Question

Which one of the following complexes will most likely absorb visible light?

(a) [Sc(H_2O)_6]^(3+)

(b) [Ti(NH_3)_6]^(4+)

(c) [V(NH_3)_6]^(3+)

(d) [Zn(NH_3)_6]^(2+)

Solution

All ligands in the option have a zero net charge.

For Sc, oxidation state is +3 and electron configuration [Ar],4s^03d^0, so electron in d orbital.

For Ti, oxidation state is +4 and electron configuration [Ar],4s^03d^0, so electron in d orbital.

For V, oxidation state is +3 and electron configuration [Ar],4s^03d^2, so two unpaired electrons in d orbital.

For Zn, oxidation state is +3 and electron configuration [Ar],4s^03d^10, so all electrons are paired in d orbital.

Light absorbed by those complexes that have unpaired electron in d orbital.

Therefore, [V(NH_3)_6]^(3+) will absorb the light.