Chemistry · JEE Advanced only

Stability of Coordination Compounds (JEE Advanced)

Not in the JEE Main syllabus, but it is in JEE Advanced. Study time: about 3 to 4 hours. Spend 1 hour on concepts and formulas, 1 hour on numerical problems involving stability constants, and 1 to 2 hours on comparative questions involving chelate effect and Irving-Williams series..

Last updated: 26 October 2026

Direct answer

Stability of coordination compounds refers to how strongly a metal ion holds onto its ligands in solution.

Stability of coordination compounds refers to how strongly a metal ion holds onto its ligands in solution. We measure this using stability constants (also called formation constants), which tell us the equilibrium position when a complex forms. A higher stability constant means the complex is more stable and less likely to fall apart.

Official syllabus

What the JEE Advanced syllabus says

“Stability”

Source: JEE Advanced 2026 Information Bulletin, Annexure-I. Closest JEE Main topic: Bonding: Valence bond approach and basic ideas of Crystal field theory.

JEE Main covers basic CFT and VBT but does not ask you to calculate or compare stability constants quantitatively. Advanced expects you to use stepwise and overall stability constants, understand factors affecting stability, and apply the chelate effect.

Key ideas

What you must understand

Stability constant (Kf or β) is the equilibrium constant for complex formation: larger Kf means more stable complex
Stepwise stability constants (K1, K2, K3...) describe addition of one ligand at a time; overall stability constant β = K1 × K2 × K3...
Chelate effect: polydentate ligands form more stable complexes than equivalent monodentate ligands due to entropy advantage
Factors increasing stability: higher charge on metal ion, smaller metal ion size, greater charge on ligand, CFSE contribution
Irving-Williams series: for divalent first-row transition metals, stability follows Mn < Fe < Co < Ni < Cu > Zn
Thermodynamic stability (Kf) is different from kinetic stability (how fast ligand exchange happens)

Formulas

Formulas and key facts

M + nL ⇌ MLn; Kf = [MLn]/([M][L]^n)
β (overall) = K1 × K2 × K3 × ... × Kn
log β = log K1 + log K2 + ... + log Kn
ΔG° = −RT ln Kf = ΔH° − TΔS°
pKd = −log Kd where Kd = 1/Kf (dissociation constant)
Chelate effect: βen > βNH3 for same metal (en = ethylenediamine)
Higher CFSE → Higher stability (for same metal oxidation state)

Avoid

Common mistakes

Confusing stability constant (Kf) with dissociation constant (Kd); they are reciprocals of each other
Forgetting that overall β is the product (not sum) of stepwise constants, but log β is the sum of log K values
Ignoring the chelate effect when comparing monodentate vs polydentate ligands with same donor atoms
Assuming thermodynamically stable complexes are always kinetically inert; Cu(II) complexes are stable but labile

Worked example

A JEE Advanced-level example

Question. The stepwise stability constants for [Cu(NH3)4]²⁺ are log K1 = 4.0, log K2 = 3.2, log K3 = 2.7, log K4 = 2.0. Calculate the overall stability constant β4 and determine the concentration of free Cu²⁺ in a solution where [Cu(NH3)4]²⁺ = 0.1 M and [NH3] = 1.0 M.

Show solution

Find log β4 = log K1 + log K2 + log K3 + log K4 = 4.0 + 3.2 + 2.7 + 2.0 = 11.9
Therefore β4 = 10^11.9 ≈ 7.94 × 10^11
Use the expression: β4 = [Cu(NH3)4²⁺]/([Cu²⁺][NH3]⁴)
Rearrange: [Cu²⁺] = [Cu(NH3)4²⁺]/(β4 × [NH3]⁴)
Substitute values: [Cu²⁺] = 0.1/(7.94 × 10^11 × 1.0⁴)
[Cu²⁺] = 0.1/(7.94 × 10^11) = 1.26 × 10^−13 M

Answer: β4 = 7.94 × 10^11; [Cu²⁺] = 1.26 × 10^−13 M

Solved twice independently; both solutions agree.

FAQs

Frequently asked questions

Is Stability of Coordination Compounds in the JEE Main syllabus?

No. It is in the JEE Advanced 2026 syllabus only. The closest JEE Main topic is Bonding: Valence bond approach and basic ideas of Crystal field theory.

How long does Stability of Coordination Compounds take to prepare for JEE Advanced?

About 3 to 4 hours. Spend 1 hour on concepts and formulas, 1 hour on numerical problems involving stability constants, and 1 to 2 hours on comparative questions involving chelate effect and Irving-Williams series., if you already know the related JEE Main topic.