12.2.00 12:06 AM1 24.2 Isomers of Coordination Complexes

Isomers of Coordination Complexes

Coordination Chemistry

12.2.00 12:06 AM2 24.2 Isomers of Coordination Complexes

GeometryCoordinate Number (CN):

Number of donor atoms bonded to metal2- Coordinate - linear4 - Coordinate tetrahedral and sq planar

ML4 , Pt(II) is always CN = 4

6- OctahedralML6, Cr(III) and Co(III) CN = 6

CN influence by size of metal ion

surrounding ligand

Small metal /large ligand - Low coordinate number

Large metal / small ligand - High coordination number

i.e., FeF63- and FeCl4

- only

12.2.00 12:06 AM3 24.2 Isomers of Coordination Complexes

Historic PerspectiveDuring early / mid 1800’s bonding was not well understood. Most widely accepted theory on bonding was the chain theory supported by Sophus Jorgensen (1837 - 1914). The structure of Co(NH3)6Cl3 was explained in the classrooms using this theory in the late 1800’s. In 1890 Alfred Werner proposed a new bonding scheme and wrote a paper called “coordination theory”. In 1913 Werner won the 14th Noble Prize for his work.

12.2.00 12:06 AM4 24.2 Isomers of Coordination Complexes

Isomers -Same formula different properties. i.e., N2O NNO

or NONStructural isomer

Compd with different atomic bond connectivity. Coordination sphere isomer Linkage isomer

Stereoisomer Same atomic connectivity but different arrangement.Geometrical isomer Optical isomer

12.2.00 12:06 AM5 24.2 Isomers of Coordination Complexes

Structural isomer-Different Atomic connectivityCoordinate sphere isomer - Complexes in which

the ligand is bonded differently to the metal.Co 3Cl 6H2O

H

HH

Cl

OO

H

Co

H

O

OH

Cl

H

H Cl • 2H2O

H

H

H

OO

O

H

H

H

Co

O

H

HO

H

O

H

H

H

Cl3 H

H

H

O

H

O

O

H

H

Co

H

O

Cl

H

O

H

H

Cl2•H2O

i) six H2O in coordination sphere.

Violet

ii) five H2O and one Cl in coordination sphere.

Dark Green

iii) four H2O and two Cl in coordination sphere.

Green

12.2.00 12:06 AM6 24.2 Isomers of Coordination Complexes

Linkage IsomersLinkage isomer - Isomer complexes in

which the ligand coordinates to the metal by different donor atoms. i.e., Nitrite ion, NO2

-

Other ligand capable of switching donor atomSCN-, CN-, 2.2’-bipyridine

Nitrito ligand as an O-donorNitro ligand as an N-donor

12.2.00 12:06 AM7 24.2 Isomers of Coordination Complexes

Linkage Isomer of 2,2’-bipyridine

Two compounds formed by the linkage isomer of bpy is shown. Small changes in ligand bonding could result in dramatic chemical property change.

C

C

C

C

C

C

C

C

C

N

C

C

C

C

N

N

C

C

Ir

C

C

C

NC

N

C

N

C

C

C

C

C

C

C

C

C

CC

C

C

C

C

C

C

C

C

C

N

C

C

C

N

N

C

C

Ir

C

C

C

NC

N

C

N

C

C

C

C

C

C

C

C

C

C

Nitrogen bonded

Carbon Bonded

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Geometric Stereoisomer

Geometric isomer - Compounds with similar atomic connectivity but different atomic arrangement in space.

Diaminedichloroplatinum(II)

Cisplatin transplatinDiaminecisdichloroplatinum(II)

diaminetransdichloroplatinum(II)

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Mirror ImageMirror images cannot be exactly superimposed over

each other. Complexes which form mirror images are called chiral

Most of the human body is chiral (the hands). Enzymes are the most highly chiral substances known.

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Optical Isomers

Optical isomer - Isomer complex in which the atomic connection are the same but arrangement is such that the two complexes are not superimposable.

Optical isomers are called enantiomer.

Chiral Complexes are also called enatiomers

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Optical Inorganic Isomers

Enantiomer - Isomer that are mirror image to each other.

Handedness:

“R” “S”

Molecules/Ions that have enantiomer are chiral

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Optical Isomer and Interaction with Light

Enatiomers rotate the plane of polarized light.

Dextrorotatory- “d” isomer Complex which rotates plane of polarized light to

the right.Levorotatory- “l” isomer

Complex which rotates plane of polarized light to the left.

Chiral molecules are optically active because effect on light.