Question

The correct order of the spin-only magnetic moment of metal ions in the following low spin complexes,

\[\ce{[V(CN)6]^{4-}, [Fe(CN)6]^{4-}, [Ru(NH3)6]^{3+} and [Cr(NH3)6]^2}\] is:

विकल्प

• \[\ce{Cr^{2+} > Ru^{3+} > Fe^{2+} > V^{2+}}\]

• \[\ce{V^{2+} > Cr^{2+} > Ru^{3+} > Fe^{2+}}\]

• \[\ce{V^{2+} > Ru^{3+} > Cr^{2+} >  Fe^{2+}}\]

• \[\ce{Cr^{2+} > V^{2+} > Ru^{3+} >  Fe^{2+}}\]

Answer 1

\[\ce{V^{2+} > Cr^{2+} > Ru^{3+} > Fe^{2+}}\]

Explanation:

In presence of strong field ligands Δ₀ > p, therefore electronic configuration becomes 2g⁴ eg⁰ giving low spin complexes. All the given complexes have strong field ligands CN^- and NH₃ respectively. Therefore they form only low-spin complexes as shown below.

Complex	Oxidation state	Configuration	No. of unpaired electrons
\[\ce{[V(CN)6}]^{4-}\]	V2+	`"t"_(2"g")^3 "eg"^0`	3
\[\ce{[Fe(CN)6]^{4-}}\]	Fe2+	`"t"_(2"g")^6 "eg"^0`	0
\[\ce{[Ru(NH3)6]^{3+}}\]	Ru3+	`"t"_(2"g")^5 "eg"^0`	1
\[\ce{[Cr(NH3)4]^{2+}}\]	Cr3+	`"t"_(2"g")^4 "eg"^0`	2

Therefore the correct order of the spin-only magnetic moment of metal ions which forms low spin complexes as follows \[\ce{V^{2+} > Cr^{2+} > Ru^{3+} > Fe^{2+}}\].