Coordination chemistry

Coordination complexes, Formation of coordination complexes, Significance of Coordination chemistry, Important terminologies in coordination chemistry with examples, Types of ligands and types of complexes, Werner’s theory of coordination compounds
with postulates, his experiments and observation, Limitations of Werner theory

1. COORDINATION CHEMISTRY PART - I By, J.PADMAPRIYA, M.Sc.

2. CONTENTS : Coordination complexes, Important terminologies, Types of ligands and complexes and Werner’s Theory.

3. COORDINATION COMPLEXES Derived from Latin words, How a coordination compound will form? Covalent bond - mutual sharing of electrons b/w two atoms. Coordinate covalent bond – one atom acts as Lewis acid (e - pair acceptor) another atom acts as Lewis base (e - pair donor) Most of the transition / d-block elements form coordination compounds.

4. Significance : Play a vital role in the biological functions, and Wide range of catalytic applications in chemical industries. Examples: Haemoglobin – iron complex, oxygen transporter of human.

5. Cobalamine – cobalt complex, an essential vitamin. Chlorophyll – Mg complex, helps in photosynthesis. Industries - Wilkinson's compound, Ziegler Natta compound are used as catalysts.

6. Werner’s theory of coordination compounds Alfred Werner – Swiss chemist – 1 st proposed this theory and explained bonding in complexes. Imaginary theory and did not have any modern instrumental techniques. This study was made using simple chemical reactions. He got Nobel prize in 1913 for his work. So he is called as “ Father of Coordination Chemistry ”.

7. Postulates: There are 2 types of valencies : Primary valency , S econdary valency . PRIMARY VALENCY SECONDARY VALENCY Corresponds to oxidation state of CMA. Corresponds to Coordination number of CMA. Always satisfied by negative ions. Satisfied by negative or positive or neutral ions called Ligands. Shown by dotted lines. Shown in thick lines and in square brackets. Non – directional in nature. Directional in nature. Ionisable valency . Non – ionisable valency .

8. In general, all the elements tend to satisfy both primary and secondary valency . But fulfillment of secondary valency is more essential. Spatial arrangement : no. of. ligands – 6 – Octahedral no. of ligands – 4 – Tetrahedral or Square planar. His experiment: He has taken different coloured cobalt (III) chloride with ammonia complexes and made to react with AgNO 3 and tested conductivity. CoCl 3 . 6NH 3 - [Co(NH 3 ) 6 ]Cl 3 CoCl 3 . 5NH 3 - [Co(NH 3 ) 5 Cl]Cl 2 CoCl 3 . 4NH 3 - [Co(NH 3 ) 4 Cl 2 ]Cl CoCl 3 . 3NH 3 - [Co(NH 3 ) 3 Cl 3 ].

9. Member Formula Complex No.of . Ions in solution Conductivity (mho) A CoCl 3 . 6NH 3 [Co(NH 3 ) 6 ]Cl 3 4(3+1) ~409 B CoCl 3 . 5NH 3 [Co(NH 3 ) 5 Cl]Cl 2 3(2+1) ~209 C CoCl 3 . 4NH 3 [Co(NH 3 ) 4 Cl 2 ]Cl 2(1+1) ~97 D CoCl 3 . 3NH 3 [Co(NH 3 ) 3 Cl 3 ] His Observation

10. Limitations: It fails to explain the colour of the complexes. It does not explain the magnetic and optical properties of complexes. This theory could not explain the directional properties of various compounds.

11. THANK YOU