PYQ Vault

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.

All Coordination Compounds notesMHT-CET Chemistry strategy

Why this matters

13 PYQs, none HARD. 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

Intuition

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): [Co(NH3)6]3+[\text{Co(NH}_3)_6]^{3+}, [Cu(NH3)4]2+[\text{Cu(NH}_3)_4]^{2+}, K3[Al(C2O4)3]\text{K}_3[\text{Al(C}_2\text{O}_4)_3], Na3[AlF6]\text{Na}_3[\text{AlF}_6], Ni(CO)4\text{Ni(CO)}_4, K2[Zn(OH)4]\text{K}_2[\text{Zn(OH)}_4].
  • Heteroleptic (two or more): [Co(NH3)4(H2O)2]Cl3[\text{Co(NH}_3)_4(\text{H}_2\text{O})_2]\text{Cl}_3, [Co(H2O)(NH3)5]I3[\text{Co(H}_2\text{O)(NH}_3)_5]\text{I}_3, [Co(NH3)3(NO2)3][\text{Co(NH}_3)_3(\text{NO}_2)_3], [Fe(H2O)5NCS]2+[\text{Fe(H}_2\text{O)}_5\text{NCS}]^{2+}, [Pt(NH3)2Cl2][\text{Pt(NH}_3)_2\text{Cl}_2].
  • Neutral sphere (no counter ion): [Co(NO2)3(NH3)3][\text{Co(NO}_2)_3(\text{NH}_3)_3], [Pt(NH3)2Cl2][\text{Pt(NH}_3)_2\text{Cl}_2], Ni(CO)4\text{Ni(CO)}_4, Fe(CO)5\text{Fe(CO)}_5.
  • Cationic sphere: [Co(NH3)5Cl]SO4[\text{Co(NH}_3)_5\text{Cl}]\text{SO}_4, [Co(NH3)6]Cl3[\text{Co(NH}_3)_6]\text{Cl}_3, [Pt(NH3)4Br2]Br2[\text{Pt(NH}_3)_4\text{Br}_2]\text{Br}_2. Anionic sphere: K4[Fe(CN)6]\text{K}_4[\text{Fe(CN)}_6], Na3[Co(NO2)6]\text{Na}_3[\text{Co(NO}_2)_6], K3[Fe(CN)6]\text{K}_3[\text{Fe(CN)}_6], Na3[AlF6]\text{Na}_3[\text{AlF}_6].
  • Both complex cation and complex anion: [Co(NH3)6][Cr(CN)6][\text{Co(NH}_3)_6][\text{Cr(CN)}_6]. A name ending in -ate marks an anionic sphere.

Sphere charge

charge on sphere=oxidation state of metal+∑ligand charges\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.
Practice this conceptself-check · 4 quick reps

From the bank · past-year question

Example 1Coordination CompoundsMODERATE
Which from following compounds contains complex cations and anions?

[Q57 · 20 April Shift II · 2025]

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

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

Watch out for (1)

Drill every past-year question on this subtopic

13 questions from the bank — paginated, with cart and Word-export support.

Drill the 13 questions

Related notes