Question

Explain the following giving reasons
(a) `[NiCI_(4)]^(2-)` is tetrahedral and paramagnetic whereas `[Ni(CN)_(4)]^(2-)` is square plannar and dimagnetic
(b) `[Fe(H_(2)O)_(6)]^(3+)` ion is more paramagnetic than `[Fe(CN)_(6)]^(3-)` ion
(c ) `Ni(CO)_(4)` is tetrahedral while `[Ni(CN)_(4)]^(2-)` ion is square planar
(d) `[Co(F_(6))]^(3-)` is a high spin complex whereas `[Co(CN)_(6)]^(3-)` ion is a low spin complex .

Answer 1

In the complex, `[NiCI_(4)]^(2)` and `[Ni(CN)_(4)]^(2-)` oxidation state of `Ni is + 2 ion `


Since `CI^(Θ)` ion is weak field ligand electronic configuration of `Ni^(2+)` in `[NiCI_(4)]^(2-)` remains the same

Since `Ni^(2+)` in `[NiCI_(4)]^(2-)` ion is `sp^(3)` hybridised and have two unpaired electrons it is tetrahedral and paramagnetic
Since `CN^(Θ)` ion is strong field ligand electronic configuration of `Ni^(2+)` in `[Ni(CN)_(4)]^(2-)` is

one electron from `3d_(x2) -_(y2)` orbital gets paired with that in `3d_(z2)` ortbital Thus one d-orbital `(3d_(x2)- _(y2)` orbital)` becomes available for `dsp^(2)` hybridisation which gives square planar geometry with `n=0` The `[Ni(CN)_(4)]^(2-)` is diamagentic
(b) Oxidation state of Fein `[Fe(H_(2)O)_(6)]^(3+)` ion is `+3`


Since `H_(2)O` is weak field ligand no pairing of electrons takes place and

i.e there are 5 uppaired electrons `n=5`
`Whereeas in `[Fe(CN)_(6)]^(3-)` oxidation state of `Fe is + 3`
Since `CN^(Θ)` ion is strong field ligand pairing up of electrons in `3d` orbitals takes place is
i.e. there is only one unpaired electron `n=1`
Since in `[Fe(H_(2)O)_(6)_(6)]^(3+)` ion number of unpaired electrons are more than `[Fe(CN)_(6)]^(3-)` ion,`[Fe(H_(2)O)_(6)]^(3+)`
more is paramagnetic `[Fe(CN)_(6)]^(3-)` ion
(c ) In `Ni (CO)_(4)` oxidation state of Ni is zero
Since `Co` is strong field ligands hence pairing of electrons takes place
Because of `sp^(3)` hybridisation `[Ni(CO)_(4)]` is tetrahedral In `[Ni(CN)_(4)]^(2)` oxidation state of `Ni is+2`
Since `CN^(Θ)` is strong field which results in pairing up of electron present in `3d_(x2)- _(y2)` and `3dd_(x2)-_(y2)` becomes available for `dsp^(2)` hybridisation
(d) `[CoF_(6)]^(3-)` is a high spin complex wherese `[Co(CN)_(6)]^(3-)` is alow spin complex This can be explained as
Since `F^(Θ)` ion is weak field ligand no pairing up of electrons present `3d` orbital takes place Since there are four unpaired electrons `[CoF_(6)]^(3-)` is paramagnetic complex Since outer orbitals (i.e 4d) are involved it is also known as high spin or outer orbital complex
Oxalate generally behaves as a weak fiels ligand but with `Co` it behaves as a strong field ligand like `NH_(3)` and `H_(2)O`
In `[Co(CN)_(6)]^(3-)` oxidation sate of Co is `+3`
Since `CN^(Θ)` is a strong field ligands pairing of `3d` electrons takes place `n=0` Since inner d orbitals `(3d)` are involved in hybridistion `(d^(2)sp^(3))` it is also known as low spin or inner orbital complex
In `[COF_(6)]^(3-), n =4` whereas in `[Co(CN_(6)]^(3-) , n=0` hence `[CoF_(6)]^(3-)` is a high spin complex whereas `[Co(CN)_(6)]^(3-)` is a low spin complex .