Lecture for B.Sc (III) On Organometallic Chemistry By Dr. Sheerin Masroor COORDINATION COMPOUNDS

 When metal atom is bound number of anions or neutral molecules.  In modern terminology such compounds are called coordination compounds.  Examples contains, Chlorophyll, haemoglobin and vitamin B12 are coordination compounds of magnesium, iron and cobalt respectively.  Coordination compounds also find many applications in electroplating, textile dyeing and medicinal chemistry. Chlorophyll Haemoglobin

Vitamin B-12 COMPONENTS OF COORDINATION COMPOUND COORDINATION ENTITY

 It contains a central metal atom or ion bonded to a fixed number of ions or molecules.

 For example, [CoCl3 (NH3 )3 ].  Here cobalt ion is surrounded by three ammonia molecules and three chloride ions.

 [Ni(CO)4 ],

 [PtCl2 (NH3 )2 ], 4–  [Fe(CN)6 ] , 3+  [Co(NH3 )6 ] . CENTRAL ATOM/ION

 The atom/ion with which a fixed number of ions/groups are bound in a definite structure/geometrical arrangement around it.  For example,

 [NiCl2 (H2O)4 ] 2+  [CoCl(NH3)5] and 3–  [Fe(CN)6 ]  The central atoms/ions in example are Ni2+, Co3+ and Fe3+, respectively which can also referred to as Lewis acids. LIGANDS

 These are ions or molecules bound to the central atom/ion in the coordination entity.  Example includes simple ions such as Cl– , small

molecules such as H2O or NH3 , larger molecules such as H2NCH2CH2NH2 (ethylenediamine) or even macromolecules, such as proteins. DENTICITY

 It is the number of donor groups present in a single or specific ligand that is binded to a central atom in a coordination complex. UNIDENTATE/MONODENTATE

 These are Lewis bases that are able to donate a single pair or mono number of electrons to a metal atom.  They can be either ions (usually anions) or neutral molecules.  Ligands with only one donor atom. - -  e.g. NH3, Cl , F etc. BIDENTATE/DIDENTATE

 They are Lewis bases that are able to donate two pairs ("bi") of electrons to a metal atom.  They have two donor atoms which can bind to a central metal atom or ion at two points.  Common examples of bidentate ligands are ethylenediamine (en), and the oxalate ion (ox). TRIDENTATE/TERDENTATE

 It has three atoms that can function as donor atoms in a coordination complex.  Forexample: diethylenetriamine, iminodiacetate anion. TETRADENTATE

 Tetradentate ligands are ligands that bind with four donor atoms to a central atom to form a coordination complex. This number of donor atoms that bind is called denticity and is a way to classify ligands.  Examples: Porphyrin, Phthalocyanine (artificial macrocyclic tetradentate ligand that is used to make blue and green pigments). PENTADENTATE

 They bind with five atoms, an example being ethylenediaminetriacetic acid. HEXADENTATE

 It bind with six atoms, an example being EDTA (ethylenediaminetetraacetate) (although it can also binds in a tetradentate manner too). AMBIDENTATE LIGAND

 These are kind of ligands which can ligate through two different atoms with metal is called ambidentate ligand.  Examples of such ligands are the NO2– and SCN– ions. NO2– ion can coordinate either through nitrogen or through oxygen to a central metal atom/ion. Similarly, SCN– ion can coordinate through the sulphur or nitrogen atom. COORDINATION NUMBER

 The coordination number (CN) of a metal ion in a complex can be defined as the number of ligand donor atoms to which the metal is directly bonded. 2–  For example, in the complex ions, [PtCl6] and 2+ [Ni(NH3)4] , the coordination number of Pt and Ni are 6 and 4 respectively. COORDINATION SPHERE

 The central metal atom or ion and the ligands attached to it are further enclosed in square bracket which can be collectively called as the coordination sphere.  While the CounterIon are the ionisable groups present outside the bracket.

 For example, in the complex K4[Fe(CN)6], the 4– coordination sphere is [Fe(CN)6] and the counter ion is K+. COORDINATION POLYHEDRON  It is the spatial arrangement of the ligand atoms which are directly attached to the central atom/ion .  The most common coordination polyhedra are octahedral, square planar and tetrahedral. 3+  For example, [Co(NH3)6] is octahedral,

 [Ni(CO)4] is tetrahedral and 2–  [PtCl4] is square planar. OXIDATION NUMBER OF CENTRAL METAL ION

 It is the charge a central metal ion would carry if all the ligands are removed from it along with the electron pairs that are shared with the central atom.  The oxidation number can be presented by a Roman numeral covered in parenthesis following the name of the coordination entity.  Example, oxidation number of copper in 3– [Cu(CN)4] is +1 and it is written as Cu(I). HOMOLEPTIC AND HETEROLEPTIC COMPLEXES

 Complexes where a metal is bound to only one kind of donor groups or ligands. 3+  For Example, [Co(NH3)6] .  Complexes where a metal is bound to more than one kind of donor groups or ligands. +  For Example, [Co(NH3)4Cl2] , are known as heteroleptic. •Organometallic chemistry, the chemistry of compounds containing metal-carbon bonds.

•It have a wide variety of chemical compounds and their reactions.

•Have compounds containing both σ and π bonds between metal atoms and carbon.

•For Example many cluster compounds, containing one or more metal-metal bonds.

[Cr(H2O)6] is a coordination complex.

[Cr(CO)6 ] is an organometallic compound which involve metal-carbon bond.

•General applications contains catalysts.