MHT-CET Chemistry · Coordination Compounds

Types of Complexes: Homoleptic or Heteroleptic, Cationic, Anionic or Neutral

A complex is homoleptic when all its ligands are the same kind and heteroleptic when they differ; its coordination sphere is cationic, anionic or neutral according to the sum of the metal's oxidation state and the ligand charges, and a salt may pair a complex cation with simple anions, a complex anion with simple cations, or a complex cation with a complex anion.

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Why this matters

17 PYQs, none HARD. Of the thirteen set from 2021 to 2025, five ask homoleptic or heteroleptic from a list of names or formulas; eight ask the charge type — the neutral complex (triamminetrinitrocobalt(III), diamminedichloroplatinum(II)), the cationic one, the anionic one, the compound with a complex anion, and the one with both complex cation and anion. One card.

Concept 1 of 1: Same Ligands or Mixed, and the Charge on the Sphere

Two independent labels. LIGAND KINDS: [Co(NH₃)₆]³⁺, [Co(C₂O₄)₃]³⁻, Fe(CO)₅, [Ni(CN)₄]²⁻ have one kind of ligand — homoleptic; anything with two names before the metal (tetraamminediaqua…, pentaammineaqua…, triamminetrinitro…, pentaaquaisothiocyanato…) is heteroleptic. SPHERE CHARGE: add the metal's oxidation state to the ligand charges. Co(III) with three NO₂⁻ and three NH₃ gives +3 − 3 = 0, a neutral complex with no counter ion; Co(III) with five NH₃ and one Cl⁻ gives +2, a cation that needs SO₄²⁻ outside; Fe(II) with six CN⁻ gives −4, an anion that needs four K⁺. In [Pt(NH₃)₄Br₂]Br₂ the sphere is a cation and the bromides outside are simple anions; [Co(NH₃)₆][Cr(CN)₆] pairs a complex cation with a complex anion.

Definition

Homoleptic (one ligand type): $[\text{Co(NH}_3)_6]^{3+}$ , $[\text{Cu(NH}_3)_4]^{2+}$ , $\text{K}_3[\text{Al(C}_2\text{O}_4)_3]$ , $\text{Na}_3[\text{AlF}_6]$ , $\text{Ni(CO)}_4$ , $\text{K}_2[\text{Zn(OH)}_4]$ .
Heteroleptic (two or more): $[\text{Co(NH}_3)_4(\text{H}_2\text{O})_2]\text{Cl}_3$ , $[\text{Co(H}_2\text{O)(NH}_3)_5]\text{I}_3$ , $[\text{Co(NH}_3)_3(\text{NO}_2)_3]$ , $[\text{Fe(H}_2\text{O)}_5\text{NCS}]^{2+}$ , $[\text{Pt(NH}_3)_2\text{Cl}_2]$ .
Neutral sphere (no counter ion): $[\text{Co(NO}_2)_3(\text{NH}_3)_3]$ , $[\text{Pt(NH}_3)_2\text{Cl}_2]$ , $\text{Ni(CO)}_4$ , $\text{Fe(CO)}_5$ .
Cationic sphere: $[\text{Co(NH}_3)_5\text{Cl}]\text{SO}_4$ , $[\text{Co(NH}_3)_6]\text{Cl}_3$ , $[\text{Pt(NH}_3)_4\text{Br}_2]\text{Br}_2$ . Anionic sphere: $\text{K}_4[\text{Fe(CN)}_6]$ , $\text{Na}_3[\text{Co(NO}_2)_6]$ , $\text{K}_3[\text{Fe(CN)}_6]$ , $\text{Na}_3[\text{AlF}_6]$ .
Both complex cation and complex anion: $[\text{Co(NH}_3)_6][\text{Cr(CN)}_6]$ . A name ending in -ate marks an anionic sphere.

Sphere charge

\text{charge on sphere} = \text{oxidation state of metal} + \sum \text{ligand charges}

Worked example

Classify [Cr(en)₂Cl₂]Cl and K[Ag(CN)₂] as homo/heteroleptic and by sphere charge.

Practise this conceptself-check · 4 quick reps

The same idea in a real exam question:

MHT-CET · 2025 · 20 April Shift II · Q57Moderate

Example 1 · Coordination Compounds · Complex Types, Homoleptic, Heteroleptic, Cationic, Anionic, Neutral

Which from following compounds contains complex cations and anions?

Calling a salt 'neutral' because the whole compound is

K₄[Fe(CN)₆] is a neutral salt with an ANIONIC complex. 'Neutral complex' means the sphere itself carries no charge — [Co(NO₂)₃(NH₃)₃], cisplatin, the carbonyls.

Drill 12 more on same ligands or mixed, and the charge on the sphere

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Formulas (1)

Same Ligands or Mixed, and the Charge on the Sphere
Sphere charge
$\text{charge on sphere} = \text{oxidation state of metal} + \sum \text{ligand charges}$

Watch out for (1)

Calling a salt 'neutral' because the whole compound is
→ Same Ligands or Mixed, and the Charge on the Sphere

Test yourself on Coordination Compounds

20 past MHT-CET questions from this chapter, timed at 18 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.

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