Types of Isomerism in Coordinate Compounds

1.GEOMETRIC ISOMERISM

More common in square planar complexes.

M M

b

b

a

a

a

a b

b

Cis form Trans form

Octahedral Complexes

M M

b

b

a

a

b

b b

b

Cis form Trans formb

b a

a

Octahedral Complexes

M M

b

b

a

a

b

b b

a

a

b a

a

Facial isomer

Meridional isomer

2.OPTICAL ISOMERS• Also called enantiomers.

• They are non superimposible mirror images of each other.

• Show chirality.

• More common in octahedral complexes.

• E.G. [Cr(C2O4)3]3-

• [PtCl2(en)2] 2+

• [CrCl2(en)(NH3)2]+

OPTICAL ISOMERS

Cr Cr

O

O

O

O

O

O

O O

O

O

O

O3- 3-

Recapitulation

• Name the two types of stereo isomers?

• What are the conditions necessary for geometric isomers?

• Which property of optical isomers is different?

• What are enantiomers?

3.IONISATION ISOMERS

• It occurs when the counter ions in the coordination compound is itself a potential ligand.

• They give different ions on ionization.

• e,.g. [Co(NO3)(NH3)5]SO4 & [Co(SO4)(NH3)5] NO3

• [PtCl2 (NH3)4]Br2 & [PtBr2 (NH3)4] Cl2

3.HYDRATE ISOMERS

• It is observed when water forms a part of coordination entity.

• [Cr (H2O)6] Cl3 - Violet

• [Cr Cl (H2O)5] Cl2.H2O - Pale Green

• [Cr Cl2 (H2O)4] Cl. 2H2O - Green

4.Linkage Isomers

• These are possible in complexes containing ambidentate ligands.

• E.g. [Co(NO2)(NH3)5]2+ &

• [Co(ONO)(NH3)5]2+

5.COORDINATION ISOMERISM• The cation & anion both are complex in such

types of isomers.• They arise due to interchange of ligands

between cation & anion entities.

• [Co(NH3)6] [Co(CN)6] & [Cr(NH3)6]

• [Co(CN)6]

• [Cu(NH3)4] [PtCl4] & [Pt (NH3)4] [CuCl4]

•

Recapitulation• Geomtetric isomer is common in ____________

& ______________complexes.• Compounds having water as a ligand show

_________isomerism.• ____________ is a didentate ligand.• Linkage isomerism arises due to _________.• Optical isomers have same _____ properties but

different __________ properties.

Home Assignment

• 1.What type of isomerism is exhibited by [PtCl2 (NH3)4]Br2 & [PtBr2 (NH3)4] Cl2?How will you differentiate between the two?

• 2.Draw the optical isomer of [CrCl2(en)(NH3)2]+

• 3.Illustrate the following with an example.

• Linkage isomer

• Coordination isomer.

VALENCE BOND THEORY• Given by Pauling in 1931.• Metal ligand bond arises by donation of pairs of

electrons by ligands to metal ion.• Metal ions must have requisite no. of vacant d-

orbitals of equal energy.• These orbitals of the metal atom hybridize to

give a set of hybrid orbitals.• Some times the unpaired electrons pair up to

make available a number of empty orbitals equal to its coordinatin no.

• With the approach of ligands , metal ligand bonds are formed.

• .

COMPLEXES HAVING C.N.-6

• [Cr(NH3)6] 3+, [Fe(CN)6]3-, (Inner orbital)-low spin

• [Co(F)6]3-(Outer orbital) -High spin

• d2sp3 or sp3 d2 hybridization

COMPLEXES HAVING C.N.-4

• Square Planar

• [Ni(CN)4] 2-

• [Cu(NH3)4] 2+

• dsp2 hybridization.

• Tetrahedral

• [Ni(CO)4]

• [Zn(NH3)4] 2+

• sp3 hybridization

DRAWBACKS OF VALENCE BOND THEORY

• Why some metal ion in a particular oxidation state are low spin while others are high spin.

• The magnetic behaviour predicted by VBT is misleading.

• It does not explain the colour of complexes.

CRYSTAL FIELD THEORY

• Given by Hans Bethe(1929) and John Vleck (1932).

• They assumed that the metal ligand bond is ionic arising purely from electrostatic interactions between metal ion & ligand.

• It treats each ligand as a point of negative charge.

• It considers the effect of ligands on the relative energies of the d- orbitals of the central atoms.

CRYSTAL FIELD THEORYIN OCTAHEDRAL COMPLEXES

∆0

dx2-y2,dz2

(eg)

dxy, dyz ,dxz( t2g )

• The difference in the energy between two sets of d-orbitals is called crystal field splitting energy.

• For any given metal ion , the magnitude of ∆0 depends on the nature of the ligands.

• I- <Br-< S2-<SCN->Cl-<F-< OH-< C2O42-<O2-

<H2O<NCS-<NH3<en<NO2-< CN-<CO

• It is known as spectrochemical series .The ligands with small value of ∆0 are called weak field ligands while those with with larger value are called strong field ligands.

CRYSTAL FIELD THEORYIN TETRAHEDRAL COMPLEXES

∆t

dx2-y2,dz2 (eg)

dxy, dyz ,dxz( t2g )

CRYSTAL FIELD THEORYIN SQUARE PLANAR COMPLEXES

dx2-y2

dxy

dz2

dxz, dyz