The spin only magnetic moment value for the complex $[\mathrm{Co}(\mathrm{CN})_{6}]^{4-}$ is ____ BM. [At. No. of $\mathrm{Co}=27$]

JEE Main · 2021 · 20 Jul 2021 · Shift 1 · Coordination Compounds

The spin only magnetic moment value for the complex

[Co (CN)_{6}]^{4 -}

is ____ BM.
[At. No. of

Co = 27

]

Answer: 1.73

Solution

Each cyanide carries one negative charge, so in

[Co (CN)_{6}]^{4 -}

cobalt is in the

+ 2

state with the configuration

[Ar] 3 d^{7}

. Cyanide is a strong field ligand and the octahedral splitting exceeds the pairing energy, so the seven electrons arrange as

t_{2 g}^{6} e_{g}^{1}

and just one remains unpaired. The spin only moment follows as

μ = n (n + 2) = 1 \times 3 = 1.73 BM

The spin only magnetic moment of the complex is

1.73 BM

JEE Main · 2021 · 20 Jul 2021 · Shift 1 · Numerical answer

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