How many of the following complexes are homoleptic?
\( \ce{[Co(NH3)6]^3+} \), \( \ce{[Co(NH3)4Cl2]^+} \), \( \ce{[Ni(CO)4]} \), \( \ce{[PtCl2(NH3)2]} \), \( \ce{[Fe(CN)6]^4-} \), \( \ce{[CoCl3(NH3)3]} \), \( \ce{[Co(en)3]^3+} \)
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 4
A complex is homoleptic when the metal is bound to only one kind of donor group; it is heteroleptic when the metal is bound to more than one kind. Only the ligands inside the square brackets are looked at.
Homoleptic:
\( \ce{[Co(NH3)6]^3+} \) (six NH3 molecules only)
\( \ce{[Ni(CO)4]} \) (four CO groups only)
\( \ce{[Fe(CN)6]^4-} \) (six CN− ions only)
\( \ce{[Co(en)3]^3+} \) (three en ligands only; each en binds through two nitrogen atoms, but all the donor groups are of one kind)
Heteroleptic:
\( \ce{[Co(NH3)4Cl2]^+} \) — NH3 and Cl−.
\( \ce{[PtCl2(NH3)2]} \) — Cl− and NH3.
\( \ce{[CoCl3(NH3)3]} \) — Cl− and NH3.
Homoleptic: 4 complexes.
NCERT (2026-27 edition):
5.2 (h) Homoleptic and heteroleptic complexes – “Complexes in which a metal is bound to only one kind of donor groups, e.g., [Co(NH3)6]3+, are known as homoleptic. Complexes in which a metal is bound to more than one kind of donor groups, e.g., [Co(NH3)4Cl2]+, are known as heteroleptic.”
5.6 Bonding in Metal Carbonyls – “The homoleptic carbonyls (compounds containing carbonyl ligands only) are formed by most of the transition metals.”