CBSE Class 12 · 2019 · Coordination CompoundsShort Answer

Out of [CoF

_{6}

]

^{3 -}

and [Co(en)

_{3}

]

^{3 +}

, which complex is:
(i) paramagnetic
(ii) more stable
(iii) an inner-orbital complex
(iv) a high-spin complex
(Atomic number of Co = 27)

Answer: (i) [CoF₆]³⁻ (4 unpaired). (ii) [Co(en)₃]³⁺ (chelate effect + strong field). (iii) [Co(en)₃]³⁺ (d²sp³). (iv) [CoF₆]³⁻.

Solution

^{3 +}

= 3d

^{6}

in both.
(i) Paramagnetic: [CoF

_{6}

]

^{3 -}

— F

^{-}

is weak-field, 4 unpaired electrons ([Co(en)

_{3}

]

^{3 +}

is diamagnetic).
(ii) More stable: [Co(en)

_{3}

]

^{3 +}

— en is a strong-field chelating ligand (chelate effect).
(iii) Inner-orbital: [Co(en)

_{3}

]

^{3 +}

— pairing gives d

^{2}

^{3}

.
(iv) High-spin: [CoF

_{6}

]

^{3 -}

— Δ

_{0}

< P, electrons stay unpaired (sp

^{3}

^{2}

CBSE Class 12 Board · 2019 · Subjective