CBSE Class 12 · 2000 · All India · Coordination CompoundsShort Answer

Explain the following:
i) [Co(NH

_{3}

)

_{6}

]

^{3 +}

is diamagnetic, whereas [CoF

_{6}

]

^{3 -}

is paramagnetic.
ii) [Fe(H

_{2}

_{6}

]

^{3 +}

is more paramagnetic than [Fe(CN)

_{6}

]

^{3 -}

Solution

(i) Co

^{3 +}

= 3d

^{6}

.
With NH

_{3}

(strong field, Δ

_{0}

> P) the six electrons pair up as t

_{2 g}^{6}

— no unpaired electron, inner-orbital d

^{2}

^{3}

: diamagnetic.
With F

^{-}

(weak field, Δ

_{0}

< P) the configuration stays t

_{2 g}^{4}

_{g}^{2}

with 4 unpaired electrons, outer-orbital sp

^{3}

^{2}

: paramagnetic.
(ii) Fe

^{3 +}

= 3d

^{5}

.
H

_{2}

O (weak field): no pairing — 5 unpaired electrons, μ ≈ 5.92 BM.
CN

^{-}

(strong field): pairing leaves t

_{2 g}^{5}

— 1 unpaired electron, μ ≈ 1.73 BM.
Hence the aqua complex is far more paramagnetic.

CBSE Class 12 Board · 2000 · All India · Subjective