Which one of the following is an outer orbital complex and exhibits paramagnetic behaviour ?

Options

A. `[Ni(NH_(3))_(6)]^(2+)`
B. `[Zn(NH_(3))_(6)]^(2+)`
C. `[Cr(NH_(3))_(6)]^(3+)`
D. `[Co(NH_(3))_(6)]^(3+)`

Answer

A

Explanation

In the formation of an outer orbital (or high spin or sopin free) complex, an outer orbital d orbital (4d) is used in hybridisation `(sp^(3) d^(2))` whil in the formation of an inner d orbital (3d) is used in hybridization.
`[Ni(NH_(3))_(6)]^(2+)`

Thus it is an outer complex and is paramagnetic due to two unpaired electrons.
`[Zn(NH_(3))_(6)]^(2+)`

It is also an outer complex but is diamagnetic due to zero unpaired electrons.
`[Cr(NH_(3))_(6)]^(3+)`

It is an inner orbital complex and is paramagnetic due to three unpaired electrons.
`[Co(NH_(3))_(6)]^(3+)`

It is an inner orbital complex and is diamagnetic due to zero unpaired electrons.