DR PREM YADAV Assistant Professor - PowerPoint Presentation

1. DR PREM YADAVAssistant ProfessorDepartment of ChemistryN.S.P.S. Government PG CollegeMagarah, Mirzapur (U.P.) INDIAe.mail: prem77yadav@gmail.comE- Content- B.Sc. II Inorganic chemistryTopicBASIC CONCEPT OF COORDINATION COMPOUND

2. CONTENTS PART:AHistory of coordination compounds DefinitionTerms use in Coordination CompoundType of LigandExamples of ligandNomenclatureEffective atomic Number(EAN)Werner’s theory

3. History of coordination compounds The first scientifically recorded observation of a completely inorganic coordination compound is German chemist, physician, and alchemist Andreas Libavius’s description in 1597 of the blue colour (due to [Cu(NH3)4]2+) formed when lime water containing sal ammoniac (NH4Cl) comes into contact with brass. In 18th century, another example of a coordination compound is the substance Prussian blue, with formula KFe[Fe(CN)6], which has been used as an artist’s pigment. Another early example of the preparation of a coordination compound is the use in 1760 of a sparingly soluble compound, potassium hexachloroplatinate(2−), K2[PtCl6], to refine the element platinum. The exact date of preparation of the first coordination compound is not exactly known. The discovery of Hexa ammine cobalt (III) chloride [Co(NH3)6]Cl3 by the French chemist B.M. Tassaert in 1798, is generally regarded as the beginning of coordination chemistry

4. Cont…. In the 19th century, as more complexes were discovered, a number of theories were proposed to account for their formation and properties. The most successful and widely accepted of these theories was the so-called chain theory (1869) of the Swedish chemist Christian Wilhelm Blomstrand Chain Theory was modified and developed by the Danish chemist Sophus Mads Jørgensen. Jørgensen’s extensive preparations of numerous complexes provided the experimental foundation not only for the Blomstrand-Jørgensen chain theory but for Alsatian-born Swiss chemist Alfred Werner’s coordination theory (1893) as well. Werner was the first inorganic chemist to be awarded the noble prize in chemistry (1913) Alfred Werner Swiss chemist put forward a theory to explain the formation of complex compound. It was the first successful explanation, become famous as the coordination theory of complex compounds, which is also known as Werner’s theory

5. DEFINITIONCoordination compounds are species in which a central metal ion (or atom) is attached to a group of surrounding molecules or ions by coordinate covalent bonds Surrounding groups are called Ligands Central metal is a Lewis acid. Ligand is a Lewis base.Coordination compounds are those molecular compounds which retain their identities when dissolved in water or any solvent.EXAMPLE: K4[Fe(CN)6] K2[PtCl4] [Co(en)2Cl2]Cl Pt(NH3)2Cl2

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7. TERMS USE IN COORDINATION COMPOUNDCentral ion or centre of coordination: Cation in which one or more neutral molecules or anion are attached Coordination Number: The number of donor atoms bound to the central atom or ionOxidation Number: represents the electric charge on the central metal atom Coordination sphere: ligands and metal combine to form the coordination sphereCharge of a complex: Sum of the charges on central metal and ligandsLigand :The Lewis bases that bind (coordinate) to the metal atom or ion are called ligands

8. Diagrammatically……

9. Type of LIGAND Monodentate ligands bond using the electron pairs of a single atom.• Bidentate ligands bond using the electron pairs of two atoms.• Polydentate ligands bond using the electron pairs of many atoms. This group includes Tridentate, Tetradentate, Pentadentate, Hexadentate etc.Ambidentate Ligands two or more donor atoms but in forming complexes only one donor atoms is attached to the metal ion at a given time.

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11. Nomenclature of Coordination CompoundsThe system of naming coordination complexes is in some ways similar to and in other ways different from naming simple inorganic salts. The rules for nomenclature are: Name the cation first and anion second. Within a complex ion, the ligands are named alphabetical order. Numbering prefixes (e.g. di, tri, …) are not used in alphabetizing. Anionic ligands end in the letter “-o,” while neutral molecules (with a few exceptions) retain their names. The prefixes di-, tri-, tetra-, penta- and hexa- are used to indicate the number of each ligand. If the ligand name includes such a prefix, the ligand name should be placed in parentheses and preceded by bis- (2), tris- (3), tetrakis- (4), pentakis- (5), and hexakis- (6). If a complex is an anion, it should end in “-ate.” Place the metal oxidation number in parentheses as a Roman numeral

12. Examples [Cr(H2O)5Cl]SO4 pentaaaquachlorochromium(III) sulfate [Cr(H2O)5Cl]2+ pentaaquachlorochromium(III) ion [Cr(NH3)3Cl3] triamminetrichlorochromium(III) K2[PtCl4] potassium tetrachloroplatinate(II)[Co(en)2Cl2]Cl dichlorobis(ethylenediamine)cobalt(III) chloride Pt(NH3)2Cl2 diamminedichloroplatinum(II)K2[PtCl4] potassium tetrachloroplatinate(II)[PtCl4]2– tetrachloroplatinate(II) ion[Co(en)2Cl2]Cl dichlorobis(ethylenediamine)cobalt(III) chloride[Cu(NH3)4]SO4 tetraamminecopper(II)sulfateK4[Fe(CN)6] potassium hexacyanoferrate(II)[Cr(NH3)6][IrCl6] hexaamminechromium(III) hexachloroiridate(III)[Cr(H2O)2BrClFI]– diaquabromochlorofluoroiodochromate(III) ion

13. EFFECTIVE ATOMIC NUMBER(EAN)Effective atomic number (EAN), number that represents the total number of electrons surrounding the nucleus of a metal atom in a metal complex. The tendency to attain an inert gas configuration is a significant factor. It is composed of the metal atom's electrons and the bonding electrons from the surrounding electron-donating atoms and molecules. EAN = Atomic number of the metal +(Number of ligands X electrons donated by each ligand) - positive oxidation state of the metal For example, Fe ⇒ atomic number is 26 and forming a complex, [Fe(CN)6]4– the number of electrons lost = 2 the number of electrons gained = 12  So, EAN = 36 It is used to check the stability of metal in coordination complex.

14. WERNER’S THEORYAlfred Werner Swiss Chemist put forward a theory to explain the formation and structure of complex compounds which is later termed as Werner’s Theory of Coordinate Compounds.Due to this theory he is awarded by Nobel Prize and he is also called the ‘Father of Coordination Chemistry’

15. Postulates of Werner’s Theory The important postulates of Werner’s theory are as follows:In coordination compounds, the central metal or metal atoms exhibit two types of valency- primary valency and the secondary valency The primary valency corresponds to oxidation state and the secondary valency corresponds to coordinate number.Every metal atom has a fixed number of secondary valencies, i.e It has fixed coordinate number. The metal atom tends to satisfy its both primary and secondary valancies. Primary valency is satisfied by negative ion whereas secondary valancies are satisfied by negative ion or by neutral molecules. The secondary valancies are always directed towards fixed position in space and this cause definite geometry of the coordinate compound. The secondary valency thus determines the stereochemistry of the complex ion. On the other hand, the primary valency is non-directional.

16. THANKSReferences: Principle of Inorganic Chemistry by Puri, Sharma & KalliaConcise of Inorganic Chemistry by J.D.Lee

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