Question

If all the halide ligands in the coordination sphere of the above complex be replaced by $F^{-}$, then the magnetic moment of the complex ion (due to spin only) will be :

• A. 2.8 B.M.
• B. 5.9 B.M.
• C. 4.9 B.M.
• D. 1.73 B.M.

Answer 1

The correct option is C 4.9 B.M.

Fluoride ion being a weak field ligand forms high spin complex. cobalt(III) ion with outer electronic configuration of $3d^6$ will have four unpaired electrons. Its spin only magnetic moment will be $\sqrt{4}(4+2)=4.9$B.M.