الفهرس 
Importance of Schiff-bases and their complexesOnly 14 pages are availabe for public view
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Abstract
I.1. Schiff-bases:
Compound with the general structure R2C=NR’ (R’ ≠ H) can be considered a subclass of imines, being either secondary ketimines or secondary aldimines
depending on their structure [1]. A number of special naming systems exist for
these compounds [2]. For instance a Schiff-base derived from an aniline, where R
is a phenyl or a substituted phenyl, can be called an anil [3], while biscompounds are often referred to as salen-type compounds. The term of
Schiff- base is normally applied to these compounds when they are being used as
ligands to form coordination complexes with metal ions. Such complexes do
occur naturally, for instance in Corrin, but the majority of Schiff-base are
artificial and are used to form many important catalysts, such as Jacobsen’s
catalyst. [2,4]
Different Schiff-base and their metal complexes had shown notable bioactivity as
chelating therapeutics, as drugs and as inhibitors of enzymes [4]. Also, some
Schiff-base acted as important analytical reagents for the gravimetric and
colorimetric determination of transition metals [5]. The presence of Cu(II) ion in
these complexes had received wide interest in the fields of the magneto-structural
relationship and the characterization of active sites in multicopper proteins [6].
Cu(II) complexes had a wide range of biological activity and some of these
complexes had been known to be antitumor, antiviral, and anti-inflammatory
agents. In addition to Cu(II) complexes especially with Schiff-base ligands were
models of physical and chemical behavior of biological Cu systems, considerable
attention had been focused on these compounds [7,8] . The Cu(II) complex of 1,
Introduction
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10-phenathroline was the first synthetic transition metal complex effectively
exhibiting nucleolytic activity [8].
The development of Schiff-base species based on transition metal compounds and
polydentate ligands had been the subject of extensive research due to their
potential applications in materials science [9, 10], environmental chemistry and
medicine. Schiff-base compounds played a vital role in coordination chemistry
are due to their ability to react with a range of metal ions forming stable
complexes which had applications in different fields. One interesting application
in the field of coordination chemistry had been to investigate the use of Schiffbase ligands to develop phenoxo-bridged binuclear complexes with homometallic
and heterometallic centres. This included design molecules containing
paramagnetic metal centers were able to self-assemblethrough metal-ligand
interactions rendering supramolecular assemblies with interesting structural and
magnetic properties [11, 12]. Schiff-base metal complexes also had applications
in biomedical [13, 14], biomimetic and catalytic systems [15, 16].
The role of Schiff-base and their metal complexes, in particular cobalt, in the
biological systems make them one interested branch in the coordination and
organometallic chemistry. Significant publications dealt with the development of
coordination chemistry were related to the preparation and characterization of
Schiff-base and their metal complexes. These included the investigation of
synthetic methods and coordination modes of Schiff-base species upon
complexation [17]. It was well known that, Schiff-base species can bind a metal
in different coordination modes [18]. The mode of bonding was investigated
through physico-chemical and spectroscopic methods. X–ray crystal structures
confirmed the preparation of six-coordinate Schiff-base complexes. It was well
documented that, Schiff-base compounds and their complexes with transition
metals had many applications in medicine, biology, industry, and catalysis [19].
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The chemistry of Schiff-base complexes had been broadly investigated [20].
Particularly in Cu(II) and Ni(II) complexes with Schiff-base ligands [21]. The
coordination chemistry of the Schiff-base ligands had been widely studied with
the 3d metal ions [23, 24]. The Schiff-base imines of ligands capable of withstand
higher oxidation states of the central metal ion through strong ligand to metal [LM] σ - donation. The strength of the hydrogen bond in Schiff-base depends on the
size and chemical environment around the metal ion. [22].
Schiff-base complexes can be utilized as catalysts for many organic reactions,
optical materials, luminescence materials, DNA binding and cleavage reagents
[25, 26]. Compounds containing Schiff-base were used as analytical reagent for
the separation and determination of some transition metal ions [27]. Schiff-base
and their metal complexes had shown notable bioactivity as chelating
therapeutics, as drugs, as inhibitors of enzymes and as intermediates in the
biosynthesis of nitrogen oxides [28]. The Cu(II) complexes with Schiff-base
ligands were models of physical and chemical behavior of biological Cu system,
considerably focused on these compounds [28, 29]. The Cu(II) complex of 2, 10
phenopthroline was first synthetic metal complex showed DNA cleavage activity
[30]. The ligands containing nitrogen, oxygen and sulphur acted as effective
chelating agents for transition and non-transition metal ions [31].
I.1.1. Synthesis of Schiff-bases:
Throughout the years Schiff-base have played an important role as chelating
ligands for a large variety of metal ions. More emphasis has been put in the
Schiff-base complexes of metals as it plays an important role in understanding
complex biochemical reactions. Schiff-base complex formation as intermediate in
biochemical reactions had already been reported long time ago [32, 33]. Large
Introduction
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number of Schiff-base complexes of metal ions are prepared in-situ, but the
isolation of the free base before its reaction with a metal ion has many
advantages. The major disadvantage in-situ reaction is that the reactants used to
prepare Schiff-base are often good coordination agents themselves. Hence, a
small excess of the one or the other of these reactants may give rise to other
complexes of the metal ion and thus contaminate the product. Also
characterization of the free ligand gave the chance of comparative study to be
made of its physico-chemical properties with those of the corresponding metal
complexes. The synthesis of some multidentate Schiff-base, which are potential
ligands for transition metal ions have been carried out and the study their
physiological properties and biochemical processes involving these metal ions
and Schiff-bases. The preparation and characterization of Schiff-base including
diimines had been carried out [30]. The formation was generally driven to the
completion separation of the product or removal of water, or both. Many
Schiff-bases can be hydrolyzed back to their aldehydes or ketones and amines by
aqueous acid or base. The mechanism of Schiff-base formation is another
variation on the theme of nucleophilic addition to the carbonyl group. In this
case, the nucleophile is the amine. In the first part of the mechanism, the amine
reacted with the aldehyde or ketone to give an unstable addition compound called
carbinolamine.The carbinolamine losed water by either acid or base catalyzed
pathways. Since the carbinolamine is an alcohol, it undergoes acid catalyzed
dehydration. Scheme 1 shows this mechanism[29,30]