The observed magnetic moment of the complex $\left[\mathrm{Mn}(\underline{\mathrm{NCS}})_{6}\right]^{\mathrm{x}-}$ is 6.06 BM. The numerical value of x is ____:

JEE Main · 2023 · 08 Apr 2023 · Shift 2 · Coordination Compounds

The observed magnetic moment of the complex

[Mn (\underline{NCS})_{6}]^{x -}

is 6.06 BM. The numerical value of x is ____:

Answer: 4

Solution

The spin-only magnetic moment is

μ = n (n + 2)

BM. A moment of about 6 BM corresponds to

n (n + 2) \approx 35

, which gives

n = 5

unpaired electrons. Five unpaired electrons require a

d^{5}

configuration, and for manganese this means the

Mn^{2 +}

ion, since the thiocyanate ion is a weak field ligand and does not force pairing. With manganese in the

+ 2

state and six singly charged

NCS^{-}

ligands, the overall charge is

2 + 6 (- 1) = - 4

. The value of

x

is therefore 4.

JEE Main · 2023 · 08 Apr 2023 · Shift 2 · Integer answer

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