Given below are two statements: Statement (I): Dimethyl glyoxime forms a six membered covalent chelate when treated…
Coordination Compounds · Class 12 · JEE Main Previous Year Question
Given below are two statements: Statement (I): Dimethyl glyoxime forms a six membered covalent chelate when treated with NiCl₂ solution in presence of NH₄OH. Statement (II): Prussian blue precipitate contains iron both in (+2) and (+3) oxidation states. Choose the most appropriate answer:
- a✓
Statement I is false but Statement II is true
- b
Both Statement I and Statement II are true
- c
Both Statement I and Statement II are false
- d
Statement I is true but Statement II is false
Statement I is false but Statement II is true
🧠 One Statement Correct, One Not
- Statement I says DMG forms a six-membered covalent chelate with . The actual chelate ring is five-membered (Ni–N=C–C=N–Ni cycle counts five atoms, including Ni). So I is false.
- Statement II says Prussian blue contains Fe in both +2 and +3. True — Prussian blue is , a mixed-valence complex. So II is true.
Combination: I false, II true → option (1).
🗺️ Verify the DMG Chelate Ring Size
The DMG ligand is (deprotonated to give as the binding form). Each DMG⁻ binds Ni²⁺ through the two N atoms. The ring goes:
Ni → N=C → C=N → Ni
Five atoms in the ring: Ni, N, C, C, N → 5-membered. Two DMG ligands per Ni²⁺, plus stabilising O–H···O hydrogen bonds connecting the two ligand units. Final geometry: square planar.
⚡ Anchor: DMG-Ni Ring Size
DMG–Ni complex → 5-membered chelate ring × 2 → square planar → bright rosy red precipitate. JEE asks variants of this annually. Always 5.
⚠️ The "6-Membered" Common Slip
Some students count the ring as six (including a hydrogen of the H-bonded bridge). H-bonds are not counted as ring members; only formal coordinate bonds and single covalent C–C, C=N etc count. Ring size for the chelate alone = 5.
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