Coordination CompoundsJEE Main
Build a complex — charge, CN & geometry — interactive Chemistry simulation for IIT-JEE.
Concept
A coordination compound is a central metal ion holding ligands by coordinate (dative) bonds inside square brackets. The coordination number counts bonded atoms — bidentate ligands like en bite twice. Complex charge = metal oxidation state + sum of ligand charges; counter-ions outside the bracket balance it.
Key formula
Derivation
Werner's insight: two kinds of valence — primary (oxidation state, satisfied by anions anywhere) and secondary (CN, satisfied only inside the sphere).
Only ionisable (outside) chloride precipitates with AgNO₃: [Co(NH₃)₆]Cl₃ gives 3 AgCl, [Co(NH₃)₅Cl]Cl₂ gives 2 — the classic experiment distinguishing isomers.
Scenarios to explore
- Coordination Compounds — Build a complex — charge, coordination number & geometry.
Real-world applications
- Haemoglobin (Fe–porphyrin), chlorophyll (Mg), vitamin B₁₂ (Co).
- cis-platin [PtCl₂(NH₃)₂] chemotherapy.
- EDTA chelation therapy & water softening.
JEE exam tips
- Naming order: ligands alphabetically, then metal (with -ate suffix if the complex is anionic).
- AgNO₃ / conductivity tests count IONISABLE ions — inside-sphere ligands don't show.
- Chelate effect: ring-forming ligands give extra entropy-driven stability.
Common mistakes
- Counting en as ONE toward CN — bidentate counts two.
- Confusing coordination number with the number of ligands.
- Oxidation state vs complex charge mix-ups.
Exam traps to avoid
- CN 4 geometry: Ni²⁺/Pt²⁺ (strong field, d⁸) go square planar; Zn²⁺ tetrahedral.
- [Co(NH₃)₄Cl₂]⁺ has cis/trans isomers — geometry drives isomer counting questions.