1.

Mention the type of hybridisation and magnetic propety of the following complexex using VB theory a [FeF_6]^(4-)b)[Fe(CN)_6]^(4-)

Answer»

SOLUTION :` (a) [FeF_6]^(4-) ` : Fe atom -outer electronic configuration `3d^(6) 4S^(2) `
` (##SUR_CHE_XII_V01_C05_E12_001_S01.png" WIDTH="80%">
`F^(-) ` is weak field ligand In ` [FeF_6]^(4-) ` the hybridisation take place is ` sp^(3) d^(2) ` The number of unpaired electrons =4.
` therefore mu =sqrt( 4(4+2) ) =sqrt(24) =4.90 BM`
The MOLECULE is paramagnetic due to the presence of unpaired electrons The geometry of the molecules is octahedral
(b) `[Fe(CN)_6]^(4-) `
` (##SUR_CHE_XII_V01_C05_E12_001_S02.png" width="80%">
In ` [Fe(CN)_6^(4-)` complex ,the ` CN^(-) ` ligand is a powerful ligand it forces the unpaired electrons in the 3d level to pair um inside.
Hence the species has no unpaired electron after hybridisation ,So the molecule is diamagnetic
` (##SUR_CHE_XII_V01_C05_E12_001_S03.png" width="80%">
The geometry of the molecule is octahedral


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