Which of the following complexes diamagnetic:

Options

A. `[AuI_(4)]^(Θ)`
B. `[Co(H_(2)O)_(6)]^(3+)`
C. `[CoI_(6)]^(3-)`
D. `[Co(CO)_(4)]^(Θ)`

Answer

A, D

Explanation

`Au^(3+)` (ground state)
Although `CI^(Θ)` is a weak ligand but due to high `Z_(eff)` value of `Au^(3+)` unpaired electrons will pair up
Hybridisation `dsp^(2)` shape square planar `(n=0)` `mu_(eff)=0`(Diamagnetic)
(b) `[Co^(III)(H_(2)O))_(6)]^(3+),(Co^(3+) =3d^(6))`(weak field ligand)
`(n =4)` Hybridisation `sp^(3)d^(2)mu_(eff) = sqrt24BM`
(Paramagnetic)
(c ) `[Co^(III)I_(6)]^(3-),(CO^(3+)=3d^(6))` (weak field ligand)
`(n =4)` Hybridisation `sp^(3)d^(2),mu_(eff) = sqrt24BM`
(Paramagnetic)
(d) `[Co^(-1)(CO)_(4)]^(Θ),Co^(-1) = 3d^(8) 4s^(2)` (strong field ligand)