The complex ion which has the highest magnetic moment among the following is

Options

A. `[CoF_(6)]^(3-)`
B. `[Co(NH_(3))_(6)]^(3+)`
C. `[Ni(NH_(3))_(4)]^(2+)`
D. `[Ni(CN)_(4)]^(2-)`

Answer

A

Explanation

(i) In `[CoF_(6)]^(3-)` ion, the oxidation state of cobalt is +3.

Here, `F^(-)` ion provides a weak ligand field and is unable to pair up the unpaired electrons of the 3d-orbitals. Thus, it is highly paramagnetic.
(ii) In `[Co(NH_(3))_(6)]^(3+)` ion, `NH_(3)` provides a strong field ligand and the electrons of metal are made to pair up, so the complex will be diamagnetic.
Formation of `[Co(NH_(3))_(6)]^(3+)`

(iii) Similarly in `[Ni(NH_(3))_(4)]^(2+), NH_(3)` is a strong field ligand and the complex is diamagnetic.

(iv) `[Ni(CN)_(4)]^(2-)` has Ni in the +2 oxidation state and `"dsp"^(2)` hybridisation. Thus it is also diamagnetic.
(v) In `[Fe(CN)_(6)]^(4-)` ions, oxidation state of Fe is +2 and `CN^(-)` ligand is a strong field ligand. Thus the resulting complex ion involves `d^(2)sp^(3)` hybridisation and diamagnetic as it does not contain any unpaired electrons.

`because` Magnetic moment `= sqrt(n (n + 2))`
Where, n = no. of unpaired relectrons
`therefore [CoF_(6)]^(3-)` has maximum magnetic moment.