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MIXED LIGAND COMPLEXES

 Format: MS WORD   Chapters: 1-5

 Pages: 63   Attributes: COMPREHENSIVE RESEARCH

 Amount: 3,000

 Feb 08, 2020 |  08:00 am |  1507

CHAPTER ONE

  INTRODUCTION

1.0.            BACKGROUND OF THE STUDY

     In chemistry, a coordination complex consists of a central atom or ion, which is usually metallic and is called the coordination center, and a surrounding array of bound molecules or ions, that are in turn known as ligands or complexing agents.  Many metal-containing compounds, especially those of transition metals, are coordination complexes. Coordination chemistry is the study of the coordination compounds or, as they are often defined, coordination complexes. These entities are distinguished by the involvement, in terms of simple bonding concepts, of one or more coordinate (or dative) covalent bonds, which differ from the traditional covalent bond mainly in the way, that we envisage they are formed. Although we are most likely to meet coordination complexes as compounds featuring a metal ion or set of metal ions at their core (and indeed this is where we will overwhelmingly meet examples herein), this is not strictly a requirement, as metalloids may also form such compounds (Lawrance, 2010).

     Coordination complexes consist of a central metal atom or ion which is usually metallic and is called the coordination centre and a surrounding array of bound molecules or ions, which are called ligands or complexing agents (Lawrance, 2010; IUPAC, 2006). Many metal-containing compounds, especially those of transition metals, are coordination complexes (Greenwood and Earnshaw 1997).

Nomenclature and terminology

Coordination complexes are so pervasive that their structures and reactions are described in many ways, sometimes confusingly. The atom within a ligand that is bonded to the central metal atom or ion is called the donor atom . In a typical complex, a metal ion is bonded to several donor atoms, which can be the same or different. A polydentate (multiple bonded) ligand is a molecule or ion that bonds to the central atom through several of the ligand's atoms; ligands with 2, 3, 4 or even 6 bonds to the central atom are common. These complexes are called chelate complexes; the formation of such complexes is called chelation, complexation, and coordination.

The central atom or ion, together with all ligands, comprises the coordination sphere. The central atoms or ion and the donor atoms comprise the first coordination sphere.

Coordination refers to the "coordinate covalent bonds" (dipolar bonds) between the ligands and the central atom. Originally, a complex implied a reversible association of molecules, atoms, or ions through such weak chemical bonds. As applied to coordination chemistry, this meaning has evolved. Some metal complexes are formed virtually irreversibly and many are bound together by bonds that are quite strong.

The number of donor atoms attached to the central atom or ion is called \the coordination number. The most common coordination numbers are 2, 4, and especially 6. A hydrated ion is one kind of a complex ion (or simply a complex), a species formed between a central metal ion and one or more surrounding ligands, molecules or ions that contain at least one lone pair of electrons,

If all the ligands are monodentate, then the number of donor atoms equals the number of ligands. For example, the cobalt(II) hexahydrate ion or the hexaaquacobalt(II) ion [Co(H2O)6]2+ is a hydrated-complex ion that consists of six water molecules attached to a metal ion Co. The oxidation state and the coordination number reflect the number of bonds formed between the metal ion and the ligands in the complex ion. However, the coordination number of Pt( en) 2+2 is 4 (rather than 2) since it has two bidentate ligands, which contain four donor atoms in total.

Any donor atom will give a pair of electrons. There are some donor atoms or groups which can offer more than one pair of electrons. Such are called bidentate (offers two pairs of electrons) or polydentate (offers more than two pairs of electrons). In some cases an atom or a group offers a pair of electrons to two similar or different central metal atoms or acceptors—by division of the electron pair—into a three-center two-electron bond. These are called bridging ligands.

History

The prehistory of coordination chemistry is very simple—there is virtually none (Kauffman et.al, 2006). Although coordination compounds have a long and honorable history of application, they were not recognized or systematically studied until the modern era. Coordination chemistry, like metallurgy, is a discipline in which technological and an esthetic application predated scientific investigation. Color has been fundamental to the cultural and historical development of modern society and is a characteristic of coordination chemistry (Orna, 2013). Probably one the first application of coordination chemistry was the use of mordant to fix dyes to fibres (Singh and Bharati, 2014) and there is evidence for the dying of cloth from 7000 BCE. The earliest dyes came from natural sources, such as plants, lichen, insects or fungi. These were extracted with water and transferred to the cloth by immersion of the fabric in the dye solution (Abel, 2012; Ferreira et.al, 2004). Some dyes alone gave good and permanent colors which did not wash off, but others only bound when additional substances, called mordant (French mordre, to bite), were present. Many of the commonest mordant are simple metal salts, in particular those of aluminum, copper, iron, chromium and tin. An early dye obtained from the root of the madder plant, Rubia tinctorum, contains alizarin (Bucklow, 2016). The general features responsible for binding the dye to a fibre involve metal ions coordinating to oxygen atoms of the alizarin and of the cloth—as a result, the dye is not removed from the fabric in a normal washing cycle. The red dyes entered popular culture and the description of British soldiers of the 18th and 19th centuries CE as “redcoats” refers to the use of Turkey Red (alizarin with an aluminum mordant) to dye their jackets. Trivial names such as Turkey Red identify the coloring material but give no clue as to their chemical constitution. Coordination complexes have been known since the beginning of modern chemistry. Early well-known coordination complexes include dyes such as Prussian blue. Their properties were first well understood in the late 1800s, following the 1869 work of Christian Wilhelm Blomstrand. Blomstrand developed what has come to be known as the complex ion chain theory. The theory claimed that the reason coordination complexes form is because in solution, ions would be bound via ammonia chains. He compared this effect to the way that various carbohydrate chains form.

     Copper and cobalt are essential trace metals to biological systems. Copper is present along with zinc in superoxide dismutase, which is a component of body’s defense mechanism (Martz, 2002). Copper has the ability to form coordination complex with ligands. The aqueous solution, copper (II) exists as [Cu(H2O)6]2+. This complex exhibits the fastest water exchange rate (speed of water ligands attaching and detaching) for any transition metal aquo complex. Adding aqeous sodium hydroxide causes the precipitation of light blue solid copper (II) hydroxide. (Wiley-Vch, 2007).

1.1.             Ligands

   Ligand is the species attached to a central metal atom / ion to form a coordination complex. The ligand is the electron rich compound with extra electrons. The nature of metal – ligand bonding can be covalent or ionic (Malik et al, 1999). Ligands can be anions, cations or neutral molecules. According to the number of donating atoms, the ligands may be bidentate, tridentate or polydentate. These may be simple ions such as Cl–, small molecules such as H2O or NH3, larger molecules such as H2NCH2CH2NH2 or N(CH2CH2NH2)3 or even macromolecules, such as proteins. When a ligand is bound to a metal ion through a single donor atom, as with Cl-, H2O or NH3, the ligand is said to be unidentate. When a ligand can bind through two donor atoms as in H2NCH2CH2NH2 (ethane-1,2-diamine) or C2O42– (oxalate), the ligand is said to be didentate and when several donor atoms are present in a single ligand as in N(CH2CH2NH2)3, the ligand is said to be polydentate (Prakash et al,2006).

    

1.2.            PURPOSE OF THE STUDY

        Transition metal such as copper and cobalt has led recent development of drugs which are based on metals. The study of these metal complexes may lead to a greater understanding of the role they play in biological systems, and may also contribute to the development of new metal-based drugs which may be considered to be candidates for pharmacological and therapeutic applications.

         In this current dispensation, we have been driven to so many advancement and higher technology in which so many company, scientist and organization are tensed to go higher in there level of more discovery and designating so many time, effort and money on research work.


1.3.            OBJECTIVE

The research work was done to understand:

          I.            Synthesis of complexes of copper II (Cu II) and cobalt II (Co II) with metronidazole and sulphamethoxazole in aqueous medium.

       II.            Identify the coordination site of the metal and ligands.

    III.            Evaluate the microbial activities of metal complexes on selected organisms/pathogens.

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