Which of the following complexes exhibits the highest paramagnetic behaviour?
where gly=glycine, en=ethylenediamine and bipy =bipyridyl
(At. no. `Ti=22, V=23, Fe=26, Co=27`)

Options

A. `[V(gly)_(2) (OH)_(2) (NH_(3))_(2)]^(+)`
B. `[Fe(en) (bgy) (NH_(3))_(2)]^(2+)`
C. `[Co(ox)_(2) (OH)_(2)]`
D. `[Ti(NH_(3))_(6)]^(3+)`

Answer

C

Explanation

Greater is the number of unpaired electrons, larger is the paramagnetism. `[V(gly)_(2) (OH)_(2) (NH_(3))_(2)]^(+)`
`V_(23)=[Ar]3d^(3), 4s^(2) `

`V^(5+)=[Ar]3d^(0)`
`[Fe(en) (bpy) (NH_(3))_(2)]^(2+)`
`Fe_(26)=[Ar]3d^(6), 4s^(2)`
`Fe^(2+)=[Ar]^(3) d^(6)`

But en, bpy and `NH_3` all are strong field ligands, so pairing occurs, thus no unpaired electrons.
`[Co(ox)_(2) (OH)_(2)]^(-)`
`Co(27)=[Ar] 3d^(7), 4s^(2)`
`Co^(5+)=[Ar] 3d^(4)`
`[Ti(NH_(3))_(6)]^(3+)`
`Ti_(22)=[Ar] 3d^(2), 4s^(2)`
`Ti^(3+) =[Ar] 3d^(1)`

Hence `[Co(ox)_(2) (OH)_(2)]^(-)` has highest paramagnetic behaviour.