans. Met. Chem. 1999, 24, 414–420.
8. Naeimi, H.; Rabiei, K.; Shameli, F. Template synthesis of some double
Schiff-base metal(II) complexes through one pot four component reac-
tions under mild and convenient conditions. J. Coord. Chem. 1999, 62,
1199–1205.
The structure of Schiff bases and their complexes was as-
signed by physical and spectroscopic data. The 1H-NMR spectra
of all Schiff bases are simple and consist of the aromatic protons
signals and three singlets due to resonance of 2OH (phenolic)
and CH (imine) protons, which appeared at the expected region.
1
The prepared Zn (II) complexes are diamagnetic. In H-NMR
spectra of complexes 6a, 6c, 6d, and 6e (Table 1), the absence
of singlets related to the OH groups of ligand, is in support
of the expected reaction and bonding of oxygen to the metal
ion. Also the chemical shift of aromatic and imine protons was
shifted about 0.1–0.3 ppm to highfield compared to those in free
ligands due to coordination to metal ion. The 1H-NMR spectra
of free Schiff base ligand 4a and its Zn (II) metal complex are
presented as an example (Scheme 2).
The IR and UV/Vis spectroscopic data of synthesized com-
plexes are listed in Table 2. The IR spectra of Schiff bases has
an absorption band at 1616–1620 cm−1, the characteristic of
C N bond of azomethine,[23] which shifted to lower frequen-
cies about 10–12 cm−1 on chelating with metal ion. Also, the
IR spectra of all ligands show a sharp bond at 1277–1290 cm−1
attributed to the C O stretching vibration mode. This band is
significantly shifted by coordination to the metal ion and ap-
peared at 1373–1381 cm−1 (Table 2).
The electronic spectra of complexes represent three intense
absorptions in UV region attributed to the charge transfer
from the π orbitals of donor atoms to the d orbitals of metal
d→π∗ [23] and intraligand n→π∗ transitions (absorption bands
at 302–412).[24] The n→π∗ transitions of complexes are shifted
to lower energy, which is in support of the coordination of the
imine nitrogen atom to the metal ion. The absorption bands at
253–273 are as a result of π→π∗ transitions of the phenol rings.
The absorption maxima at 420–476 nm attributed to a π→π∗
transition of dipolar zwitterionic keto-amine tautomerization of
ligand.[25]
9. Demir, I.; Bayrakci, M.; Mutlu, K.; Pekacar, A.I. Synthesis and charac-
terization of a novel iminooxime Schiff Base ligand and its complexation
with copper(II),nickel(II), zinc(II), cadmium(II), and cobalt(II). Acta Chim.
Slov. 2008, 55, 120–124.
10. Mazloum Ardakani, M.; Hassan Mirhoseini, S.; Salavati-Niasari, M. Cop-
per selective electrode based on 1,8-bis(2-hydroxynaphthaldiminato)3,6-
dioxaoctane. Acta. Chim. Slov. 2006, 53, 197–203.
11. Ibrahim, M.N.; Sharif, S.E.A. synthesis, characterization and use of Schiff
Bases as fluorimetric analytical reagents. E-J. Chem. 2007, 4, 531–535.
12. Khanmohammadi, H.; Salehifard, M.; Abnosi, M.H. Synthesis, Character-
ization, biological and thermal Studies of Cu(II) complexes of Salen and
tetrahedrosalen ligands. J. Iran. Chem. Soc. 2009, 6, 300–309.
13. Kumar, S.; Dhar, D.N.; Saxena, P.N. Applications of metal complexes of
Schiff bases: a review. J. Sci. Ind. Res. 2009, 68, 181–187.
14. Osowole, A.A.; Kolawole, G.A.; Kempe, R.; Fagade, O.E. Spectro-
scopic, magnetic and biological studies on some metal(II) complexes
of 3-(4,6-Dimethyl-2Pyrimidinylamino)-1-Phenyl-2-Butenone and their
adducts with 2,2-Bipyridine and 1,10-Phenanthroline. Synth. React. Inorg.
M. 2009, 39, 165–174.
15. Aliyu, H.N.; Abdullahi, H.J. Synthesis and characterization of divalent
metal complexes of N, Nꢁ-bis(Benzoin)-o-phenylenediiminato complexes.
African Scientist 2009, 10, 199–202.
16. (a) Hansen, K.B.; Leighton, J.L.; Jacobsen, E.N. On the mechanism
of asymmetric nucleophilic ring-opening of epoxides catalyzed by
(Salen)Cr(III) complexes. J. Am. Chem. Soc. 1996, 118, 10924–10925.
(b) Tokunaga, M.; Larrow, J.F.; Kakiuchi, F.; Jacobsen, E.N. Asymmetric
catalysis with water: efficient kinetic resolution of terminal epoxides by
means of catalytic hydrolysis. Science 1997, 277, 936–938.
17. Sun, S.; Stern, C.L.; Nguyen, S.T.; Hupp, J.T. Directed-assembly of
transition-metal-coordinated molecular loops and squares from salen-type
components. Examples of metallation-controlled structural conversion. J.
Am. Chem. Soc. 2004, 126, 6314–6326.
The yield and elemental analysis data of complexes are pre-
sented in Table 3. The physical and spectroscopic data (Table 2)
support a binuclear structure for all complexes. Our method
suggests itself as a useful one for the further investigation of
these uncommon metal complexes.
The antibacterial activity of free ligands and synthesized
complexes was tested against Staphylococcus aureus and Es-
Mobinikhaledi, Akbar
