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)]^(2+)`
B. `[Fe(en)(py)(NH_(3))_(2)]^(2+)`
C. `[Co("ox")_(2)(OH)_(2)]^(-)`
D. `[Ti(NH_(3))_(6)]^(3+)`

Answer

C

Explanation

The electronic configuration of `V(23)=[Ar]4s^(2),3d^(3)`
Let in `[V(gly)_(2)(OH)_(2)(NH_(3))_(2)]^(+)` oxidation state of V is x.
`x+(-1)xx2+(-1)2+(0xx2)=+1`
`x=+5`
`V^(5+)=[Ar] 4s^(0), 3d^(0)` (no unpaired electrons)
Theelectronic configuration of
`Fe(26)=[Ar] 4s^(2), 3d^(6)`
Let the oxidation state of `[Fe(en)(ppy)(NH_(3))_(2)]^(2+)` is x.
`[x+(0)+(0)+(0)xx2]=+2`
`x=+2`
`Fe^(2+)=[Ar], 3d^(6)(because 4 "unpaired electron")` but, bpy, en and `NH_(3)` all are strong field ligands, so pairing occurs and thus, `Fe^(2+)` contains no unpaired electron
The electronic configuration of
`Co(27)=[Ar] 4s^(2),3d^(7)`
Let the oxidation state Co in `[Co(o x)_(2)(OH)_(2)]^(-)` is x
`x+(-2)xx2+(-1)xx2=-1`
`x=+5`
`Co^(5+)=[Ar].3d^(4)` [4 unpaired electrons]
ox and OH are weak field ligands, thus pairing of electron units does not occur.
The electronic configuration of `Ti(22)=[Ar] 4s^(2), 3d^(2)`
Oxidation state of Ti in `[Ti(NH_(3))_(6)]^(3+)` is 3.
`Ti^(3+)=[Ar] 3d^(1)` (one unpaired electron) Hence, complex `[Co(o x)_(2)(OH)_(2)]^(-)` has maximum number of unpaired electrons, thus show maximum paramagnetism