Among the following complexes (K-P), $\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]$ ($\mathbf{K}$), $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]\mathrm{Cl}_{3}$ ($\mathbf{L}$), $\mathrm{Na}_{3}\left[\mathrm{Co}(\text{oxalate})_{3}\right]$ ($\mathbf{M}$), $\left[\mathrm{Ni}\left(\mathrm{H}_{2}\mathrm{O}\right)_{6}\right]\mathrm{Cl}_{2}$ ($\mathbf{N}$), $\mathrm{K}_{2}\left[\mathrm{Pt}(\mathrm{CN})_{4}\right]$ ($\mathbf{O}$) and $\left[\mathrm{Zn}\left(\mathrm{H}_{2}\mathrm{O}\right)_{6}\right]\left(\mathrm{NO}_{3}\right)_{2}$ ($\mathbf{P}$) the diamagnetic complexes are

JEE Advanced · 2011 · 10 Apr 2011 · Paper 2 · Coordination Compounds

Among the following complexes (K-P),

K_{3} [Fe (CN)_{6}]

(

K

[Co (NH_{3})_{6}] Cl_{3}

(

L

Na_{3} [Co (oxalate)_{3}]

(

M

[Ni (H_{2} O)_{6}] Cl_{2}

(

N

K_{2} [Pt (CN)_{4}]

(

O

) and

[Zn (H_{2} O)_{6}] (NO_{3})_{2}

(

P

) the diamagnetic complexes are

Answer: (C)

Diamagnetic complexes have all electrons paired (no unpaired electrons).

$L$ : $[Co (NH_{3})_{6}] Cl_{3}$ — $Co^{3 +}$ with strong-field $NH_{3}$ ligands, $d^{6}$ low-spin, all paired → diamagnetic
$M$ : $Na_{3} [Co (oxalate)_{3}]$ — $Co^{3 +}$ with strong-field oxalate, $d^{6}$ low-spin → diamagnetic
$O$ : $K_{2} [Pt (CN)_{4}]$ — $Pt^{2 +}$ with strong-field $CN^{-}$ , $d^{8}$ square planar, all paired → diamagnetic
$P$ : $[Zn (H_{2} O)_{6}] (NO_{3})_{2}$ — $Zn^{2 +}$ is $d^{10}$ , all paired → diamagnetic

Thus L, M, O, P are diamagnetic.

JEE Advanced · 2011 · 10 Apr 2011 · Paper 2 · Single correct option