17. LECT17 - Classification OF Isomerism IN Transition Metal Complexes PDF

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CLASSIFICATION OF ISOMERISM IN TRANSITION METAL COMPLEXES 

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Stereoisomerism o Geometrical o Optical (Enantiomerism) Structural Isomerism o Ionisation o Hydrate o Coordination o Linkage o Ligand o (Polymerisation)

Geometrical Isomerism  

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Tetrahedral complexes – not found/expected Square planar complexes – frequently occurs o Can distinguish b/t 2 by measuring dipole moments /from IR spectroscopy  Measuring dipole moments:  Depends on where the e- are attracted to  (Cl)2Pt(NH3)2 pulls e- towards (Cl)2 polar molecule w/ direction towards Cl2 Octahedral complexes – very common o Facial isomer (fac): ligands of one type form equilateral triangle on one phas  1,2,3 isomer o Meridional isomer (mer): ligands of one type span 3 positions such that two trans to each other  1,2,6 isomer

Enantiomerism 

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Tetrahedral complexes – expected but too labile to be resolved o Tetrahedral complexes containing unsymmetrical chelate ligands are resolvable  Optically active as they don’t contain a plane of symmetry/inversion centre Square planar – very rare except w/ unusual chelation Octahedral – optical activity should occur in non-chelate complexes w/ 3/+ different ligands and no more that 2 of one kind o In practise these are not resolvable due to lability o Difficult to synthesise and separate from their geometrical isomers …

Ionisation Isomers 

Complex salts (cation + anion) w/ same composition but yielding different ions in solution

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Distinguish using AgCl – would form ppt w/ 2nd one

**chelating ligand = substance whose molecules can form several bonds to a single metal ion (eg. EDTA) RNH2 = amine NH3 = ammine

Ligand Isomerism  

NH2-CH2-CH2-CH2-NH2 o NH2-CH2-CH(NH2)-CH3 NCS = ambidentate ligand o Can bond through N and S o Isomer: CSN

Linkage Isomerism  

Molecule that can bond in two ways (i.e. NCS) Eg. Co-N(O)2 & Co-O-N=O Nitro nitrito

Coordination Isomerism    

[Co(NH3)5Cl] [CoF6]  [Co(NH3)5F] [CoF5Cl] same OS of ligands [Co(NH3)6] [CrF6]  [Cr(NH3)6] [CoF6]  [Co(NH3)2F4] [Cr(NH3)4F2]...