Consider the following complex ions, $P, Q$ and $R$. \[\boldsymbol{P}=[FeF_{6}]^{3-}, \boldsymbol{Q}=[V(H_{2}O)_{6}]^{2+}\text{ and }\boldsymbol{R}=[Fe(H_{2}O)_{6}]^{2+}.\] The correct order of the complex ions, according to their spin-only magnetic moment values (in B.M.) is

(B) $\boldsymbol{Q}<\boldsymbol{R}<\boldsymbol{P}$

(A) $\boldsymbol{R}<\boldsymbol{Q}<\boldsymbol{P}$

(C) $\boldsymbol{R}<\boldsymbol{P}<\boldsymbol{Q}$

(D) $\boldsymbol{Q}<\boldsymbol{P}<\boldsymbol{R}$

JEE Advanced · 2013 · 02 Jun 2013 · Paper 1 · Coordination Compounds

Consider the following complex ions,

P, Q

and

R

P = [F e F_{6}]^{3 -}, Q = [V (H_{2} O)_{6}]^{2 +} and R = [F e (H_{2} O)_{6}]^{2 +} .

The correct order of the complex ions, according to their spin-only magnetic moment values (in B.M.) is

Answer: (B)

For each complex, determine the number of unpaired electrons:

P:

[F e F_{6}]^{3 -}

F e^{3 +}

has configuration

3 d^{5}

F^{-}

is a weak field ligand → high spin → 5 unpaired electrons.

Q:

[V (H_{2} O)_{6}]^{2 +}

V^{2 +}

has configuration

3 d^{3}

→ 3 unpaired electrons.

R:

[F e (H_{2} O)_{6}]^{2 +}

F e^{2 +}

has configuration

3 d^{6}

H_{2} O

is a weak field ligand → high spin → 4 unpaired electrons.

Magnetic moment

μ = n (n + 2)

increases with number of unpaired electrons.

Order:

Q (3) < R (4) < P (5)

JEE Advanced · 2013 · 02 Jun 2013 · Paper 1 · Single correct option