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)]^(2+)`
D. `[Co(NH_(3))_(6)]^(2+)`

Answer

A

Explanation

Outer orbital complex utilises (n -1) d-orbitals for bonding and exhibit paramagnetic behaviour, only if there present unpaired electrons.
(a) In`[Ni(NH_(3))_(6)]^(2+)`:

So, this is an outer orbital complex as it involve 4d- orbitals for bonding, but having paramagnetic character.
(b) In `[Zn(NH_(3))_(6)]^(2+):`

Thus, it is also an outer orbital complex as it involve 4d-orbitals for bonding but it is diamagnetic as all the electrons are paired.
(c) In `[Cr(NH_(3))_(6)]^(3+),Cr^(3+)=[Ar]3d^(3)`

Because of the involvement of (n-1) d, i.e. 3d-orbital in hybridisation, it is an inner orbital complex. Its nature is paramagnetic because of the presence of three unpaired electrons.
(d) In `[Co(NH_(3))_(6)]^(3+):`

Because of the involvement of (n-1) d orbital in hybridisation, it is an inner orbital complex. As all the electrons are paired, it is a diamagnetic complex.