The coordination environment of Ca²⁺ ion in its complex with EDTA⁴⁻ is:
Coordination Compounds · Class 12 · JEE Main Previous Year Question
The coordination environment of Ca²⁺ ion in its complex with EDTA⁴⁻ is:
- a
tetrahedral
- b
trigonal prismatic
- c✓
octahedral
- d
square planar
octahedral
🧠 Ca²⁺ + EDTA = 6-Coordinate
EDTA (ethylenediaminetetraacetate) is hexadentate: 2 amine N + 4 carboxylate O. When EDTA wraps a single metal ion, the metal is necessarily 6-coordinate octahedral.
Ca²⁺ is large enough to accept all 6 donors → octahedral .
🗺️ Eliminate the Wrong Geometries
- (1) Tetrahedral — only 4 sites, but EDTA needs 6. ✗
- (2) Trigonal prismatic — 6-coordinate but only seen for very specific d⁰/d¹⁰ ions (W, Mo); not Ca²⁺. ✗
- (3) Octahedral — 6 sites, fits EDTA perfectly. ✓
- (4) Square-planar — only 4 sites. ✗
⚡ The "EDTA → Octahedral" Default
For any small-to-medium-sized metal, EDTA gives an octahedral chelate. Only for very large metals (lanthanides) does the geometry expand beyond 6.
⚠️ Don't Confuse Ca with Pt or Pd
Square-planar geometries belong to d⁸ ions (Pt²⁺, Pd²⁺, Ni²⁺ + strong field). Ca²⁺ is (a main-group ion in the s-block) — never square-planar.
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