Which one of the following coordination complexes exhibit the lowest value of magnetic moment (in BM)?

Options

A. `[Cr(CN)_(6)]^(3-)`
B. `[Mn(CN)_(6)]^(3-)`
C. `[Fe(CN)_(6)]^(3-)`
D. `[Co(CN)_(6)]^(3-)`

Answer

D

Explanation

(I) `[Cr (CN)_(6) ]^(3-), Cr^(3+) rArr 3d^(3)`

`therefore`CN is strong field ligand .
`therefore` Number of unpaired `e^(-) = 3 `
`rArr N = sqrt(n (n + 2)) = sqrt(3 sqrt(3 + 2)) = sqrt(15)` BM
(II) ` [Mn(CN)_(6)]^(3-), Mn^(3+) rArr 3d^(4)`
`therefore` CN is a strong field ligand.
`therefore` Number of unpaired `e^(-)` = 2
`rArr " " N = sqrt(2(2 + 2)) = sqrt(8)` BM
(III) `[Fe(CN)_(6)]^(3-) , Fe^(3+) rarrr 3d^(5)`
`therefore` CN is a strong field ligand.
`therefore`Number of unpaired `e^(-)` = 2
N = `sqrt(2(2 + 2)) = sqrt(8)` BM
(IV) `[Co(CN)_(6) ]^(3-), Co^(3+) rarr 3d^(6)`
`therefore CN^(-)` is a strong field ligand.
`therefore` Number of unpaired `e^(-)` = 0
`rArr " "` N = 0
Hence, minimum values of magnetic moment is for
`[Co(CN)_(6)]^(3-)`.