Isomerism

Isomerism in Co-ordination complexes

1. Shri shankaracharya mahavidyalaya junwani , bhilai Presented by Dr. Neelam Department of chemistry Isomerism in coordination chemistry

2. ISOMERISM Compound having same molecular formula but different physical & chemical properties difference properties because of different structure difference properties because of different orientation

3. STRUCTURAL ISOMERISM : Compound having same mol. formula difference in physical properties because of different structure. (A) Ionisation isomerism : This type of isomerism occurs when the counter ion in a coordination compound is itself a potential ligand and can displace a ligand which can then become the counter ion. For example: (B) Solvate / hydrate isomerism : It occurs when water forms a part of the coordination entity or is outside it. This is similar to ionisation isomerism. For examples:

4. (C) Linkage isomerism : In some ligands , like ambidentate ligands , there are two possible coordination sites. In such cases, linkage isomerism exist. NO 2 group can be bonded to metal ions through (-NO 2 ) or (-ONO), SCN : (-SCN) or (-NCS). (D) Coordination isomerism : Coordination compounds made up of cationic and anionic coordination entities show this type of isomerism due to the interchange of ligands between the cation and anion entities. For examples:

5. (E) Ligand isomerism : Since many ligands are organic compounds which have possibilities for isomerism, the resulting complexes can show isomerism from this source. For example : ligands 1,2-diaminopropane( propylenediamine or pn ) and 1,3-diaminopropane( trimethylenediamine or tn ) (F) Polymerisation isomerism : Considered to be a special case of coordination isomerism, in this the various isomers differ in formula weight from one another For example : These all have the empirical formula [Pt(NH 3 ) 2 Cl 2 ] 1: 2 :2 [Pt(NH 3 ) 2 Cl 2 ] Pt:NH 3 :Cl 1: 2 :2 [Pt(NH 3 ) 4 ] [PtCl 4 ] Pt:NH 3 :Cl 2: 4 :4

6. Stereoisomers : Compound having same mol. formula difference in physical properties because of different orientation. Geometrical Isomerism Cis isomer When ligands are present on same side When ligands are present at 90 to each other trans isomer When ligands are present on opposite side When ligands are present at 180 to each other

7. Coordination Number Four : Tetrahedral Complex : The tetrahedral compounds can not show geometrical isomerism as we all know that all four positions are equivalent in tetrahedral geometry. [MA 4 ], [MA 3 B ] not show G. I. Square Planar Complex : In a square planar complex of formula [MA 2 B 2 ] [A and B are unidentate ], the two ligands .A. may be arranged adjacent to each other in a cis isomer, or opposite to each other in a trans isomer as depicted. [MA 2 B 2 ], [M(AB) 2 ], [MA 2 BC], [MABCD] show G. I.

8. Coordination Number 6 : Geometrical isomerism is also possible in octahedral complexes. [MA 6 ], [MA 5 B], [M(AA) 3 ] not show G. I. [MA 2 B 2 C 2 ], [MA 2 B 2 CD], [MA 2 BCE], [MABCDEF], [M(AB) 3 ], [MA 4 B 2 ], [MA 3 B 3 ] show G. I. Optical Isomerism : Plane of symmetry Center of symmetry Axis of symmetry Should not be present

9. Tetrahedral complexes with formula [MABCD] show optical isomers and octahedral complexes ( cis form) exhibit optical isomerism. Optical isomerism is common in octahedral complexes involving didentate ligands . Cis -isomer of [PtCl 2 (en) 2 ] 2+ show optical isomerism as shown below because of the absence of plane of symmetry as well as centre of symmetry.

10. 10 Thank you