CBSE Class 12 · 2010 · Delhi Compartment · Coordination CompoundsShort Answer

Using the valence bond theory, predict the geometry and magnetic behaviour of [CoF

_{6}

]

^{3 -}

. (Atomic number of Co = 27)

Answer: Octahedral, sp³d² (outer orbital); paramagnetic — 4 unpaired electrons.

Solution

^{3 +}

= 3d

^{6}

. F

^{-}

is a weak-field ligand — no pairing: t

_{2 g}^{4}

_{g}^{2}

retains 4 unpaired electrons.
The ligands use 4s, three 4p and two 4d orbitals: sp

^{3}

^{2}

— an outer-orbital (high-spin) complex.
Geometry: octahedral.
Magnetism: 4 unpaired electrons → paramagnetic, μ = √24 ≈ 4.90 BM.

CBSE Class 12 Board · 2010 · Delhi Compartment · Subjective