Question

Consider the following complex ions, $P,Q$ and $R$.
$P=[Fe{F}_6{]}^{3-},Q=[V(H_{2}O{)}_6{]}^{2+}andR=[Fe(H_{2}O{)}_6{]}^{2+}$
The correct order of the complex ions, according to their spin-only magnetic moment values (in $B.M.$) is

• A. $R<Q<P$
• B. $Q<R<P$
• C. $R<P<Q$
• D. $Q<P<R$

Answer 1

Answer: (B)

PLAN Spin only magnetic moment have the formula $\sqrt{n(n+2)}BM,$
where N is tr.e number of unpaired electrons. In the presence of
weak ligand (as $H_{2}O,C{I}^{-},F^{-})$ there is no pairing of electrons,
and electrons donated by ligands are filled in outer vacant
orbitals
In the presence of strong ligand (as $C{N}^{-},CO,N{H}_3,en)$
electrons are paired and electrons from ligands are filled in
available inner orbitals
Thus, order of spin-only magnetic moment = Q < R < P